


PERLRUN(1)       Perl Programmers Reference Guide      PERLRUN(1)


NAME
       perlrun - how to execute the Perl interpreter

SYNOPSIS
       perl [ -sTtuUWX ]      [ -hv ] [ -V[:configvar] ]
            [ -cw ] [ -d[t][:debugger] ] [ -D[number/list] ]
            [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal/hexadecimal] ]
            [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -f ]
            [ -C [number/list] ]      [ -P ]      [ -S ]
            [ -x[dir] ]      [ -i[extension] ]
            [ [-e|-E] 'command' ] [ -- ] [ programfile ] [ argument ]...

DESCRIPTION
       The normal way to run a Perl program is by making it
       directly executable, or else by passing the name of the
       source file as an argument on the command line.  (An
       interactive Perl environment is also possible--see
       perldebug for details on how to do that.)  Upon startup,
       Perl looks for your program in one of the following
       places:

       1.  Specified line by line via -e or -E switches on the
           command line.

       2.  Contained in the file specified by the first filename
           on the command line.  (Note that systems supporting
           the #! notation invoke interpreters this way. See
           "Location of Perl".)

       3.  Passed in implicitly via standard input.  This works
           only if there are no filename arguments--to pass
           arguments to a STDIN-read program you must explicitly
           specify a "-" for the program name.

       With methods 2 and 3, Perl starts parsing the input file
       from the beginning, unless you've specified a -x switch,
       in which case it scans for the first line starting with #!
       and containing the word "perl", and starts there instead.
       This is useful for running a program embedded in a larger
       message.  (In this case you would indicate the end of the
       program using the "__END__" token.)

       The #! line is always examined for switches as the line is
       being parsed.  Thus, if you're on a machine that allows
       only one argument with the #! line, or worse, doesn't even
       recognize the #! line, you still can get consistent switch
       behavior regardless of how Perl was invoked, even if -x
       was used to find the beginning of the program.

       Because historically some operating systems silently
       chopped off kernel interpretation of the #! line after 32
       characters, some switches may be passed in on the command
       line, and some may not; you could even get a "-" without
       its letter, if you're not careful.  You probably want to



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       make sure that all your switches fall either before or
       after that 32-character boundary.  Most switches don't
       actually care if they're processed redundantly, but
       getting a "-" instead of a complete switch could cause
       Perl to try to execute standard input instead of your
       program.  And a partial -I switch could also cause odd
       results.

       Some switches do care if they are processed twice, for
       instance combinations of -l and -0.  Either put all the
       switches after the 32-character boundary (if applicable),
       or replace the use of -0digits by "BEGIN{ $/ = "\0digits";
       }".

       Parsing of the #! switches starts wherever "perl" is
       mentioned in the line.  The sequences "-*" and "- " are
       specifically ignored so that you could, if you were so
       inclined, say

           #!/bin/sh
           #! -*-perl-*-
           eval 'exec perl -x -wS $0 ${1+"$@"}'
               if 0;

       to let Perl see the -p switch.

       A similar trick involves the env program, if you have it.

           #!/usr/bin/env perl

       The examples above use a relative path to the perl
       interpreter, getting whatever version is first in the
       user's path.  If you want a specific version of Perl, say,
       perl5.005_57, you should place that directly in the #!
       line's path.

       If the #! line does not contain the word "perl", the
       program named after the #! is executed instead of the Perl
       interpreter.  This is slightly bizarre, but it helps
       people on machines that don't do #!, because they can tell
       a program that their SHELL is /usr/bin/perl, and Perl will
       then dispatch the program to the correct interpreter for
       them.

       After locating your program, Perl compiles the entire
       program to an internal form.  If there are any compilation
       errors, execution of the program is not attempted.  (This
       is unlike the typical shell script, which might run part-
       way through before finding a syntax error.)

       If the program is syntactically correct, it is executed.
       If the program runs off the end without hitting an exit()
       or die() operator, an implicit exit(0) is provided to
       indicate successful completion.



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   #! and quoting on non-Unix systems
       Unix's #! technique can be simulated on other systems:

       OS/2
           Put

               extproc perl -S -your_switches

           as the first line in "*.cmd" file (-S due to a bug in
           cmd.exe's `extproc' handling).

       MS-DOS
           Create a batch file to run your program, and codify it
           in "ALTERNATE_SHEBANG" (see the dosish.h file in the
           source distribution for more information).

       Win95/NT
           The Win95/NT installation, when using the ActiveState
           installer for Perl, will modify the Registry to
           associate the .pl extension with the perl interpreter.
           If you install Perl by other means (including building
           from the sources), you may have to modify the Registry
           yourself.  Note that this means you can no longer tell
           the difference between an executable Perl program and
           a Perl library file.

       Macintosh
           Under "Classic" MacOS, a perl program will have the
           appropriate Creator and Type, so that double-clicking
           them will invoke the MacPerl application.  Under Mac
           OS X, clickable apps can be made from any "#!" script
           using Wil Sanchez' DropScript utility:
           http://www.wsanchez.net/software/ .

