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NAME
       perlfunc - Perl builtin functions

DESCRIPTION
       The functions in this section can serve as terms in an
       expression.  They fall into two major categories: list
       operators and named unary operators.  These differ in
       their precedence relationship with a following comma.
       (See the precedence table in perlop.)  List operators take
       more than one argument, while unary operators can never
       take more than one argument.  Thus, a comma terminates the
       argument of a unary operator, but merely separates the
       arguments of a list operator.  A unary operator generally
       provides a scalar context to its argument, while a list
       operator may provide either scalar or list contexts for
       its arguments.  If it does both, the scalar arguments will
       be first, and the list argument will follow.  (Note that
       there can ever be only one such list argument.)  For
       instance, splice() has three scalar arguments followed by
       a list, whereas gethostbyname() has four scalar arguments.

       In the syntax descriptions that follow, list operators
       that expect a list (and provide list context for the
       elements of the list) are shown with LIST as an argument.
       Such a list may consist of any combination of scalar
       arguments or list values; the list values will be included
       in the list as if each individual element were
       interpolated at that point in the list, forming a longer
       single-dimensional list value.  Commas should separate
       elements of the LIST.

       Any function in the list below may be used either with or
       without parentheses around its arguments.  (The syntax
       descriptions omit the parentheses.)  If you use the
       parentheses, the simple (but occasionally surprising) rule
       is this: It looks like a function, therefore it is a
       function, and precedence doesn't matter.  Otherwise it's a
       list operator or unary operator, and precedence does
       matter.  And whitespace between the function and left
       parenthesis doesn't count--so you need to be careful
       sometimes:

           print 1+2+4;        # Prints 7.
           print(1+2) + 4;     # Prints 3.
           print (1+2)+4;      # Also prints 3!
           print +(1+2)+4;     # Prints 7.
           print ((1+2)+4);    # Prints 7.

       If you run Perl with the -w switch it can warn you about
       this.  For example, the third line above produces:

           print (...) interpreted as function at - line 1.
           Useless use of integer addition in void context at - line 1.




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       A few functions take no arguments at all, and therefore
       work as neither unary nor list operators.  These include
       such functions as "time" and "endpwent".  For example,
       "time+86_400" always means "time() + 86_400".

       For functions that can be used in either a scalar or list
       context, nonabortive failure is generally indicated in a
       scalar context by returning the undefined value, and in a
       list context by returning the null list.

       Remember the following important rule: There is no rule
       that relates the behavior of an expression in list context
       to its behavior in scalar context, or vice versa.  It
       might do two totally different things.  Each operator and
       function decides which sort of value it would be most
       appropriate to return in scalar context.  Some operators
       return the length of the list that would have been
       returned in list context.  Some operators return the first
       value in the list.  Some operators return the last value
       in the list.  Some operators return a count of successful
       operations.  In general, they do what you want, unless you
       want consistency.

       A named array in scalar context is quite different from
       what would at first glance appear to be a list in scalar
       context.  You can't get a list like "(1,2,3)" into being
       in scalar context, because the compiler knows the context
       at compile time.  It would generate the scalar comma
       operator there, not the list construction version of the
       comma.  That means it was never a list to start with.

       In general, functions in Perl that serve as wrappers for
       system calls of the same name (like chown(2), fork(2),
       closedir(2), etc.) all return true when they succeed and
       "undef" otherwise, as is usually mentioned in the
       descriptions below.  This is different from the C
       interfaces, which return "-1" on failure.  Exceptions to
       this rule are "wait", "waitpid", and "syscall".  System
       calls also set the special $!  variable on failure.  Other
       functions do not, except accidentally.

   Perl Functions by Category
       Here are Perl's functions (including things that look like
       functions, like some keywords and named operators)
       arranged by category.  Some functions appear in more than
       one place.

       Functions for SCALARs or strings
           "chomp", "chop", "chr", "crypt", "hex", "index", "lc",
           "lcfirst", "length", "oct", "ord", "pack", "q//",
           "qq//", "reverse", "rindex", "sprintf", "substr",
           "tr///", "uc", "ucfirst", "y///"





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       Regular expressions and pattern matching
           "m//", "pos", "quotemeta", "s///", "split", "study",
           "qr//"

       Numeric functions
           "abs", "atan2", "cos", "exp", "hex", "int", "log",
           "oct", "rand", "sin", "sqrt", "srand"

       Functions for real @ARRAYs
           "pop", "push", "shift", "splice", "unshift"

       Functions for list data
           "grep", "join", "map", "qw//", "reverse", "sort",
           "unpack"

       Functions for real %HASHes
           "delete", "each", "exists", "keys", "values"

       Input and output functions
           "binmode", "close", "closedir", "dbmclose", "dbmopen",
           "die", "eof", "fileno", "flock", "format", "getc",
           "print", "printf", "read", "readdir", "rewinddir",
           "say", "seek", "seekdir", "select", "syscall",
           "sysread", "sysseek", "syswrite", "tell", "telldir",
           "truncate", "warn", "write"

       Functions for fixed length data or records
           "pack", "read", "syscall", "sysread", "syswrite",
           "unpack", "vec"

       Functions for filehandles, files, or directories
           "-X", "chdir", "chmod", "chown", "chroot", "fcntl",
           "glob", "ioctl", "link", "lstat", "mkdir", "open",
           "opendir", "readlink", "rename", "rmdir", "stat",
           "symlink", "sysopen", "umask", "unlink", "utime"

       Keywords related to the control flow of your Perl program
           "caller", "continue", "die", "do", "dump", "eval",
           "exit", "goto", "last", "next", "redo", "return",
           "sub", "wantarray"

       Keywords related to switch
           "break", "continue", "given", "when", "default"

           (These are only available if you enable the "switch"
           feature.  See feature and "Switch statements" in
           perlsyn.)

       Keywords related to scoping
           "caller", "import", "local", "my", "our", "state",
           "package", "use"

           ("state" is only available if the "state" feature is
           enabled. See feature.)



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       Miscellaneous functions
           "defined", "dump", "eval", "formline", "local", "my",
           "our", "reset", "scalar", "state", "undef",
           "wantarray"

       Functions for processes and process groups
           "alarm", "exec", "fork", "getpgrp", "getppid",
           "getpriority", "kill", "pipe", "qx//", "setpgrp",
           "setpriority", "sleep", "system", "times", "wait",
           "waitpid"

       Keywords related to perl modules
           "do", "import", "no", "package", "require", "use"

       Keywords related to classes and object-orientation
           "bless", "dbmclose", "dbmopen", "package", "ref",
           "tie", "tied", "untie", "use"

       Low-level socket functions
           "accept", "bind", "connect", "getpeername",
           "getsockname", "getsockopt", "listen", "recv", "send",
           "setsockopt", "shutdown", "socket", "socketpair"

       System V interprocess communication functions
           "msgctl", "msgget", "msgrcv", "msgsnd", "semctl",
           "semget", "semop", "shmctl", "shmget", "shmread",
           "shmwrite"

       Fetching user and group info
           "endgrent", "endhostent", "endnetent", "endpwent",
           "getgrent", "getgrgid", "getgrnam", "getlogin",
           "getpwent", "getpwnam", "getpwuid", "setgrent",
           "setpwent"

       Fetching network info
           "endprotoent", "endservent", "gethostbyaddr",
           "gethostbyname", "gethostent", "getnetbyaddr",
           "getnetbyname", "getnetent", "getprotobyname",
           "getprotobynumber", "getprotoent", "getservbyname",
           "getservbyport", "getservent", "sethostent",
           "setnetent", "setprotoent", "setservent"

       Time-related functions
           "gmtime", "localtime", "time", "times"

       Functions new in perl5
           "abs", "bless", "break", "chomp", "chr", "continue",
           "default", "exists", "formline", "given", "glob",
           "import", "lc", "lcfirst", "lock", "map", "my", "no",
           "our", "prototype", "qr//", "qw//", "qx//",
           "readline", "readpipe", "ref", "sub"*, "sysopen",
           "tie", "tied", "uc", "ucfirst", "untie", "use", "when"

           * - "sub" was a keyword in perl4, but in perl5 it is



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           an operator, which can be used in expressions.

       Functions obsoleted in perl5
           "dbmclose", "dbmopen"

   Portability
       Perl was born in Unix and can therefore access all common
       Unix system calls.  In non-Unix environments, the
       functionality of some Unix system calls may not be
       available, or details of the available functionality may
       differ slightly.  The Perl functions affected by this are:

       "-X", "binmode", "chmod", "chown", "chroot", "crypt",
       "dbmclose", "dbmopen", "dump", "endgrent", "endhostent",
       "endnetent", "endprotoent", "endpwent", "endservent",
       "exec", "fcntl", "flock", "fork", "getgrent", "getgrgid",
       "gethostbyname", "gethostent", "getlogin", "getnetbyaddr",
       "getnetbyname", "getnetent", "getppid", "getpgrp",
       "getpriority", "getprotobynumber", "getprotoent",
       "getpwent", "getpwnam", "getpwuid", "getservbyport",
       "getservent", "getsockopt", "glob", "ioctl", "kill",
       "link", "lstat", "msgctl", "msgget", "msgrcv", "msgsnd",
       "open", "pipe", "readlink", "rename", "select", "semctl",
       "semget", "semop", "setgrent", "sethostent", "setnetent",
       "setpgrp", "setpriority", "setprotoent", "setpwent",
       "setservent", "setsockopt", "shmctl", "shmget", "shmread",
       "shmwrite", "socket", "socketpair", "stat", "symlink",
       "syscall", "sysopen", "system", "times", "truncate",
       "umask", "unlink", "utime", "wait", "waitpid"

       For more information about the portability of these
       functions, see perlport and other available platform-
       specific documentation.

   Alphabetical Listing of Perl Functions
       -X FILEHANDLE
       -X EXPR
       -X DIRHANDLE
       -X      A file test, where X is one of the letters listed
               below.  This unary operator takes one argument,
               either a filename, a filehandle, or a dirhandle,
               and tests the associated file to see if something
               is true about it.  If the argument is omitted,
               tests $_, except for "-t", which tests STDIN.
               Unless otherwise documented, it returns 1 for true
               and '' for false, or the undefined value if the
               file doesn't exist.  Despite the funny names,
               precedence is the same as any other named unary
               operator.  The operator may be any of:

                   -r  File is readable by effective uid/gid.
                   -w  File is writable by effective uid/gid.
                   -x  File is executable by effective uid/gid.
                   -o  File is owned by effective uid.



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                   -R  File is readable by real uid/gid.
                   -W  File is writable by real uid/gid.
                   -X  File is executable by real uid/gid.
                   -O  File is owned by real uid.

                   -e  File exists.
                   -z  File has zero size (is empty).
                   -s  File has nonzero size (returns size in bytes).

                   -f  File is a plain file.
                   -d  File is a directory.
                   -l  File is a symbolic link.
                   -p  File is a named pipe (FIFO), or Filehandle is a pipe.
                   -S  File is a socket.
                   -b  File is a block special file.
                   -c  File is a character special file.
                   -t  Filehandle is opened to a tty.

                   -u  File has setuid bit set.
                   -g  File has setgid bit set.
                   -k  File has sticky bit set.

                   -T  File is an ASCII text file (heuristic guess).
                   -B  File is a "binary" file (opposite of -T).

                   -M  Script start time minus file modification time, in days.
                   -A  Same for access time.
                   -C  Same for inode change time (Unix, may differ for other platforms)

               Example:

                   while (<>) {
                       chomp;
                       next unless -f $_;      # ignore specials
                       #...
                   }

               The interpretation of the file permission
               operators "-r", "-R", "-w", "-W", "-x", and "-X"
               is by default based solely on the mode of the file
               and the uids and gids of the user.  There may be
               other reasons you can't actually read, write, or
               execute the file: for example network filesystem
               access controls, ACLs (access control lists),
               read-only filesystems, and unrecognized executable
               formats.  Note that the use of these six specific
               operators to verify if some operation is possible
               is usually a mistake, because it may be open to
               race conditions.

               Also note that, for the superuser on the local
               filesystems, the "-r", "-R", "-w", and "-W" tests
               always return 1, and "-x" and "-X" return 1 if any



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               execute bit is set in the mode.  Scripts run by
               the superuser may thus need to do a stat() to
               determine the actual mode of the file, or
               temporarily set their effective uid to something
               else.

               If you are using ACLs, there is a pragma called
               "filetest" that may produce more accurate results
               than the bare stat() mode bits.  When under the
               "use filetest 'access'" the above-mentioned
               filetests will test whether the permission can
               (not) be granted using the access() family of
               system calls.  Also note that the "-x" and "-X"
               may under this pragma return true even if there
               are no execute permission bits set (nor any extra
               execute permission ACLs).  This strangeness is due
               to the underlying system calls' definitions. Note
               also that, due to the implementation of "use
               filetest 'access'", the "_" special filehandle
               won't cache the results of the file tests when
               this pragma is in effect.  Read the documentation
               for the "filetest" pragma for more information.

               Note that "-s/a/b/" does not do a negated
               substitution.  Saying "-exp($foo)" still works as
               expected, however--only single letters following a
               minus are interpreted as file tests.

               The "-T" and "-B" switches work as follows.  The
               first block or so of the file is examined for odd
               characters such as strange control codes or
               characters with the high bit set.  If too many
               strange characters (>30%) are found, it's a "-B"
               file; otherwise it's a "-T" file.  Also, any file
               containing null in the first block is considered a
               binary file.  If "-T" or "-B" is used on a
               filehandle, the current IO buffer is examined
               rather than the first block.  Both "-T" and "-B"
               return true on a null file, or a file at EOF when
               testing a filehandle.  Because you have to read a
               file to do the "-T" test, on most occasions you
               want to use a "-f" against the file first, as in
               "next unless -f $file && -T $file".

               If any of the file tests (or either the "stat" or
               "lstat" operators) are given the special
               filehandle consisting of a solitary underline,
               then the stat structure of the previous file test
               (or stat operator) is used, saving a system call.
               (This doesn't work with "-t", and you need to
               remember that lstat() and "-l" will leave values
               in the stat structure for the symbolic link, not
               the real file.)  (Also, if the stat buffer was
               filled by an "lstat" call, "-T" and "-B" will



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               reset it with the results of "stat _").  Example:

                   print "Can do.\n" if -r $a || -w _ || -x _;

                   stat($filename);
                   print "Readable\n" if -r _;
                   print "Writable\n" if -w _;
                   print "Executable\n" if -x _;
                   print "Setuid\n" if -u _;
                   print "Setgid\n" if -g _;
                   print "Sticky\n" if -k _;
                   print "Text\n" if -T _;
                   print "Binary\n" if -B _;

               As of Perl 5.9.1, as a form of purely syntactic
               sugar, you can stack file test operators, in a way
               that "-f -w -x $file" is equivalent to "-x $file
               && -w _ && -f _". (This is only syntax fancy: if
               you use the return value of "-f $file" as an
               argument to another filetest operator, no special
               magic will happen.)

       abs VALUE
       abs     Returns the absolute value of its argument.  If
               VALUE is omitted, uses $_.

       accept NEWSOCKET,GENERICSOCKET
               Accepts an incoming socket connect, just as the
               accept(2) system call does.  Returns the packed
               address if it succeeded, false otherwise.  See the
               example in "Sockets: Client/Server Communication"
               in perlipc.

               On systems that support a close-on-exec flag on
               files, the flag will be set for the newly opened
               file descriptor, as determined by the value of
               $^F.  See "$^F" in perlvar.

       alarm SECONDS
       alarm   Arranges to have a SIGALRM delivered to this
               process after the specified number of wallclock
               seconds has elapsed.  If SECONDS is not specified,
               the value stored in $_ is used. (On some machines,
               unfortunately, the elapsed time may be up to one
               second less or more than you specified because of
               how seconds are counted, and process scheduling
               may delay the delivery of the signal even
               further.)

               Only one timer may be counting at once.  Each call
               disables the previous timer, and an argument of 0
               may be supplied to cancel the previous timer
               without starting a new one.  The returned value is
               the amount of time remaining on the previous



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               timer.

               For delays of finer granularity than one second,
               the Time::HiRes module (from CPAN, and starting
               from Perl 5.8 part of the standard distribution)
               provides ualarm().  You may also use Perl's four-
               argument version of select() leaving the first
               three arguments undefined, or you might be able to
               use the "syscall" interface to access setitimer(2)
               if your system supports it. See perlfaq8 for
               details.

               It is usually a mistake to intermix "alarm" and
               "sleep" calls.  ("sleep" may be internally
               implemented in your system with "alarm")

               If you want to use "alarm" to time out a system
               call you need to use an "eval"/"die" pair.  You
               can't rely on the alarm causing the system call to
               fail with $! set to "EINTR" because Perl sets up
               signal handlers to restart system calls on some
               systems.  Using "eval"/"die" always works, modulo
               the caveats given in "Signals" in perlipc.

                   eval {
                       local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
                       alarm $timeout;
                       $nread = sysread SOCKET, $buffer, $size;
                       alarm 0;
                   };
                   if ($@) {
                       die unless $@ eq "alarm\n";   # propagate unexpected errors
                       # timed out
                   }
                   else {
                       # didn't
                   }

               For more information see perlipc.

       atan2 Y,X
               Returns the arctangent of Y/X in the range -PI to
               PI.

               For the tangent operation, you may use the
               "Math::Trig::tan" function, or use the familiar
               relation:

                   sub tan { sin($_[0]) / cos($_[0])  }

               The return value for "atan2(0,0)" is
               implementation-defined; consult your atan2(3)
               manpage for more information.




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       bind SOCKET,NAME
               Binds a network address to a socket, just as the
               bind system call does.  Returns true if it
               succeeded, false otherwise.  NAME should be a
               packed address of the appropriate type for the
               socket.  See the examples in "Sockets:
               Client/Server Communication" in perlipc.

       binmode FILEHANDLE, LAYER
       binmode FILEHANDLE
               Arranges for FILEHANDLE to be read or written in
               "binary" or "text" mode on systems where the run-
               time libraries distinguish between binary and text
               files.  If FILEHANDLE is an expression, the value
               is taken as the name of the filehandle.  Returns
               true on success, otherwise it returns "undef" and
               sets $! (errno).

               On some systems (in general, DOS and Windows-based
               systems) binmode() is necessary when you're not
               working with a text file.  For the sake of
               portability it is a good idea to always use it
               when appropriate, and to never use it when it
               isn't appropriate.  Also, people can set their I/O
               to be by default UTF-8 encoded Unicode, not bytes.

               In other words: regardless of platform, use
               binmode() on binary data, like for example images.

               If LAYER is present it is a single string, but may
               contain multiple directives. The directives alter
               the behaviour of the file handle.  When LAYER is
               present using binmode on a text file makes sense.

               If LAYER is omitted or specified as ":raw" the
               filehandle is made suitable for passing binary
               data. This includes turning off possible CRLF
               translation and marking it as bytes (as opposed to
               Unicode characters).  Note that, despite what may
               be implied in "Programming Perl" (the Camel) or
               elsewhere, ":raw" is not simply the inverse of
               ":crlf" -- other layers which would affect the
               binary nature of the stream are also disabled. See
               PerlIO, perlrun and the discussion about the
               PERLIO environment variable.

               The ":bytes", ":crlf", and ":utf8", and any other
               directives of the form ":...", are called I/O
               layers.  The "open" pragma can be used to
               establish default I/O layers.  See open.

               The LAYER parameter of the binmode() function is
               described as "DISCIPLINE" in "Programming Perl,
               3rd Edition".  However, since the publishing of



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               this book, by many known as "Camel III", the
               consensus of the naming of this functionality has
               moved from "discipline" to "layer".  All
               documentation of this version of Perl therefore
               refers to "layers" rather than to "disciplines".
               Now back to the regularly scheduled
               documentation...

               To mark FILEHANDLE as UTF-8, use ":utf8" or
               ":encoding(utf8)".  ":utf8" just marks the data as
               UTF-8 without further checking, while
               ":encoding(utf8)" checks the data for actually
               being valid UTF-8. More details can be found in
               PerlIO::encoding.

               In general, binmode() should be called after
               open() but before any I/O is done on the
               filehandle.  Calling binmode() will normally flush
               any pending buffered output data (and perhaps
               pending input data) on the handle.  An exception
               to this is the ":encoding" layer that changes the
               default character encoding of the handle, see
               open.  The ":encoding" layer sometimes needs to be
               called in mid-stream, and it doesn't flush the
               stream.  The ":encoding" also implicitly pushes on
               top of itself the ":utf8" layer because internally
               Perl will operate on UTF-8 encoded Unicode
               characters.

               The operating system, device drivers, C libraries,
               and Perl run-time system all work together to let
               the programmer treat a single character ("\n") as
               the line terminator, irrespective of the external
               representation.  On many operating systems, the
               native text file representation matches the
               internal representation, but on some platforms the
               external representation of "\n" is made up of more
               than one character.

               Mac OS, all variants of Unix, and Stream_LF files
               on VMS use a single character to end each line in
               the external representation of text (even though
               that single character is CARRIAGE RETURN on Mac OS
               and LINE FEED on Unix and most VMS files). In
               other systems like OS/2, DOS and the various
               flavors of MS-Windows your program sees a "\n" as
               a simple "\cJ", but what's stored in text files
               are the two characters "\cM\cJ".  That means that,
               if you don't use binmode() on these systems,
               "\cM\cJ" sequences on disk will be converted to
               "\n" on input, and any "\n" in your program will
               be converted back to "\cM\cJ" on output.  This is
               what you want for text files, but it can be
               disastrous for binary files.



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               Another consequence of using binmode() (on some
               systems) is that special end-of-file markers will
               be seen as part of the data stream.  For systems
               from the Microsoft family this means that if your
               binary data contains "\cZ", the I/O subsystem will
               regard it as the end of the file, unless you use
               binmode().

               binmode() is not only important for readline() and
               print() operations, but also when using read(),
               seek(), sysread(), syswrite() and tell() (see
               perlport for more details).  See the $/ and "$\"
               variables in perlvar for how to manually set your
               input and output line-termination sequences.

       bless REF,CLASSNAME
       bless REF
               This function tells the thingy referenced by REF
               that it is now an object in the CLASSNAME package.
               If CLASSNAME is omitted, the current package is
               used.  Because a "bless" is often the last thing
               in a constructor, it returns the reference for
               convenience.  Always use the two-argument version
               if a derived class might inherit the function
               doing the blessing.  See perltoot and perlobj for
               more about the blessing (and blessings) of
               objects.

               Consider always blessing objects in CLASSNAMEs
               that are mixed case.  Namespaces with all
               lowercase names are considered reserved for Perl
               pragmata.  Builtin types have all uppercase names.
               To prevent confusion, you may wish to avoid such
               package names as well.  Make sure that CLASSNAME
               is a true value.

               See "Perl Modules" in perlmod.

       break   Break out of a "given()" block.

               This keyword is enabled by the "switch" feature:
               see feature for more information.

       caller EXPR
       caller  Returns the context of the current subroutine
               call.  In scalar context, returns the caller's
               package name if there is a caller, that is, if
               we're in a subroutine or "eval" or "require", and
               the undefined value otherwise.  In list context,
               returns

                   # 0         1          2
                   ($package, $filename, $line) = caller;




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               With EXPR, it returns some extra information that
               the debugger uses to print a stack trace.  The
               value of EXPR indicates how many call frames to go
               back before the current one.

                   #  0         1          2      3            4
                   ($package, $filename, $line, $subroutine, $hasargs,

                   #  5          6          7            8       9         10
                   $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash)
                    = caller($i);

               Here $subroutine may be "(eval)" if the frame is
               not a subroutine call, but an "eval".  In such a
               case additional elements $evaltext and $is_require
               are set: $is_require is true if the frame is
               created by a "require" or "use" statement,
               $evaltext contains the text of the "eval EXPR"
               statement.  In particular, for an "eval BLOCK"
               statement, $subroutine is "(eval)", but $evaltext
               is undefined.  (Note also that each "use"
               statement creates a "require" frame inside an
               "eval EXPR" frame.)  $subroutine may also be
               "(unknown)" if this particular subroutine happens
               to have been deleted from the symbol table.
               $hasargs is true if a new instance of @_ was set
               up for the frame.  $hints and $bitmask contain
               pragmatic hints that the caller was compiled with.
               The $hints and $bitmask values are subject to
               change between versions of Perl, and are not meant
               for external use.

               $hinthash is a reference to a hash containing the
               value of "%^H" when the caller was compiled, or
               "undef" if "%^H" was empty. Do not modify the
               values of this hash, as they are the actual values
               stored in the optree.

               Furthermore, when called from within the DB
               package, caller returns more detailed information:
               it sets the list variable @DB::args to be the
               arguments with which the subroutine was invoked.

               Be aware that the optimizer might have optimized
               call frames away before "caller" had a chance to
               get the information.  That means that caller(N)
               might not return information about the call frame
               you expect it do, for "N > 1".  In particular,
               @DB::args might have information from the previous
               time "caller" was called.

       chdir EXPR
       chdir FILEHANDLE




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       chdir DIRHANDLE
       chdir   Changes the working directory to EXPR, if
               possible. If EXPR is omitted, changes to the
               directory specified by $ENV{HOME}, if set; if not,
               changes to the directory specified by
               $ENV{LOGDIR}. (Under VMS, the variable
               $ENV{SYS$LOGIN} is also checked, and used if it is
               set.) If neither is set, "chdir" does nothing. It
               returns true upon success, false otherwise. See
               the example under "die".

               On systems that support fchdir, you might pass a
               file handle or directory handle as argument.  On
               systems that don't support fchdir, passing handles
               produces a fatal error at run time.

       chmod LIST
               Changes the permissions of a list of files.  The
               first element of the list must be the numerical
               mode, which should probably be an octal number,
               and which definitely should not be a string of
               octal digits: 0644 is okay, '0644' is not.
               Returns the number of files successfully changed.
               See also "oct", if all you have is a string.

                   $cnt = chmod 0755, 'foo', 'bar';
                   chmod 0755, @executables;
                   $mode = '0644'; chmod $mode, 'foo';      # !!! sets mode to
                                                            # --w----r-T
                   $mode = '0644'; chmod oct($mode), 'foo'; # this is better
                   $mode = 0644;   chmod $mode, 'foo';      # this is best

               On systems that support fchmod, you might pass
               file handles among the files.  On systems that
               don't support fchmod, passing file handles
               produces a fatal error at run time.   The file
               handles must be passed as globs or references to
               be recognized.  Barewords are considered file
               names.

                   open(my $fh, "<", "foo");
                   my $perm = (stat $fh)[2] & 07777;
                   chmod($perm | 0600, $fh);

               You can also import the symbolic "S_I*" constants
               from the Fcntl module:

                   use Fcntl ':mode';

                   chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
                   # This is identical to the chmod 0755 of the above example.

       chomp VARIABLE




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       chomp( LIST )
       chomp   This safer version of "chop" removes any trailing
               string that corresponds to the current value of $/
               (also known as $INPUT_RECORD_SEPARATOR in the
               "English" module).  It returns the total number of
               characters removed from all its arguments.  It's
               often used to remove the newline from the end of
               an input record when you're worried that the final
               record may be missing its newline.  When in
               paragraph mode ("$/ = """), it removes all
               trailing newlines from the string.  When in slurp
               mode ("$/ = undef") or fixed-length record mode
               ($/ is a reference to an integer or the like, see
               perlvar) chomp() won't remove anything.  If
               VARIABLE is omitted, it chomps $_.  Example:

                   while (<>) {
                       chomp;  # avoid \n on last field
                       @array = split(/:/);
                       # ...
                   }

               If VARIABLE is a hash, it chomps the hash's
               values, but not its keys.

               You can actually chomp anything that's an lvalue,
               including an assignment:

                   chomp($cwd = `pwd`);
                   chomp($answer = <STDIN>);

               If you chomp a list, each element is chomped, and
               the total number of characters removed is
               returned.

               Note that parentheses are necessary when you're
               chomping anything that is not a simple variable.
               This is because "chomp $cwd = `pwd`;" is
               interpreted as "(chomp $cwd) = `pwd`;", rather
               than as "chomp( $cwd = `pwd` )" which you might
               expect.  Similarly, "chomp $a, $b" is interpreted
               as "chomp($a), $b" rather than as "chomp($a, $b)".

       chop VARIABLE
       chop( LIST )
       chop    Chops off the last character of a string and
               returns the character chopped.  It is much more
               efficient than "s/.$//s" because it neither scans
               nor copies the string.  If VARIABLE is omitted,
               chops $_.  If VARIABLE is a hash, it chops the
               hash's values, but not its keys.

               You can actually chop anything that's an lvalue,
               including an assignment.



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               If you chop a list, each element is chopped.  Only
               the value of the last "chop" is returned.

               Note that "chop" returns the last character.  To
               return all but the last character, use
               "substr($string, 0, -1)".

               See also "chomp".

       chown LIST
               Changes the owner (and group) of a list of files.
               The first two elements of the list must be the
               numeric uid and gid, in that order.  A value of -1
               in either position is interpreted by most systems
               to leave that value unchanged.  Returns the number
               of files successfully changed.

                   $cnt = chown $uid, $gid, 'foo', 'bar';
                   chown $uid, $gid, @filenames;

               On systems that support fchown, you might pass
               file handles among the files.  On systems that
               don't support fchown, passing file handles
               produces a fatal error at run time.  The file
               handles must be passed as globs or references to
               be recognized.  Barewords are considered file
               names.

               Here's an example that looks up nonnumeric uids in
               the passwd file:

                   print "User: ";
                   chomp($user = <STDIN>);
                   print "Files: ";
                   chomp($pattern = <STDIN>);

                   ($login,$pass,$uid,$gid) = getpwnam($user)
                       or die "$user not in passwd file";

                   @ary = glob($pattern);      # expand filenames
                   chown $uid, $gid, @ary;

               On most systems, you are not allowed to change the
               ownership of the file unless you're the superuser,
               although you should be able to change the group to
               any of your secondary groups.  On insecure
               systems, these restrictions may be relaxed, but
               this is not a portable assumption.  On POSIX
               systems, you can detect this condition this way:

                   use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
                   $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);





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       chr NUMBER
       chr     Returns the character represented by that NUMBER
               in the character set.  For example, "chr(65)" is
               "A" in either ASCII or Unicode, and chr(0x263a) is
               a Unicode smiley face.

               Negative values give the Unicode replacement
               character (chr(0xfffd)), except under the bytes
               pragma, where low eight bits of the value
               (truncated to an integer) are used.

               If NUMBER is omitted, uses $_.

               For the reverse, use "ord".

               Note that characters from 128 to 255 (inclusive)
               are by default internally not encoded as UTF-8 for
               backward compatibility reasons.

               See perlunicode for more about Unicode.

       chroot FILENAME
       chroot  This function works like the system call by the
               same name: it makes the named directory the new
               root directory for all further pathnames that
               begin with a "/" by your process and all its
               children.  (It doesn't change your current working
               directory, which is unaffected.)  For security
               reasons, this call is restricted to the superuser.
               If FILENAME is omitted, does a "chroot" to $_.

       close FILEHANDLE
       close   Closes the file or pipe associated with the file
               handle, flushes the IO buffers, and closes the
               system file descriptor.  Returns true if those
               operations have succeeded and if no error was
               reported by any PerlIO layer.  Closes the
               currently selected filehandle if the argument is
               omitted.

               You don't have to close FILEHANDLE if you are
               immediately going to do another "open" on it,
               because "open" will close it for you.  (See
               "open".)  However, an explicit "close" on an input
               file resets the line counter ($.), while the
               implicit close done by "open" does not.

               If the file handle came from a piped open, "close"
               will additionally return false if one of the other
               system calls involved fails, or if the program
               exits with non-zero status.  (If the only problem
               was that the program exited non-zero, $! will be
               set to 0.)  Closing a pipe also waits for the
               process executing on the pipe to complete, in case



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               you want to look at the output of the pipe
               afterwards, and implicitly puts the exit status
               value of that command into $? and
               "${^CHILD_ERROR_NATIVE}".

               Prematurely closing the read end of a pipe (i.e.
               before the process writing to it at the other end
               has closed it) will result in a SIGPIPE being
               delivered to the writer.  If the other end can't
               handle that, be sure to read all the data before
               closing the pipe.

               Example:

                   open(OUTPUT, '|sort >foo')  # pipe to sort
                       or die "Can't start sort: $!";
                   #...                        # print stuff to output
                   close OUTPUT                # wait for sort to finish
                       or warn $! ? "Error closing sort pipe: $!"
                                  : "Exit status $? from sort";
                   open(INPUT, 'foo')          # get sort's results
                       or die "Can't open 'foo' for input: $!";

               FILEHANDLE may be an expression whose value can be
               used as an indirect filehandle, usually the real
               filehandle name.

       closedir DIRHANDLE
               Closes a directory opened by "opendir" and returns
               the success of that system call.

       connect SOCKET,NAME
               Attempts to connect to a remote socket, just as
               the connect system call does.  Returns true if it
               succeeded, false otherwise.  NAME should be a
               packed address of the appropriate type for the
               socket.  See the examples in "Sockets:
               Client/Server Communication" in perlipc.

       continue BLOCK
       continue
               "continue" is actually a flow control statement
               rather than a function.  If there is a "continue"
               BLOCK attached to a BLOCK (typically in a "while"
               or "foreach"), it is always executed just before
               the conditional is about to be evaluated again,
               just like the third part of a "for" loop in C.
               Thus it can be used to increment a loop variable,
               even when the loop has been continued via the
               "next" statement (which is similar to the C
               "continue" statement).

               "last", "next", or "redo" may appear within a
               "continue" block.  "last" and "redo" will behave



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               as if they had been executed within the main
               block.  So will "next", but since it will execute
               a "continue" block, it may be more entertaining.

                   while (EXPR) {
                       ### redo always comes here
                       do_something;
                   } continue {
                       ### next always comes here
                       do_something_else;
                       # then back the top to re-check EXPR
                   }
                   ### last always comes here

               Omitting the "continue" section is semantically
               equivalent to using an empty one, logically
               enough.  In that case, "next" goes directly back
               to check the condition at the top of the loop.

               If the "switch" feature is enabled, "continue" is
               also a function that will break out of the current
               "when" or "default" block, and fall through to the
               next case. See feature and "Switch statements" in
               perlsyn for more information.

       cos EXPR
       cos     Returns the cosine of EXPR (expressed in radians).
               If EXPR is omitted, takes cosine of $_.

               For the inverse cosine operation, you may use the
               "Math::Trig::acos()" function, or use this
               relation:

                   sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }

       crypt PLAINTEXT,SALT
               Creates a digest string exactly like the crypt(3)
               function in the C library (assuming that you
               actually have a version there that has not been
               extirpated as a potential munition).

               crypt() is a one-way hash function.  The PLAINTEXT
               and SALT is turned into a short string, called a
               digest, which is returned.  The same PLAINTEXT and
               SALT will always return the same string, but there
               is no (known) way to get the original PLAINTEXT
               from the hash.  Small changes in the PLAINTEXT or
               SALT will result in large changes in the digest.

               There is no decrypt function.  This function isn't
               all that useful for cryptography (for that, look
               for Crypt modules on your nearby CPAN mirror) and
               the name "crypt" is a bit of a misnomer.  Instead
               it is primarily used to check if two pieces of



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               text are the same without having to transmit or
               store the text itself.  An example is checking if
               a correct password is given.  The digest of the
               password is stored, not the password itself.  The
               user types in a password that is crypt()'d with
               the same salt as the stored digest.  If the two
               digests match the password is correct.

               When verifying an existing digest string you
               should use the digest as the salt (like
               "crypt($plain, $digest) eq $digest").  The SALT
               used to create the digest is visible as part of
               the digest.  This ensures crypt() will hash the
               new string with the same salt as the digest.  This
               allows your code to work with the standard crypt
               and with more exotic implementations.  In other
               words, do not assume anything about the returned
               string itself, or how many bytes in the digest
               matter.

               Traditionally the result is a string of 13 bytes:
               two first bytes of the salt, followed by 11 bytes
               from the set "[./0-9A-Za-z]", and only the first
               eight bytes of PLAINTEXT mattered. But alternative
               hashing schemes (like MD5), higher level security
               schemes (like C2), and implementations on non-UNIX
               platforms may produce different strings.

               When choosing a new salt create a random two
               character string whose characters come from the
               set "[./0-9A-Za-z]" (like "join '', ('.', '/',
               0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]").
               This set of characters is just a recommendation;
               the characters allowed in the salt depend solely
               on your system's crypt library, and Perl can't
               restrict what salts "crypt()" accepts.

               Here's an example that makes sure that whoever
               runs this program knows their password:

                   $pwd = (getpwuid($<))[1];

                   system "stty -echo";
                   print "Password: ";
                   chomp($word = <STDIN>);
                   print "\n";
                   system "stty echo";

                   if (crypt($word, $pwd) ne $pwd) {
                       die "Sorry...\n";
                   } else {
                       print "ok\n";
                   }




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               Of course, typing in your own password to whoever
               asks you for it is unwise.

               The crypt function is unsuitable for hashing large
               quantities of data, not least of all because you
               can't get the information back.  Look at the
               Digest module for more robust algorithms.

               If using crypt() on a Unicode string (which
               potentially has characters with codepoints above
               255), Perl tries to make sense of the situation by
               trying to downgrade (a copy of the string) the
               string back to an eight-bit byte string before
               calling crypt() (on that copy).  If that works,
               good.  If not, crypt() dies with "Wide character
               in crypt".

       dbmclose HASH
               [This function has been largely superseded by the
               "untie" function.]

               Breaks the binding between a DBM file and a hash.

       dbmopen HASH,DBNAME,MASK
               [This function has been largely superseded by the
               "tie" function.]

               This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or
               Berkeley DB file to a hash.  HASH is the name of
               the hash.  (Unlike normal "open", the first
               argument is not a filehandle, even though it looks
               like one).  DBNAME is the name of the database
               (without the .dir or .pag extension if any).  If
               the database does not exist, it is created with
               protection specified by MASK (as modified by the
               "umask").  If your system supports only the older
               DBM functions, you may perform only one "dbmopen"
               in your program.  In older versions of Perl, if
               your system had neither DBM nor ndbm, calling
               "dbmopen" produced a fatal error; it now falls
               back to sdbm(3).

               If you don't have write access to the DBM file,
               you can only read hash variables, not set them.
               If you want to test whether you can write, either
               use file tests or try setting a dummy hash entry
               inside an "eval", which will trap the error.

               Note that functions such as "keys" and "values"
               may return huge lists when used on large DBM
               files.  You may prefer to use the "each" function
               to iterate over large DBM files.  Example:





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                   # print out history file offsets
                   dbmopen(%HIST,'/usr/lib/news/history',0666);
                   while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";
                   }
                   dbmclose(%HIST);

               See also AnyDBM_File for a more general
               description of the pros and cons of the various
               dbm approaches, as well as DB_File for a
               particularly rich implementation.

               You can control which DBM library you use by
               loading that library before you call dbmopen():

                   use DB_File;
                   dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
                       or die "Can't open netscape history file: $!";

       defined EXPR
       defined Returns a Boolean value telling whether EXPR has a
               value other than the undefined value "undef".  If
               EXPR is not present, $_ will be checked.

               Many operations return "undef" to indicate
               failure, end of file, system error, uninitialized
               variable, and other exceptional conditions.  This
               function allows you to distinguish "undef" from
               other values.  (A simple Boolean test will not
               distinguish among "undef", zero, the empty string,
               and "0", which are all equally false.)  Note that
               since "undef" is a valid scalar, its presence
               doesn't necessarily indicate an exceptional
               condition: "pop" returns "undef" when its argument
               is an empty array, or when the element to return
               happens to be "undef".

               You may also use "defined(&func)" to check whether
               subroutine &func has ever been defined.  The
               return value is unaffected by any forward
               declarations of &func.  Note that a subroutine
               which is not defined may still be callable: its
               package may have an "AUTOLOAD" method that makes
               it spring into existence the first time that it is
               called -- see perlsub.

               Use of "defined" on aggregates (hashes and arrays)
               is deprecated.  It used to report whether memory
               for that aggregate has ever been allocated.  This
               behavior may disappear in future versions of Perl.
               You should instead use a simple test for size:

                   if (@an_array) { print "has array elements\n" }
                   if (%a_hash)   { print "has hash members\n"   }



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               When used on a hash element, it tells you whether
               the value is defined, not whether the key exists
               in the hash.  Use "exists" for the latter purpose.

               Examples:

                   print if defined $switch{'D'};
                   print "$val\n" while defined($val = pop(@ary));
                   die "Can't readlink $sym: $!"
                       unless defined($value = readlink $sym);
                   sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
                   $debugging = 0 unless defined $debugging;

               Note:  Many folks tend to overuse "defined", and
               then are surprised to discover that the number 0
               and "" (the zero-length string) are, in fact,
               defined values.  For example, if you say

                   "ab" =~ /a(.*)b/;

               The pattern match succeeds, and $1 is defined,
               despite the fact that it matched "nothing".  It
               didn't really fail to match anything.  Rather, it
               matched something that happened to be zero
               characters long.  This is all very above-board and
               honest.  When a function returns an undefined
               value, it's an admission that it couldn't give you
               an honest answer.  So you should use "defined"
               only when you're questioning the integrity of what
               you're trying to do.  At other times, a simple
               comparison to 0 or "" is what you want.

               See also "undef", "exists", "ref".

       delete EXPR
               Given an expression that specifies a hash element,
               array element, hash slice, or array slice, deletes
               the specified element(s) from the hash or array.
               In the case of an array, if the array elements
               happen to be at the end, the size of the array
               will shrink to the highest element that tests true
               for exists() (or 0 if no such element exists).

               Returns a list with the same number of elements as
               the number of elements for which deletion was
               attempted.  Each element of that list consists of
               either the value of the element deleted, or the
               undefined value.  In scalar context, this means
               that you get the value of the last element deleted
               (or the undefined value if that element did not
               exist).






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                   %hash = (foo => 11, bar => 22, baz => 33);
                   $scalar = delete $hash{foo};             # $scalar is 11
                   $scalar = delete @hash{qw(foo bar)};     # $scalar is 22
                   @array  = delete @hash{qw(foo bar baz)}; # @array  is (undef,undef,33)

               Deleting from %ENV modifies the environment.
               Deleting from a hash tied to a DBM file deletes
               the entry from the DBM file.  Deleting from a
               "tie"d hash or array may not necessarily return
               anything.

               Deleting an array element effectively returns that
               position of the array to its initial,
               uninitialized state.  Subsequently testing for the
               same element with exists() will return false.
               Also, deleting array elements in the middle of an
               array will not shift the index of the elements
               after them down.  Use splice() for that.  See
               "exists".

               The following (inefficiently) deletes all the
               values of %HASH and @ARRAY:

                   foreach $key (keys %HASH) {
                       delete $HASH{$key};
                   }

                   foreach $index (0 .. $#ARRAY) {
                       delete $ARRAY[$index];
                   }

               And so do these:

                   delete @HASH{keys %HASH};

                   delete @ARRAY[0 .. $#ARRAY];

               But both of these are slower than just assigning
               the empty list or undefining %HASH or @ARRAY:

                   %HASH = ();         # completely empty %HASH
                   undef %HASH;        # forget %HASH ever existed

                   @ARRAY = ();        # completely empty @ARRAY
                   undef @ARRAY;       # forget @ARRAY ever existed

               Note that the EXPR can be arbitrarily complicated
               as long as the final operation is a hash element,
               array element,  hash slice, or array slice lookup:

                   delete $ref->[$x][$y]{$key};
                   delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};

                   delete $ref->[$x][$y][$index];



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                   delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];

       die LIST
               Outside an "eval", prints the value of LIST to
               "STDERR" and exits with the current value of $!
               (errno).  If $! is 0, exits with the value of "($?
               >> 8)" (backtick `command` status).  If "($? >>
               8)" is 0, exits with 255.  Inside an "eval()," the
               error message is stuffed into $@ and the "eval" is
               terminated with the undefined value.  This makes
               "die" the way to raise an exception.

               Equivalent examples:

                   die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
                   chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"

               If the last element of LIST does not end in a
               newline, the current script line number and input
               line number (if any) are also printed, and a
               newline is supplied.  Note that the "input line
               number" (also known as "chunk") is subject to
               whatever notion of "line" happens to be currently
               in effect, and is also available as the special
               variable $..  See "$/" in perlvar and "$." in
               perlvar.

               Hint: sometimes appending ", stopped" to your
               message will cause it to make better sense when
               the string "at foo line 123" is appended.  Suppose
               you are running script "canasta".

                   die "/etc/games is no good";
                   die "/etc/games is no good, stopped";

               produce, respectively

                   /etc/games is no good at canasta line 123.
                   /etc/games is no good, stopped at canasta line 123.

               See also exit(), warn(), and the Carp module.

               If LIST is empty and $@ already contains a value
               (typically from a previous eval) that value is
               reused after appending "\t...propagated".  This is
               useful for propagating exceptions:

                   eval { ... };
                   die unless $@ =~ /Expected exception/;

               If LIST is empty and $@ contains an object
               reference that has a "PROPAGATE" method, that
               method will be called with additional file and
               line number parameters.  The return value replaces



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               the value in $@.  i.e. as if "$@ = eval {
               $@->PROPAGATE(__FILE__, __LINE__) };" were called.

               If $@ is empty then the string "Died" is used.

               die() can also be called with a reference
               argument.  If this happens to be trapped within an
               eval(), $@ contains the reference.  This behavior
               permits a more elaborate exception handling
               implementation using objects that maintain
               arbitrary state about the nature of the exception.
               Such a scheme is sometimes preferable to matching
               particular string values of $@ using regular
               expressions.  Because $@ is a global variable, and
               eval() may be used within object implementations,
               care must be taken that analyzing the error object
               doesn't replace the reference in the global
               variable.  The easiest solution is to make a local
               copy of the reference before doing other
               manipulations.  Here's an example:

                   use Scalar::Util 'blessed';

                   eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
                   if (my $ev_err = $@) {
                       if (blessed($ev_err) && $ev_err->isa("Some::Module::Exception")) {
                           # handle Some::Module::Exception
                       }
                       else {
                           # handle all other possible exceptions
                       }
                   }

               Because perl will stringify uncaught exception
               messages before displaying them, you may want to
               overload stringification operations on such custom
               exception objects.  See overload for details about
               that.

               You can arrange for a callback to be run just
               before the "die" does its deed, by setting the
               $SIG{__DIE__} hook.  The associated handler will
               be called with the error text and can change the
               error message, if it sees fit, by calling "die"
               again.  See "$SIG{expr}" in perlvar for details on
               setting %SIG entries, and "eval BLOCK" for some
               examples.  Although this feature was to be run
               only right before your program was to exit, this
               is not currently the case--the $SIG{__DIE__} hook
               is currently called even inside eval()ed
               blocks/strings!  If one wants the hook to do
               nothing in such situations, put

                       die @_ if $^S;



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               as the first line of the handler (see "$^S" in
               perlvar).  Because this promotes strange action at
               a distance, this counterintuitive behavior may be
               fixed in a future release.

       do BLOCK
               Not really a function.  Returns the value of the
               last command in the sequence of commands indicated
               by BLOCK.  When modified by the "while" or "until"
               loop modifier, executes the BLOCK once before
               testing the loop condition. (On other statements
               the loop modifiers test the conditional first.)

               "do BLOCK" does not count as a loop, so the loop
               control statements "next", "last", or "redo"
               cannot be used to leave or restart the block.  See
               perlsyn for alternative strategies.

       do SUBROUTINE(LIST)
               This form of subroutine call is deprecated.  See
               perlsub.

       do EXPR Uses the value of EXPR as a filename and executes
               the contents of the file as a Perl script.

                   do 'stat.pl';

               is just like

                   eval `cat stat.pl`;

               except that it's more efficient and concise, keeps
               track of the current filename for error messages,
               searches the @INC directories, and updates %INC if
               the file is found.  See "Predefined Names" in
               perlvar for these variables.  It also differs in
               that code evaluated with "do FILENAME" cannot see
               lexicals in the enclosing scope; "eval STRING"
               does.  It's the same, however, in that it does
               reparse the file every time you call it, so you
               probably don't want to do this inside a loop.

               If "do" cannot read the file, it returns undef and
               sets $! to the error.  If "do" can read the file
               but cannot compile it, it returns undef and sets
               an error message in $@.   If the file is
               successfully compiled, "do" returns the value of
               the last expression evaluated.

               Note that inclusion of library modules is better
               done with the "use" and "require" operators, which
               also do automatic error checking and raise an
               exception if there's a problem.




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               You might like to use "do" to read in a program
               configuration file.  Manual error checking can be
               done this way:

                   # read in config files: system first, then user
                   for $file ("/share/prog/defaults.rc",
                              "$ENV{HOME}/.someprogrc")
                  {
                       unless ($return = do $file) {
                           warn "couldn't parse $file: $@" if $@;
                           warn "couldn't do $file: $!"    unless defined $return;
                           warn "couldn't run $file"       unless $return;
                       }
                   }

       dump LABEL
       dump    This function causes an immediate core dump.  See
               also the -u command-line switch in perlrun, which
               does the same thing.  Primarily this is so that
               you can use the undump program (not supplied) to
               turn your core dump into an executable binary
               after having initialized all your variables at the
               beginning of the program.  When the new binary is
               executed it will begin by executing a "goto LABEL"
               (with all the restrictions that "goto" suffers).
               Think of it as a goto with an intervening core
               dump and reincarnation.  If "LABEL" is omitted,
               restarts the program from the top.

               WARNING: Any files opened at the time of the dump
               will not be open any more when the program is
               reincarnated, with possible resulting confusion on
               the part of Perl.

               This function is now largely obsolete, mostly
               because it's very hard to convert a core file into
               an executable. That's why you should now invoke it
               as "CORE::dump()", if you don't want to be warned
               against a possible typo.

       each HASH
               When called in list context, returns a 2-element
               list consisting of the key and value for the next
               element of a hash, so that you can iterate over
               it.  When called in scalar context, returns only
               the key for the next element in the hash.

               Entries are returned in an apparently random
               order.  The actual random order is subject to
               change in future versions of perl, but it is
               guaranteed to be in the same order as either the
               "keys" or "values" function would produce on the
               same (unmodified) hash.  Since Perl 5.8.2 the
               ordering can be different even between different



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               runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

               When the hash is entirely read, a null array is
               returned in list context (which when assigned
               produces a false (0) value), and "undef" in scalar
               context.  The next call to "each" after that will
               start iterating again.  There is a single iterator
               for each hash, shared by all "each", "keys", and
               "values" function calls in the program; it can be
               reset by reading all the elements from the hash,
               or by evaluating "keys HASH" or "values HASH".  If
               you add or delete elements of a hash while you're
               iterating over it, you may get entries skipped or
               duplicated, so don't.  Exception: It is always
               safe to delete the item most recently returned by
               "each()", which means that the following code will
               work:

                       while (($key, $value) = each %hash) {
                         print $key, "\n";
                         delete $hash{$key};   # This is safe
                       }

               The following prints out your environment like the
               printenv(1) program, only in a different order:

                   while (($key,$value) = each %ENV) {
                       print "$key=$value\n";
                   }

               See also "keys", "values" and "sort".

       eof FILEHANDLE
       eof ()
       eof     Returns 1 if the next read on FILEHANDLE will
               return end of file, or if FILEHANDLE is not open.
               FILEHANDLE may be an expression whose value gives
               the real filehandle.  (Note that this function
               actually reads a character and then "ungetc"s it,
               so isn't very useful in an interactive context.)
               Do not read from a terminal file (or call
               "eof(FILEHANDLE)" on it) after end-of-file is
               reached.  File types such as terminals may lose
               the end-of-file condition if you do.

               An "eof" without an argument uses the last file
               read.  Using "eof()" with empty parentheses is
               very different.  It refers to the pseudo file
               formed from the files listed on the command line
               and accessed via the "<>" operator.  Since "<>"
               isn't explicitly opened, as a normal filehandle
               is, an "eof()" before "<>" has been used will
               cause @ARGV to be examined to determine if input



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               is available.   Similarly, an "eof()" after "<>"
               has returned end-of-file will assume you are
               processing another @ARGV list, and if you haven't
               set @ARGV, will read input from "STDIN"; see "I/O
               Operators" in perlop.

               In a "while (<>)" loop, "eof" or "eof(ARGV)" can
               be used to detect the end of each file, "eof()"
               will only detect the end of the last file.
               Examples:

                   # reset line numbering on each input file
                   while (<>) {
                       next if /^\s*#/;        # skip comments
                       print "$.\t$_";
                   } continue {
                       close ARGV  if eof;     # Not eof()!
                   }

                   # insert dashes just before last line of last file
                   while (<>) {
                       if (eof()) {            # check for end of last file
                           print "--------------\n";
                       }
                       print;
                       last if eof();          # needed if we're reading from a terminal
                   }

               Practical hint: you almost never need to use "eof"
               in Perl, because the input operators typically
               return "undef" when they run out of data, or if
               there was an error.

       eval EXPR
       eval BLOCK
       eval    In the first form, the return value of EXPR is
               parsed and executed as if it were a little Perl
               program.  The value of the expression (which is
               itself determined within scalar context) is first
               parsed, and if there weren't any errors, executed
               in the lexical context of the current Perl
               program, so that any variable settings or
               subroutine and format definitions remain
               afterwards.  Note that the value is parsed every
               time the "eval" executes.  If EXPR is omitted,
               evaluates $_.  This form is typically used to
               delay parsing and subsequent execution of the text
               of EXPR until run time.

               In the second form, the code within the BLOCK is
               parsed only once--at the same time the code
               surrounding the "eval" itself was parsed--and
               executed within the context of the current Perl
               program.  This form is typically used to trap



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               exceptions more efficiently than the first (see
               below), while also providing the benefit of
               checking the code within BLOCK at compile time.

               The final semicolon, if any, may be omitted from
               the value of EXPR or within the BLOCK.

               In both forms, the value returned is the value of
               the last expression evaluated inside the mini-
               program; a return statement may be also used, just
               as with subroutines.  The expression providing the
               return value is evaluated in void, scalar, or list
               context, depending on the context of the "eval"
               itself.  See "wantarray" for more on how the
               evaluation context can be determined.

               If there is a syntax error or runtime error, or a
               "die" statement is executed, "eval" returns an
               undefined value in scalar context or an empty list
               in list context, and $@ is set to the error
               message.  If there was no error, $@ is guaranteed
               to be a null string.  Beware that using "eval"
               neither silences perl from printing warnings to
               STDERR, nor does it stuff the text of warning
               messages into $@.  To do either of those, you have
               to use the $SIG{__WARN__} facility, or turn off
               warnings inside the BLOCK or EXPR using
               "no warnings 'all'".  See "warn", perlvar,
               warnings and perllexwarn.

               Note that, because "eval" traps otherwise-fatal
               errors, it is useful for determining whether a
               particular feature (such as "socket" or "symlink")
               is implemented.  It is also Perl's exception
               trapping mechanism, where the die operator is used
               to raise exceptions.

               If you want to trap errors when loading an XS
               module, some problems with the binary interface
               (such as Perl version skew) may be fatal even with
               "eval" unless $ENV{PERL_DL_NONLAZY} is set. See
               perlrun.

               If the code to be executed doesn't vary, you may
               use the eval-BLOCK form to trap run-time errors
               without incurring the penalty of recompiling each
               time.  The error, if any, is still returned in $@.
               Examples:

                   # make divide-by-zero nonfatal
                   eval { $answer = $a / $b; }; warn $@ if $@;

                   # same thing, but less efficient
                   eval '$answer = $a / $b'; warn $@ if $@;



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                   # a compile-time error
                   eval { $answer = };                 # WRONG

                   # a run-time error
                   eval '$answer =';   # sets $@

               Using the "eval{}" form as an exception trap in
               libraries does have some issues.  Due to the
               current arguably broken state of "__DIE__" hooks,
               you may wish not to trigger any "__DIE__" hooks
               that user code may have installed.  You can use
               the "local $SIG{__DIE__}" construct for this
               purpose, as shown in this example:

                   # a very private exception trap for divide-by-zero
                   eval { local $SIG{'__DIE__'}; $answer = $a / $b; };
                   warn $@ if $@;

               This is especially significant, given that
               "__DIE__" hooks can call "die" again, which has
               the effect of changing their error messages:

                   # __DIE__ hooks may modify error messages
                   {
                      local $SIG{'__DIE__'} =
                             sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
                      eval { die "foo lives here" };
                      print $@ if $@;                # prints "bar lives here"
                   }

               Because this promotes action at a distance, this
               counterintuitive behavior may be fixed in a future
               release.

               With an "eval", you should be especially careful
               to remember what's being looked at when:

                   eval $x;            # CASE 1
                   eval "$x";          # CASE 2

                   eval '$x';          # CASE 3
                   eval { $x };        # CASE 4

                   eval "\$$x++";      # CASE 5
                   $$x++;              # CASE 6

               Cases 1 and 2 above behave identically: they run
               the code contained in the variable $x.  (Although
               case 2 has misleading double quotes making the
               reader wonder what else might be happening
               (nothing is).)  Cases 3 and 4 likewise behave in
               the same way: they run the code '$x', which does
               nothing but return the value of $x.  (Case 4 is



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               preferred for purely visual reasons, but it also
               has the advantage of compiling at compile-time
               instead of at run-time.)  Case 5 is a place where
               normally you would like to use double quotes,
               except that in this particular situation, you can
               just use symbolic references instead, as in case
               6.

               The assignment to $@ occurs before restoration of
               localised variables, which means a temporary is
               required if you want to mask some but not all
               errors:

                   # alter $@ on nefarious repugnancy only
                   {
                      my $e;
                      {
                         local $@; # protect existing $@
                         eval { test_repugnancy() };
                         # $@ =~ /nefarious/ and die $@; # DOES NOT WORK
                         $@ =~ /nefarious/ and $e = $@;
                      }
                      die $e if defined $e
                   }

               "eval BLOCK" does not count as a loop, so the loop
               control statements "next", "last", or "redo"
               cannot be used to leave or restart the block.

               Note that as a very special case, an "eval ''"
               executed within the "DB" package doesn't see the
               usual surrounding lexical scope, but rather the
               scope of the first non-DB piece of code that
               called it. You don't normally need to worry about
               this unless you are writing a Perl debugger.

       exec LIST
       exec PROGRAM LIST
               The "exec" function executes a system command and
               never returns-- use "system" instead of "exec" if
               you want it to return.  It fails and returns false
               only if the command does not exist and it is
               executed directly instead of via your system's
               command shell (see below).

               Since it's a common mistake to use "exec" instead
               of "system", Perl warns you if there is a
               following statement which isn't "die", "warn", or
               "exit" (if "-w" is set  -  but you always do
               that).   If you really want to follow an "exec"
               with some other statement, you can use one of
               these styles to avoid the warning:





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                   exec ('foo')   or print STDERR "couldn't exec foo: $!";
                   { exec ('foo') }; print STDERR "couldn't exec foo: $!";

               If there is more than one argument in LIST, or if
               LIST is an array with more than one value, calls
               execvp(3) with the arguments in LIST.  If there is
               only one scalar argument or an array with one
               element in it, the argument is checked for shell
               metacharacters, and if there are any, the entire
               argument is passed to the system's command shell
               for parsing (this is "/bin/sh -c" on Unix
               platforms, but varies on other platforms).  If
               there are no shell metacharacters in the argument,
               it is split into words and passed directly to
               "execvp", which is more efficient.  Examples:

                   exec '/bin/echo', 'Your arguments are: ', @ARGV;
                   exec "sort $outfile | uniq";

               If you don't really want to execute the first
               argument, but want to lie to the program you are
               executing about its own name, you can specify the
               program you actually want to run as an "indirect
               object" (without a comma) in front of the LIST.
               (This always forces interpretation of the LIST as
               a multivalued list, even if there is only a single
               scalar in the list.)  Example:

                   $shell = '/bin/csh';
                   exec $shell '-sh';          # pretend it's a login shell

               or, more directly,

                   exec {'/bin/csh'} '-sh';    # pretend it's a login shell

               When the arguments get executed via the system
               shell, results will be subject to its quirks and
               capabilities.  See "`STRING`" in perlop for
               details.

               Using an indirect object with "exec" or "system"
               is also more secure.  This usage (which also works
               fine with system()) forces interpretation of the
               arguments as a multivalued list, even if the list
               had just one argument.  That way you're safe from
               the shell expanding wildcards or splitting up
               words with whitespace in them.

                   @args = ( "echo surprise" );

                   exec @args;               # subject to shell escapes
                                               # if @args == 1
                   exec { $args[0] } @args;  # safe even with one-arg list




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               The first version, the one without the indirect
               object, ran the echo program, passing it
               "surprise" an argument.  The second version
               didn't--it tried to run a program literally called
               "echo surprise", didn't find it, and set $? to a
               non-zero value indicating failure.

               Beginning with v5.6.0, Perl will attempt to flush
               all files opened for output before the exec, but
               this may not be supported on some platforms (see
               perlport).  To be safe, you may need to set $|
               ($AUTOFLUSH in English) or call the "autoflush()"
               method of "IO::Handle" on any open handles in
               order to avoid lost output.

               Note that "exec" will not call your "END" blocks,
               nor will it call any "DESTROY" methods in your
               objects.

       exists EXPR
               Given an expression that specifies a hash element
               or array element, returns true if the specified
               element in the hash or array has ever been
               initialized, even if the corresponding value is
               undefined.

                   print "Exists\n"    if exists $hash{$key};
                   print "Defined\n"   if defined $hash{$key};
                   print "True\n"      if $hash{$key};

                   print "Exists\n"    if exists $array[$index];
                   print "Defined\n"   if defined $array[$index];
                   print "True\n"      if $array[$index];

               A hash or array element can be true only if it's
               defined, and defined if it exists, but the reverse
               doesn't necessarily hold true.

               Given an expression that specifies the name of a
               subroutine, returns true if the specified
               subroutine has ever been declared, even if it is
               undefined.  Mentioning a subroutine name for
               exists or defined does not count as declaring it.
               Note that a subroutine which does not exist may
               still be callable: its package may have an
               "AUTOLOAD" method that makes it spring into
               existence the first time that it is called -- see
               perlsub.

                   print "Exists\n"    if exists &subroutine;
                   print "Defined\n"   if defined &subroutine;

               Note that the EXPR can be arbitrarily complicated
               as long as the final operation is a hash or array



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               key lookup or subroutine name:

                   if (exists $ref->{A}->{B}->{$key})  { }
                   if (exists $hash{A}{B}{$key})       { }

                   if (exists $ref->{A}->{B}->[$ix])   { }
                   if (exists $hash{A}{B}[$ix])        { }

                   if (exists &{$ref->{A}{B}{$key}})   { }

               Although the deepest nested array or hash will not
               spring into existence just because its existence
               was tested, any intervening ones will.  Thus
               "$ref->{"A"}" and "$ref->{"A"}->{"B"}" will spring
               into existence due to the existence test for the
               $key element above.  This happens anywhere the
               arrow operator is used, including even:

                   undef $ref;
                   if (exists $ref->{"Some key"})      { }
                   print $ref;             # prints HASH(0x80d3d5c)

               This surprising autovivification in what does not
               at first--or even second--glance appear to be an
               lvalue context may be fixed in a future release.

               Use of a subroutine call, rather than a subroutine
               name, as an argument to exists() is an error.

                   exists &sub;        # OK
                   exists &sub();      # Error

       exit EXPR
       exit    Evaluates EXPR and exits immediately with that
               value.    Example:

                   $ans = <STDIN>;
                   exit 0 if $ans =~ /^[Xx]/;

               See also "die".  If EXPR is omitted, exits with 0
               status.  The only universally recognized values
               for EXPR are 0 for success and 1 for error; other
               values are subject to interpretation depending on
               the environment in which the Perl program is
               running.  For example, exiting 69 (EX_UNAVAILABLE)
               from a sendmail incoming-mail filter will cause
               the mailer to return the item undelivered, but
               that's not true everywhere.

               Don't use "exit" to abort a subroutine if there's
               any chance that someone might want to trap
               whatever error happened.  Use "die" instead, which
               can be trapped by an "eval".




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               The exit() function does not always exit
               immediately.  It calls any defined "END" routines
               first, but these "END" routines may not themselves
               abort the exit.  Likewise any object destructors
               that need to be called are called before the real
               exit.  If this is a problem, you can call
               "POSIX:_exit($status)" to avoid END and destructor
               processing.  See perlmod for details.

       exp EXPR
       exp     Returns e (the natural logarithm base) to the
               power of EXPR.  If EXPR is omitted, gives
               "exp($_)".

       fcntl FILEHANDLE,FUNCTION,SCALAR
               Implements the fcntl(2) function.  You'll probably
               have to say

                   use Fcntl;

               first to get the correct constant definitions.
               Argument processing and value return works just
               like "ioctl" below.  For example:

                   use Fcntl;
                   fcntl($filehandle, F_GETFL, $packed_return_buffer)
                       or die "can't fcntl F_GETFL: $!";

               You don't have to check for "defined" on the
               return from "fcntl".  Like "ioctl", it maps a 0
               return from the system call into "0 but true" in
               Perl.  This string is true in boolean context and
               0 in numeric context.  It is also exempt from the
               normal -w warnings on improper numeric
               conversions.

               Note that "fcntl" will produce a fatal error if
               used on a machine that doesn't implement fcntl(2).
               See the Fcntl module or your fcntl(2) manpage to
               learn what functions are available on your system.

               Here's an example of setting a filehandle named
               "REMOTE" to be non-blocking at the system level.
               You'll have to negotiate $| on your own, though.

                   use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);

                   $flags = fcntl(REMOTE, F_GETFL, 0)
                               or die "Can't get flags for the socket: $!\n";

                   $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
                               or die "Can't set flags for the socket: $!\n";





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       fileno FILEHANDLE
               Returns the file descriptor for a filehandle, or
               undefined if the filehandle is not open.  This is
               mainly useful for constructing bitmaps for
               "select" and low-level POSIX tty-handling
               operations.  If FILEHANDLE is an expression, the
               value is taken as an indirect filehandle,
               generally its name.

               You can use this to find out whether two handles
               refer to the same underlying descriptor:

                   if (fileno(THIS) == fileno(THAT)) {
                       print "THIS and THAT are dups\n";
                   }

               (Filehandles connected to memory objects via new
               features of "open" may return undefined even
               though they are open.)

       flock FILEHANDLE,OPERATION
               Calls flock(2), or an emulation of it, on
               FILEHANDLE.  Returns true for success, false on
               failure.  Produces a fatal error if used on a
               machine that doesn't implement flock(2), fcntl(2)
               locking, or lockf(3).  "flock" is Perl's portable
               file locking interface, although it locks only
               entire files, not records.

               Two potentially non-obvious but traditional
               "flock" semantics are that it waits indefinitely
               until the lock is granted, and that its locks
               merely advisory.  Such discretionary locks are
               more flexible, but offer fewer guarantees.  This
               means that programs that do not also use "flock"
               may modify files locked with "flock".  See
               perlport, your port's specific documentation, or
               your system-specific local manpages for details.
               It's best to assume traditional behavior if you're
               writing portable programs.  (But if you're not,
               you should as always feel perfectly free to write
               for your own system's idiosyncrasies (sometimes
               called "features").  Slavish adherence to
               portability concerns shouldn't get in the way of
               your getting your job done.)

               OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN,
               possibly combined with LOCK_NB.  These constants
               are traditionally valued 1, 2, 8 and 4, but you
               can use the symbolic names if you import them from
               the Fcntl module, either individually, or as a
               group using the ':flock' tag.  LOCK_SH requests a
               shared lock, LOCK_EX requests an exclusive lock,
               and LOCK_UN releases a previously requested lock.



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               If LOCK_NB is bitwise-or'ed with LOCK_SH or
               LOCK_EX then "flock" will return immediately
               rather than blocking waiting for the lock (check
               the return status to see if you got it).

               To avoid the possibility of miscoordination, Perl
               now flushes FILEHANDLE before locking or unlocking
               it.

               Note that the emulation built with lockf(3)
               doesn't provide shared locks, and it requires that
               FILEHANDLE be open with write intent.  These are
               the semantics that lockf(3) implements.  Most if
               not all systems implement lockf(3) in terms of
               fcntl(2) locking, though, so the differing
               semantics shouldn't bite too many people.

               Note that the fcntl(2) emulation of flock(3)
               requires that FILEHANDLE be open with read intent
               to use LOCK_SH and requires that it be open with
               write intent to use LOCK_EX.

               Note also that some versions of "flock" cannot
               lock things over the network; you would need to
               use the more system-specific "fcntl" for that.  If
               you like you can force Perl to ignore your
               system's flock(2) function, and so provide its own
               fcntl(2)-based emulation, by passing the switch
               "-Ud_flock" to the Configure program when you
               configure perl.

               Here's a mailbox appender for BSD systems.

                   use Fcntl qw(:flock SEEK_END); # import LOCK_* and SEEK_END constants

                   sub lock {
                       my ($fh) = @_;
                       flock($fh, LOCK_EX) or die "Cannot lock mailbox - $!\n";

                       # and, in case someone appended while we were waiting...
                       seek($fh, 0, SEEK_END) or die "Cannot seek - $!\n";
                   }

                   sub unlock {
                       my ($fh) = @_;
                       flock($fh, LOCK_UN) or die "Cannot unlock mailbox - $!\n";
                   }

                   open(my $mbox, ">>", "/usr/spool/mail/$ENV{'USER'}")
                           or die "Can't open mailbox: $!";

                   lock($mbox);
                   print $mbox $msg,"\n\n";
                   unlock($mbox);



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               On systems that support a real flock(), locks are
               inherited across fork() calls, whereas those that
               must resort to the more capricious fcntl()
               function lose the locks, making it harder to write
               servers.

               See also DB_File for other flock() examples.

       fork    Does a fork(2) system call to create a new process
               running the same program at the same point.  It
               returns the child pid to the parent process, 0 to
               the child process, or "undef" if the fork is
               unsuccessful.  File descriptors (and sometimes
               locks on those descriptors) are shared, while
               everything else is copied.  On most systems
               supporting fork(), great care has gone into making
               it extremely efficient (for example, using copy-
               on-write technology on data pages), making it the
               dominant paradigm for multitasking over the last
               few decades.

               Beginning with v5.6.0, Perl will attempt to flush
               all files opened for output before forking the
               child process, but this may not be supported on
               some platforms (see perlport).  To be safe, you
               may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any
               open handles in order to avoid duplicate output.

               If you "fork" without ever waiting on your
               children, you will accumulate zombies.  On some
               systems, you can avoid this by setting $SIG{CHLD}
               to "IGNORE".  See also perlipc for more examples
               of forking and reaping moribund children.

               Note that if your forked child inherits system
               file descriptors like STDIN and STDOUT that are
               actually connected by a pipe or socket, even if
               you exit, then the remote server (such as, say, a
               CGI script or a backgrounded job launched from a
               remote shell) won't think you're done.  You should
               reopen those to /dev/null if it's any issue.

       format  Declare a picture format for use by the "write"
               function.  For example:

                   format Something =
                       Test: @<<<<<<<< @||||| @>>>>>
                             $str,     $%,    '$' . int($num)
                   .

                   $str = "widget";
                   $num = $cost/$quantity;
                   $~ = 'Something';



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                   write;

               See perlform for many details and examples.

       formline PICTURE,LIST
               This is an internal function used by "format"s,
               though you may call it, too.  It formats (see
               perlform) a list of values according to the
               contents of PICTURE, placing the output into the
               format output accumulator, $^A (or $ACCUMULATOR in
               English).  Eventually, when a "write" is done, the
               contents of $^A are written to some filehandle.
               You could also read $^A and then set $^A back to
               "".  Note that a format typically does one
               "formline" per line of form, but the "formline"
               function itself doesn't care how many newlines are
               embedded in the PICTURE.  This means that the "~"
               and "~~" tokens will treat the entire PICTURE as a
               single line.  You may therefore need to use
               multiple formlines to implement a single record
               format, just like the format compiler.

               Be careful if you put double quotes around the
               picture, because an "@" character may be taken to
               mean the beginning of an array name.  "formline"
               always returns true.  See perlform for other
               examples.

       getc FILEHANDLE
       getc    Returns the next character from the input file
               attached to FILEHANDLE, or the undefined value at
               end of file, or if there was an error (in the
               latter case $! is set).  If FILEHANDLE is omitted,
               reads from STDIN.  This is not particularly
               efficient.  However, it cannot be used by itself
               to fetch single characters without waiting for the
               user to hit enter.  For that, try something more
               like:

                   if ($BSD_STYLE) {
                       system "stty cbreak </dev/tty >/dev/tty 2>&1";
                   }
                   else {
                       system "stty", '-icanon', 'eol', "\001";
                   }

                   $key = getc(STDIN);

                   if ($BSD_STYLE) {
                       system "stty -cbreak </dev/tty >/dev/tty 2>&1";
                   }
                   else {
                       system "stty", 'icanon', 'eol', '^@'; # ASCII null
                   }



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                   print "\n";

               Determination of whether $BSD_STYLE should be set
               is left as an exercise to the reader.

               The "POSIX::getattr" function can do this more
               portably on systems purporting POSIX compliance.
               See also the "Term::ReadKey" module from your
               nearest CPAN site; details on CPAN can be found on
               "CPAN" in perlmodlib.

       getlogin
               This implements the C library function of the same
               name, which on most systems returns the current
               login from /etc/utmp, if any.  If null, use
               "getpwuid".

                   $login = getlogin || getpwuid($<) || "Kilroy";

               Do not consider "getlogin" for authentication: it
               is not as secure as "getpwuid".

       getpeername SOCKET
               Returns the packed sockaddr address of other end
               of the SOCKET connection.

                   use Socket;
                   $hersockaddr    = getpeername(SOCK);
                   ($port, $iaddr) = sockaddr_in($hersockaddr);
                   $herhostname    = gethostbyaddr($iaddr, AF_INET);
                   $herstraddr     = inet_ntoa($iaddr);

       getpgrp PID
               Returns the current process group for the
               specified PID.  Use a PID of 0 to get the current
               process group for the current process.  Will raise
               an exception if used on a machine that doesn't
               implement getpgrp(2).  If PID is omitted, returns
               process group of current process.  Note that the
               POSIX version of "getpgrp" does not accept a PID
               argument, so only "PID==0" is truly portable.

       getppid Returns the process id of the parent process.

               Note for Linux users: on Linux, the C functions
               "getpid()" and "getppid()" return different values
               from different threads. In order to be portable,
               this behavior is not reflected by the perl-level
               function "getppid()", that returns a consistent
               value across threads. If you want to call the
               underlying "getppid()", you may use the CPAN
               module "Linux::Pid".





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       getpriority WHICH,WHO
               Returns the current priority for a process, a
               process group, or a user.  (See getpriority(2).)
               Will raise a fatal exception if used on a machine
               that doesn't implement getpriority(2).

       getpwnam NAME
       getgrnam NAME
       gethostbyname NAME
       getnetbyname NAME
       getprotobyname NAME
       getpwuid UID
       getgrgid GID
       getservbyname NAME,PROTO
       gethostbyaddr ADDR,ADDRTYPE
       getnetbyaddr ADDR,ADDRTYPE
       getprotobynumber NUMBER
       getservbyport PORT,PROTO
       getpwent
       getgrent
       gethostent
       getnetent
       getprotoent
       getservent
       setpwent
       setgrent
       sethostent STAYOPEN
       setnetent STAYOPEN
       setprotoent STAYOPEN
       setservent STAYOPEN
       endpwent
       endgrent
       endhostent
       endnetent
       endprotoent
       endservent
               These routines perform the same functions as their
               counterparts in the system library.  In list
               context, the return values from the various get
               routines are as follows:

                   ($name,$passwd,$uid,$gid,
                      $quota,$comment,$gcos,$dir,$shell,$expire) = getpw*
                   ($name,$passwd,$gid,$members) = getgr*
                   ($name,$aliases,$addrtype,$length,@addrs) = gethost*
                   ($name,$aliases,$addrtype,$net) = getnet*
                   ($name,$aliases,$proto) = getproto*
                   ($name,$aliases,$port,$proto) = getserv*

               (If the entry doesn't exist you get a null list.)

               The exact meaning of the $gcos field varies but it
               usually contains the real name of the user (as
               opposed to the login name) and other information



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               pertaining to the user.  Beware, however, that in
               many system users are able to change this
               information and therefore it cannot be trusted and
               therefore the $gcos is tainted (see perlsec).  The
               $passwd and $shell, user's encrypted password and
               login shell, are also tainted, because of the same
               reason.

               In scalar context, you get the name, unless the
               function was a lookup by name, in which case you
               get the other thing, whatever it is.  (If the
               entry doesn't exist you get the undefined value.)
               For example:

                   $uid   = getpwnam($name);
                   $name  = getpwuid($num);
                   $name  = getpwent();
                   $gid   = getgrnam($name);
                   $name  = getgrgid($num);
                   $name  = getgrent();
                   #etc.

               In getpw*() the fields $quota, $comment, and
               $expire are special cases in the sense that in
               many systems they are unsupported.  If the $quota
               is unsupported, it is an empty scalar.  If it is
               supported, it usually encodes the disk quota.  If
               the $comment field is unsupported, it is an empty
               scalar.  If it is supported it usually encodes
               some administrative comment about the user.  In
               some systems the $quota field may be $change or
               $age, fields that have to do with password aging.
               In some systems the $comment field may be $class.
               The $expire field, if present, encodes the
               expiration period of the account or the password.
               For the availability and the exact meaning of
               these fields in your system, please consult your
               getpwnam(3) documentation and your pwd.h file.
               You can also find out from within Perl what your
               $quota and $comment fields mean and whether you
               have the $expire field by using the "Config"
               module and the values "d_pwquota", "d_pwage",
               "d_pwchange", "d_pwcomment", and "d_pwexpire".
               Shadow password files are only supported if your
               vendor has implemented them in the intuitive
               fashion that calling the regular C library
               routines gets the shadow versions if you're
               running under privilege or if there exists the
               shadow(3) functions as found in System V (this
               includes Solaris and Linux.)  Those systems that
               implement a proprietary shadow password facility
               are unlikely to be supported.

               The $members value returned by getgr*() is a space



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               separated list of the login names of the members
               of the group.

               For the gethost*() functions, if the "h_errno"
               variable is supported in C, it will be returned to
               you via $? if the function call fails.  The @addrs
               value returned by a successful call is a list of
               the raw addresses returned by the corresponding
               system library call.  In the Internet domain, each
               address is four bytes long and you can unpack it
               by saying something like:

                   ($a,$b,$c,$d) = unpack('W4',$addr[0]);

               The Socket library makes this slightly easier:

                   use Socket;
                   $iaddr = inet_aton("127.1"); # or whatever address
                   $name  = gethostbyaddr($iaddr, AF_INET);

                   # or going the other way
                   $straddr = inet_ntoa($iaddr);

               In the opposite way, to resolve a hostname to the
               IP address you can write this:

                   use Socket;
                   $packed_ip = gethostbyname("www.perl.org");
                   if (defined $packed_ip) {
                       $ip_address = inet_ntoa($packed_ip);
                   }

               Make sure <gethostbyname()> is called in SCALAR
               context and that its return value is checked for
               definedness.

               If you get tired of remembering which element of
               the return list contains which return value, by-
               name interfaces are provided in standard modules:
               "File::stat", "Net::hostent", "Net::netent",
               "Net::protoent", "Net::servent", "Time::gmtime",
               "Time::localtime", and "User::grent".  These
               override the normal built-ins, supplying versions
               that return objects with the appropriate names for
               each field.  For example:

                  use File::stat;
                  use User::pwent;
                  $is_his = (stat($filename)->uid == pwent($whoever)->uid);

               Even though it looks like they're the same method
               calls (uid), they aren't, because a "File::stat"
               object is different from a "User::pwent" object.




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       getsockname SOCKET
               Returns the packed sockaddr address of this end of
               the SOCKET connection, in case you don't know the
               address because you have several different IPs
               that the connection might have come in on.

                   use Socket;
                   $mysockaddr = getsockname(SOCK);
                   ($port, $myaddr) = sockaddr_in($mysockaddr);
                   printf "Connect to %s [%s]\n",
                      scalar gethostbyaddr($myaddr, AF_INET),
                      inet_ntoa($myaddr);

       getsockopt SOCKET,LEVEL,OPTNAME
               Queries the option named OPTNAME associated with
               SOCKET at a given LEVEL.  Options may exist at
               multiple protocol levels depending on the socket
               type, but at least the uppermost socket level
               SOL_SOCKET (defined in the "Socket" module) will
               exist. To query options at another level the
               protocol number of the appropriate protocol
               controlling the option should be supplied. For
               example, to indicate that an option is to be
               interpreted by the TCP protocol, LEVEL should be
               set to the protocol number of TCP, which you can
               get using getprotobyname.

               The call returns a packed string representing the
               requested socket option, or "undef" if there is an
               error (the error reason will be in $!). What
               exactly is in the packed string depends in the
               LEVEL and OPTNAME, consult your system
               documentation for details. A very common case
               however is that the option is an integer, in which
               case the result will be a packed integer which you
               can decode using unpack with the "i" (or "I")
               format.

               An example testing if Nagle's algorithm is turned
               on on a socket:

                   use Socket qw(:all);

                   defined(my $tcp = getprotobyname("tcp"))
                       or die "Could not determine the protocol number for tcp";
                   # my $tcp = IPPROTO_TCP; # Alternative
                   my $packed = getsockopt($socket, $tcp, TCP_NODELAY)
                       or die "Could not query TCP_NODELAY socket option: $!";
                   my $nodelay = unpack("I", $packed);
                   print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";

       glob EXPR
       glob    In list context, returns a (possibly empty) list
               of filename expansions on the value of EXPR such



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               as the standard Unix shell /bin/csh would do. In
               scalar context, glob iterates through such
               filename expansions, returning undef when the list
               is exhausted. This is the internal function
               implementing the "<*.c>" operator, but you can use
               it directly. If EXPR is omitted, $_ is used.  The
               "<*.c>" operator is discussed in more detail in
               "I/O Operators" in perlop.

               Note that "glob" will split its arguments on
               whitespace, treating each segment as separate
               pattern.  As such, "glob('*.c *.h')" would match
               all files with a .c or .h extension.  The
               expression "glob('.* *')" would match all files in
               the current working directory.

               Beginning with v5.6.0, this operator is
               implemented using the standard "File::Glob"
               extension.  See File::Glob for details, including
               "bsd_glob" which does not treat whitespace as a
               pattern separator.

       gmtime EXPR
       gmtime  Works just like localtime but the returned values
               are localized for the standard Greenwich time
               zone.

               Note: when called in list context, $isdst, the
               last value returned by gmtime is always 0.  There
               is no Daylight Saving Time in GMT.

               See "gmtime" in perlport for portability concerns.

       goto LABEL
       goto EXPR
       goto &NAME
               The "goto-LABEL" form finds the statement labeled
               with LABEL and resumes execution there.  It may
               not be used to go into any construct that requires
               initialization, such as a subroutine or a
               "foreach" loop.  It also can't be used to go into
               a construct that is optimized away, or to get out
               of a block or subroutine given to "sort".  It can
               be used to go almost anywhere else within the
               dynamic scope, including out of subroutines, but
               it's usually better to use some other construct
               such as "last" or "die".  The author of Perl has
               never felt the need to use this form of "goto" (in
               Perl, that is--C is another matter).  (The
               difference being that C does not offer named loops
               combined with loop control.  Perl does, and this
               replaces most structured uses of "goto" in other
               languages.)




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               The "goto-EXPR" form expects a label name, whose
               scope will be resolved dynamically.  This allows
               for computed "goto"s per FORTRAN, but isn't
               necessarily recommended if you're optimizing for
               maintainability:

                   goto ("FOO", "BAR", "GLARCH")[$i];

               The "goto-&NAME" form is quite different from the
               other forms of "goto".  In fact, it isn't a goto
               in the normal sense at all, and doesn't have the
               stigma associated with other gotos.  Instead, it
               exits the current subroutine (losing any changes
               set by local()) and immediately calls in its place
               the named subroutine using the current value of
               @_.  This is used by "AUTOLOAD" subroutines that
               wish to load another subroutine and then pretend
               that the other subroutine had been called in the
               first place (except that any modifications to @_
               in the current subroutine are propagated to the
               other subroutine.)  After the "goto", not even
               "caller" will be able to tell that this routine
               was called first.

               NAME needn't be the name of a subroutine; it can
               be a scalar variable containing a code reference,
               or a block that evaluates to a code reference.

       grep BLOCK LIST
       grep EXPR,LIST
               This is similar in spirit to, but not the same as,
               grep(1) and its relatives.  In particular, it is
               not limited to using regular expressions.

               Evaluates the BLOCK or EXPR for each element of
               LIST (locally setting $_ to each element) and
               returns the list value consisting of those
               elements for which the expression evaluated to
               true.  In scalar context, returns the number of
               times the expression was true.

                   @foo = grep(!/^#/, @bar);    # weed out comments

               or equivalently,

                   @foo = grep {!/^#/} @bar;    # weed out comments

               Note that $_ is an alias to the list value, so it
               can be used to modify the elements of the LIST.
               While this is useful and supported, it can cause
               bizarre results if the elements of LIST are not
               variables.  Similarly, grep returns aliases into
               the original list, much as a for loop's index
               variable aliases the list elements.  That is,



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               modifying an element of a list returned by grep
               (for example, in a "foreach", "map" or another
               "grep") actually modifies the element in the
               original list.  This is usually something to be
               avoided when writing clear code.

               If $_ is lexical in the scope where the "grep"
               appears (because it has been declared with "my
               $_") then, in addition to being locally aliased to
               the list elements, $_ keeps being lexical inside
               the block; i.e. it can't be seen from the outside,
               avoiding any potential side-effects.

               See also "map" for a list composed of the results
               of the BLOCK or EXPR.

       hex EXPR
       hex     Interprets EXPR as a hex string and returns the
               corresponding value.  (To convert strings that
               might start with either 0, "0x", or "0b", see
               "oct".)  If EXPR is omitted, uses $_.

                   print hex '0xAf'; # prints '175'
                   print hex 'aF';   # same

               Hex strings may only represent integers.  Strings
               that would cause integer overflow trigger a
               warning.  Leading whitespace is not stripped,
               unlike oct(). To present something as hex, look
               into "printf", "sprintf", or "unpack".

       import LIST
               There is no builtin "import" function.  It is just
               an ordinary method (subroutine) defined (or
               inherited) by modules that wish to export names to
               another module.  The "use" function calls the
               "import" method for the package used.  See also
               "use", perlmod, and Exporter.

       index STR,SUBSTR,POSITION
       index STR,SUBSTR
               The index function searches for one string within
               another, but without the wildcard-like behavior of
               a full regular-expression pattern match.  It
               returns the position of the first occurrence of
               SUBSTR in STR at or after POSITION.  If POSITION
               is omitted, starts searching from the beginning of
               the string.  POSITION before the beginning of the
               string or after its end is treated as if it were
               the beginning or the end, respectively.  POSITION
               and the return value are based at 0 (or whatever
               you've set the $[ variable to--but don't do that).
               If the substring is not found, "index" returns one
               less than the base, ordinarily "-1".



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       int EXPR
       int     Returns the integer portion of EXPR.  If EXPR is
               omitted, uses $_.  You should not use this
               function for rounding: one because it truncates
               towards 0, and two because machine representations
               of floating point numbers can sometimes produce
               counterintuitive results.  For example,
               "int(-6.725/0.025)" produces -268 rather than the
               correct -269; that's because it's really more like
               -268.99999999999994315658 instead.  Usually, the
               "sprintf", "printf", or the "POSIX::floor" and
               "POSIX::ceil" functions will serve you better than
               will int().

       ioctl FILEHANDLE,FUNCTION,SCALAR
               Implements the ioctl(2) function.  You'll probably
               first have to say

                   require "sys/ioctl.ph";     # probably in $Config{archlib}/sys/ioctl.ph

               to get the correct function definitions.  If
               sys/ioctl.ph doesn't exist or doesn't have the
               correct definitions you'll have to roll your own,
               based on your C header files such as
               <sys/ioctl.h>.  (There is a Perl script called
               h2ph that comes with the Perl kit that may help
               you in this, but it's nontrivial.)  SCALAR will be
               read and/or written depending on the FUNCTION--a
               pointer to the string value of SCALAR will be
               passed as the third argument of the actual "ioctl"
               call.  (If SCALAR has no string value but does
               have a numeric value, that value will be passed
               rather than a pointer to the string value.  To
               guarantee this to be true, add a 0 to the scalar
               before using it.)  The "pack" and "unpack"
               functions may be needed to manipulate the values
               of structures used by "ioctl".

               The return value of "ioctl" (and "fcntl") is as
               follows:

                       if OS returns:          then Perl returns:
                           -1                    undefined value
                            0                  string "0 but true"
                       anything else               that number

               Thus Perl returns true on success and false on
               failure, yet you can still easily determine the
               actual value returned by the operating system:

                   $retval = ioctl(...) || -1;
                   printf "System returned %d\n", $retval;

               The special string "0 but true" is exempt from -w



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               complaints about improper numeric conversions.

       join EXPR,LIST
               Joins the separate strings of LIST into a single
               string with fields separated by the value of EXPR,
               and returns that new string.  Example:

                   $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);

               Beware that unlike "split", "join" doesn't take a
               pattern as its first argument.  Compare "split".

       keys HASH
               Returns a list consisting of all the keys of the
               named hash.  (In scalar context, returns the
               number of keys.)

               The keys are returned in an apparently random
               order.  The actual random order is subject to
               change in future versions of perl, but it is
               guaranteed to be the same order as either the
               "values" or "each" function produces (given that
               the hash has not been modified).  Since Perl 5.8.1
               the ordering is different even between different
               runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

               As a side effect, calling keys() resets the HASH's
               internal iterator (see "each").  In particular,
               calling keys() in void context resets the iterator
               with no other overhead.

               Here is yet another way to print your environment:

                   @keys = keys %ENV;
                   @values = values %ENV;
                   while (@keys) {
                       print pop(@keys), '=', pop(@values), "\n";
                   }

               or how about sorted by key:

                   foreach $key (sort(keys %ENV)) {
                       print $key, '=', $ENV{$key}, "\n";
                   }

               The returned values are copies of the original
               keys in the hash, so modifying them will not
               affect the original hash.  Compare "values".

               To sort a hash by value, you'll need to use a
               "sort" function.  Here's a descending numeric sort
               of a hash by its values:




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                   foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
                       printf "%4d %s\n", $hash{$key}, $key;
                   }

               As an lvalue "keys" allows you to increase the
               number of hash buckets allocated for the given
               hash.  This can gain you a measure of efficiency
               if you know the hash is going to get big.  (This
               is similar to pre-extending an array by assigning
               a larger number to $#array.)  If you say

                   keys %hash = 200;

               then %hash will have at least 200 buckets
               allocated for it--256 of them, in fact, since it
               rounds up to the next power of two.  These buckets
               will be retained even if you do "%hash = ()", use
               "undef %hash" if you want to free the storage
               while %hash is still in scope.  You can't shrink
               the number of buckets allocated for the hash using
               "keys" in this way (but you needn't worry about
               doing this by accident, as trying has no effect).

               See also "each", "values" and "sort".

       kill SIGNAL, LIST
               Sends a signal to a list of processes.  Returns
               the number of processes successfully signaled
               (which is not necessarily the same as the number
               actually killed).

                   $cnt = kill 1, $child1, $child2;
                   kill 9, @goners;

               If SIGNAL is zero, no signal is sent to the
               process, but the kill(2) system call will check
               whether it's possible to send a signal to it (that
               means, to be brief, that the process is owned by
               the same user, or we are the super-user).  This is
               a useful way to check that a child process is
               alive (even if only as a zombie) and hasn't
               changed its UID.  See perlport for notes on the
               portability of this construct.

               Unlike in the shell, if SIGNAL is negative, it
               kills process groups instead of processes.  (On
               System V, a negative PROCESS number will also kill
               process groups, but that's not portable.)  That
               means you usually want to use positive not
               negative signals.  You may also use a signal name
               in quotes.

               See "Signals" in perlipc for more details.




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       last LABEL
       last    The "last" command is like the "break" statement
               in C (as used in loops); it immediately exits the
               loop in question.  If the LABEL is omitted, the
               command refers to the innermost enclosing loop.
               The "continue" block, if any, is not executed:

                   LINE: while (<STDIN>) {
                       last LINE if /^$/;      # exit when done with header
                       #...
                   }

               "last" cannot be used to exit a block which
               returns a value such as "eval {}", "sub {}" or "do
               {}", and should not be used to exit a grep() or
               map() operation.

               Note that a block by itself is semantically
               identical to a loop that executes once.  Thus
               "last" can be used to effect an early exit out of
               such a block.

               See also "continue" for an illustration of how
               "last", "next", and "redo" work.

       lc EXPR
       lc      Returns a lowercased version of EXPR.  This is the
               internal function implementing the "\L" escape in
               double-quoted strings.  Respects current LC_CTYPE
               locale if "use locale" in force.  See perllocale
               and perlunicode for more details about locale and
               Unicode support.

               If EXPR is omitted, uses $_.

       lcfirst EXPR
       lcfirst Returns the value of EXPR with the first character
               lowercased.  This is the internal function
               implementing the "\l" escape in double-quoted
               strings.  Respects current LC_CTYPE locale if "use
               locale" in force.  See perllocale and perlunicode
               for more details about locale and Unicode support.

               If EXPR is omitted, uses $_.

       length EXPR
       length  Returns the length in characters of the value of
               EXPR.  If EXPR is omitted, returns length of $_.
               Note that this cannot be used on an entire array
               or hash to find out how many elements these have.
               For that, use "scalar @array" and "scalar keys
               %hash" respectively.

               Note the characters: if the EXPR is in Unicode,



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               you will get the number of characters, not the
               number of bytes.  To get the length of the
               internal string in bytes, use
               "bytes::length(EXPR)", see bytes.  Note that the
               internal encoding is variable, and the number of
               bytes usually meaningless.  To get the number of
               bytes that the string would have when encoded as
               UTF-8, use "length(Encoding::encode_utf8(EXPR))".

       link OLDFILE,NEWFILE
               Creates a new filename linked to the old filename.
               Returns true for success, false otherwise.

       listen SOCKET,QUEUESIZE
               Does the same thing that the listen system call
               does.  Returns true if it succeeded, false
               otherwise.  See the example in "Sockets:
               Client/Server Communication" in perlipc.

       local EXPR
               You really probably want to be using "my" instead,
               because "local" isn't what most people think of as
               "local".  See "Private Variables via my()" in
               perlsub for details.

               A local modifies the listed variables to be local
               to the enclosing block, file, or eval.  If more
               than one value is listed, the list must be placed
               in parentheses.  See "Temporary Values via
               local()" in perlsub for details, including issues
               with tied arrays and hashes.

       localtime EXPR
       localtime
               Converts a time as returned by the time function
               to a 9-element list with the time analyzed for the
               local time zone.  Typically used as follows:

                   #  0    1    2     3     4    5     6     7     8
                   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                               localtime(time);

               All list elements are numeric, and come straight
               out of the C `struct tm'.  $sec, $min, and $hour
               are the seconds, minutes, and hours of the
               specified time.

               $mday is the day of the month, and $mon is the
               month itself, in the range 0..11 with 0 indicating
               January and 11 indicating December.  This makes it
               easy to get a month name from a list:






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                   my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
                   print "$abbr[$mon] $mday";
                   # $mon=9, $mday=18 gives "Oct 18"

               $year is the number of years since 1900, not just
               the last two digits of the year.  That is, $year
               is 123 in year 2023.  The proper way to get a
               complete 4-digit year is simply:

                   $year += 1900;

               Otherwise you create non-Y2K-compliant
               programs--and you wouldn't want to do that, would
               you?

               To get the last two digits of the year (e.g., '01'
               in 2001) do:

                   $year = sprintf("%02d", $year % 100);

               $wday is the day of the week, with 0 indicating
               Sunday and 3 indicating Wednesday.  $yday is the
               day of the year, in the range 0..364 (or 0..365 in
               leap years.)

               $isdst is true if the specified time occurs during
               Daylight Saving Time, false otherwise.

               If EXPR is omitted, "localtime()" uses the current
               time (as returned by time(3)).

               In scalar context, "localtime()" returns the
               ctime(3) value:

                   $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994"

               This scalar value is not locale dependent but is a
               Perl builtin. For GMT instead of local time use
               the "gmtime" builtin. See also the "Time::Local"
               module (to convert the second, minutes, hours, ...
               back to the integer value returned by time()), and
               the POSIX module's strftime(3) and mktime(3)
               functions.

               To get somewhat similar but locale dependent date
               strings, set up your locale environment variables
               appropriately (please see perllocale) and try for
               example:

                   use POSIX qw(strftime);
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
                   # or for GMT formatted appropriately for your locale:
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;




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               Note that the %a and %b, the short forms of the
               day of the week and the month of the year, may not
               necessarily be three characters wide.

               See "localtime" in perlport for portability
               concerns.

               The Time::gmtime and Time::localtime modules
               provides a convenient, by-name access mechanism to
               the gmtime() and localtime() functions,
               respectively.

               For a comprehensive date and time representation
               look at the DateTime module on CPAN.

       lock THING
               This function places an advisory lock on a shared
               variable, or referenced object contained in THING
               until the lock goes out of scope.

               lock() is a "weak keyword" : this means that if
               you've defined a function by this name (before any
               calls to it), that function will be called
               instead. (However, if you've said "use threads",
               lock() is always a keyword.) See threads.

       log EXPR
       log     Returns the natural logarithm (base e) of EXPR.
               If EXPR is omitted, returns log of $_.  To get the
               log of another base, use basic algebra: The base-N
               log of a number is equal to the natural log of
               that number divided by the natural log of N.  For
               example:

                   sub log10 {
                       my $n = shift;
                       return log($n)/log(10);
                   }

               See also "exp" for the inverse operation.

       lstat EXPR
       lstat   Does the same thing as the "stat" function
               (including setting the special "_" filehandle) but
               stats a symbolic link instead of the file the
               symbolic link points to.  If symbolic links are
               unimplemented on your system, a normal "stat" is
               done.  For much more detailed information, please
               see the documentation for "stat".

               If EXPR is omitted, stats $_.

       m//     The match operator.  See "Regexp Quote-Like
               Operators" in perlop.



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       map BLOCK LIST
       map EXPR,LIST
               Evaluates the BLOCK or EXPR for each element of
               LIST (locally setting $_ to each element) and
               returns the list value composed of the results of
               each such evaluation.  In scalar context, returns
               the total number of elements so generated.
               Evaluates BLOCK or EXPR in list context, so each
               element of LIST may produce zero, one, or more
               elements in the returned value.

                   @chars = map(chr, @nums);

               translates a list of numbers to the corresponding
               characters.  And

                   %hash = map { get_a_key_for($_) => $_ } @array;

               is just a funny way to write

                   %hash = ();
                   foreach (@array) {
                       $hash{get_a_key_for($_)} = $_;
                   }

               Note that $_ is an alias to the list value, so it
               can be used to modify the elements of the LIST.
               While this is useful and supported, it can cause
               bizarre results if the elements of LIST are not
               variables.  Using a regular "foreach" loop for
               this purpose would be clearer in most cases.  See
               also "grep" for an array composed of those items
               of the original list for which the BLOCK or EXPR
               evaluates to true.

               If $_ is lexical in the scope where the "map"
               appears (because it has been declared with "my
               $_"), then, in addition to being locally aliased
               to the list elements, $_ keeps being lexical
               inside the block; that is, it can't be seen from
               the outside, avoiding any potential side-effects.

               "{" starts both hash references and blocks, so
               "map { ..." could be either the start of map BLOCK
               LIST or map EXPR, LIST. Because perl doesn't look
               ahead for the closing "}" it has to take a guess
               at which its dealing with based what it finds just
               after the "{". Usually it gets it right, but if it
               doesn't it won't realize something is wrong until
               it gets to the "}" and encounters the missing (or
               unexpected) comma. The syntax error will be
               reported close to the "}" but you'll need to
               change something near the "{" such as using a
               unary "+" to give perl some help:



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                   %hash = map {  "\L$_", 1  } @array  # perl guesses EXPR.  wrong
                   %hash = map { +"\L$_", 1  } @array  # perl guesses BLOCK. right
                   %hash = map { ("\L$_", 1) } @array  # this also works
                   %hash = map {  lc($_), 1  } @array  # as does this.
                   %hash = map +( lc($_), 1 ), @array  # this is EXPR and works!

                   %hash = map  ( lc($_), 1 ), @array  # evaluates to (1, @array)

               or to force an anon hash constructor use "+{":

                  @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end

               and you get list of anonymous hashes each with
               only 1 entry.

       mkdir FILENAME,MASK
       mkdir FILENAME
       mkdir   Creates the directory specified by FILENAME, with
               permissions specified by MASK (as modified by
               "umask").  If it succeeds it returns true,
               otherwise it returns false and sets $! (errno).
               If omitted, MASK defaults to 0777. If omitted,
               FILENAME defaults to $_.

               In general, it is better to create directories
               with permissive MASK, and let the user modify that
               with their "umask", than it is to supply a
               restrictive MASK and give the user no way to be
               more permissive.  The exceptions to this rule are
               when the file or directory should be kept private
               (mail files, for instance).  The perlfunc(1) entry
               on "umask" discusses the choice of MASK in more
               detail.

               Note that according to the POSIX 1003.1-1996 the
               FILENAME may have any number of trailing slashes.
               Some operating and filesystems do not get this
               right, so Perl automatically removes all trailing
               slashes to keep everyone happy.

               In order to recursively create a directory
               structure look at the "mkpath" function of the
               File::Path module.

       msgctl ID,CMD,ARG
               Calls the System V IPC function msgctl(2).  You'll
               probably have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If
               CMD is "IPC_STAT", then ARG must be a variable
               that will hold the returned "msqid_ds" structure.
               Returns like "ioctl": the undefined value for



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               error, "0 but true" for zero, or the actual return
               value otherwise.  See also "SysV IPC" in perlipc,
               "IPC::SysV", and "IPC::Semaphore" documentation.

       msgget KEY,FLAGS
               Calls the System V IPC function msgget(2).
               Returns the message queue id, or the undefined
               value if there is an error.  See also "SysV IPC"
               in perlipc and "IPC::SysV" and "IPC::Msg"
               documentation.

       msgrcv ID,VAR,SIZE,TYPE,FLAGS
               Calls the System V IPC function msgrcv to receive
               a message from message queue ID into variable VAR
               with a maximum message size of SIZE.  Note that
               when a message is received, the message type as a
               native long integer will be the first thing in
               VAR, followed by the actual message.  This packing
               may be opened with "unpack("l! a*")".  Taints the
               variable.  Returns true if successful, or false if
               there is an error.  See also "SysV IPC" in
               perlipc, "IPC::SysV", and "IPC::SysV::Msg"
               documentation.

       msgsnd ID,MSG,FLAGS
               Calls the System V IPC function msgsnd to send the
               message MSG to the message queue ID.  MSG must
               begin with the native long integer message type,
               and be followed by the length of the actual
               message, and finally the message itself.  This
               kind of packing can be achieved with "pack("l!
               a*", $type, $message)".  Returns true if
               successful, or false if there is an error.  See
               also "IPC::SysV" and "IPC::SysV::Msg"
               documentation.

       my EXPR
       my TYPE EXPR
       my EXPR : ATTRS
       my TYPE EXPR : ATTRS
               A "my" declares the listed variables to be local
               (lexically) to the enclosing block, file, or
               "eval".  If more than one value is listed, the
               list must be placed in parentheses.

               The exact semantics and interface of TYPE and
               ATTRS are still evolving.  TYPE is currently bound
               to the use of "fields" pragma, and attributes are
               handled using the "attributes" pragma, or starting
               from Perl 5.8.0 also via the "Attribute::Handlers"
               module.  See "Private Variables via my()" in
               perlsub for details, and fields, attributes, and
               Attribute::Handlers.




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       next LABEL
       next    The "next" command is like the "continue"
               statement in C; it starts the next iteration of
               the loop:

                   LINE: while (<STDIN>) {
                       next LINE if /^#/;      # discard comments
                       #...
                   }

               Note that if there were a "continue" block on the
               above, it would get executed even on discarded
               lines.  If the LABEL is omitted, the command
               refers to the innermost enclosing loop.

               "next" cannot be used to exit a block which
               returns a value such as "eval {}", "sub {}" or "do
               {}", and should not be used to exit a grep() or
               map() operation.

               Note that a block by itself is semantically
               identical to a loop that executes once.  Thus
               "next" will exit such a block early.

               See also "continue" for an illustration of how
               "last", "next", and "redo" work.

       no Module VERSION LIST
       no Module VERSION
       no Module LIST
       no Module
       no VERSION
               See the "use" function, of which "no" is the
               opposite.

       oct EXPR
       oct     Interprets EXPR as an octal string and returns the
               corresponding value.  (If EXPR happens to start
               off with "0x", interprets it as a hex string.  If
               EXPR starts off with "0b", it is interpreted as a
               binary string.  Leading whitespace is ignored in
               all three cases.)  The following will handle
               decimal, binary, octal, and hex in the standard
               Perl or C notation:

                   $val = oct($val) if $val =~ /^0/;

               If EXPR is omitted, uses $_.   To go the other way
               (produce a number in octal), use sprintf() or
               printf():

                   $perms = (stat("filename"))[2] & 07777;
                   $oct_perms = sprintf "%lo", $perms;




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               The oct() function is commonly used when a string
               such as 644 needs to be converted into a file
               mode, for example. (Although perl will
               automatically convert strings into numbers as
               needed, this automatic conversion assumes base
               10.)

       open FILEHANDLE,EXPR
       open FILEHANDLE,MODE,EXPR
       open FILEHANDLE,MODE,EXPR,LIST
       open FILEHANDLE,MODE,REFERENCE
       open FILEHANDLE
               Opens the file whose filename is given by EXPR,
               and associates it with FILEHANDLE.

               Simple examples to open a file for reading:

                   open(my $fh, '<', "input.txt") or die $!;

               and for writing:

                   open(my $fh, '>', "output.txt") or die $!;

               (The following is a comprehensive reference to
               open(): for a gentler introduction you may
               consider perlopentut.)

               If FILEHANDLE is an undefined scalar variable (or
               array or hash element) the variable is assigned a
               reference to a new anonymous filehandle, otherwise
               if FILEHANDLE is an expression, its value is used
               as the name of the real filehandle wanted.  (This
               is considered a symbolic reference, so "use strict
               'refs'" should not be in effect.)

               If EXPR is omitted, the scalar variable of the
               same name as the FILEHANDLE contains the filename.
               (Note that lexical variables--those declared with
               "my"--will not work for this purpose; so if you're
               using "my", specify EXPR in your call to open.)

               If three or more arguments are specified then the
               mode of opening and the file name are separate. If
               MODE is '<' or nothing, the file is opened for
               input.  If MODE is '>', the file is truncated and
               opened for output, being created if necessary.  If
               MODE is '>>', the file is opened for appending,
               again being created if necessary.

               You can put a '+' in front of the '>' or '<' to
               indicate that you want both read and write access
               to the file; thus '+<' is almost always preferred
               for read/write updates--the '+>' mode would
               clobber the file first.  You can't usually use



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               either read-write mode for updating textfiles,
               since they have variable length records.  See the
               -i switch in perlrun for a better approach.  The
               file is created with permissions of 0666 modified
               by the process' "umask" value.

               These various prefixes correspond to the fopen(3)
               modes of 'r', 'r+', 'w', 'w+', 'a', and 'a+'.

               In the 2-arguments (and 1-argument) form of the
               call the mode and filename should be concatenated
               (in this order), possibly separated by spaces.  It
               is possible to omit the mode in these forms if the
               mode is '<'.

               If the filename begins with '|', the filename is
               interpreted as a command to which output is to be
               piped, and if the filename ends with a '|', the
               filename is interpreted as a command which pipes
               output to us.  See "Using open() for IPC" in
               perlipc for more examples of this.  (You are not
               allowed to "open" to a command that pipes both in
               and out, but see IPC::Open2, IPC::Open3, and
               "Bidirectional Communication with Another Process"
               in perlipc for alternatives.)

               For three or more arguments if MODE is '|-', the
               filename is interpreted as a command to which
               output is to be piped, and if MODE is '-|', the
               filename is interpreted as a command which pipes
               output to us.  In the 2-arguments (and 1-argument)
               form one should replace dash ('-') with the
               command.  See "Using open() for IPC" in perlipc
               for more examples of this.  (You are not allowed
               to "open" to a command that pipes both in and out,
               but see IPC::Open2, IPC::Open3, and "Bidirectional
               Communication" in perlipc for alternatives.)

               In the three-or-more argument form of pipe opens,
               if LIST is specified (extra arguments after the
               command name) then LIST becomes arguments to the
               command invoked if the platform supports it.  The
               meaning of "open" with more than three arguments
               for non-pipe modes is not yet specified.
               Experimental "layers" may give extra LIST
               arguments meaning.

               In the 2-arguments (and 1-argument) form opening
               '-' opens STDIN and opening '>-' opens STDOUT.

               You may use the three-argument form of open to
               specify IO "layers" (sometimes also referred to as
               "disciplines") to be applied to the handle that
               affect how the input and output are processed (see



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               open and PerlIO for more details). For example

                 open(my $fh, "<:encoding(UTF-8)", "file")

               will open the UTF-8 encoded file containing
               Unicode characters, see perluniintro. Note that if
               layers are specified in the three-arg form then
               default layers stored in ${^OPEN} (see perlvar;
               usually set by the open pragma or the switch
               -CioD) are ignored.

               Open returns nonzero upon success, the undefined
               value otherwise.  If the "open" involved a pipe,
               the return value happens to be the pid of the
               subprocess.

               If you're running Perl on a system that
               distinguishes between text files and binary files,
               then you should check out "binmode" for tips for
               dealing with this.  The key distinction between
               systems that need "binmode" and those that don't
               is their text file formats.  Systems like Unix,
               Mac OS, and Plan 9, which delimit lines with a
               single character, and which encode that character
               in C as "\n", do not need "binmode".  The rest
               need it.

               When opening a file, it's usually a bad idea to
               continue normal execution if the request failed,
               so "open" is frequently used in connection with
               "die".  Even if "die" won't do what you want (say,
               in a CGI script, where you want to make a nicely
               formatted error message (but there are modules
               that can help with that problem)) you should
               always check the return value from opening a file.
               The infrequent exception is when working with an
               unopened filehandle is actually what you want to
               do.

               As a special case the 3-arg form with a read/write
               mode and the third argument being "undef":

                   open(my $tmp, "+>", undef) or die ...

               opens a filehandle to an anonymous temporary file.
               Also using "+<" works for symmetry, but you really
               should consider writing something to the temporary
               file first.  You will need to seek() to do the
               reading.

               Since v5.8.0, perl has built using PerlIO by
               default.  Unless you've changed this (i.e.
               Configure -Uuseperlio), you can open file handles
               to "in memory" files held in Perl scalars via:



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                   open($fh, '>', \$variable) || ..

               Though if you try to re-open "STDOUT" or "STDERR"
               as an "in memory" file, you have to close it
               first:

                   close STDOUT;
                   open STDOUT, '>', \$variable or die "Can't open STDOUT: $!";

               Examples:

                   $ARTICLE = 100;
                   open ARTICLE or die "Can't find article $ARTICLE: $!\n";
                   while (<ARTICLE>) {...

                   open(LOG, '>>/usr/spool/news/twitlog');     # (log is reserved)
                   # if the open fails, output is discarded

                   open(my $dbase, '+<', 'dbase.mine')         # open for update
                       or die "Can't open 'dbase.mine' for update: $!";

                   open(my $dbase, '+<dbase.mine')                     # ditto
                       or die "Can't open 'dbase.mine' for update: $!";

                   open(ARTICLE, '-|', "caesar <$article")     # decrypt article
                       or die "Can't start caesar: $!";

                   open(ARTICLE, "caesar <$article |")         # ditto
                       or die "Can't start caesar: $!";

                   open(EXTRACT, "|sort >Tmp$$")               # $$ is our process id
                       or die "Can't start sort: $!";

                   # in memory files
                   open(MEMORY,'>', \$var)
                       or die "Can't open memory file: $!";
                   print MEMORY "foo!\n";                      # output will end up in $var

                   # process argument list of files along with any includes

                   foreach $file (@ARGV) {
                       process($file, 'fh00');
                   }

                   sub process {
                       my($filename, $input) = @_;
                       $input++;               # this is a string increment
                       unless (open($input, $filename)) {
                           print STDERR "Can't open $filename: $!\n";
                           return;
                       }

                       local $_;
                       while (<$input>) {              # note use of indirection



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                           if (/^#include "(.*)"/) {
                               process($1, $input);
                               next;
                           }
                           #...                # whatever
                       }
                   }

               See perliol for detailed info on PerlIO.

               You may also, in the Bourne shell tradition,
               specify an EXPR beginning with '>&', in which case
               the rest of the string is interpreted as the name
               of a filehandle (or file descriptor, if numeric)
               to be duped (as dup(2)) and opened.  You may use
               "&" after ">", ">>", "<", "+>", "+>>", and "+<".
               The mode you specify should match the mode of the
               original filehandle.  (Duping a filehandle does
               not take into account any existing contents of IO
               buffers.) If you use the 3-arg form then you can
               pass either a number, the name of a filehandle or
               the normal "reference to a glob".

               Here is a script that saves, redirects, and
               restores "STDOUT" and "STDERR" using various
               methods:

                   #!/usr/bin/perl
                   open my $oldout, ">&STDOUT"     or die "Can't dup STDOUT: $!";
                   open OLDERR,     ">&", \*STDERR or die "Can't dup STDERR: $!";

                   open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!";
                   open STDERR, ">&STDOUT"     or die "Can't dup STDOUT: $!";

                   select STDERR; $| = 1;      # make unbuffered
                   select STDOUT; $| = 1;      # make unbuffered

                   print STDOUT "stdout 1\n";  # this works for
                   print STDERR "stderr 1\n";  # subprocesses too

                   open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
                   open STDERR, ">&OLDERR"    or die "Can't dup OLDERR: $!";

                   print STDOUT "stdout 2\n";
                   print STDERR "stderr 2\n";

               If you specify '<&=X', where "X" is a file
               descriptor number or a filehandle, then Perl will
               do an equivalent of C's "fdopen" of that file
               descriptor (and not call dup(2)); this is more
               parsimonious of file descriptors.  For example:

                   # open for input, reusing the fileno of $fd
                   open(FILEHANDLE, "<&=$fd")



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               or

                   open(FILEHANDLE, "<&=", $fd)

               or

                   # open for append, using the fileno of OLDFH
                   open(FH, ">>&=", OLDFH)

               or

                   open(FH, ">>&=OLDFH")

               Being parsimonious on filehandles is also useful
               (besides being parsimonious) for example when
               something is dependent on file descriptors, like
               for example locking using flock().  If you do just
               "open(A, '>>&B')", the filehandle A will not have
               the same file descriptor as B, and therefore
               flock(A) will not flock(B), and vice versa.  But
               with "open(A, '>>&=B')" the filehandles will share
               the same file descriptor.

               Note that if you are using Perls older than 5.8.0,
               Perl will be using the standard C libraries'
               fdopen() to implement the "=" functionality.  On
               many UNIX systems fdopen() fails when file
               descriptors exceed a certain value, typically 255.
               For Perls 5.8.0 and later, PerlIO is most often
               the default.

               You can see whether Perl has been compiled with
               PerlIO or not by running "perl -V" and looking for
               "useperlio=" line.  If "useperlio" is "define",
               you have PerlIO, otherwise you don't.

               If you open a pipe on the command '-', i.e.,
               either '|-' or '-|' with 2-arguments (or
               1-argument) form of open(), then there is an
               implicit fork done, and the return value of open
               is the pid of the child within the parent process,
               and 0 within the child process.  (Use
               "defined($pid)" to determine whether the open was
               successful.)  The filehandle behaves normally for
               the parent, but i/o to that filehandle is piped
               from/to the STDOUT/STDIN of the child process.  In
               the child process the filehandle isn't opened--i/o
               happens from/to the new STDOUT or STDIN.
               Typically this is used like the normal piped open
               when you want to exercise more control over just
               how the pipe command gets executed, such as when
               you are running setuid, and don't want to have to
               scan shell commands for metacharacters.  The
               following triples are more or less equivalent:



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                   open(FOO, "|tr '[a-z]' '[A-Z]'");
                   open(FOO, '|-', "tr '[a-z]' '[A-Z]'");
                   open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]';
                   open(FOO, '|-', "tr", '[a-z]', '[A-Z]');

                   open(FOO, "cat -n '$file'|");
                   open(FOO, '-|', "cat -n '$file'");
                   open(FOO, '-|') || exec 'cat', '-n', $file;
                   open(FOO, '-|', "cat", '-n', $file);

               The last example in each block shows the pipe as
               "list form", which is not yet supported on all
               platforms.  A good rule of thumb is that if your
               platform has true "fork()" (in other words, if
               your platform is UNIX) you can use the list form.

               See "Safe Pipe Opens" in perlipc for more examples
               of this.

               Beginning with v5.6.0, Perl will attempt to flush
               all files opened for output before any operation
               that may do a fork, but this may not be supported
               on some platforms (see perlport).  To be safe, you
               may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any
               open handles.

               On systems that support a close-on-exec flag on
               files, the flag will be set for the newly opened
               file descriptor as determined by the value of $^F.
               See "$^F" in perlvar.

               Closing any piped filehandle causes the parent
               process to wait for the child to finish, and
               returns the status value in $? and
               "${^CHILD_ERROR_NATIVE}".

               The filename passed to 2-argument (or 1-argument)
               form of open() will have leading and trailing
               whitespace deleted, and the normal redirection
               characters honored.  This property, known as
               "magic open", can often be used to good effect.  A
               user could specify a filename of "rsh cat file |",
               or you could change certain filenames as needed:

                   $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/;
                   open(FH, $filename) or die "Can't open $filename: $!";

               Use 3-argument form to open a file with arbitrary
               weird characters in it,

                   open(FOO, '<', $file);

               otherwise it's necessary to protect any leading



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               and trailing whitespace:

                   $file =~ s#^(\s)#./$1#;
                   open(FOO, "< $file\0");

               (this may not work on some bizarre filesystems).
               One should conscientiously choose between the
               magic and 3-arguments form of open():

                   open IN, $ARGV[0];

               will allow the user to specify an argument of the
               form "rsh cat file |", but will not work on a
               filename which happens to have a trailing space,
               while

                   open IN, '<', $ARGV[0];

               will have exactly the opposite restrictions.

               If you want a "real" C "open" (see open(2) on your
               system), then you should use the "sysopen"
               function, which involves no such magic (but may
               use subtly different filemodes than Perl open(),
               which is mapped to C fopen()).  This is another
               way to protect your filenames from interpretation.
               For example:

                   use IO::Handle;
                   sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
                       or die "sysopen $path: $!";
                   $oldfh = select(HANDLE); $| = 1; select($oldfh);
                   print HANDLE "stuff $$\n";
                   seek(HANDLE, 0, 0);
                   print "File contains: ", <HANDLE>;

               Using the constructor from the "IO::Handle"
               package (or one of its subclasses, such as
               "IO::File" or "IO::Socket"), you can generate
               anonymous filehandles that have the scope of
               whatever variables hold references to them, and
               automatically close whenever and however you leave
               that scope:














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                   use IO::File;
                   #...
                   sub read_myfile_munged {
                       my $ALL = shift;
                       my $handle = IO::File->new;
                       open($handle, "myfile") or die "myfile: $!";
                       $first = <$handle>
                           or return ();     # Automatically closed here.
                       mung $first or die "mung failed";       # Or here.
                       return $first, <$handle> if $ALL;       # Or here.
                       $first;                                 # Or here.
                   }

               See "seek" for some details about mixing reading
               and writing.

       opendir DIRHANDLE,EXPR
               Opens a directory named EXPR for processing by
               "readdir", "telldir", "seekdir", "rewinddir", and
               "closedir".  Returns true if successful.
               DIRHANDLE may be an expression whose value can be
               used as an indirect dirhandle, usually the real
               dirhandle name.  If DIRHANDLE is an undefined
               scalar variable (or array or hash element), the
               variable is assigned a reference to a new
               anonymous dirhandle.  DIRHANDLEs have their own
               namespace separate from FILEHANDLEs.

               See example at "readdir".

       ord EXPR
       ord     Returns the numeric (the native 8-bit encoding,
               like ASCII or EBCDIC, or Unicode) value of the
               first character of EXPR.  If EXPR is omitted, uses
               $_.

               For the reverse, see "chr".  See perlunicode for
               more about Unicode.

       our EXPR
       our TYPE EXPR
       our EXPR : ATTRS
       our TYPE EXPR : ATTRS
               "our" associates a simple name with a package
               variable in the current package for use within the
               current scope.  When "use strict 'vars'" is in
               effect, "our" lets you use declared global
               variables without qualifying them with package
               names, within the lexical scope of the "our"
               declaration.  In this way "our" differs from "use
               vars", which is package scoped.

               Unlike "my", which both allocates storage for a
               variable and associates a simple name with that



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               storage for use within the current scope, "our"
               associates a simple name with a package variable
               in the current package, for use within the current
               scope.  In other words, "our" has the same scoping
               rules as "my", but does not necessarily create a
               variable.

               If more than one value is listed, the list must be
               placed in parentheses.

                   our $foo;
                   our($bar, $baz);

               An "our" declaration declares a global variable
               that will be visible across its entire lexical
               scope, even across package boundaries.  The
               package in which the variable is entered is
               determined at the point of the declaration, not at
               the point of use.  This means the following
               behavior holds:

                   package Foo;
                   our $bar;           # declares $Foo::bar for rest of lexical scope
                   $bar = 20;

                   package Bar;
                   print $bar;         # prints 20, as it refers to $Foo::bar

               Multiple "our" declarations with the same name in
               the same lexical scope are allowed if they are in
               different packages.  If they happen to be in the
               same package, Perl will emit warnings if you have
               asked for them, just like multiple "my"
               declarations.  Unlike a second "my" declaration,
               which will bind the name to a fresh variable, a
               second "our" declaration in the same package, in
               the same scope, is merely redundant.

                   use warnings;
                   package Foo;
                   our $bar;           # declares $Foo::bar for rest of lexical scope
                   $bar = 20;

                   package Bar;
                   our $bar = 30;      # declares $Bar::bar for rest of lexical scope
                   print $bar;         # prints 30

                   our $bar;           # emits warning but has no other effect
                   print $bar;         # still prints 30

               An "our" declaration may also have a list of
               attributes associated with it.

               The exact semantics and interface of TYPE and



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               ATTRS are still evolving.  TYPE is currently bound
               to the use of "fields" pragma, and attributes are
               handled using the "attributes" pragma, or starting
               from Perl 5.8.0 also via the "Attribute::Handlers"
               module.  See "Private Variables via my()" in
               perlsub for details, and fields, attributes, and
               Attribute::Handlers.

       pack TEMPLATE,LIST
               Takes a LIST of values and converts it into a
               string using the rules given by the TEMPLATE.  The
               resulting string is the concatenation of the
               converted values.  Typically, each converted value
               looks like its machine-level representation.  For
               example, on 32-bit machines an integer may be
               represented by a sequence of 4 bytes that will be
               converted to a sequence of 4 characters.

               The TEMPLATE is a sequence of characters that give
               the order and type of values, as follows:

                   a   A string with arbitrary binary data, will be null padded.
                   A   A text (ASCII) string, will be space padded.
                   Z   A null terminated (ASCIZ) string, will be null padded.

                   b   A bit string (ascending bit order inside each byte, like vec()).
                   B   A bit string (descending bit order inside each byte).
                   h   A hex string (low nybble first).
                   H   A hex string (high nybble first).

                   c   A signed char (8-bit) value.
                   C   An unsigned char (octet) value.
                   W   An unsigned char value (can be greater than 255).

                   s   A signed short (16-bit) value.
                   S   An unsigned short value.

                   l   A signed long (32-bit) value.
                   L   An unsigned long value.

                   q   A signed quad (64-bit) value.
                   Q   An unsigned quad value.
                         (Quads are available only if your system supports 64-bit
                          integer values _and_ if Perl has been compiled to support those.
                          Causes a fatal error otherwise.)

                   i   A signed integer value.
                   I   A unsigned integer value.
                         (This 'integer' is _at_least_ 32 bits wide.  Its exact
                          size depends on what a local C compiler calls 'int'.)

                   n   An unsigned short (16-bit) in "network" (big-endian) order.
                   N   An unsigned long (32-bit) in "network" (big-endian) order.
                   v   An unsigned short (16-bit) in "VAX" (little-endian) order.



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                   V   An unsigned long (32-bit) in "VAX" (little-endian) order.

                   j   A Perl internal signed integer value (IV).
                   J   A Perl internal unsigned integer value (UV).

                   f   A single-precision float in the native format.
                   d   A double-precision float in the native format.

                   F   A Perl internal floating point value (NV) in the native format
                   D   A long double-precision float in the native format.
                         (Long doubles are available only if your system supports long
                          double values _and_ if Perl has been compiled to support those.
                          Causes a fatal error otherwise.)

                   p   A pointer to a null-terminated string.
                   P   A pointer to a structure (fixed-length string).

                   u   A uuencoded string.
                   U   A Unicode character number.  Encodes to a character in character mode
                       and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in byte mode.

                   w   A BER compressed integer (not an ASN.1 BER, see perlpacktut for
                       details).  Its bytes represent an unsigned integer in base 128,
                       most significant digit first, with as few digits as possible.  Bit
                       eight (the high bit) is set on each byte except the last.

                   x   A null byte.
                   X   Back up a byte.
                   @   Null fill or truncate to absolute position, counted from the
                       start of the innermost ()-group.
                   .   Null fill or truncate to absolute position specified by value.
                   (   Start of a ()-group.

               One or more of the modifiers below may optionally
               follow some letters in the TEMPLATE (the second
               column lists the letters for which the modifier is
               valid):

                   !   sSlLiI     Forces native (short, long, int) sizes instead
                                  of fixed (16-/32-bit) sizes.

                       xX         Make x and X act as alignment commands.

                       nNvV       Treat integers as signed instead of unsigned.

                       @.         Specify position as byte offset in the internal
                                  representation of the packed string. Efficient but
                                  dangerous.

                   >   sSiIlLqQ   Force big-endian byte-order on the type.
                       jJfFdDpP   (The "big end" touches the construct.)

                   <   sSiIlLqQ   Force little-endian byte-order on the type.
                       jJfFdDpP   (The "little end" touches the construct.)



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               The ">" and "<" modifiers can also be used on
               "()"-groups, in which case they force a certain
               byte-order on all components of that group,
               including subgroups.

               The following rules apply:

               o       Each letter may optionally be followed by
                       a number giving a repeat count.  With all
                       types except "a", "A", "Z", "b", "B", "h",
                       "H", "@", ".", "x", "X" and "P" the pack
                       function will gobble up that many values
                       from the LIST.  A "*" for the repeat count
                       means to use however many items are left,
                       except for "@", "x", "X", where it is
                       equivalent to 0, for <.> where it means
                       relative to string start and "u", where it
                       is equivalent to 1 (or 45, which is the
                       same).  A numeric repeat count may
                       optionally be enclosed in brackets, as in
                       "pack 'C[80]', @arr".

                       One can replace the numeric repeat count
                       by a template enclosed in brackets; then
                       the packed length of this template in
                       bytes is used as a count.  For example,
                       "x[L]" skips a long (it skips the number
                       of bytes in a long); the template "$t
                       X[$t] $t" unpack()s twice what $t unpacks.
                       If the template in brackets contains
                       alignment commands (such as "x![d]"), its
                       packed length is calculated as if the
                       start of the template has the maximal
                       possible alignment.

                       When used with "Z", "*" results in the
                       addition of a trailing null byte (so the
                       packed result will be one longer than the
                       byte "length" of the item).

                       When used with "@", the repeat count
                       represents an offset from the start of the
                       innermost () group.

                       When used with ".", the repeat count is
                       used to determine the starting position
                       from where the value offset is calculated.
                       If the repeat count is 0, it's relative to
                       the current position. If the repeat count
                       is "*", the offset is relative to the
                       start of the packed string. And if its an
                       integer "n" the offset is relative to the
                       start of the n-th innermost () group (or
                       the start of the string if "n" is bigger



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                       then the group level).

                       The repeat count for "u" is interpreted as
                       the maximal number of bytes to encode per
                       line of output, with 0, 1 and 2 replaced
                       by 45. The repeat count should not be more
                       than 65.

               o       The "a", "A", and "Z" types gobble just
                       one value, but pack it as a string of
                       length count, padding with nulls or spaces
                       as necessary.  When unpacking, "A" strips
                       trailing whitespace and nulls, "Z" strips
                       everything after the first null, and "a"
                       returns data verbatim.

                       If the value-to-pack is too long, it is
                       truncated.  If too long and an explicit
                       count is provided, "Z" packs only
                       "$count-1" bytes, followed by a null byte.
                       Thus "Z" always packs a trailing null
                       (except when the count is 0).

               o       Likewise, the "b" and "B" fields pack a
                       string that many bits long.  Each
                       character of the input field of pack()
                       generates 1 bit of the result.  Each
                       result bit is based on the least-
                       significant bit of the corresponding input
                       character, i.e., on "ord($char)%2".  In
                       particular, characters "0" and "1"
                       generate bits 0 and 1, as do characters
                       "\0" and "\1".

                       Starting from the beginning of the input
                       string of pack(), each 8-tuple of
                       characters is converted to 1 character of
                       output.  With format "b" the first
                       character of the 8-tuple determines the
                       least-significant bit of a character, and
                       with format "B" it determines the most-
                       significant bit of a character.

                       If the length of the input string is not
                       exactly divisible by 8, the remainder is
                       packed as if the input string were padded
                       by null characters at the end.  Similarly,
                       during unpack()ing the "extra" bits are
                       ignored.

                       If the input string of pack() is longer
                       than needed, extra characters are ignored.
                       A "*" for the repeat count of pack() means
                       to use all the characters of the input



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                       field.  On unpack()ing the bits are
                       converted to a string of "0"s and "1"s.

               o       The "h" and "H" fields pack a string that
                       many nybbles (4-bit groups, representable
                       as hexadecimal digits, 0-9a-f) long.

                       Each character of the input field of
                       pack() generates 4 bits of the result.
                       For non-alphabetical characters the result
                       is based on the 4 least-significant bits
                       of the input character, i.e., on
                       "ord($char)%16".  In particular,
                       characters "0" and "1" generate nybbles 0
                       and 1, as do bytes "\0" and "\1".  For
                       characters "a".."f" and "A".."F" the
                       result is compatible with the usual
                       hexadecimal digits, so that "a" and "A"
                       both generate the nybble "0xa==10".  The
                       result for characters "g".."z" and
                       "G".."Z" is not well-defined.

                       Starting from the beginning of the input
                       string of pack(), each pair of characters
                       is converted to 1 character of output.
                       With format "h" the first character of the
                       pair determines the least-significant
                       nybble of the output character, and with
                       format "H" it determines the most-
                       significant nybble.

                       If the length of the input string is not
                       even, it behaves as if padded by a null
                       character at the end.  Similarly, during
                       unpack()ing the "extra" nybbles are
                       ignored.

                       If the input string of pack() is longer
                       than needed, extra characters are ignored.
                       A "*" for the repeat count of pack() means
                       to use all the characters of the input
                       field.  On unpack()ing the nybbles are
                       converted to a string of hexadecimal
                       digits.

               o       The "p" type packs a pointer to a null-
                       terminated string.  You are responsible
                       for ensuring the string is not a temporary
                       value (which can potentially get
                       deallocated before you get around to using
                       the packed result).  The "P" type packs a
                       pointer to a structure of the size
                       indicated by the length.  A NULL pointer
                       is created if the corresponding value for



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                       "p" or "P" is "undef", similarly for
                       unpack().

                       If your system has a strange pointer size
                       (i.e. a pointer is neither as big as an
                       int nor as big as a long), it may not be
                       possible to pack or unpack pointers in
                       big- or little-endian byte order.
                       Attempting to do so will result in a fatal
                       error.

               o       The "/" template character allows packing
                       and unpacking of a sequence of items where
                       the packed structure contains a packed
                       item count followed by the packed items
                       themselves.

                       For "pack" you write length-
                       item"/"sequence-item and the length-item
                       describes how the length value is packed.
                       The ones likely to be of most use are
                       integer-packing ones like "n" (for Java
                       strings), "w" (for ASN.1 or SNMP) and "N"
                       (for Sun XDR).

                       For "pack", the sequence-item may have a
                       repeat count, in which case the minimum of
                       that and the number of available items is
                       used as argument for the length-item. If
                       it has no repeat count or uses a '*', the
                       number of available items is used.

                       For "unpack" an internal stack of integer
                       arguments unpacked so far is used. You
                       write "/"sequence-item and the repeat
                       count is obtained by popping off the last
                       element from the stack. The sequence-item
                       must not have a repeat count.

                       If the sequence-item refers to a string
                       type ("A", "a" or "Z"), the length-item is
                       a string length, not a number of strings.
                       If there is an explicit repeat count for
                       pack, the packed string will be adjusted
                       to that given length.

                           unpack 'W/a', "\04Gurusamy";            gives ('Guru')
                           unpack 'a3/A A*', '007 Bond  J ';       gives (' Bond', 'J')
                           unpack 'a3 x2 /A A*', '007: Bond, J.';  gives ('Bond, J', '.')
                           pack 'n/a* w/a','hello,','world';       gives "\000\006hello,\005world"
                           pack 'a/W2', ord('a') .. ord('z');      gives '2ab'

                       The length-item is not returned explicitly
                       from "unpack".



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                       Adding a count to the length-item letter
                       is unlikely to do anything useful, unless
                       that letter is "A", "a" or "Z".  Packing
                       with a length-item of "a" or "Z" may
                       introduce "\000" characters, which Perl
                       does not regard as legal in numeric
                       strings.

               o       The integer types "s", "S", "l", and "L"
                       may be followed by a "!" modifier to
                       signify native shorts or longs--as you can
                       see from above for example a bare "l" does
                       mean exactly 32 bits, the native "long"
                       (as seen by the local C compiler) may be
                       larger.  This is an issue mainly in 64-bit
                       platforms.  You can see whether using "!"
                       makes any difference by

                               print length(pack("s")), " ", length(pack("s!")), "\n";
                               print length(pack("l")), " ", length(pack("l!")), "\n";

                       "i!" and "I!" also work but only because
                       of completeness; they are identical to "i"
                       and "I".

                       The actual sizes (in bytes) of native
                       shorts, ints, longs, and long longs on the
                       platform where Perl was built are also
                       available via Config:

                              use Config;
                              print $Config{shortsize},    "\n";
                              print $Config{intsize},      "\n";
                              print $Config{longsize},     "\n";
                              print $Config{longlongsize}, "\n";

                       (The $Config{longlongsize} will be
                       undefined if your system does not support
                       long longs.)

               o       The integer formats "s", "S", "i", "I",
                       "l", "L", "j", and "J" are inherently non-
                       portable between processors and operating
                       systems because they obey the native
                       byteorder and endianness.  For example a
                       4-byte integer 0x12345678 (305419896
                       decimal) would be ordered natively
                       (arranged in and handled by the CPU
                       registers) into bytes as

                               0x12 0x34 0x56 0x78     # big-endian
                               0x78 0x56 0x34 0x12     # little-endian

                       Basically, the Intel and VAX CPUs are



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                       little-endian, while everybody else, for
                       example Motorola m68k/88k, PPC, Sparc, HP
                       PA, Power, and Cray are big-endian.  Alpha
                       and MIPS can be either: Digital/Compaq
                       used/uses them in little-endian mode;
                       SGI/Cray uses them in big-endian mode.

                       The names `big-endian' and `little-endian'
                       are comic references to the classic
                       "Gulliver's Travels" (via the paper "On
                       Holy Wars and a Plea for Peace" by Danny
                       Cohen, USC/ISI IEN 137, April 1, 1980) and
                       the egg-eating habits of the Lilliputians.

                       Some systems may have even weirder byte
                       orders such as

                               0x56 0x78 0x12 0x34
                               0x34 0x12 0x78 0x56

                       You can see your system's preference with

                               print join(" ", map { sprintf "%#02x", $_ }
                                                   unpack("W*",pack("L",0x12345678))), "\n";

                       The byteorder on the platform where Perl
                       was built is also available via Config:

                               use Config;
                               print $Config{byteorder}, "\n";

                       Byteorders '1234' and '12345678' are
                       little-endian, '4321' and '87654321' are
                       big-endian.

                       If you want portable packed integers you
                       can either use the formats "n", "N", "v",
                       and "V", or you can use the ">" and "<"
                       modifiers.  These modifiers are only
                       available as of perl 5.9.2.  See also
                       perlport.

               o       All integer and floating point formats as
                       well as "p" and "P" and "()"-groups may be
                       followed by the ">" or "<" modifiers to
                       force big- or little- endian byte-order,
                       respectively.  This is especially useful,
                       since "n", "N", "v" and "V" don't cover
                       signed integers, 64-bit integers and
                       floating point values.  However, there are
                       some things to keep in mind.

                       Exchanging signed integers between
                       different platforms only works if all



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                       platforms store them in the same format.
                       Most platforms store signed integers in
                       two's complement, so usually this is not
                       an issue.

                       The ">" or "<" modifiers can only be used
                       on floating point formats on big- or
                       little-endian machines.  Otherwise,
                       attempting to do so will result in a fatal
                       error.

                       Forcing big- or little-endian byte-order
                       on floating point values for data exchange
                       can only work if all platforms are using
                       the same binary representation (e.g. IEEE
                       floating point format).  Even if all
                       platforms are using IEEE, there may be
                       subtle differences.  Being able to use ">"
                       or "<" on floating point values can be
                       very useful, but also very dangerous if
                       you don't know exactly what you're doing.
                       It is definitely not a general way to
                       portably store floating point values.

                       When using ">" or "<" on an "()"-group,
                       this will affect all types inside the
                       group that accept the byte-order
                       modifiers, including all subgroups.  It
                       will silently be ignored for all other
                       types.  You are not allowed to override
                       the byte-order within a group that already
                       has a byte-order modifier suffix.

               o       Real numbers (floats and doubles) are in
                       the native machine format only; due to the
                       multiplicity of floating formats around,
                       and the lack of a standard "network"
                       representation, no facility for
                       interchange has been made.  This means
                       that packed floating point data written on
                       one machine may not be readable on another
                       - even if both use IEEE floating point
                       arithmetic (as the endian-ness of the
                       memory representation is not part of the
                       IEEE spec).  See also perlport.

                       If you know exactly what you're doing, you
                       can use the ">" or "<" modifiers to force
                       big- or little-endian byte-order on
                       floating point values.

                       Note that Perl uses doubles (or long
                       doubles, if configured) internally for all
                       numeric calculation, and converting from



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                       double into float and thence back to
                       double again will lose precision (i.e.,
                       "unpack("f", pack("f", $foo)") will not in
                       general equal $foo).

               o       Pack and unpack can operate in two modes,
                       character mode ("C0" mode) where the
                       packed string is processed per character
                       and UTF-8 mode ("U0" mode) where the
                       packed string is processed in its
                       UTF-8-encoded Unicode form on a byte by
                       byte basis. Character mode is the default
                       unless the format string starts with an
                       "U". You can switch mode at any moment
                       with an explicit "C0" or "U0" in the
                       format. A mode is in effect until the next
                       mode switch or until the end of the
                       ()-group in which it was entered.

               o       You must yourself do any alignment or
                       padding by inserting for example enough
                       'x'es while packing.  There is no way to
                       pack() and unpack() could know where the
                       characters are going to or coming from.
                       Therefore "pack" (and "unpack") handle
                       their output and input as flat sequences
                       of characters.

               o       A ()-group is a sub-TEMPLATE enclosed in
                       parentheses.  A group may take a repeat
                       count, both as postfix, and for unpack()
                       also via the "/" template character.
                       Within each repetition of a group,
                       positioning with "@" starts again at 0.
                       Therefore, the result of

                           pack( '@1A((@2A)@3A)', 'a', 'b', 'c' )

                       is the string "\0a\0\0bc".

               o       "x" and "X" accept "!" modifier.  In this
                       case they act as alignment commands: they
                       jump forward/back to the closest position
                       aligned at a multiple of "count"
                       characters. For example, to pack() or
                       unpack() C's "struct {char c; double d;
                       char cc[2]}" one may need to use the
                       template "W x![d] d W[2]"; this assumes
                       that doubles must be aligned on the
                       double's size.

                       For alignment commands "count" of 0 is
                       equivalent to "count" of 1; both result in
                       no-ops.



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               o       "n", "N", "v" and "V" accept the "!"
                       modifier. In this case they will represent
                       signed 16-/32-bit integers in
                       big-/little-endian order.  This is only
                       portable if all platforms sharing the
                       packed data use the same binary
                       representation for signed integers (e.g.
                       all platforms are using two's complement
                       representation).

               o       A comment in a TEMPLATE starts with "#"
                       and goes to the end of line.  White space
                       may be used to separate pack codes from
                       each other, but modifiers and a repeat
                       count must follow immediately.

               o       If TEMPLATE requires more arguments to
                       pack() than actually given, pack() assumes
                       additional "" arguments.  If TEMPLATE
                       requires fewer arguments to pack() than
                       actually given, extra arguments are
                       ignored.

               Examples:

                   $foo = pack("WWWW",65,66,67,68);
                   # foo eq "ABCD"
                   $foo = pack("W4",65,66,67,68);
                   # same thing
                   $foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # same thing with Unicode circled letters.
                   $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # same thing with Unicode circled letters. You don't get the UTF-8
                   # bytes because the U at the start of the format caused a switch to
                   # U0-mode, so the UTF-8 bytes get joined into characters
                   $foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
                   # This is the UTF-8 encoding of the string in the previous example

                   $foo = pack("ccxxcc",65,66,67,68);
                   # foo eq "AB\0\0CD"

                   # note: the above examples featuring "W" and "c" are true
                   # only on ASCII and ASCII-derived systems such as ISO Latin 1
                   # and UTF-8.  In EBCDIC the first example would be
                   # $foo = pack("WWWW",193,194,195,196);

                   $foo = pack("s2",1,2);
                   # "\1\0\2\0" on little-endian
                   # "\0\1\0\2" on big-endian

                   $foo = pack("a4","abcd","x","y","z");
                   # "abcd"




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                   $foo = pack("aaaa","abcd","x","y","z");
                   # "axyz"

                   $foo = pack("a14","abcdefg");
                   # "abcdefg\0\0\0\0\0\0\0"

                   $foo = pack("i9pl", gmtime);
                   # a real struct tm (on my system anyway)

                   $utmp_template = "Z8 Z8 Z16 L";
                   $utmp = pack($utmp_template, @utmp1);
                   # a struct utmp (BSDish)

                   @utmp2 = unpack($utmp_template, $utmp);
                   # "@utmp1" eq "@utmp2"

                   sub bintodec {
                       unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
                   }

                   $foo = pack('sx2l', 12, 34);
                   # short 12, two zero bytes padding, long 34
                   $bar = pack('s@4l', 12, 34);
                   # short 12, zero fill to position 4, long 34
                   # $foo eq $bar
                   $baz = pack('s.l', 12, 4, 34);
                   # short 12, zero fill to position 4, long 34

                   $foo = pack('nN', 42, 4711);
                   # pack big-endian 16- and 32-bit unsigned integers
                   $foo = pack('S>L>', 42, 4711);
                   # exactly the same
                   $foo = pack('s<l<', -42, 4711);
                   # pack little-endian 16- and 32-bit signed integers
                   $foo = pack('(sl)<', -42, 4711);
                   # exactly the same

               The same template may generally also be used in
               unpack().

       package NAMESPACE
       package Declares the compilation unit as being in the
               given namespace.  The scope of the package
               declaration is from the declaration itself through
               the end of the enclosing block, file, or eval (the
               same as the "my" operator).  All further
               unqualified dynamic identifiers will be in this
               namespace.  A package statement affects only
               dynamic variables--including those you've used
               "local" on--but not lexical variables, which are
               created with "my".  Typically it would be the
               first declaration in a file to be included by the
               "require" or "use" operator.  You can switch into
               a package in more than one place; it merely



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               influences which symbol table is used by the
               compiler for the rest of that block.  You can
               refer to variables and filehandles in other
               packages by prefixing the identifier with the
               package name and a double colon:
               $Package::Variable.  If the package name is null,
               the "main" package as assumed.  That is, $::sail
               is equivalent to $main::sail (as well as to
               "$main'sail", still seen in older code).

               See "Packages" in perlmod for more information
               about packages, modules, and classes.  See perlsub
               for other scoping issues.

       pipe READHANDLE,WRITEHANDLE
               Opens a pair of connected pipes like the
               corresponding system call.  Note that if you set
               up a loop of piped processes, deadlock can occur
               unless you are very careful.  In addition, note
               that Perl's pipes use IO buffering, so you may
               need to set $| to flush your WRITEHANDLE after
               each command, depending on the application.

               See IPC::Open2, IPC::Open3, and "Bidirectional
               Communication" in perlipc for examples of such
               things.

               On systems that support a close-on-exec flag on
               files, the flag will be set for the newly opened
               file descriptors as determined by the value of
               $^F.  See "$^F" in perlvar.

       pop ARRAY
       pop     Pops and returns the last value of the array,
               shortening the array by one element.

               If there are no elements in the array, returns the
               undefined value (although this may happen at other
               times as well).  If ARRAY is omitted, pops the
               @ARGV array in the main program, and the @_ array
               in subroutines, just like "shift".

       pos SCALAR
       pos     Returns the offset of where the last "m//g" search
               left off for the variable in question ($_ is used
               when the variable is not specified).  Note that 0
               is a valid match offset.  "undef" indicates that
               the search position is reset (usually due to match
               failure, but can also be because no match has yet
               been performed on the scalar). "pos" directly
               accesses the location used by the regexp engine to
               store the offset, so assigning to "pos" will
               change that offset, and so will also influence the
               "\G" zero-width assertion in regular expressions.



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               Because a failed "m//gc" match doesn't reset the
               offset, the return from "pos" won't change either
               in this case.  See perlre and perlop.

       print FILEHANDLE LIST
       print LIST
       print   Prints a string or a list of strings.  Returns
               true if successful.  FILEHANDLE may be a scalar
               variable name, in which case the variable contains
               the name of or a reference to the filehandle, thus
               introducing one level of indirection.  (NOTE: If
               FILEHANDLE is a variable and the next token is a
               term, it may be misinterpreted as an operator
               unless you interpose a "+" or put parentheses
               around the arguments.)  If FILEHANDLE is omitted,
               prints by default to standard output (or to the
               last selected output channel--see "select").  If
               LIST is also omitted, prints $_ to the currently
               selected output channel.  To set the default
               output channel to something other than STDOUT use
               the select operation.  The current value of $, (if
               any) is printed between each LIST item.  The
               current value of "$\" (if any) is printed after
               the entire LIST has been printed.  Because print
               takes a LIST, anything in the LIST is evaluated in
               list context, and any subroutine that you call
               will have one or more of its expressions evaluated
               in list context.  Also be careful not to follow
               the print keyword with a left parenthesis unless
               you want the corresponding right parenthesis to
               terminate the arguments to the print--interpose a
               "+" or put parentheses around all the arguments.

               Note that if you're storing FILEHANDLEs in an
               array, or if you're using any other expression
               more complex than a scalar variable to retrieve
               it, you will have to use a block returning the
               filehandle value instead:

                   print { $files[$i] } "stuff\n";
                   print { $OK ? STDOUT : STDERR } "stuff\n";

       printf FILEHANDLE FORMAT, LIST
       printf FORMAT, LIST
               Equivalent to "print FILEHANDLE sprintf(FORMAT,
               LIST)", except that "$\" (the output record
               separator) is not appended.  The first argument of
               the list will be interpreted as the "printf"
               format. See "sprintf" for an explanation of the
               format argument.  If "use locale" is in effect,
               and POSIX::setlocale() has been called, the
               character used for the decimal separator in
               formatted floating point numbers is affected by
               the LC_NUMERIC locale.  See perllocale and POSIX.



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               Don't fall into the trap of using a "printf" when
               a simple "print" would do.  The "print" is more
               efficient and less error prone.

       prototype FUNCTION
               Returns the prototype of a function as a string
               (or "undef" if the function has no prototype).
               FUNCTION is a reference to, or the name of, the
               function whose prototype you want to retrieve.

               If FUNCTION is a string starting with "CORE::",
               the rest is taken as a name for Perl builtin.  If
               the builtin is not overridable (such as "qw//") or
               if its arguments cannot be adequately expressed by
               a prototype (such as "system"), prototype()
               returns "undef", because the builtin does not
               really behave like a Perl function.  Otherwise,
               the string describing the equivalent prototype is
               returned.

       push ARRAY,LIST
               Treats ARRAY as a stack, and pushes the values of
               LIST onto the end of ARRAY.  The length of ARRAY
               increases by the length of LIST.  Has the same
               effect as

                   for $value (LIST) {
                       $ARRAY[++$#ARRAY] = $value;
                   }

               but is more efficient.  Returns the number of
               elements in the array following the completed
               "push".

       q/STRING/
       qq/STRING/
       qx/STRING/
       qw/STRING/
               Generalized quotes.  See "Quote-Like Operators" in
               perlop.

       qr/STRING/
               Regexp-like quote.  See "Regexp Quote-Like
               Operators" in perlop.

       quotemeta EXPR
       quotemeta
               Returns the value of EXPR with all non-"word"
               characters backslashed.  (That is, all characters
               not matching "/[A-Za-z_0-9]/" will be preceded by
               a backslash in the returned string, regardless of
               any locale settings.)  This is the internal
               function implementing the "\Q" escape in double-
               quoted strings.



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               If EXPR is omitted, uses $_.

       rand EXPR
       rand    Returns a random fractional number greater than or
               equal to 0 and less than the value of EXPR.  (EXPR
               should be positive.)  If EXPR is omitted, the
               value 1 is used.  Currently EXPR with the value 0
               is also special-cased as 1 - this has not been
               documented before perl 5.8.0 and is subject to
               change in future versions of perl.  Automatically
               calls "srand" unless "srand" has already been
               called.  See also "srand".

               Apply "int()" to the value returned by "rand()" if
               you want random integers instead of random
               fractional numbers.  For example,

                   int(rand(10))

               returns a random integer between 0 and 9,
               inclusive.

               (Note: If your rand function consistently returns
               numbers that are too large or too small, then your
               version of Perl was probably compiled with the
               wrong number of RANDBITS.)

       read FILEHANDLE,SCALAR,LENGTH,OFFSET
       read FILEHANDLE,SCALAR,LENGTH
               Attempts to read LENGTH characters of data into
               variable SCALAR from the specified FILEHANDLE.
               Returns the number of characters actually read, 0
               at end of file, or undef if there was an error (in
               the latter case $! is also set).  SCALAR will be
               grown or shrunk so that the last character
               actually read is the last character of the scalar
               after the read.

               An OFFSET may be specified to place the read data
               at some place in the string other than the
               beginning.  A negative OFFSET specifies placement
               at that many characters counting backwards from
               the end of the string.  A positive OFFSET greater
               than the length of SCALAR results in the string
               being padded to the required size with "\0" bytes
               before the result of the read is appended.

               The call is actually implemented in terms of
               either Perl's or system's fread() call.  To get a
               true read(2) system call, see "sysread".

               Note the characters: depending on the status of
               the filehandle, either (8-bit) bytes or characters
               are read.  By default all filehandles operate on



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               bytes, but for example if the filehandle has been
               opened with the ":utf8" I/O layer (see "open", and
               the "open" pragma, open), the I/O will operate on
               UTF-8 encoded Unicode characters, not bytes.
               Similarly for the ":encoding" pragma: in that case
               pretty much any characters can be read.

       readdir DIRHANDLE
               Returns the next directory entry for a directory
               opened by "opendir".  If used in list context,
               returns all the rest of the entries in the
               directory.  If there are no more entries, returns
               an undefined value in scalar context or a null
               list in list context.

               If you're planning to filetest the return values
               out of a "readdir", you'd better prepend the
               directory in question.  Otherwise, because we
               didn't "chdir" there, it would have been testing
               the wrong file.

                   opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!";
                   @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh);
                   closedir $dh;

       readline EXPR
       readline
               Reads from the filehandle whose typeglob is
               contained in EXPR (or from *ARGV if EXPR is not
               provided).  In scalar context, each call reads and
               returns the next line, until end-of-file is
               reached, whereupon the subsequent call returns
               undef.  In list context, reads until end-of-file
               is reached and returns a list of lines.  Note that
               the notion of "line" used here is however you may
               have defined it with $/ or
               $INPUT_RECORD_SEPARATOR).  See "$/" in perlvar.

               When $/ is set to "undef", when readline() is in
               scalar context (i.e. file slurp mode), and when an
               empty file is read, it returns '' the first time,
               followed by "undef" subsequently.

               This is the internal function implementing the
               "<EXPR>" operator, but you can use it directly.
               The "<EXPR>" operator is discussed in more detail
               in "I/O Operators" in perlop.

                   $line = <STDIN>;
                   $line = readline(*STDIN);           # same thing

               If readline encounters an operating system error,
               $! will be set with the corresponding error
               message.  It can be helpful to check $! when you



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               are reading from filehandles you don't trust, such
               as a tty or a socket.  The following example uses
               the operator form of "readline", and takes the
               necessary steps to ensure that "readline" was
               successful.

                   for (;;) {
                       undef $!;
                       unless (defined( $line = <> )) {
                           last if eof;
                           die $! if $!;
                       }
                       # ...
                   }

       readlink EXPR
       readlink
               Returns the value of a symbolic link, if symbolic
               links are implemented.  If not, gives a fatal
               error.  If there is some system error, returns the
               undefined value and sets $! (errno).  If EXPR is
               omitted, uses $_.

       readpipe EXPR
       readpipe
               EXPR is executed as a system command.  The
               collected standard output of the command is
               returned.  In scalar context, it comes back as a
               single (potentially multi-line) string.  In list
               context, returns a list of lines (however you've
               defined lines with $/ or $INPUT_RECORD_SEPARATOR).
               This is the internal function implementing the
               "qx/EXPR/" operator, but you can use it directly.
               The "qx/EXPR/" operator is discussed in more
               detail in "I/O Operators" in perlop.  If EXPR is
               omitted, uses $_.

       recv SOCKET,SCALAR,LENGTH,FLAGS
               Receives a message on a socket.  Attempts to
               receive LENGTH characters of data into variable
               SCALAR from the specified SOCKET filehandle.
               SCALAR will be grown or shrunk to the length
               actually read.  Takes the same flags as the system
               call of the same name.  Returns the address of the
               sender if SOCKET's protocol supports this; returns
               an empty string otherwise.  If there's an error,
               returns the undefined value.  This call is
               actually implemented in terms of recvfrom(2)
               system call.  See "UDP: Message Passing" in
               perlipc for examples.

               Note the characters: depending on the status of
               the socket, either (8-bit) bytes or characters are
               received.  By default all sockets operate on



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               bytes, but for example if the socket has been
               changed using binmode() to operate with the
               ":encoding(utf8)" I/O layer (see the "open"
               pragma, open), the I/O will operate on UTF-8
               encoded Unicode characters, not bytes.  Similarly
               for the ":encoding" pragma: in that case pretty
               much any characters can be read.

       redo LABEL
       redo    The "redo" command restarts the loop block without
               evaluating the conditional again.  The "continue"
               block, if any, is not executed.  If the LABEL is
               omitted, the command refers to the innermost
               enclosing loop.  Programs that want to lie to
               themselves about what was just input normally use
               this command:

                   # a simpleminded Pascal comment stripper
                   # (warning: assumes no { or } in strings)
                   LINE: while (<STDIN>) {
                       while (s|({.*}.*){.*}|$1 |) {}
                       s|{.*}| |;
                       if (s|{.*| |) {
                           $front = $_;
                           while (<STDIN>) {
                               if (/}/) {      # end of comment?
                                   s|^|$front\{|;
                                   redo LINE;
                               }
                           }
                       }
                       print;
                   }

               "redo" cannot be used to retry a block which
               returns a value such as "eval {}", "sub {}" or "do
               {}", and should not be used to exit a grep() or
               map() operation.

               Note that a block by itself is semantically
               identical to a loop that executes once.  Thus
               "redo" inside such a block will effectively turn
               it into a looping construct.

               See also "continue" for an illustration of how
               "last", "next", and "redo" work.

       ref EXPR
       ref     Returns a non-empty string if EXPR is a reference,
               the empty string otherwise. If EXPR is not
               specified, $_ will be used.  The value returned
               depends on the type of thing the reference is a
               reference to.  Builtin types include:




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                   SCALAR
                   ARRAY
                   HASH
                   CODE
                   REF
                   GLOB
                   LVALUE
                   FORMAT
                   IO
                   VSTRING
                   Regexp

               If the referenced object has been blessed into a
               package, then that package name is returned
               instead.  You can think of "ref" as a "typeof"
               operator.

                   if (ref($r) eq "HASH") {
                       print "r is a reference to a hash.\n";
                   }
                   unless (ref($r)) {
                       print "r is not a reference at all.\n";
                   }

               The return value "LVALUE" indicates a reference to
               an lvalue that is not a variable. You get this
               from taking the reference of function calls like
               "pos()" or "substr()". "VSTRING" is returned if
               the reference points to a version string.

               The result "Regexp" indicates that the argument is
               a regular expression resulting from "qr//".

               See also perlref.

       rename OLDNAME,NEWNAME
               Changes the name of a file; an existing file
               NEWNAME will be clobbered.  Returns true for
               success, false otherwise.

               Behavior of this function varies wildly depending
               on your system implementation.  For example, it
               will usually not work across file system
               boundaries, even though the system mv command
               sometimes compensates for this.  Other
               restrictions include whether it works on
               directories, open files, or pre-existing files.
               Check perlport and either the rename(2) manpage or
               equivalent system documentation for details.

               For a platform independent "move" function look at
               the File::Copy module.





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       require VERSION
       require EXPR
       require Demands a version of Perl specified by VERSION, or
               demands some semantics specified by EXPR or by $_
               if EXPR is not supplied.

               VERSION may be either a numeric argument such as
               5.006, which will be compared to $], or a literal
               of the form v5.6.1, which will be compared to $^V
               (aka $PERL_VERSION).  A fatal error is produced at
               run time if VERSION is greater than the version of
               the current Perl interpreter.  Compare with "use",
               which can do a similar check at compile time.

               Specifying VERSION as a literal of the form v5.6.1
               should generally be avoided, because it leads to
               misleading error messages under earlier versions
               of Perl that do not support this syntax.  The
               equivalent numeric version should be used instead.

                   require v5.6.1;     # run time version check
                   require 5.6.1;      # ditto
                   require 5.006_001;  # ditto; preferred for backwards compatibility

               Otherwise, "require" demands that a library file
               be included if it hasn't already been included.
               The file is included via the do-FILE mechanism,
               which is essentially just a variety of "eval" with
               the caveat that lexical variables in the invoking
               script will be invisible to the included code.
               Has semantics similar to the following subroutine:

                   sub require {
                      my ($filename) = @_;
                      if (exists $INC{$filename}) {
                          return 1 if $INC{$filename};
                          die "Compilation failed in require";
                      }
                      my ($realfilename,$result);
                      ITER: {
                          foreach $prefix (@INC) {
                              $realfilename = "$prefix/$filename";
                              if (-f $realfilename) {
                                  $INC{$filename} = $realfilename;
                                  $result = do $realfilename;
                                  last ITER;
                              }
                          }
                          die "Can't find $filename in \@INC";
                      }
                      if ($@) {
                          $INC{$filename} = undef;
                          die $@;
                      } elsif (!$result) {



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                          delete $INC{$filename};
                          die "$filename did not return true value";
                      } else {
                          return $result;
                      }
                   }

               Note that the file will not be included twice
               under the same specified name.

               The file must return true as the last statement to
               indicate successful execution of any
               initialization code, so it's customary to end such
               a file with "1;" unless you're sure it'll return
               true otherwise.  But it's better just to put the
               "1;", in case you add more statements.

               If EXPR is a bareword, the require assumes a ".pm"
               extension and replaces "::" with "/" in the
               filename for you, to make it easy to load standard
               modules.  This form of loading of modules does not
               risk altering your namespace.

               In other words, if you try this:

                       require Foo::Bar;    # a splendid bareword

               The require function will actually look for the
               "Foo/Bar.pm" file in the directories specified in
               the @INC array.

               But if you try this:

                       $class = 'Foo::Bar';
                       require $class;      # $class is not a bareword
                   #or
                       require "Foo::Bar";  # not a bareword because of the ""

               The require function will look for the "Foo::Bar"
               file in the @INC array and will complain about not
               finding "Foo::Bar" there.  In this case you can
               do:

                       eval "require $class";

               Now that you understand how "require" looks for
               files in the case of a bareword argument, there is
               a little extra functionality going on behind the
               scenes.  Before "require" looks for a ".pm"
               extension, it will first look for a similar
               filename with a ".pmc" extension. If this file is
               found, it will be loaded in place of any file
               ending in a ".pm" extension.




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               You can also insert hooks into the import
               facility, by putting directly Perl code into the
               @INC array.  There are three forms of hooks:
               subroutine references, array references and
               blessed objects.

               Subroutine references are the simplest case.  When
               the inclusion system walks through @INC and
               encounters a subroutine, this subroutine gets
               called with two parameters, the first being a
               reference to itself, and the second the name of
               the file to be included (e.g. "Foo/Bar.pm").  The
               subroutine should return nothing, or a list of up
               to three values in the following order:

               1.  A filehandle, from which the file will be
                   read.

               2.  A reference to a subroutine. If there is no
                   filehandle (previous item), then this
                   subroutine is expected to generate one line of
                   source code per call, writing the line into $_
                   and returning 1, then returning 0 at "end of
                   file". If there is a filehandle, then the
                   subroutine will be called to act as a simple
                   source filter, with the line as read in $_.
                   Again, return 1 for each valid line, and 0
                   after all lines have been returned.

               3.  Optional state for the subroutine. The state
                   is passed in as $_[1]. A reference to the
                   subroutine itself is passed in as $_[0].

               If an empty list, "undef", or nothing that matches
               the first 3 values above is returned then
               "require" will look at the remaining elements of
               @INC.  Note that this file handle must be a real
               file handle (strictly a typeglob, or reference to
               a typeglob, blessed or unblessed) - tied file
               handles will be ignored and return value
               processing will stop there.

               If the hook is an array reference, its first
               element must be a subroutine reference.  This
               subroutine is called as above, but the first
               parameter is the array reference.  This enables to
               pass indirectly some arguments to the subroutine.

               In other words, you can write:








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                   push @INC, \&my_sub;
                   sub my_sub {
                       my ($coderef, $filename) = @_;  # $coderef is \&my_sub
                       ...
                   }

               or:

                   push @INC, [ \&my_sub, $x, $y, ... ];
                   sub my_sub {
                       my ($arrayref, $filename) = @_;
                       # Retrieve $x, $y, ...
                       my @parameters = @$arrayref[1..$#$arrayref];
                       ...
                   }

               If the hook is an object, it must provide an INC
               method that will be called as above, the first
               parameter being the object itself.  (Note that you
               must fully qualify the sub's name, as unqualified
               "INC" is always forced into package "main".)  Here
               is a typical code layout:

                   # In Foo.pm
                   package Foo;
                   sub new { ... }
                   sub Foo::INC {
                       my ($self, $filename) = @_;
                       ...
                   }

                   # In the main program
                   push @INC, Foo->new(...);

               Note that these hooks are also permitted to set
               the %INC entry corresponding to the files they
               have loaded. See "%INC" in perlvar.

               For a yet-more-powerful import facility, see "use"
               and perlmod.

       reset EXPR
       reset   Generally used in a "continue" block at the end of
               a loop to clear variables and reset "??" searches
               so that they work again.  The expression is
               interpreted as a list of single characters
               (hyphens allowed for ranges).  All variables and
               arrays beginning with one of those letters are
               reset to their pristine state.  If the expression
               is omitted, one-match searches ("?pattern?") are
               reset to match again.  Resets only variables or
               searches in the current package.  Always returns
               1.  Examples:




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                   reset 'X';          # reset all X variables
                   reset 'a-z';        # reset lower case variables
                   reset;              # just reset ?one-time? searches

               Resetting "A-Z" is not recommended because you'll
               wipe out your @ARGV and @INC arrays and your %ENV
               hash.  Resets only package variables--lexical
               variables are unaffected, but they clean
               themselves up on scope exit anyway, so you'll
               probably want to use them instead.  See "my".

       return EXPR
       return  Returns from a subroutine, "eval", or "do FILE"
               with the value given in EXPR.  Evaluation of EXPR
               may be in list, scalar, or void context, depending
               on how the return value will be used, and the
               context may vary from one execution to the next
               (see "wantarray").  If no EXPR is given, returns
               an empty list in list context, the undefined value
               in scalar context, and (of course) nothing at all
               in a void context.

               (Note that in the absence of an explicit "return",
               a subroutine, eval, or do FILE will automatically
               return the value of the last expression
               evaluated.)

       reverse LIST
               In list context, returns a list value consisting
               of the elements of LIST in the opposite order.  In
               scalar context, concatenates the elements of LIST
               and returns a string value with all characters in
               the opposite order.

                   print join(", ", reverse "world", "Hello"); # Hello, world

                   print scalar reverse "dlrow ,", "olleH";    # Hello, world

               Used without arguments in scalar context,
               reverse() reverses $_.

                   $_ = "dlrow ,olleH";
                   print reverse;                              # No output, list context
                   print scalar reverse;                       # Hello, world

               This operator is also handy for inverting a hash,
               although there are some caveats.  If a value is
               duplicated in the original hash, only one of those
               can be represented as a key in the inverted hash.
               Also, this has to unwind one hash and build a
               whole new one, which may take some time on a large
               hash, such as from a DBM file.

                   %by_name = reverse %by_address;     # Invert the hash



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       rewinddir DIRHANDLE
               Sets the current position to the beginning of the
               directory for the "readdir" routine on DIRHANDLE.

       rindex STR,SUBSTR,POSITION
       rindex STR,SUBSTR
               Works just like index() except that it returns the
               position of the last occurrence of SUBSTR in STR.
               If POSITION is specified, returns the last
               occurrence beginning at or before that position.

       rmdir FILENAME
       rmdir   Deletes the directory specified by FILENAME if
               that directory is empty.  If it succeeds it
               returns true, otherwise it returns false and sets
               $! (errno).  If FILENAME is omitted, uses $_.

               To remove a directory tree recursively ("rm -rf"
               on unix) look at the "rmtree" function of the
               File::Path module.

       s///    The substitution operator.  See "Regexp Quote-Like
               Operators" in perlop.

       say FILEHANDLE LIST
       say LIST
       say     Just like "print", but implicitly appends a
               newline.  "say LIST" is simply an abbreviation for
               "{ local $\ = "\n"; print LIST }".

               This keyword is only available when the "say"
               feature is enabled: see feature.

       scalar EXPR
               Forces EXPR to be interpreted in scalar context
               and returns the value of EXPR.

                   @counts = ( scalar @a, scalar @b, scalar @c );

               There is no equivalent operator to force an
               expression to be interpolated in list context
               because in practice, this is never needed.  If you
               really wanted to do so, however, you could use the
               construction "@{[ (some expression) ]}", but
               usually a simple "(some expression)" suffices.

               Because "scalar" is unary operator, if you
               accidentally use for EXPR a parenthesized list,
               this behaves as a scalar comma expression,
               evaluating all but the last element in void
               context and returning the final element evaluated
               in scalar context.  This is seldom what you want.

               The following single statement:



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                       print uc(scalar(&foo,$bar)),$baz;

               is the moral equivalent of these two:

                       &foo;
                       print(uc($bar),$baz);

               See perlop for more details on unary operators and
               the comma operator.

       seek FILEHANDLE,POSITION,WHENCE
               Sets FILEHANDLE's position, just like the "fseek"
               call of "stdio".  FILEHANDLE may be an expression
               whose value gives the name of the filehandle.  The
               values for WHENCE are 0 to set the new position in
               bytes to POSITION, 1 to set it to the current
               position plus POSITION, and 2 to set it to EOF
               plus POSITION (typically negative).  For WHENCE
               you may use the constants "SEEK_SET", "SEEK_CUR",
               and "SEEK_END" (start of the file, current
               position, end of the file) from the Fcntl module.
               Returns 1 upon success, 0 otherwise.

               Note the in bytes: even if the filehandle has been
               set to operate on characters (for example by using
               the ":encoding(utf8)" open layer), tell() will
               return byte offsets, not character offsets
               (because implementing that would render seek() and
               tell() rather slow).

               If you want to position file for "sysread" or
               "syswrite", don't use "seek"--buffering makes its
               effect on the file's system position unpredictable
               and non-portable.  Use "sysseek" instead.

               Due to the rules and rigors of ANSI C, on some
               systems you have to do a seek whenever you switch
               between reading and writing.  Amongst other
               things, this may have the effect of calling
               stdio's clearerr(3).  A WHENCE of 1 ("SEEK_CUR")
               is useful for not moving the file position:

                   seek(TEST,0,1);

               This is also useful for applications emulating
               "tail -f".  Once you hit EOF on your read, and
               then sleep for a while, you might have to stick in
               a seek() to reset things.  The "seek" doesn't
               change the current position, but it does clear the
               end-of-file condition on the handle, so that the
               next "<FILE>" makes Perl try again to read
               something.  We hope.

               If that doesn't work (some IO implementations are



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               particularly cantankerous), then you may need
               something more like this:

                   for (;;) {
                       for ($curpos = tell(FILE); $_ = <FILE>;
                            $curpos = tell(FILE)) {
                           # search for some stuff and put it into files
                       }
                       sleep($for_a_while);
                       seek(FILE, $curpos, 0);
                   }

       seekdir DIRHANDLE,POS
               Sets the current position for the "readdir"
               routine on DIRHANDLE.  POS must be a value
               returned by "telldir".  "seekdir" also has the
               same caveats about possible directory compaction
               as the corresponding system library routine.

       select FILEHANDLE
       select  Returns the currently selected filehandle.  If
               FILEHANDLE is supplied, sets the new current
               default filehandle for output.  This has two
               effects: first, a "write" or a "print" without a
               filehandle will default to this FILEHANDLE.
               Second, references to variables related to output
               will refer to this output channel.  For example,
               if you have to set the top of form format for more
               than one output channel, you might do the
               following:

                   select(REPORT1);
                   $^ = 'report1_top';
                   select(REPORT2);
                   $^ = 'report2_top';

               FILEHANDLE may be an expression whose value gives
               the name of the actual filehandle.  Thus:

                   $oldfh = select(STDERR); $| = 1; select($oldfh);

               Some programmers may prefer to think of
               filehandles as objects with methods, preferring to
               write the last example as:

                   use IO::Handle;
                   STDERR->autoflush(1);

       select RBITS,WBITS,EBITS,TIMEOUT
               This calls the select(2) system call with the bit
               masks specified, which can be constructed using
               "fileno" and "vec", along these lines:





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                   $rin = $win = $ein = '';
                   vec($rin,fileno(STDIN),1) = 1;
                   vec($win,fileno(STDOUT),1) = 1;
                   $ein = $rin | $win;

               If you want to select on many filehandles you
               might wish to write a subroutine:

                   sub fhbits {
                       my(@fhlist) = split(' ',$_[0]);
                       my($bits);
                       for (@fhlist) {
                           vec($bits,fileno($_),1) = 1;
                       }
                       $bits;
                   }
                   $rin = fhbits('STDIN TTY SOCK');

               The usual idiom is:

                   ($nfound,$timeleft) =
                     select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

               or to block until something becomes ready just do
               this

                   $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);

               Most systems do not bother to return anything
               useful in $timeleft, so calling select() in scalar
               context just returns $nfound.

               Any of the bit masks can also be undef.  The
               timeout, if specified, is in seconds, which may be
               fractional.  Note: not all implementations are
               capable of returning the $timeleft.  If not, they
               always return $timeleft equal to the supplied
               $timeout.

               You can effect a sleep of 250 milliseconds this
               way:

                   select(undef, undef, undef, 0.25);

               Note that whether "select" gets restarted after
               signals (say, SIGALRM) is implementation-
               dependent.  See also perlport for notes on the
               portability of "select".

               On error, "select" behaves like the select(2)
               system call : it returns -1 and sets $!.

               Note: on some Unixes, the select(2) system call
               may report a socket file descriptor as "ready for



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               reading", when actually no data is available, thus
               a subsequent read blocks. It can be avoided using
               always the O_NONBLOCK flag on the socket. See
               select(2) and fcntl(2) for further details.

               WARNING: One should not attempt to mix buffered
               I/O (like "read" or <FH>) with "select", except as
               permitted by POSIX, and even then only on POSIX
               systems.  You have to use "sysread" instead.

       semctl ID,SEMNUM,CMD,ARG
               Calls the System V IPC function "semctl".  You'll
               probably have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If
               CMD is IPC_STAT or GETALL, then ARG must be a
               variable that will hold the returned semid_ds
               structure or semaphore value array.  Returns like
               "ioctl": the undefined value for error, ""0 but
               true"" for zero, or the actual return value
               otherwise.  The ARG must consist of a vector of
               native short integers, which may be created with
               "pack("s!",(0)x$nsem)".  See also "SysV IPC" in
               perlipc, "IPC::SysV", "IPC::Semaphore"
               documentation.

       semget KEY,NSEMS,FLAGS
               Calls the System V IPC function semget.  Returns
               the semaphore id, or the undefined value if there
               is an error.  See also "SysV IPC" in perlipc,
               "IPC::SysV", "IPC::SysV::Semaphore" documentation.

       semop KEY,OPSTRING
               Calls the System V IPC function semop to perform
               semaphore operations such as signalling and
               waiting.  OPSTRING must be a packed array of semop
               structures.  Each semop structure can be generated
               with "pack("s!3", $semnum, $semop, $semflag)".
               The length of OPSTRING implies the number of
               semaphore operations.  Returns true if successful,
               or false if there is an error.  As an example, the
               following code waits on semaphore $semnum of
               semaphore id $semid:

                   $semop = pack("s!3", $semnum, -1, 0);
                   die "Semaphore trouble: $!\n" unless semop($semid, $semop);

               To signal the semaphore, replace "-1" with 1.  See
               also "SysV IPC" in perlipc, "IPC::SysV", and
               "IPC::SysV::Semaphore" documentation.





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       send SOCKET,MSG,FLAGS,TO
       send SOCKET,MSG,FLAGS
               Sends a message on a socket.  Attempts to send the
               scalar MSG to the SOCKET filehandle.  Takes the
               same flags as the system call of the same name.
               On unconnected sockets you must specify a
               destination to send TO, in which case it does a C
               "sendto".  Returns the number of characters sent,
               or the undefined value if there is an error.  The
               C system call sendmsg(2) is currently
               unimplemented.  See "UDP: Message Passing" in
               perlipc for examples.

               Note the characters: depending on the status of
               the socket, either (8-bit) bytes or characters are
               sent.  By default all sockets operate on bytes,
               but for example if the socket has been changed
               using binmode() to operate with the
               ":encoding(utf8)" I/O layer (see "open", or the
               "open" pragma, open), the I/O will operate on
               UTF-8 encoded Unicode characters, not bytes.
               Similarly for the ":encoding" pragma: in that case
               pretty much any characters can be sent.

       setpgrp PID,PGRP
               Sets the current process group for the specified
               PID, 0 for the current process.  Will produce a
               fatal error if used on a machine that doesn't
               implement POSIX setpgid(2) or BSD setpgrp(2).  If
               the arguments are omitted, it defaults to "0,0".
               Note that the BSD 4.2 version of "setpgrp" does
               not accept any arguments, so only "setpgrp(0,0)"
               is portable.  See also "POSIX::setsid()".

       setpriority WHICH,WHO,PRIORITY
               Sets the current priority for a process, a process
               group, or a user.  (See setpriority(2).)  Will
               produce a fatal error if used on a machine that
               doesn't implement setpriority(2).

       setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
               Sets the socket option requested.  Returns
               undefined if there is an error.  Use integer
               constants provided by the "Socket" module for
               LEVEL and OPNAME.  Values for LEVEL can also be
               obtained from getprotobyname.  OPTVAL might either
               be a packed string or an integer.  An integer
               OPTVAL is shorthand for pack("i", OPTVAL).

               An example disabling the Nagle's algorithm for a
               socket:

                   use Socket qw(IPPROTO_TCP TCP_NODELAY);
                   setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1);



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       shift ARRAY
       shift   Shifts the first value of the array off and
               returns it, shortening the array by 1 and moving
               everything down.  If there are no elements in the
               array, returns the undefined value.  If ARRAY is
               omitted, shifts the @_ array within the lexical
               scope of subroutines and formats, and the @ARGV
               array outside of a subroutine and also within the
               lexical scopes established by the "eval STRING",
               "BEGIN {}", "INIT {}", "CHECK {}", "UNITCHECK {}"
               and "END {}" constructs.

               See also "unshift", "push", and "pop".  "shift"
               and "unshift" do the same thing to the left end of
               an array that "pop" and "push" do to the right
               end.

       shmctl ID,CMD,ARG
               Calls the System V IPC function shmctl.  You'll
               probably have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If
               CMD is "IPC_STAT", then ARG must be a variable
               that will hold the returned "shmid_ds" structure.
               Returns like ioctl: the undefined value for error,
               "0 but true" for zero, or the actual return value
               otherwise.  See also "SysV IPC" in perlipc and
               "IPC::SysV" documentation.

       shmget KEY,SIZE,FLAGS
               Calls the System V IPC function shmget.  Returns
               the shared memory segment id, or the undefined
               value if there is an error.  See also "SysV IPC"
               in perlipc and "IPC::SysV" documentation.

       shmread ID,VAR,POS,SIZE
       shmwrite ID,STRING,POS,SIZE
               Reads or writes the System V shared memory segment
               ID starting at position POS for size SIZE by
               attaching to it, copying in/out, and detaching
               from it.  When reading, VAR must be a variable
               that will hold the data read.  When writing, if
               STRING is too long, only SIZE bytes are used; if
               STRING is too short, nulls are written to fill out
               SIZE bytes.  Return true if successful, or false
               if there is an error.  shmread() taints the
               variable. See also "SysV IPC" in perlipc,
               "IPC::SysV" documentation, and the
               "IPC::Shareable" module from CPAN.

       shutdown SOCKET,HOW
               Shuts down a socket connection in the manner



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               indicated by HOW, which has the same
               interpretation as in the system call of the same
               name.

                   shutdown(SOCKET, 0);    # I/we have stopped reading data
                   shutdown(SOCKET, 1);    # I/we have stopped writing data
                   shutdown(SOCKET, 2);    # I/we have stopped using this socket

               This is useful with sockets when you want to tell
               the other side you're done writing but not done
               reading, or vice versa.  It's also a more
               insistent form of close because it also disables
               the file descriptor in any forked copies in other
               processes.

               Returns 1 for success. In the case of error,
               returns "undef" if the first argument is not a
               valid filehandle, or returns 0 and sets $! for any
               other failure.

       sin EXPR
       sin     Returns the sine of EXPR (expressed in radians).
               If EXPR is omitted, returns sine of $_.

               For the inverse sine operation, you may use the
               "Math::Trig::asin" function, or use this relation:

                   sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }

       sleep EXPR
       sleep   Causes the script to sleep for EXPR seconds, or
               forever if no EXPR.  Returns the number of seconds
               actually slept.

               May be interrupted if the process receives a
               signal such as "SIGALRM".

                   eval {
                       local $SIG{ALARM} = sub { die "Alarm!\n" };
                       sleep;
                   };
                   die $@ unless $@ eq "Alarm!\n";

               You probably cannot mix "alarm" and "sleep" calls,
               because "sleep" is often implemented using
               "alarm".

               On some older systems, it may sleep up to a full
               second less than what you requested, depending on
               how it counts seconds.  Most modern systems always
               sleep the full amount.  They may appear to sleep
               longer than that, however, because your process
               might not be scheduled right away in a busy
               multitasking system.



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               For delays of finer granularity than one second,
               the Time::HiRes module (from CPAN, and starting
               from Perl 5.8 part of the standard distribution)
               provides usleep().  You may also use Perl's four-
               argument version of select() leaving the first
               three arguments undefined, or you might be able to
               use the "syscall" interface to access setitimer(2)
               if your system supports it. See perlfaq8 for
               details.

               See also the POSIX module's "pause" function.

       socket SOCKET,DOMAIN,TYPE,PROTOCOL
               Opens a socket of the specified kind and attaches
               it to filehandle SOCKET.  DOMAIN, TYPE, and
               PROTOCOL are specified the same as for the system
               call of the same name.  You should "use Socket"
               first to get the proper definitions imported.  See
               the examples in "Sockets: Client/Server
               Communication" in perlipc.

               On systems that support a close-on-exec flag on
               files, the flag will be set for the newly opened
               file descriptor, as determined by the value of
               $^F.  See "$^F" in perlvar.

       socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
               Creates an unnamed pair of sockets in the
               specified domain, of the specified type.  DOMAIN,
               TYPE, and PROTOCOL are specified the same as for
               the system call of the same name.  If
               unimplemented, yields a fatal error.  Returns true
               if successful.

               On systems that support a close-on-exec flag on
               files, the flag will be set for the newly opened
               file descriptors, as determined by the value of
               $^F.  See "$^F" in perlvar.

               Some systems defined "pipe" in terms of
               "socketpair", in which a call to "pipe(Rdr, Wtr)"
               is essentially:

                   use Socket;
                   socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
                   shutdown(Rdr, 1);        # no more writing for reader
                   shutdown(Wtr, 0);        # no more reading for writer

               See perlipc for an example of socketpair use.
               Perl 5.8 and later will emulate socketpair using
               IP sockets to localhost if your system implements
               sockets but not socketpair.





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       sort SUBNAME LIST
       sort BLOCK LIST
       sort LIST
               In list context, this sorts the LIST and returns
               the sorted list value.  In scalar context, the
               behaviour of "sort()" is undefined.

               If SUBNAME or BLOCK is omitted, "sort"s in
               standard string comparison order.  If SUBNAME is
               specified, it gives the name of a subroutine that
               returns an integer less than, equal to, or greater
               than 0, depending on how the elements of the list
               are to be ordered.  (The "<=>" and "cmp" operators
               are extremely useful in such routines.)  SUBNAME
               may be a scalar variable name (unsubscripted), in
               which case the value provides the name of (or a
               reference to) the actual subroutine to use.  In
               place of a SUBNAME, you can provide a BLOCK as an
               anonymous, in-line sort subroutine.

               If the subroutine's prototype is "($$)", the
               elements to be compared are passed by reference in
               @_, as for a normal subroutine.  This is slower
               than unprototyped subroutines, where the elements
               to be compared are passed into the subroutine as
               the package global variables $a and $b (see
               example below).  Note that in the latter case, it
               is usually counter-productive to declare $a and $b
               as lexicals.

               The values to be compared are always passed by
               reference and should not be modified.

               You also cannot exit out of the sort block or
               subroutine using any of the loop control operators
               described in perlsyn or with "goto".

               When "use locale" is in effect, "sort LIST" sorts
               LIST according to the current collation locale.
               See perllocale.

               sort() returns aliases into the original list,
               much as a for loop's index variable aliases the
               list elements.  That is, modifying an element of a
               list returned by sort() (for example, in a
               "foreach", "map" or "grep") actually modifies the
               element in the original list.  This is usually
               something to be avoided when writing clear code.

               Perl 5.6 and earlier used a quicksort algorithm to
               implement sort.  That algorithm was not stable,
               and could go quadratic.  (A stable sort preserves
               the input order of elements that compare equal.
               Although quicksort's run time is O(NlogN) when



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               averaged over all arrays of length N, the time can
               be O(N**2), quadratic behavior, for some inputs.)
               In 5.7, the quicksort implementation was replaced
               with a stable mergesort algorithm whose worst-case
               behavior is O(NlogN).  But benchmarks indicated
               that for some inputs, on some platforms, the
               original quicksort was faster.  5.8 has a sort
               pragma for limited control of the sort.  Its
               rather blunt control of the underlying algorithm
               may not persist into future Perls, but the ability
               to characterize the input or output in
               implementation independent ways quite probably
               will.  See the sort pragma.

               Examples:

                   # sort lexically
                   @articles = sort @files;

                   # same thing, but with explicit sort routine
                   @articles = sort {$a cmp $b} @files;

                   # now case-insensitively
                   @articles = sort {uc($a) cmp uc($b)} @files;

                   # same thing in reversed order
                   @articles = sort {$b cmp $a} @files;

                   # sort numerically ascending
                   @articles = sort {$a <=> $b} @files;

                   # sort numerically descending
                   @articles = sort {$b <=> $a} @files;

                   # this sorts the %age hash by value instead of key
                   # using an in-line function
                   @eldest = sort { $age{$b} <=> $age{$a} } keys %age;

                   # sort using explicit subroutine name
                   sub byage {
                       $age{$a} <=> $age{$b};  # presuming numeric
                   }
                   @sortedclass = sort byage @class;

                   sub backwards { $b cmp $a }
                   @harry  = qw(dog cat x Cain Abel);
                   @george = qw(gone chased yz Punished Axed);
                   print sort @harry;
                           # prints AbelCaincatdogx
                   print sort backwards @harry;
                           # prints xdogcatCainAbel
                   print sort @george, 'to', @harry;
                           # prints AbelAxedCainPunishedcatchaseddoggonetoxyz




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                   # inefficiently sort by descending numeric compare using
                   # the first integer after the first = sign, or the
                   # whole record case-insensitively otherwise

                   @new = sort {
                       ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
                                           ||
                                   uc($a)  cmp  uc($b)
                   } @old;

                   # same thing, but much more efficiently;
                   # we'll build auxiliary indices instead
                   # for speed
                   @nums = @caps = ();
                   for (@old) {
                       push @nums, /=(\d+)/;
                       push @caps, uc($_);
                   }

                   @new = @old[ sort {
                                       $nums[$b] <=> $nums[$a]
                                                ||
                                       $caps[$a] cmp $caps[$b]
                                      } 0..$#old
                              ];

                   # same thing, but without any temps
                   @new = map { $_->[0] }
                          sort { $b->[1] <=> $a->[1]
                                          ||
                                 $a->[2] cmp $b->[2]
                          } map { [$_, /=(\d+)/, uc($_)] } @old;

                   # using a prototype allows you to use any comparison subroutine
                   # as a sort subroutine (including other package's subroutines)
                   package other;
                   sub backwards ($$) { $_[1] cmp $_[0]; }     # $a and $b are not set here

                   package main;
                   @new = sort other::backwards @old;

                   # guarantee stability, regardless of algorithm
                   use sort 'stable';
                   @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

                   # force use of mergesort (not portable outside Perl 5.8)
                   use sort '_mergesort';  # note discouraging _
                   @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

               Warning: syntactical care is required when sorting
               the list returned from a function. If you want to
               sort the list returned by the function call
               "find_records(@key)", you can use:




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                   @contact = sort { $a cmp $b } find_records @key;
                   @contact = sort +find_records(@key);
                   @contact = sort &find_records(@key);
                   @contact = sort(find_records(@key));

               If instead you want to sort the array @key with
               the comparison routine "find_records()" then you
               can use:

                   @contact = sort { find_records() } @key;
                   @contact = sort find_records(@key);
                   @contact = sort(find_records @key);
                   @contact = sort(find_records (@key));

               If you're using strict, you must not declare $a
               and $b as lexicals.  They are package globals.
               That means that if you're in the "main" package
               and type

                   @articles = sort {$b <=> $a} @files;

               then $a and $b are $main::a and $main::b (or $::a
               and $::b), but if you're in the "FooPack" package,
               it's the same as typing

                   @articles = sort {$FooPack::b <=> $FooPack::a} @files;

               The comparison function is required to behave.  If
               it returns inconsistent results (sometimes saying
               $x[1] is less than $x[2] and sometimes saying the
               opposite, for example) the results are not well-
               defined.

               Because "<=>" returns "undef" when either operand
               is "NaN" (not-a-number), and because "sort" will
               trigger a fatal error unless the result of a
               comparison is defined, when sorting with a
               comparison function like "$a <=> $b", be careful
               about lists that might contain a "NaN".  The
               following example takes advantage of the fact that
               "NaN != NaN" to eliminate any "NaN"s from the
               input.

                   @result = sort { $a <=> $b } grep { $_ == $_ } @input;

       splice ARRAY,OFFSET,LENGTH,LIST
       splice ARRAY,OFFSET,LENGTH
       splice ARRAY,OFFSET
       splice ARRAY
               Removes the elements designated by OFFSET and
               LENGTH from an array, and replaces them with the
               elements of LIST, if any.  In list context,
               returns the elements removed from the array.  In
               scalar context, returns the last element removed,



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               or "undef" if no elements are removed.  The array
               grows or shrinks as necessary.  If OFFSET is
               negative then it starts that far from the end of
               the array.  If LENGTH is omitted, removes
               everything from OFFSET onward.  If LENGTH is
               negative, removes the elements from OFFSET onward
               except for -LENGTH elements at the end of the
               array.  If both OFFSET and LENGTH are omitted,
               removes everything. If OFFSET is past the end of
               the array, perl issues a warning, and splices at
               the end of the array.

               The following equivalences hold (assuming "$[ == 0
               and $#a >= $i" )

                   push(@a,$x,$y)      splice(@a,@a,0,$x,$y)
                   pop(@a)             splice(@a,-1)
                   shift(@a)           splice(@a,0,1)
                   unshift(@a,$x,$y)   splice(@a,0,0,$x,$y)
                   $a[$i] = $y         splice(@a,$i,1,$y)

               Example, assuming array lengths are passed before
               arrays:

                   sub aeq {   # compare two list values
                       my(@a) = splice(@_,0,shift);
                       my(@b) = splice(@_,0,shift);
                       return 0 unless @a == @b;       # same len?
                       while (@a) {
                           return 0 if pop(@a) ne pop(@b);
                       }
                       return 1;
                   }
                   if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }

       split /PATTERN/,EXPR,LIMIT
       split /PATTERN/,EXPR
       split /PATTERN/
       split   Splits the string EXPR into a list of strings and
               returns that list.  By default, empty leading
               fields are preserved, and empty trailing ones are
               deleted.  (If all fields are empty, they are
               considered to be trailing.)

               In scalar context, returns the number of fields
               found. In scalar and void context it splits into
               the @_ array.  Use of split in scalar and void
               context is deprecated, however, because it
               clobbers your subroutine arguments.

               If EXPR is omitted, splits the $_ string.  If
               PATTERN is also omitted, splits on whitespace
               (after skipping any leading whitespace).  Anything
               matching PATTERN is taken to be a delimiter



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               separating the fields.  (Note that the delimiter
               may be longer than one character.)

               If LIMIT is specified and positive, it represents
               the maximum number of fields the EXPR will be
               split into, though the actual number of fields
               returned depends on the number of times PATTERN
               matches within EXPR.  If LIMIT is unspecified or
               zero, trailing null fields are stripped (which
               potential users of "pop" would do well to
               remember).  If LIMIT is negative, it is treated as
               if an arbitrarily large LIMIT had been specified.
               Note that splitting an EXPR that evaluates to the
               empty string always returns the empty list,
               regardless of the LIMIT specified.

               A pattern matching the null string (not to be
               confused with a null pattern "//", which is just
               one member of the set of patterns matching a null
               string) will split the value of EXPR into separate
               characters at each point it matches that way.  For
               example:

                   print join(':', split(/ */, 'hi there')), "\n";

               produces the output 'h:i:t:h:e:r:e'.

               As a special case for "split", using the empty
               pattern "//" specifically matches only the null
               string, and is not be confused with the regular
               use of "//" to mean "the last successful pattern
               match".  So, for "split", the following:

                   print join(':', split(//, 'hi there')), "\n";

               produces the output 'h:i: :t:h:e:r:e'.

               Empty leading fields are produced when there are
               positive-width matches at the beginning of the
               string; a zero-width match at the beginning of the
               string does not produce an empty field. For
               example:

                  print join(':', split(/(?=\w)/, 'hi there!'));

               produces the output 'h:i :t:h:e:r:e!'. Empty
               trailing fields, on the other hand, are produced
               when there is a match at the end of the string
               (and when LIMIT is given and is not 0), regardless
               of the length of the match.  For example:

                  print join(':', split(//,   'hi there!', -1)), "\n";
                  print join(':', split(/\W/, 'hi there!', -1)), "\n";




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               produce the output 'h:i: :t:h:e:r:e:!:' and
               'hi:there:', respectively, both with an empty
               trailing field.

               The LIMIT parameter can be used to split a line
               partially

                   ($login, $passwd, $remainder) = split(/:/, $_, 3);

               When assigning to a list, if LIMIT is omitted, or
               zero, Perl supplies a LIMIT one larger than the
               number of variables in the list, to avoid
               unnecessary work.  For the list above LIMIT would
               have been 4 by default.  In time critical
               applications it behooves you not to split into
               more fields than you really need.

               If the PATTERN contains parentheses, additional
               list elements are created from each matching
               substring in the delimiter.

                   split(/([,-])/, "1-10,20", 3);

               produces the list value

                   (1, '-', 10, ',', 20)

               If you had the entire header of a normal Unix
               email message in $header, you could split it up
               into fields and their values this way:

                   $header =~ s/\n(?=\s)//g;  # fix continuation lines
                   %hdrs   =  (UNIX_FROM => split /^(\S*?):\s*/m, $header);

               The pattern "/PATTERN/" may be replaced with an
               expression to specify patterns that vary at
               runtime.  (To do runtime compilation only once,
               use "/$variable/o".)

               As a special case, specifying a PATTERN of space
               (' ') will split on white space just as "split"
               with no arguments does.  Thus, "split(' ')" can be
               used to emulate awk's default behavior, whereas
               "split(/ /)" will give you as many null initial
               fields as there are leading spaces.  A "split" on
               "/\s+/" is like a "split(' ')" except that any
               leading whitespace produces a null first field.  A
               "split" with no arguments really does a
               "split(' ', $_)" internally.

               A PATTERN of "/^/" is treated as if it were
               "/^/m", since it isn't much use otherwise.

               Example:



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                   open(PASSWD, '/etc/passwd');
                   while (<PASSWD>) {
                       chomp;
                       ($login, $passwd, $uid, $gid,
                        $gcos, $home, $shell) = split(/:/);
                       #...
                   }

               As with regular pattern matching, any capturing
               parentheses that are not matched in a "split()"
               will be set to "undef" when returned:

                   @fields = split /(A)|B/, "1A2B3";
                   # @fields is (1, 'A', 2, undef, 3)

       sprintf FORMAT, LIST
               Returns a string formatted by the usual "printf"
               conventions of the C library function "sprintf".
               See below for more details and see sprintf(3) or
               printf(3) on your system for an explanation of the
               general principles.

               For example:

                       # Format number with up to 8 leading zeroes
                       $result = sprintf("%08d", $number);

                       # Round number to 3 digits after decimal point
                       $rounded = sprintf("%.3f", $number);

               Perl does its own "sprintf" formatting--it
               emulates the C function "sprintf", but it doesn't
               use it (except for floating-point numbers, and
               even then only the standard modifiers are
               allowed).  As a result, any non-standard
               extensions in your local "sprintf" are not
               available from Perl.

               Unlike "printf", "sprintf" does not do what you
               probably mean when you pass it an array as your
               first argument. The array is given scalar context,
               and instead of using the 0th element of the array
               as the format, Perl will use the count of elements
               in the array as the format, which is almost never
               useful.

               Perl's "sprintf" permits the following
               universally-known conversions:









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                  %%   a percent sign
                  %c   a character with the given number
                  %s   a string
                  %d   a signed integer, in decimal
                  %u   an unsigned integer, in decimal
                  %o   an unsigned integer, in octal
                  %x   an unsigned integer, in hexadecimal
                  %e   a floating-point number, in scientific notation
                  %f   a floating-point number, in fixed decimal notation
                  %g   a floating-point number, in %e or %f notation

               In addition, Perl permits the following widely-
               supported conversions:

                  %X   like %x, but using upper-case letters
                  %E   like %e, but using an upper-case "E"
                  %G   like %g, but with an upper-case "E" (if applicable)
                  %b   an unsigned integer, in binary
                  %B   like %b, but using an upper-case "B" with the # flag
                  %p   a pointer (outputs the Perl value's address in hexadecimal)
                  %n   special: *stores* the number of characters output so far
                       into the next variable in the parameter list

               Finally, for backward (and we do mean "backward")
               compatibility, Perl permits these unnecessary but
               widely-supported conversions:

                  %i   a synonym for %d
                  %D   a synonym for %ld
                  %U   a synonym for %lu
                  %O   a synonym for %lo
                  %F   a synonym for %f

               Note that the number of exponent digits in the
               scientific notation produced by %e, %E, %g and %G
               for numbers with the modulus of the exponent less
               than 100 is system-dependent: it may be three or
               less (zero-padded as necessary).  In other words,
               1.23 times ten to the 99th may be either "1.23e99"
               or "1.23e099".

               Between the "%" and the format letter, you may
               specify a number of additional attributes
               controlling the interpretation of the format.  In
               order, these are:

               format parameter index
                   An explicit format parameter index, such as
                   "2$". By default sprintf will format the next
                   unused argument in the list, but this allows
                   you to take the arguments out of order, e.g.:

                     printf '%2$d %1$d', 12, 34;      # prints "34 12"
                     printf '%3$d %d %1$d', 1, 2, 3;  # prints "3 1 1"



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               flags
                   one or more of:

                      space   prefix non-negative number with a space
                      +       prefix non-negative number with a plus sign
                      -       left-justify within the field
                      0       use zeros, not spaces, to right-justify
                      #       ensure the leading "0" for any octal,
                              prefix non-zero hexadecimal with "0x" or "0X",
                              prefix non-zero binary with "0b" or "0B"

                   For example:

                     printf '<% d>',  12;   # prints "< 12>"
                     printf '<%+d>',  12;   # prints "<+12>"
                     printf '<%6s>',  12;   # prints "<    12>"
                     printf '<%-6s>', 12;   # prints "<12    >"
                     printf '<%06s>', 12;   # prints "<000012>"
                     printf '<%#o>',  12;   # prints "<014>"
                     printf '<%#x>',  12;   # prints "<0xc>"
                     printf '<%#X>',  12;   # prints "<0XC>"
                     printf '<%#b>',  12;   # prints "<0b1100>"
                     printf '<%#B>',  12;   # prints "<0B1100>"

                   When a space and a plus sign are given as the
                   flags at once, a plus sign is used to prefix a
                   positive number.

                     printf '<%+ d>', 12;   # prints "<+12>"
                     printf '<% +d>', 12;   # prints "<+12>"

                   When the # flag and a precision are given in
                   the %o conversion, the precision is
                   incremented if it's necessary for the leading
                   "0".

                     printf '<%#.5o>', 012;      # prints "<00012>"
                     printf '<%#.5o>', 012345;   # prints "<012345>"
                     printf '<%#.0o>', 0;        # prints "<0>"

               vector flag
                   This flag tells perl to interpret the supplied
                   string as a vector of integers, one for each
                   character in the string. Perl applies the
                   format to each integer in turn, then joins the
                   resulting strings with a separator (a dot "."
                   by default). This can be useful for displaying
                   ordinal values of characters in arbitrary
                   strings:

                     printf "%vd", "AB\x{100}";           # prints "65.66.256"
                     printf "version is v%vd\n", $^V;     # Perl's version

                   Put an asterisk "*" before the "v" to override



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                   the string to use to separate the numbers:

                     printf "address is %*vX\n", ":", $addr;   # IPv6 address
                     printf "bits are %0*v8b\n", " ", $bits;   # random bitstring

                   You can also explicitly specify the argument
                   number to use for the join string using e.g.
                   "*2$v":

                     printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":";   # 3 IPv6 addresses

               (minimum) width
                   Arguments are usually formatted to be only as
                   wide as required to display the given value.
                   You can override the width by putting a number
                   here, or get the width from the next argument
                   (with "*") or from a specified argument (with
                   e.g. "*2$"):

                     printf '<%s>', "a";       # prints "<a>"
                     printf '<%6s>', "a";      # prints "<     a>"
                     printf '<%*s>', 6, "a";   # prints "<     a>"
                     printf '<%*2$s>', "a", 6; # prints "<     a>"
                     printf '<%2s>', "long";   # prints "<long>" (does not truncate)

                   If a field width obtained through "*" is
                   negative, it has the same effect as the "-"
                   flag: left-justification.

               precision, or maximum width
                   You can specify a precision (for numeric
                   conversions) or a maximum width (for string
                   conversions) by specifying a "." followed by a
                   number.  For floating point formats, with the
                   exception of 'g' and 'G', this specifies the
                   number of decimal places to show (the default
                   being 6), e.g.:

                     # these examples are subject to system-specific variation
                     printf '<%f>', 1;    # prints "<1.000000>"
                     printf '<%.1f>', 1;  # prints "<1.0>"
                     printf '<%.0f>', 1;  # prints "<1>"
                     printf '<%e>', 10;   # prints "<1.000000e+01>"
                     printf '<%.1e>', 10; # prints "<1.0e+01>"

                   For 'g' and 'G', this specifies the maximum
                   number of digits to show, including prior to
                   the decimal point as well as after it, e.g.:









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                     # these examples are subject to system-specific variation
                     printf '<%g>', 1;        # prints "<1>"
                     printf '<%.10g>', 1;     # prints "<1>"
                     printf '<%g>', 100;      # prints "<100>"
                     printf '<%.1g>', 100;    # prints "<1e+02>"
                     printf '<%.2g>', 100.01; # prints "<1e+02>"
                     printf '<%.5g>', 100.01; # prints "<100.01>"
                     printf '<%.4g>', 100.01; # prints "<100>"

                   For integer conversions, specifying a
                   precision implies that the output of the
                   number itself should be zero-padded to this
                   width, where the 0 flag is ignored:

                     printf '<%.6d>', 1;      # prints "<000001>"
                     printf '<%+.6d>', 1;     # prints "<+000001>"
                     printf '<%-10.6d>', 1;   # prints "<000001    >"
                     printf '<%10.6d>', 1;    # prints "<    000001>"
                     printf '<%010.6d>', 1;   # prints "<    000001>"
                     printf '<%+10.6d>', 1;   # prints "<   +000001>"

                     printf '<%.6x>', 1;      # prints "<000001>"
                     printf '<%#.6x>', 1;     # prints "<0x000001>"
                     printf '<%-10.6x>', 1;   # prints "<000001    >"
                     printf '<%10.6x>', 1;    # prints "<    000001>"
                     printf '<%010.6x>', 1;   # prints "<    000001>"
                     printf '<%#10.6x>', 1;   # prints "<  0x000001>"

                   For string conversions, specifying a precision
                   truncates the string to fit in the specified
                   width:

                     printf '<%.5s>', "truncated";   # prints "<trunc>"
                     printf '<%10.5s>', "truncated"; # prints "<     trunc>"

                   You can also get the precision from the next
                   argument using ".*":

                     printf '<%.6x>', 1;       # prints "<000001>"
                     printf '<%.*x>', 6, 1;    # prints "<000001>"

                   If a precision obtained through "*" is
                   negative, it has the same effect as no
                   precision.

                     printf '<%.*s>',  7, "string";   # prints "<string>"
                     printf '<%.*s>',  3, "string";   # prints "<str>"
                     printf '<%.*s>',  0, "string";   # prints "<>"
                     printf '<%.*s>', -1, "string";   # prints "<string>"

                     printf '<%.*d>',  1, 0;   # prints "<0>"
                     printf '<%.*d>',  0, 0;   # prints "<>"
                     printf '<%.*d>', -1, 0;   # prints "<0>"




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                   You cannot currently get the precision from a
                   specified number, but it is intended that this
                   will be possible in the future using e.g.
                   ".*2$":

                     printf '<%.*2$x>', 1, 6;   # INVALID, but in future will print "<000001>"

               size
                   For numeric conversions, you can specify the
                   size to interpret the number as using "l",
                   "h", "V", "q", "L", or "ll". For integer
                   conversions ("d u o x X b i D U O"), numbers
                   are usually assumed to be whatever the default
                   integer size is on your platform (usually 32
                   or 64 bits), but you can override this to use
                   instead one of the standard C types, as
                   supported by the compiler used to build Perl:

                      l           interpret integer as C type "long" or "unsigned long"
                      h           interpret integer as C type "short" or "unsigned short"
                      q, L or ll  interpret integer as C type "long long", "unsigned long long".
                                  or "quads" (typically 64-bit integers)

                   The last will produce errors if Perl does not
                   understand "quads" in your installation. (This
                   requires that either the platform natively
                   supports quads or Perl was specifically
                   compiled to support quads.) You can find out
                   whether your Perl supports quads via Config:

                           use Config;
                           ($Config{use64bitint} eq 'define' || $Config{longsize} >= 8) &&
                                   print "quads\n";

                   For floating point conversions ("e f g E F
                   G"), numbers are usually assumed to be the
                   default floating point size on your platform
                   (double or long double), but you can force
                   'long double' with "q", "L", or "ll" if your
                   platform supports them. You can find out
                   whether your Perl supports long doubles via
                   Config:

                           use Config;
                           $Config{d_longdbl} eq 'define' && print "long doubles\n";

                   You can find out whether Perl considers 'long
                   double' to be the default floating point size
                   to use on your platform via Config:

                           use Config;
                           ($Config{uselongdouble} eq 'define') &&
                                   print "long doubles by default\n";




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                   It can also be the case that long doubles and
                   doubles are the same thing:

                           use Config;
                           ($Config{doublesize} == $Config{longdblsize}) &&
                                   print "doubles are long doubles\n";

                   The size specifier "V" has no effect for Perl
                   code, but it is supported for compatibility
                   with XS code; it means 'use the standard size
                   for a Perl integer (or floating-point
                   number)', which is already the default for
                   Perl code.

               order of arguments
                   Normally, sprintf takes the next unused
                   argument as the value to format for each
                   format specification. If the format
                   specification uses "*" to require additional
                   arguments, these are consumed from the
                   argument list in the order in which they
                   appear in the format specification before the
                   value to format. Where an argument is
                   specified using an explicit index, this does
                   not affect the normal order for the arguments
                   (even when the explicitly specified index
                   would have been the next argument in any
                   case).

                   So:

                     printf '<%*.*s>', $a, $b, $c;

                   would use $a for the width, $b for the
                   precision and $c as the value to format,
                   while:

                     printf '<%*1$.*s>', $a, $b;

                   would use $a for the width and the precision,
                   and $b as the value to format.

                   Here are some more examples - beware that when
                   using an explicit index, the "$" may need to
                   be escaped:

                     printf "%2\$d %d\n",    12, 34;               # will print "34 12\n"
                     printf "%2\$d %d %d\n", 12, 34;               # will print "34 12 34\n"
                     printf "%3\$d %d %d\n", 12, 34, 56;           # will print "56 12 34\n"
                     printf "%2\$*3\$d %d\n", 12, 34, 3;           # will print " 34 12\n"

               If "use locale" is in effect, and
               POSIX::setlocale() has been called, the character
               used for the decimal separator in formatted



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               floating point numbers is affected by the
               LC_NUMERIC locale.  See perllocale and POSIX.

       sqrt EXPR
       sqrt    Return the square root of EXPR.  If EXPR is
               omitted, returns square root of $_.  Only works on
               non-negative operands, unless you've loaded the
               standard Math::Complex module.

                   use Math::Complex;
                   print sqrt(-2);    # prints 1.4142135623731i

       srand EXPR
       srand   Sets the random number seed for the "rand"
               operator.

               The point of the function is to "seed" the "rand"
               function so that "rand" can produce a different
               sequence each time you run your program.

               If srand() is not called explicitly, it is called
               implicitly at the first use of the "rand"
               operator.  However, this was not the case in
               versions of Perl before 5.004, so if your script
               will run under older Perl versions, it should call
               "srand".

               Most programs won't even call srand() at all,
               except those that need a cryptographically-strong
               starting point rather than the generally
               acceptable default, which is based on time of day,
               process ID, and memory allocation, or the
               /dev/urandom device, if available.

               You can call srand($seed) with the same $seed to
               reproduce the same sequence from rand(), but this
               is usually reserved for generating predictable
               results for testing or debugging.  Otherwise,
               don't call srand() more than once in your program.

               Do not call srand() (i.e. without an argument)
               more than once in a script.  The internal state of
               the random number generator should contain more
               entropy than can be provided by any seed, so
               calling srand() again actually loses randomness.

               Most implementations of "srand" take an integer
               and will silently truncate decimal numbers.  This
               means "srand(42)" will usually produce the same
               results as "srand(42.1)".  To be safe, always pass
               "srand" an integer.

               In versions of Perl prior to 5.004 the default
               seed was just the current "time".  This isn't a



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               particularly good seed, so many old programs
               supply their own seed value (often "time ^ $$" or
               "time ^ ($$ + ($$ << 15))"), but that isn't
               necessary any more.

               For cryptographic purposes, however, you need
               something much more random than the default seed.
               Checksumming the compressed output of one or more
               rapidly changing operating system status programs
               is the usual method.  For example:

                   srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip -f`);

               If you're particularly concerned with this, see
               the "Math::TrulyRandom" module in CPAN.

               Frequently called programs (like CGI scripts) that
               simply use

                   time ^ $$

               for a seed can fall prey to the mathematical
               property that

                   a^b == (a+1)^(b+1)

               one-third of the time.  So don't do that.

       stat FILEHANDLE
       stat EXPR
       stat DIRHANDLE
       stat    Returns a 13-element list giving the status info
               for a file, either the file opened via FILEHANDLE
               or DIRHANDLE, or named by EXPR.  If EXPR is
               omitted, it stats $_.  Returns a null list if the
               stat fails.  Typically used as follows:

                   ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
                      $atime,$mtime,$ctime,$blksize,$blocks)
                          = stat($filename);

               Not all fields are supported on all filesystem
               types.  Here are the meanings of the fields:

                 0 dev      device number of filesystem
                 1 ino      inode number
                 2 mode     file mode  (type and permissions)
                 3 nlink    number of (hard) links to the file
                 4 uid      numeric user ID of file's owner
                 5 gid      numeric group ID of file's owner
                 6 rdev     the device identifier (special files only)
                 7 size     total size of file, in bytes
                 8 atime    last access time in seconds since the epoch
                 9 mtime    last modify time in seconds since the epoch



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                10 ctime    inode change time in seconds since the epoch (*)
                11 blksize  preferred block size for file system I/O
                12 blocks   actual number of blocks allocated

               (The epoch was at 00:00 January 1, 1970 GMT.)

               (*) Not all fields are supported on all filesystem
               types. Notably, the ctime field is non-portable.
               In particular, you cannot expect it to be a
               "creation time", see "Files and Filesystems" in
               perlport for details.

               If "stat" is passed the special filehandle
               consisting of an underline, no stat is done, but
               the current contents of the stat structure from
               the last "stat", "lstat", or filetest are
               returned.  Example:

                   if (-x $file && (($d) = stat(_)) && $d < 0) {
                       print "$file is executable NFS file\n";
                   }

               (This works on machines only for which the device
               number is negative under NFS.)

               Because the mode contains both the file type and
               its permissions, you should mask off the file type
               portion and (s)printf using a "%o" if you want to
               see the real permissions.

                   $mode = (stat($filename))[2];
                   printf "Permissions are %04o\n", $mode & 07777;

               In scalar context, "stat" returns a boolean value
               indicating success or failure, and, if successful,
               sets the information associated with the special
               filehandle "_".

               The File::stat module provides a convenient, by-
               name access mechanism:

                   use File::stat;
                   $sb = stat($filename);
                   printf "File is %s, size is %s, perm %04o, mtime %s\n",
                       $filename, $sb->size, $sb->mode & 07777,
                       scalar localtime $sb->mtime;

               You can import symbolic mode constants ("S_IF*")
               and functions ("S_IS*") from the Fcntl module:

                   use Fcntl ':mode';

                   $mode = (stat($filename))[2];




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                   $user_rwx      = ($mode & S_IRWXU) >> 6;
                   $group_read    = ($mode & S_IRGRP) >> 3;
                   $other_execute =  $mode & S_IXOTH;

                   printf "Permissions are %04o\n", S_IMODE($mode), "\n";

                   $is_setuid     =  $mode & S_ISUID;
                   $is_directory  =  S_ISDIR($mode);

               You could write the last two using the "-u" and
               "-d" operators.  The commonly available "S_IF*"
               constants are

                   # Permissions: read, write, execute, for user, group, others.

                   S_IRWXU S_IRUSR S_IWUSR S_IXUSR
                   S_IRWXG S_IRGRP S_IWGRP S_IXGRP
                   S_IRWXO S_IROTH S_IWOTH S_IXOTH

                   # Setuid/Setgid/Stickiness/SaveText.
                   # Note that the exact meaning of these is system dependent.

                   S_ISUID S_ISGID S_ISVTX S_ISTXT

                   # File types.  Not necessarily all are available on your system.

                   S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT

                   # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR.

                   S_IREAD S_IWRITE S_IEXEC

               and the "S_IF*" functions are

                   S_IMODE($mode)      the part of $mode containing the permission bits
                                       and the setuid/setgid/sticky bits

                   S_IFMT($mode)       the part of $mode containing the file type
                                       which can be bit-anded with e.g. S_IFREG
                                       or with the following functions

                   # The operators -f, -d, -l, -b, -c, -p, and -S.

                   S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode)
                   S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode)

                   # No direct -X operator counterpart, but for the first one
                   # the -g operator is often equivalent.  The ENFMT stands for
                   # record flocking enforcement, a platform-dependent feature.

                   S_ISENFMT($mode) S_ISWHT($mode)

               See your native chmod(2) and stat(2) documentation
               for more details about the "S_*" constants.  To



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               get status info for a symbolic link instead of the
               target file behind the link, use the "lstat"
               function.

       state EXPR
       state TYPE EXPR
       state EXPR : ATTRS
       state TYPE EXPR : ATTRS
               "state" declares a lexically scoped variable, just
               like "my" does.  However, those variables will
               never be reinitialized, contrary to lexical
               variables that are reinitialized each time their
               enclosing block is entered.

               "state" variables are only enabled when the
               "feature 'state'" pragma is in effect.  See
               feature.

       study SCALAR
       study   Takes extra time to study SCALAR ($_ if
               unspecified) in anticipation of doing many pattern
               matches on the string before it is next modified.
               This may or may not save time, depending on the
               nature and number of patterns you are searching
               on, and on the distribution of character
               frequencies in the string to be searched--you
               probably want to compare run times with and
               without it to see which runs faster.  Those loops
               that scan for many short constant strings
               (including the constant parts of more complex
               patterns) will benefit most.  You may have only
               one "study" active at a time--if you study a
               different scalar the first is "unstudied".  (The
               way "study" works is this: a linked list of every
               character in the string to be searched is made, so
               we know, for example, where all the 'k' characters
               are.  From each search string, the rarest
               character is selected, based on some static
               frequency tables constructed from some C programs
               and English text.  Only those places that contain
               this "rarest" character are examined.)

               For example, here is a loop that inserts index
               producing entries before any line containing a
               certain pattern:

                   while (<>) {
                       study;
                       print ".IX foo\n"       if /\bfoo\b/;
                       print ".IX bar\n"       if /\bbar\b/;
                       print ".IX blurfl\n"    if /\bblurfl\b/;
                       # ...
                       print;
                   }



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               In searching for "/\bfoo\b/", only those locations
               in $_ that contain "f" will be looked at, because
               "f" is rarer than "o".  In general, this is a big
               win except in pathological cases.  The only
               question is whether it saves you more time than it
               took to build the linked list in the first place.

               Note that if you have to look for strings that you
               don't know till runtime, you can build an entire
               loop as a string and "eval" that to avoid
               recompiling all your patterns all the time.
               Together with undefining $/ to input entire files
               as one record, this can be very fast, often faster
               than specialized programs like fgrep(1).  The
               following scans a list of files (@files) for a
               list of words (@words), and prints out the names
               of those files that contain a match:

                   $search = 'while (<>) { study;';
                   foreach $word (@words) {
                       $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
                   }
                   $search .= "}";
                   @ARGV = @files;
                   undef $/;
                   eval $search;               # this screams
                   $/ = "\n";          # put back to normal input delimiter
                   foreach $file (sort keys(%seen)) {
                       print $file, "\n";
                   }

       sub NAME BLOCK
       sub NAME (PROTO) BLOCK
       sub NAME : ATTRS BLOCK
       sub NAME (PROTO) : ATTRS BLOCK
               This is subroutine definition, not a real function
               per se.  Without a BLOCK it's just a forward
               declaration.  Without a NAME, it's an anonymous
               function declaration, and does actually return a
               value: the CODE ref of the closure you just
               created.

               See perlsub and perlref for details about
               subroutines and references, and attributes and
               Attribute::Handlers for more information about
               attributes.

       substr EXPR,OFFSET,LENGTH,REPLACEMENT
       substr EXPR,OFFSET,LENGTH
       substr EXPR,OFFSET
               Extracts a substring out of EXPR and returns it.
               First character is at offset 0, or whatever you've
               set $[ to (but don't do that).  If OFFSET is
               negative (or more precisely, less than $[), starts



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               that far from the end of the string.  If LENGTH is
               omitted, returns everything to the end of the
               string.  If LENGTH is negative, leaves that many
               characters off the end of the string.

                   my $s = "The black cat climbed the green tree";
                   my $color  = substr $s, 4, 5;       # black
                   my $middle = substr $s, 4, -11;     # black cat climbed the
                   my $end    = substr $s, 14;         # climbed the green tree
                   my $tail   = substr $s, -4;         # tree
                   my $z      = substr $s, -4, 2;      # tr

               You can use the substr() function as an lvalue, in
               which case EXPR must itself be an lvalue.  If you
               assign something shorter than LENGTH, the string
               will shrink, and if you assign something longer
               than LENGTH, the string will grow to accommodate
               it.  To keep the string the same length you may
               need to pad or chop your value using "sprintf".

               If OFFSET and LENGTH specify a substring that is
               partly outside the string, only the part within
               the string is returned.  If the substring is
               beyond either end of the string, substr() returns
               the undefined value and produces a warning.  When
               used as an lvalue, specifying a substring that is
               entirely outside the string is a fatal error.
               Here's an example showing the behavior for
               boundary cases:

                   my $name = 'fred';
                   substr($name, 4) = 'dy';            # $name is now 'freddy'
                   my $null = substr $name, 6, 2;      # returns '' (no warning)
                   my $oops = substr $name, 7;         # returns undef, with warning
                   substr($name, 7) = 'gap';           # fatal error

               An alternative to using substr() as an lvalue is
               to specify the replacement string as the 4th
               argument.  This allows you to replace parts of the
               EXPR and return what was there before in one
               operation, just as you can with splice().

                   my $s = "The black cat climbed the green tree";
                   my $z = substr $s, 14, 7, "jumped from";    # climbed
                   # $s is now "The black cat jumped from the green tree"

               Note that the lvalue returned by the 3-arg version
               of substr() acts as a 'magic bullet'; each time it
               is assigned to, it remembers which part of the
               original string is being modified; for example:







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                   $x = '1234';
                   for (substr($x,1,2)) {
                       $_ = 'a';   print $x,"\n";      # prints 1a4
                       $_ = 'xyz'; print $x,"\n";      # prints 1xyz4
                       $x = '56789';
                       $_ = 'pq';  print $x,"\n";      # prints 5pq9
                   }

               Prior to Perl version 5.9.1, the result of using
               an lvalue multiple times was unspecified.

       symlink OLDFILE,NEWFILE
               Creates a new filename symbolically linked to the
               old filename.  Returns 1 for success, 0 otherwise.
               On systems that don't support symbolic links,
               produces a fatal error at run time.  To check for
               that, use eval:

                   $symlink_exists = eval { symlink("",""); 1 };

       syscall NUMBER, LIST
               Calls the system call specified as the first
               element of the list, passing the remaining
               elements as arguments to the system call.  If
               unimplemented, produces a fatal error.  The
               arguments are interpreted as follows: if a given
               argument is numeric, the argument is passed as an
               int.  If not, the pointer to the string value is
               passed.  You are responsible to make sure a string
               is pre-extended long enough to receive any result
               that might be written into a string.  You can't
               use a string literal (or other read-only string)
               as an argument to "syscall" because Perl has to
               assume that any string pointer might be written
               through.  If your integer arguments are not
               literals and have never been interpreted in a
               numeric context, you may need to add 0 to them to
               force them to look like numbers.  This emulates
               the "syswrite" function (or vice versa):

                   require 'syscall.ph';               # may need to run h2ph
                   $s = "hi there\n";
                   syscall(&SYS_write, fileno(STDOUT), $s, length $s);

               Note that Perl supports passing of up to only 14
               arguments to your system call, which in practice
               should usually suffice.

               Syscall returns whatever value returned by the
               system call it calls.  If the system call fails,
               "syscall" returns "-1" and sets $! (errno).  Note
               that some system calls can legitimately return
               "-1".  The proper way to handle such calls is to
               assign "$!=0;" before the call and check the value



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               of $! if syscall returns "-1".

               There's a problem with "syscall(&SYS_pipe)": it
               returns the file number of the read end of the
               pipe it creates.  There is no way to retrieve the
               file number of the other end.  You can avoid this
               problem by using "pipe" instead.

       sysopen FILEHANDLE,FILENAME,MODE
       sysopen FILEHANDLE,FILENAME,MODE,PERMS
               Opens the file whose filename is given by
               FILENAME, and associates it with FILEHANDLE.  If
               FILEHANDLE is an expression, its value is used as
               the name of the real filehandle wanted.  This
               function calls the underlying operating system's
               "open" function with the parameters FILENAME,
               MODE, PERMS.

               The possible values and flag bits of the MODE
               parameter are system-dependent; they are available
               via the standard module "Fcntl".  See the
               documentation of your operating system's "open" to
               see which values and flag bits are available.  You
               may combine several flags using the "|"-operator.

               Some of the most common values are "O_RDONLY" for
               opening the file in read-only mode, "O_WRONLY" for
               opening the file in write-only mode, and "O_RDWR"
               for opening the file in read-write mode.

               For historical reasons, some values work on almost
               every system supported by perl: zero means read-
               only, one means write-only, and two means
               read/write.  We know that these values do not work
               under OS/390 & VM/ESA Unix and on the Macintosh;
               you probably don't want to use them in new code.

               If the file named by FILENAME does not exist and
               the "open" call creates it (typically because MODE
               includes the "O_CREAT" flag), then the value of
               PERMS specifies the permissions of the newly
               created file.  If you omit the PERMS argument to
               "sysopen", Perl uses the octal value 0666.  These
               permission values need to be in octal, and are
               modified by your process's current "umask".

               In many systems the "O_EXCL" flag is available for
               opening files in exclusive mode.  This is not
               locking: exclusiveness means here that if the file
               already exists, sysopen() fails.  "O_EXCL" may not
               work on network filesystems, and has no effect
               unless the "O_CREAT" flag is set as well.  Setting
               "O_CREAT|O_EXCL" prevents the file from being
               opened if it is a symbolic link.  It does not



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               protect against symbolic links in the file's path.

               Sometimes you may want to truncate an already-
               existing file.  This can be done using the
               "O_TRUNC" flag.  The behavior of "O_TRUNC" with
               "O_RDONLY" is undefined.

               You should seldom if ever use 0644 as argument to
               "sysopen", because that takes away the user's
               option to have a more permissive umask.  Better to
               omit it.  See the perlfunc(1) entry on "umask" for
               more on this.

               Note that "sysopen" depends on the fdopen() C
               library function.  On many UNIX systems, fdopen()
               is known to fail when file descriptors exceed a
               certain value, typically 255. If you need more
               file descriptors than that, consider rebuilding
               Perl to use the "sfio" library, or perhaps using
               the POSIX::open() function.

               See perlopentut for a kinder, gentler explanation
               of opening files.

       sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
       sysread FILEHANDLE,SCALAR,LENGTH
               Attempts to read LENGTH bytes of data into
               variable SCALAR from the specified FILEHANDLE,
               using the system call read(2).  It bypasses
               buffered IO, so mixing this with other kinds of
               reads, "print", "write", "seek", "tell", or "eof"
               can cause confusion because the perlio or stdio
               layers usually buffers data.  Returns the number
               of bytes actually read, 0 at end of file, or undef
               if there was an error (in the latter case $! is
               also set).  SCALAR will be grown or shrunk so that
               the last byte actually read is the last byte of
               the scalar after the read.

               An OFFSET may be specified to place the read data
               at some place in the string other than the
               beginning.  A negative OFFSET specifies placement
               at that many characters counting backwards from
               the end of the string.  A positive OFFSET greater
               than the length of SCALAR results in the string
               being padded to the required size with "\0" bytes
               before the result of the read is appended.

               There is no syseof() function, which is ok, since
               eof() doesn't work very well on device files (like
               ttys) anyway.  Use sysread() and check for a
               return value for 0 to decide whether you're done.

               Note that if the filehandle has been marked as



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               ":utf8" Unicode characters are read instead of
               bytes (the LENGTH, OFFSET, and the return value of
               sysread() are in Unicode characters).  The
               ":encoding(...)" layer implicitly introduces the
               ":utf8" layer.  See "binmode", "open", and the
               "open" pragma, open.

       sysseek FILEHANDLE,POSITION,WHENCE
               Sets FILEHANDLE's system position in bytes using
               the system call lseek(2).  FILEHANDLE may be an
               expression whose value gives the name of the
               filehandle.  The values for WHENCE are 0 to set
               the new position to POSITION, 1 to set the it to
               the current position plus POSITION, and 2 to set
               it to EOF plus POSITION (typically negative).

               Note the in bytes: even if the filehandle has been
               set to operate on characters (for example by using
               the ":encoding(utf8)" I/O layer), tell() will
               return byte offsets, not character offsets
               (because implementing that would render sysseek()
               very slow).

               sysseek() bypasses normal buffered IO, so mixing
               this with reads (other than "sysread", for example
               "<>" or read()) "print", "write", "seek", "tell",
               or "eof" may cause confusion.

               For WHENCE, you may also use the constants
               "SEEK_SET", "SEEK_CUR", and "SEEK_END" (start of
               the file, current position, end of the file) from
               the Fcntl module.  Use of the constants is also
               more portable than relying on 0, 1, and 2.  For
               example to define a "systell" function:

                       use Fcntl 'SEEK_CUR';
                       sub systell { sysseek($_[0], 0, SEEK_CUR) }

               Returns the new position, or the undefined value
               on failure.  A position of zero is returned as the
               string "0 but true"; thus "sysseek" returns true
               on success and false on failure, yet you can still
               easily determine the new position.

       system LIST
       system PROGRAM LIST
               Does exactly the same thing as "exec LIST", except
               that a fork is done first, and the parent process
               waits for the child process to complete.  Note
               that argument processing varies depending on the
               number of arguments.  If there is more than one
               argument in LIST, or if LIST is an array with more
               than one value, starts the program given by the
               first element of the list with arguments given by



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               the rest of the list.  If there is only one scalar
               argument, the argument is checked for shell
               metacharacters, and if there are any, the entire
               argument is passed to the system's command shell
               for parsing (this is "/bin/sh -c" on Unix
               platforms, but varies on other platforms).  If
               there are no shell metacharacters in the argument,
               it is split into words and passed directly to
               "execvp", which is more efficient.

               Beginning with v5.6.0, Perl will attempt to flush
               all files opened for output before any operation
               that may do a fork, but this may not be supported
               on some platforms (see perlport).  To be safe, you
               may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any
               open handles.

               The return value is the exit status of the program
               as returned by the "wait" call.  To get the actual
               exit value, shift right by eight (see below). See
               also "exec".  This is not what you want to use to
               capture the output from a command, for that you
               should use merely backticks or "qx//", as
               described in "`STRING`" in perlop.  Return value
               of -1 indicates a failure to start the program or
               an error of the wait(2) system call (inspect $!
               for the reason).

               If you'd like to make "system" (and many other
               bits of Perl) die on error, have a look at the
               autodie pragma.

               Like "exec", "system" allows you to lie to a
               program about its name if you use the "system
               PROGRAM LIST" syntax.  Again, see "exec".

               Since "SIGINT" and "SIGQUIT" are ignored during
               the execution of "system", if you expect your
               program to terminate on receipt of these signals
               you will need to arrange to do so yourself based
               on the return value.

                   @args = ("command", "arg1", "arg2");
                   system(@args) == 0
                        or die "system @args failed: $?"

               If you'd like to manually inspect "system"'s
               failure, you can check all possible failure modes
               by inspecting $? like this:







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                   if ($? == -1) {
                       print "failed to execute: $!\n";
                   }
                   elsif ($? & 127) {
                       printf "child died with signal %d, %s coredump\n",
                           ($? & 127),  ($? & 128) ? 'with' : 'without';
                   }
                   else {
                       printf "child exited with value %d\n", $? >> 8;
                   }

               Alternatively you might inspect the value of
               "${^CHILD_ERROR_NATIVE}" with the W*() calls of
               the POSIX extension.

               When the arguments get executed via the system
               shell, results and return codes will be subject to
               its quirks and capabilities.  See "`STRING`" in
               perlop and "exec" for details.

       syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
       syswrite FILEHANDLE,SCALAR,LENGTH
       syswrite FILEHANDLE,SCALAR
               Attempts to write LENGTH bytes of data from
               variable SCALAR to the specified FILEHANDLE, using
               the system call write(2).  If LENGTH is not
               specified, writes whole SCALAR.  It bypasses
               buffered IO, so mixing this with reads (other than
               sysread()), "print", "write", "seek", "tell", or
               "eof" may cause confusion because the perlio and
               stdio layers usually buffers data.  Returns the
               number of bytes actually written, or "undef" if
               there was an error (in this case the errno
               variable $! is also set).  If the LENGTH is
               greater than the available data in the SCALAR
               after the OFFSET, only as much data as is
               available will be written.

               An OFFSET may be specified to write the data from
               some part of the string other than the beginning.
               A negative OFFSET specifies writing that many
               characters counting backwards from the end of the
               string.  In the case the SCALAR is empty you can
               use OFFSET but only zero offset.

               Note that if the filehandle has been marked as
               ":utf8", Unicode characters are written instead of
               bytes (the LENGTH, OFFSET, and the return value of
               syswrite() are in UTF-8 encoded Unicode
               characters).  The ":encoding(...)" layer
               implicitly introduces the ":utf8" layer.  See
               "binmode", "open", and the "open" pragma, open.





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       tell FILEHANDLE
       tell    Returns the current position in bytes for
               FILEHANDLE, or -1 on error.  FILEHANDLE may be an
               expression whose value gives the name of the
               actual filehandle.  If FILEHANDLE is omitted,
               assumes the file last read.

               Note the in bytes: even if the filehandle has been
               set to operate on characters (for example by using
               the ":encoding(utf8)" open layer), tell() will
               return byte offsets, not character offsets
               (because that would render seek() and tell()
               rather slow).

               The return value of tell() for the standard
               streams like the STDIN depends on the operating
               system: it may return -1 or something else.
               tell() on pipes, fifos, and sockets usually
               returns -1.

               There is no "systell" function.  Use "sysseek(FH,
               0, 1)" for that.

               Do not use tell() (or other buffered I/O
               operations) on a file handle that has been
               manipulated by sysread(), syswrite() or sysseek().
               Those functions ignore the buffering, while tell()
               does not.

       telldir DIRHANDLE
               Returns the current position of the "readdir"
               routines on DIRHANDLE.  Value may be given to
               "seekdir" to access a particular location in a
               directory.  "telldir" has the same caveats about
               possible directory compaction as the corresponding
               system library routine.

       tie VARIABLE,CLASSNAME,LIST
               This function binds a variable to a package class
               that will provide the implementation for the
               variable.  VARIABLE is the name of the variable to
               be enchanted.  CLASSNAME is the name of a class
               implementing objects of correct type.  Any
               additional arguments are passed to the "new"
               method of the class (meaning "TIESCALAR",
               "TIEHANDLE", "TIEARRAY", or "TIEHASH").  Typically
               these are arguments such as might be passed to the
               "dbm_open()" function of C.  The object returned
               by the "new" method is also returned by the "tie"
               function, which would be useful if you want to
               access other methods in CLASSNAME.

               Note that functions such as "keys" and "values"
               may return huge lists when used on large objects,



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               like DBM files.  You may prefer to use the "each"
               function to iterate over such.  Example:

                   # print out history file offsets
                   use NDBM_File;
                   tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
                   while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";
                   }
                   untie(%HIST);

               A class implementing a hash should have the
               following methods:

                   TIEHASH classname, LIST
                   FETCH this, key
                   STORE this, key, value
                   DELETE this, key
                   CLEAR this
                   EXISTS this, key
                   FIRSTKEY this
                   NEXTKEY this, lastkey
                   SCALAR this
                   DESTROY this
                   UNTIE this

               A class implementing an ordinary array should have
               the following methods:

                   TIEARRAY classname, LIST
                   FETCH this, key
                   STORE this, key, value
                   FETCHSIZE this
                   STORESIZE this, count
                   CLEAR this
                   PUSH this, LIST
                   POP this
                   SHIFT this
                   UNSHIFT this, LIST
                   SPLICE this, offset, length, LIST
                   EXTEND this, count
                   DESTROY this
                   UNTIE this

               A class implementing a file handle should have the
               following methods:











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                   TIEHANDLE classname, LIST
                   READ this, scalar, length, offset
                   READLINE this
                   GETC this
                   WRITE this, scalar, length, offset
                   PRINT this, LIST
                   PRINTF this, format, LIST
                   BINMODE this
                   EOF this
                   FILENO this
                   SEEK this, position, whence
                   TELL this
                   OPEN this, mode, LIST
                   CLOSE this
                   DESTROY this
                   UNTIE this

               A class implementing a scalar should have the
               following methods:

                   TIESCALAR classname, LIST
                   FETCH this,
                   STORE this, value
                   DESTROY this
                   UNTIE this

               Not all methods indicated above need be
               implemented.  See perltie, Tie::Hash, Tie::Array,
               Tie::Scalar, and Tie::Handle.

               Unlike "dbmopen", the "tie" function will not use
               or require a module for you--you need to do that
               explicitly yourself.  See DB_File or the Config
               module for interesting "tie" implementations.

               For further details see perltie, "tied VARIABLE".

       tied VARIABLE
               Returns a reference to the object underlying
               VARIABLE (the same value that was originally
               returned by the "tie" call that bound the variable
               to a package.)  Returns the undefined value if
               VARIABLE isn't tied to a package.

       time    Returns the number of non-leap seconds since
               whatever time the system considers to be the
               epoch, suitable for feeding to "gmtime" and
               "localtime". On most systems the epoch is 00:00:00
               UTC, January 1, 1970; a prominent exception being
               Mac OS Classic which uses 00:00:00, January 1,
               1904 in the current local time zone for its epoch.

               For measuring time in better granularity than one
               second, you may use either the Time::HiRes module



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               (from CPAN, and starting from Perl 5.8 part of the
               standard distribution), or if you have
               gettimeofday(2), you may be able to use the
               "syscall" interface of Perl.  See perlfaq8 for
               details.

               For date and time processing look at the many
               related modules on CPAN.  For a comprehensive date
               and time representation look at the DateTime
               module.

       times   Returns a four-element list giving the user and
               system times, in seconds, for this process and the
               children of this process.

                   ($user,$system,$cuser,$csystem) = times;

               In scalar context, "times" returns $user.

               Note that times for children are included only
               after they terminate.

       tr///   The transliteration operator.  Same as "y///".
               See "Quote and Quote-like Operators" in perlop.

       truncate FILEHANDLE,LENGTH
       truncate EXPR,LENGTH
               Truncates the file opened on FILEHANDLE, or named
               by EXPR, to the specified length.  Produces a
               fatal error if truncate isn't implemented on your
               system.  Returns true if successful, the undefined
               value otherwise.

               The behavior is undefined if LENGTH is greater
               than the length of the file.

               The position in the file of FILEHANDLE is left
               unchanged.  You may want to call seek before
               writing to the file.

       uc EXPR
       uc      Returns an uppercased version of EXPR.  This is
               the internal function implementing the "\U" escape
               in double-quoted strings.  Respects current
               LC_CTYPE locale if "use locale" in force.  See
               perllocale and perlunicode for more details about
               locale and Unicode support.  It does not attempt
               to do titlecase mapping on initial letters.  See
               "ucfirst" for that.

               If EXPR is omitted, uses $_.

       ucfirst EXPR
       ucfirst Returns the value of EXPR with the first character



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               in uppercase (titlecase in Unicode).  This is the
               internal function implementing the "\u" escape in
               double-quoted strings.  Respects current LC_CTYPE
               locale if "use locale" in force.  See perllocale
               and perlunicode for more details about locale and
               Unicode support.

               If EXPR is omitted, uses $_.

       umask EXPR
       umask   Sets the umask for the process to EXPR and returns
               the previous value.  If EXPR is omitted, merely
               returns the current umask.

               The Unix permission "rwxr-x---" is represented as
               three sets of three bits, or three octal digits:
               0750 (the leading 0 indicates octal and isn't one
               of the digits).  The "umask" value is such a
               number representing disabled permissions bits.
               The permission (or "mode") values you pass "mkdir"
               or "sysopen" are modified by your umask, so even
               if you tell "sysopen" to create a file with
               permissions 0777, if your umask is 0022 then the
               file will actually be created with permissions
               0755.  If your "umask" were 0027 (group can't
               write; others can't read, write, or execute), then
               passing "sysopen" 0666 would create a file with
               mode 0640 ("0666 &~ 027" is 0640).

               Here's some advice: supply a creation mode of 0666
               for regular files (in "sysopen") and one of 0777
               for directories (in "mkdir") and executable files.
               This gives users the freedom of choice: if they
               want protected files, they might choose process
               umasks of 022, 027, or even the particularly
               antisocial mask of 077.  Programs should rarely if
               ever make policy decisions better left to the
               user.  The exception to this is when writing files
               that should be kept private: mail files, web
               browser cookies, .rhosts files, and so on.

               If umask(2) is not implemented on your system and
               you are trying to restrict access for yourself
               (i.e., (EXPR & 0700) > 0), produces a fatal error
               at run time.  If umask(2) is not implemented and
               you are not trying to restrict access for
               yourself, returns "undef".

               Remember that a umask is a number, usually given
               in octal; it is not a string of octal digits.  See
               also "oct", if all you have is a string.

       undef EXPR
       undef   Undefines the value of EXPR, which must be an



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               lvalue.  Use only on a scalar value, an array
               (using "@"), a hash (using "%"), a subroutine
               (using "&"), or a typeglob (using "*").  (Saying
               "undef $hash{$key}" will probably not do what you
               expect on most predefined variables or DBM list
               values, so don't do that; see delete.)  Always
               returns the undefined value.  You can omit the
               EXPR, in which case nothing is undefined, but you
               still get an undefined value that you could, for
               instance, return from a subroutine, assign to a
               variable or pass as a parameter.  Examples:

                   undef $foo;
                   undef $bar{'blurfl'};      # Compare to: delete $bar{'blurfl'};
                   undef @ary;
                   undef %hash;
                   undef &mysub;
                   undef *xyz;       # destroys $xyz, @xyz, %xyz, &xyz, etc.
                   return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
                   select undef, undef, undef, 0.25;
                   ($a, $b, undef, $c) = &foo;       # Ignore third value returned

               Note that this is a unary operator, not a list
               operator.

       unlink LIST
       unlink  Deletes a list of files.  Returns the number of
               files successfully deleted.

                   $cnt = unlink 'a', 'b', 'c';
                   unlink @goners;
                   unlink <*.bak>;

               Note: "unlink" will not attempt to delete
               directories unless you are superuser and the -U
               flag is supplied to Perl.  Even if these
               conditions are met, be warned that unlinking a
               directory can inflict damage on your filesystem.
               Finally, using "unlink" on directories is not
               supported on many operating systems.  Use "rmdir"
               instead.

               If LIST is omitted, uses $_.

       unpack TEMPLATE,EXPR
       unpack TEMPLATE
               "unpack" does the reverse of "pack": it takes a
               string and expands it out into a list of values.
               (In scalar context, it returns merely the first
               value produced.)

               If EXPR is omitted, unpacks the $_ string.

               The string is broken into chunks described by the



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               TEMPLATE.  Each chunk is converted separately to a
               value.  Typically, either the string is a result
               of "pack", or the characters of the string
               represent a C structure of some kind.

               The TEMPLATE has the same format as in the "pack"
               function.  Here's a subroutine that does
               substring:

                   sub substr {
                       my($what,$where,$howmuch) = @_;
                       unpack("x$where a$howmuch", $what);
                   }

               and then there's

                   sub ordinal { unpack("W",$_[0]); } # same as ord()

               In addition to fields allowed in pack(), you may
               prefix a field with a %<number> to indicate that
               you want a <number>-bit checksum of the items
               instead of the items themselves.  Default is a
               16-bit checksum.  Checksum is calculated by
               summing numeric values of expanded values (for
               string fields the sum of "ord($char)" is taken,
               for bit fields the sum of zeroes and ones).

               For example, the following computes the same
               number as the System V sum program:

                   $checksum = do {
                       local $/;  # slurp!
                       unpack("%32W*",<>) % 65535;
                   };

               The following efficiently counts the number of set
               bits in a bit vector:

                   $setbits = unpack("%32b*", $selectmask);

               The "p" and "P" formats should be used with care.
               Since Perl has no way of checking whether the
               value passed to "unpack()" corresponds to a valid
               memory location, passing a pointer value that's
               not known to be valid is likely to have disastrous
               consequences.

               If there are more pack codes or if the repeat
               count of a field or a group is larger than what
               the remainder of the input string allows, the
               result is not well defined: in some cases, the
               repeat count is decreased, or "unpack()" will
               produce null strings or zeroes, or terminate with
               an error. If the input string is longer than one



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               described by the TEMPLATE, the rest is ignored.

               See "pack" for more examples and notes.

       untie VARIABLE
               Breaks the binding between a variable and a
               package.  (See "tie".)  Has no effect if the
               variable is not tied.

       unshift ARRAY,LIST
               Does the opposite of a "shift".  Or the opposite
               of a "push", depending on how you look at it.
               Prepends list to the front of the array, and
               returns the new number of elements in the array.

                   unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;

               Note the LIST is prepended whole, not one element
               at a time, so the prepended elements stay in the
               same order.  Use "reverse" to do the reverse.

       use Module VERSION LIST
       use Module VERSION
       use Module LIST
       use Module
       use VERSION
               Imports some semantics into the current package
               from the named module, generally by aliasing
               certain subroutine or variable names into your
               package.  It is exactly equivalent to

                   BEGIN { require Module; Module->import( LIST ); }

               except that Module must be a bareword.

               In the peculiar "use VERSION" form, VERSION may be
               either a numeric argument such as 5.006, which
               will be compared to $], or a literal of the form
               v5.6.1, which will be compared to $^V (aka
               $PERL_VERSION).  A fatal error is produced if
               VERSION is greater than the version of the current
               Perl interpreter; Perl will not attempt to parse
               the rest of the file.  Compare with "require",
               which can do a similar check at run time.
               Symmetrically, "no VERSION" allows you to specify
               that you want a version of perl older than the
               specified one.

               Specifying VERSION as a literal of the form v5.6.1
               should generally be avoided, because it leads to
               misleading error messages under earlier versions
               of Perl (that is, prior to 5.6.0) that do not
               support this syntax.  The equivalent numeric
               version should be used instead.



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                   use v5.6.1;         # compile time version check
                   use 5.6.1;          # ditto
                   use 5.006_001;      # ditto; preferred for backwards compatibility

               This is often useful if you need to check the
               current Perl version before "use"ing library
               modules that won't work with older versions of
               Perl.  (We try not to do this more than we have
               to.)

               Also, if the specified perl version is greater
               than or equal to 5.9.5, "use VERSION" will also
               load the "feature" pragma and enable all features
               available in the requested version.  See feature.

               The "BEGIN" forces the "require" and "import" to
               happen at compile time.  The "require" makes sure
               the module is loaded into memory if it hasn't been
               yet.  The "import" is not a builtin--it's just an
               ordinary static method call into the "Module"
               package to tell the module to import the list of
               features back into the current package.  The
               module can implement its "import" method any way
               it likes, though most modules just choose to
               derive their "import" method via inheritance from
               the "Exporter" class that is defined in the
               "Exporter" module.  See Exporter.  If no "import"
               method can be found then the call is skipped, even
               if there is an AUTOLOAD method.

               If you do not want to call the package's "import"
               method (for instance, to stop your namespace from
               being altered), explicitly supply the empty list:

                   use Module ();

               That is exactly equivalent to

                   BEGIN { require Module }

               If the VERSION argument is present between Module
               and LIST, then the "use" will call the VERSION
               method in class Module with the given version as
               an argument.  The default VERSION method,
               inherited from the UNIVERSAL class, croaks if the
               given version is larger than the value of the
               variable $Module::VERSION.

               Again, there is a distinction between omitting
               LIST ("import" called with no arguments) and an
               explicit empty LIST "()" ("import" not called).
               Note that there is no comma after VERSION!

               Because this is a wide-open interface, pragmas



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               (compiler directives) are also implemented this
               way.  Currently implemented pragmas are:

                   use constant;
                   use diagnostics;
                   use integer;
                   use sigtrap  qw(SEGV BUS);
                   use strict   qw(subs vars refs);
                   use subs     qw(afunc blurfl);
                   use warnings qw(all);
                   use sort     qw(stable _quicksort _mergesort);

               Some of these pseudo-modules import semantics into
               the current block scope (like "strict" or
               "integer", unlike ordinary modules, which import
               symbols into the current package (which are
               effective through the end of the file).

               There's a corresponding "no" command that
               unimports meanings imported by "use", i.e., it
               calls "unimport Module LIST" instead of "import".
               It behaves exactly as "import" does with respect
               to VERSION, an omitted LIST, empty LIST, or no
               unimport method being found.

                   no integer;
                   no strict 'refs';
                   no warnings;

               See perlmodlib for a list of standard modules and
               pragmas.  See perlrun for the "-M" and "-m"
               command-line options to perl that give "use"
               functionality from the command-line.

       utime LIST
               Changes the access and modification times on each
               file of a list of files.  The first two elements
               of the list must be the NUMERICAL access and
               modification times, in that order.  Returns the
               number of files successfully changed.  The inode
               change time of each file is set to the current
               time.  For example, this code has the same effect
               as the Unix touch(1) command when the files
               already exist and belong to the user running the
               program:

                   #!/usr/bin/perl
                   $atime = $mtime = time;
                   utime $atime, $mtime, @ARGV;

               Since perl 5.7.2, if the first two elements of the
               list are "undef", then the utime(2) function in
               the C library will be called with a null second
               argument. On most systems, this will set the



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               file's access and modification times to the
               current time (i.e. equivalent to the example
               above) and will even work on other users' files
               where you have write permission:

                   utime undef, undef, @ARGV;

               Under NFS this will use the time of the NFS
               server, not the time of the local machine.  If
               there is a time synchronization problem, the NFS
               server and local machine will have different
               times.  The Unix touch(1) command will in fact
               normally use this form instead of the one shown in
               the first example.

               Note that only passing one of the first two
               elements as "undef" will be equivalent of passing
               it as 0 and will not have the same effect as
               described when they are both "undef".  This case
               will also trigger an uninitialized warning.

               On systems that support futimes, you might pass
               file handles among the files.  On systems that
               don't support futimes, passing file handles
               produces a fatal error at run time.  The file
               handles must be passed as globs or references to
               be recognized.  Barewords are considered file
               names.

       values HASH
               Returns a list consisting of all the values of the
               named hash.  (In a scalar context, returns the
               number of values.)

               The values are returned in an apparently random
               order.  The actual random order is subject to
               change in future versions of perl, but it is
               guaranteed to be the same order as either the
               "keys" or "each" function would produce on the
               same (unmodified) hash.  Since Perl 5.8.1 the
               ordering is different even between different runs
               of Perl for security reasons (see "Algorithmic
               Complexity Attacks" in perlsec).

               As a side effect, calling values() resets the
               HASH's internal iterator, see "each". (In
               particular, calling values() in void context
               resets the iterator with no other overhead.)

               Note that the values are not copied, which means
               modifying them will modify the contents of the
               hash:





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                   for (values %hash)      { s/foo/bar/g }   # modifies %hash values
                   for (@hash{keys %hash}) { s/foo/bar/g }   # same

               See also "keys", "each", and "sort".

       vec EXPR,OFFSET,BITS
               Treats the string in EXPR as a bit vector made up
               of elements of width BITS, and returns the value
               of the element specified by OFFSET as an unsigned
               integer.  BITS therefore specifies the number of
               bits that are reserved for each element in the bit
               vector.  This must be a power of two from 1 to 32
               (or 64, if your platform supports that).

               If BITS is 8, "elements" coincide with bytes of
               the input string.

               If BITS is 16 or more, bytes of the input string
               are grouped into chunks of size BITS/8, and each
               group is converted to a number as with
               pack()/unpack() with big-endian formats "n"/"N"
               (and analogously for BITS==64).  See "pack" for
               details.

               If bits is 4 or less, the string is broken into
               bytes, then the bits of each byte are broken into
               8/BITS groups.  Bits of a byte are numbered in a
               little-endian-ish way, as in 0x01, 0x02, 0x04,
               0x08, 0x10, 0x20, 0x40, 0x80.  For example,
               breaking the single input byte "chr(0x36)" into
               two groups gives a list "(0x6, 0x3)"; breaking it
               into 4 groups gives "(0x2, 0x1, 0x3, 0x0)".

               "vec" may also be assigned to, in which case
               parentheses are needed to give the expression the
               correct precedence as in

                   vec($image, $max_x * $x + $y, 8) = 3;

               If the selected element is outside the string, the
               value 0 is returned.  If an element off the end of
               the string is written to, Perl will first extend
               the string with sufficiently many zero bytes.   It
               is an error to try to write off the beginning of
               the string (i.e. negative OFFSET).

               If the string happens to be encoded as UTF-8
               internally (and thus has the UTF8 flag set), this
               is ignored by "vec", and it operates on the
               internal byte string, not the conceptual character
               string, even if you only have characters with
               values less than 256.

               Strings created with "vec" can also be manipulated



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               with the logical operators "|", "&", "^", and "~".
               These operators will assume a bit vector operation
               is desired when both operands are strings.  See
               "Bitwise String Operators" in perlop.

               The following code will build up an ASCII string
               saying 'PerlPerlPerl'.  The comments show the
               string after each step.  Note that this code works
               in the same way on big-endian or little-endian
               machines.

                   my $foo = '';
                   vec($foo,  0, 32) = 0x5065726C;     # 'Perl'

                   # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits
                   print vec($foo, 0, 8);              # prints 80 == 0x50 == ord('P')

                   vec($foo,  2, 16) = 0x5065;         # 'PerlPe'
                   vec($foo,  3, 16) = 0x726C;         # 'PerlPerl'
                   vec($foo,  8,  8) = 0x50;           # 'PerlPerlP'
                   vec($foo,  9,  8) = 0x65;           # 'PerlPerlPe'
                   vec($foo, 20,  4) = 2;              # 'PerlPerlPe'   . "\x02"
                   vec($foo, 21,  4) = 7;              # 'PerlPerlPer'
                                                       # 'r' is "\x72"
                   vec($foo, 45,  2) = 3;              # 'PerlPerlPer'  . "\x0c"
                   vec($foo, 93,  1) = 1;              # 'PerlPerlPer'  . "\x2c"
                   vec($foo, 94,  1) = 1;              # 'PerlPerlPerl'
                                                       # 'l' is "\x6c"

               To transform a bit vector into a string or list of
               0's and 1's, use these:

                   $bits = unpack("b*", $vector);
                   @bits = split(//, unpack("b*", $vector));

               If you know the exact length in bits, it can be
               used in place of the "*".

               Here is an example to illustrate how the bits
               actually fall in place:

                   #!/usr/bin/perl -wl

                   print <<'EOT';
                                                     0         1         2         3
                                      unpack("V",$_) 01234567890123456789012345678901
                   ------------------------------------------------------------------
                   EOT

                   for $w (0..3) {
                       $width = 2**$w;
                       for ($shift=0; $shift < $width; ++$shift) {
                           for ($off=0; $off < 32/$width; ++$off) {
                               $str = pack("B*", "0"x32);



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                               $bits = (1<<$shift);
                               vec($str, $off, $width) = $bits;
                               $res = unpack("b*",$str);
                               $val = unpack("V", $str);
                               write;
                           }
                       }
                   }

                   format STDOUT =
                   vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
                   $off, $width, $bits, $val, $res
                   .
                   __END__

               Regardless of the machine architecture on which it
               is run, the above example should print the
               following table:

                                                     0         1         2         3
                                      unpack("V",$_) 01234567890123456789012345678901
                   ------------------------------------------------------------------
                   vec($_, 0, 1) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 1) = 1   ==          2 01000000000000000000000000000000
                   vec($_, 2, 1) = 1   ==          4 00100000000000000000000000000000
                   vec($_, 3, 1) = 1   ==          8 00010000000000000000000000000000
                   vec($_, 4, 1) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 5, 1) = 1   ==         32 00000100000000000000000000000000
                   vec($_, 6, 1) = 1   ==         64 00000010000000000000000000000000
                   vec($_, 7, 1) = 1   ==        128 00000001000000000000000000000000
                   vec($_, 8, 1) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 9, 1) = 1   ==        512 00000000010000000000000000000000
                   vec($_,10, 1) = 1   ==       1024 00000000001000000000000000000000
                   vec($_,11, 1) = 1   ==       2048 00000000000100000000000000000000
                   vec($_,12, 1) = 1   ==       4096 00000000000010000000000000000000
                   vec($_,13, 1) = 1   ==       8192 00000000000001000000000000000000
                   vec($_,14, 1) = 1   ==      16384 00000000000000100000000000000000
                   vec($_,15, 1) = 1   ==      32768 00000000000000010000000000000000
                   vec($_,16, 1) = 1   ==      65536 00000000000000001000000000000000
                   vec($_,17, 1) = 1   ==     131072 00000000000000000100000000000000
                   vec($_,18, 1) = 1   ==     262144 00000000000000000010000000000000
                   vec($_,19, 1) = 1   ==     524288 00000000000000000001000000000000
                   vec($_,20, 1) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_,21, 1) = 1   ==    2097152 00000000000000000000010000000000
                   vec($_,22, 1) = 1   ==    4194304 00000000000000000000001000000000
                   vec($_,23, 1) = 1   ==    8388608 00000000000000000000000100000000
                   vec($_,24, 1) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_,25, 1) = 1   ==   33554432 00000000000000000000000001000000
                   vec($_,26, 1) = 1   ==   67108864 00000000000000000000000000100000
                   vec($_,27, 1) = 1   ==  134217728 00000000000000000000000000010000
                   vec($_,28, 1) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_,29, 1) = 1   ==  536870912 00000000000000000000000000000100
                   vec($_,30, 1) = 1   == 1073741824 00000000000000000000000000000010
                   vec($_,31, 1) = 1   == 2147483648 00000000000000000000000000000001



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                   vec($_, 0, 2) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 2) = 1   ==          4 00100000000000000000000000000000
                   vec($_, 2, 2) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 3, 2) = 1   ==         64 00000010000000000000000000000000
                   vec($_, 4, 2) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 5, 2) = 1   ==       1024 00000000001000000000000000000000
                   vec($_, 6, 2) = 1   ==       4096 00000000000010000000000000000000
                   vec($_, 7, 2) = 1   ==      16384 00000000000000100000000000000000
                   vec($_, 8, 2) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 9, 2) = 1   ==     262144 00000000000000000010000000000000
                   vec($_,10, 2) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_,11, 2) = 1   ==    4194304 00000000000000000000001000000000
                   vec($_,12, 2) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_,13, 2) = 1   ==   67108864 00000000000000000000000000100000
                   vec($_,14, 2) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_,15, 2) = 1   == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 2) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 2) = 2   ==          8 00010000000000000000000000000000
                   vec($_, 2, 2) = 2   ==         32 00000100000000000000000000000000
                   vec($_, 3, 2) = 2   ==        128 00000001000000000000000000000000
                   vec($_, 4, 2) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 5, 2) = 2   ==       2048 00000000000100000000000000000000
                   vec($_, 6, 2) = 2   ==       8192 00000000000001000000000000000000
                   vec($_, 7, 2) = 2   ==      32768 00000000000000010000000000000000
                   vec($_, 8, 2) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 9, 2) = 2   ==     524288 00000000000000000001000000000000
                   vec($_,10, 2) = 2   ==    2097152 00000000000000000000010000000000
                   vec($_,11, 2) = 2   ==    8388608 00000000000000000000000100000000
                   vec($_,12, 2) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_,13, 2) = 2   ==  134217728 00000000000000000000000000010000
                   vec($_,14, 2) = 2   ==  536870912 00000000000000000000000000000100
                   vec($_,15, 2) = 2   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 4) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 4) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 2, 4) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 3, 4) = 1   ==       4096 00000000000010000000000000000000
                   vec($_, 4, 4) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 5, 4) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_, 6, 4) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_, 7, 4) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_, 0, 4) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 4) = 2   ==         32 00000100000000000000000000000000
                   vec($_, 2, 4) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 3, 4) = 2   ==       8192 00000000000001000000000000000000
                   vec($_, 4, 4) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 5, 4) = 2   ==    2097152 00000000000000000000010000000000
                   vec($_, 6, 4) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_, 7, 4) = 2   ==  536870912 00000000000000000000000000000100
                   vec($_, 0, 4) = 4   ==          4 00100000000000000000000000000000
                   vec($_, 1, 4) = 4   ==         64 00000010000000000000000000000000
                   vec($_, 2, 4) = 4   ==       1024 00000000001000000000000000000000
                   vec($_, 3, 4) = 4   ==      16384 00000000000000100000000000000000
                   vec($_, 4, 4) = 4   ==     262144 00000000000000000010000000000000
                   vec($_, 5, 4) = 4   ==    4194304 00000000000000000000001000000000



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                   vec($_, 6, 4) = 4   ==   67108864 00000000000000000000000000100000
                   vec($_, 7, 4) = 4   == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 4) = 8   ==          8 00010000000000000000000000000000
                   vec($_, 1, 4) = 8   ==        128 00000001000000000000000000000000
                   vec($_, 2, 4) = 8   ==       2048 00000000000100000000000000000000
                   vec($_, 3, 4) = 8   ==      32768 00000000000000010000000000000000
                   vec($_, 4, 4) = 8   ==     524288 00000000000000000001000000000000
                   vec($_, 5, 4) = 8   ==    8388608 00000000000000000000000100000000
                   vec($_, 6, 4) = 8   ==  134217728 00000000000000000000000000010000
                   vec($_, 7, 4) = 8   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 8) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 8) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 2, 8) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 3, 8) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_, 0, 8) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 8) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 2, 8) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 3, 8) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_, 0, 8) = 4   ==          4 00100000000000000000000000000000
                   vec($_, 1, 8) = 4   ==       1024 00000000001000000000000000000000
                   vec($_, 2, 8) = 4   ==     262144 00000000000000000010000000000000
                   vec($_, 3, 8) = 4   ==   67108864 00000000000000000000000000100000
                   vec($_, 0, 8) = 8   ==          8 00010000000000000000000000000000
                   vec($_, 1, 8) = 8   ==       2048 00000000000100000000000000000000
                   vec($_, 2, 8) = 8   ==     524288 00000000000000000001000000000000
                   vec($_, 3, 8) = 8   ==  134217728 00000000000000000000000000010000
                   vec($_, 0, 8) = 16  ==         16 00001000000000000000000000000000
                   vec($_, 1, 8) = 16  ==       4096 00000000000010000000000000000000
                   vec($_, 2, 8) = 16  ==    1048576 00000000000000000000100000000000
                   vec($_, 3, 8) = 16  ==  268435456 00000000000000000000000000001000
                   vec($_, 0, 8) = 32  ==         32 00000100000000000000000000000000
                   vec($_, 1, 8) = 32  ==       8192 00000000000001000000000000000000
                   vec($_, 2, 8) = 32  ==    2097152 00000000000000000000010000000000
                   vec($_, 3, 8) = 32  ==  536870912 00000000000000000000000000000100
                   vec($_, 0, 8) = 64  ==         64 00000010000000000000000000000000
                   vec($_, 1, 8) = 64  ==      16384 00000000000000100000000000000000
                   vec($_, 2, 8) = 64  ==    4194304 00000000000000000000001000000000
                   vec($_, 3, 8) = 64  == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 8) = 128 ==        128 00000001000000000000000000000000
                   vec($_, 1, 8) = 128 ==      32768 00000000000000010000000000000000
                   vec($_, 2, 8) = 128 ==    8388608 00000000000000000000000100000000
                   vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001

       wait    Behaves like the wait(2) system call on your
               system: it waits for a child process to terminate
               and returns the pid of the deceased process, or
               "-1" if there are no child processes.  The status
               is returned in $?  and "${^CHILD_ERROR_NATIVE}".
               Note that a return value of "-1" could mean that
               child processes are being automatically reaped, as
               described in perlipc.

       waitpid PID,FLAGS
               Waits for a particular child process to terminate



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               and returns the pid of the deceased process, or
               "-1" if there is no such child process.  On some
               systems, a value of 0 indicates that there are
               processes still running.  The status is returned
               in $? and "${^CHILD_ERROR_NATIVE}".  If you say

                   use POSIX ":sys_wait_h";
                   #...
                   do {
                       $kid = waitpid(-1, WNOHANG);
                   } while $kid > 0;

               then you can do a non-blocking wait for all
               pending zombie processes.  Non-blocking wait is
               available on machines supporting either the
               waitpid(2) or wait4(2) system calls.  However,
               waiting for a particular pid with FLAGS of 0 is
               implemented everywhere.  (Perl emulates the system
               call by remembering the status values of processes
               that have exited but have not been harvested by
               the Perl script yet.)

               Note that on some systems, a return value of "-1"
               could mean that child processes are being
               automatically reaped.  See perlipc for details,
               and for other examples.

       wantarray
               Returns true if the context of the currently
               executing subroutine or "eval" is looking for a
               list value.  Returns false if the context is
               looking for a scalar.  Returns the undefined value
               if the context is looking for no value (void
               context).

                   return unless defined wantarray;    # don't bother doing more
                   my @a = complex_calculation();
                   return wantarray ? @a : "@a";

               "wantarray()"'s result is unspecified in the top
               level of a file, in a "BEGIN", "UNITCHECK",
               "CHECK", "INIT" or "END" block, or in a "DESTROY"
               method.

               This function should have been named wantlist()
               instead.

       warn LIST
               Prints the value of LIST to STDERR.  If the last
               element of LIST does not end in a newline, it
               appends the same file/line number text as "die"
               does.

               If LIST is empty and $@ already contains a value



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               (typically from a previous eval) that value is
               used after appending "\t...caught" to $@.  This is
               useful for staying almost, but not entirely
               similar to "die".

               If $@ is empty then the string "Warning:
               Something's wrong" is used.

               No message is printed if there is a $SIG{__WARN__}
               handler installed.  It is the handler's
               responsibility to deal with the message as it sees
               fit (like, for instance, converting it into a
               "die").  Most handlers must therefore make
               arrangements to actually display the warnings that
               they are not prepared to deal with, by calling
               "warn" again in the handler.  Note that this is
               quite safe and will not produce an endless loop,
               since "__WARN__" hooks are not called from inside
               one.

               You will find this behavior is slightly different
               from that of $SIG{__DIE__} handlers (which don't
               suppress the error text, but can instead call
               "die" again to change it).

               Using a "__WARN__" handler provides a powerful way
               to silence all warnings (even the so-called
               mandatory ones).  An example:

                   # wipe out *all* compile-time warnings
                   BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } }
                   my $foo = 10;
                   my $foo = 20;          # no warning about duplicate my $foo,
                                          # but hey, you asked for it!
                   # no compile-time or run-time warnings before here
                   $DOWARN = 1;

                   # run-time warnings enabled after here
                   warn "\$foo is alive and $foo!";     # does show up

               See perlvar for details on setting %SIG entries,
               and for more examples.  See the Carp module for
               other kinds of warnings using its carp() and
               cluck() functions.

       write FILEHANDLE
       write EXPR
       write   Writes a formatted record (possibly multi-line) to
               the specified FILEHANDLE, using the format
               associated with that file.  By default the format
               for a file is the one having the same name as the
               filehandle, but the format for the current output
               channel (see the "select" function) may be set
               explicitly by assigning the name of the format to



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               the $~ variable.

               Top of form processing is handled automatically:
               if there is insufficient room on the current page
               for the formatted record, the page is advanced by
               writing a form feed, a special top-of-page format
               is used to format the new page header, and then
               the record is written.  By default the top-of-page
               format is the name of the filehandle with "_TOP"
               appended, but it may be dynamically set to the
               format of your choice by assigning the name to the
               $^ variable while the filehandle is selected.  The
               number of lines remaining on the current page is
               in variable "$-", which can be set to 0 to force a
               new page.

               If FILEHANDLE is unspecified, output goes to the
               current default output channel, which starts out
               as STDOUT but may be changed by the "select"
               operator.  If the FILEHANDLE is an EXPR, then the
               expression is evaluated and the resulting string
               is used to look up the name of the FILEHANDLE at
               run time.  For more on formats, see perlform.

               Note that write is not the opposite of "read".
               Unfortunately.

       y///    The transliteration operator.  Same as "tr///".
               See "Quote and Quote-like Operators" in perlop.




























perl v5.10.1                2009-10-12                        150