       VMS Put

               $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
               $ exit++ + ++$status != 0 and $exit = $status = undef;

           at the top of your program, where -mysw are any
           command line switches you want to pass to Perl.  You
           can now invoke the program directly, by saying "perl
           program", or as a DCL procedure, by saying @program
           (or implicitly via DCL$PATH by just using the name of
           the program).

           This incantation is a bit much to remember, but Perl
           will display it for you if you say "perl
           "-V:startperl"".

       Command-interpreters on non-Unix systems have rather
       different ideas on quoting than Unix shells.  You'll need
       to learn the special characters in your command-
       interpreter ("*", "\" and """ are common) and how to



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       protect whitespace and these characters to run one-liners
       (see -e below).

       On some systems, you may have to change single-quotes to
       double ones, which you must not do on Unix or Plan 9
       systems.  You might also have to change a single % to a
       %%.

       For example:

           # Unix
           perl -e 'print "Hello world\n"'

           # MS-DOS, etc.
           perl -e "print \"Hello world\n\""

           # Macintosh
           print "Hello world\n"
            (then Run "Myscript" or Shift-Command-R)

           # VMS
           perl -e "print ""Hello world\n"""

       The problem is that none of this is reliable: it depends
       on the command and it is entirely possible neither works.
       If 4DOS were the command shell, this would probably work
       better:

           perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""

       CMD.EXE in Windows NT slipped a lot of standard Unix
       functionality in when nobody was looking, but just try to
       find documentation for its quoting rules.

       Under the Macintosh, it depends which environment you are
       using.  The MacPerl shell, or MPW, is much like Unix
       shells in its support for several quoting variants, except
       that it makes free use of the Macintosh's non-ASCII
       characters as control characters.

       There is no general solution to all of this.  It's just a
       mess.

   Location of Perl
       It may seem obvious to say, but Perl is useful only when
       users can easily find it.  When possible, it's good for
       both /usr/bin/perl and /usr/local/bin/perl to be symlinks
       to the actual binary.  If that can't be done, system
       administrators are strongly encouraged to put (symlinks
       to) perl and its accompanying utilities into a directory
       typically found along a user's PATH, or in some other
       obvious and convenient place.

       In this documentation, "#!/usr/bin/perl" on the first line



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       of the program will stand in for whatever method works on
       your system.  You are advised to use a specific path if
       you care about a specific version.

           #!/usr/local/bin/perl5.00554

       or if you just want to be running at least version, place
       a statement like this at the top of your program:

           use 5.005_54;

   Command Switches
       As with all standard commands, a single-character switch
       may be clustered with the following switch, if any.

           #!/usr/bin/perl -spi.orig   # same as -s -p -i.orig

       Switches include:

       -0[octal/hexadecimal]
            specifies the input record separator ($/) as an octal
            or hexadecimal number.  If there are no digits, the
            null character is the separator.  Other switches may
            precede or follow the digits.  For example, if you
            have a version of find which can print filenames
            terminated by the null character, you can say this:

                find . -name '*.orig' -print0 | perl -n0e unlink

            The special value 00 will cause Perl to slurp files
            in paragraph mode.  The value 0777 will cause Perl to
            slurp files whole because there is no legal byte with
            that value.

            If you want to specify any Unicode character, use the
            hexadecimal format: "-0xHHH...", where the "H" are
            valid hexadecimal digits.  (This means that you
            cannot use the "-x" with a directory name that
            consists of hexadecimal digits.)

       -a   turns on autosplit mode when used with a -n or -p.
            An implicit split command to the @F array is done as
            the first thing inside the implicit while loop
            produced by the -n or -p.

                perl -ane 'print pop(@F), "\n";'

            is equivalent to

                while (<>) {
                    @F = split(' ');
                    print pop(@F), "\n";
                }




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            An alternate delimiter may be specified using -F.

       -C [number/list]
            The "-C" flag controls some of the Perl Unicode
            features.

            As of 5.8.1, the "-C" can be followed either by a
            number or a list of option letters.  The letters,
            their numeric values, and effects are as follows;
            listing the letters is equal to summing the numbers.

                I     1   STDIN is assumed to be in UTF-8
                O     2   STDOUT will be in UTF-8
                E     4   STDERR will be in UTF-8
                S     7   I + O + E
                i     8   UTF-8 is the default PerlIO layer for input streams
                o    16   UTF-8 is the default PerlIO layer for output streams
                D    24   i + o
                A    32   the @ARGV elements are expected to be strings encoded
                          in UTF-8
                L    64   normally the "IOEioA" are unconditional,
                          the L makes them conditional on the locale environment
                          variables (the LC_ALL, LC_TYPE, and LANG, in the order
                          of decreasing precedence) -- if the variables indicate
                          UTF-8, then the selected "IOEioA" are in effect
                a   256   Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
                          debugging mode.

            For example, "-COE" and "-C6" will both turn on
            UTF-8-ness on both STDOUT and STDERR.  Repeating
            letters is just redundant, not cumulative nor
            toggling.

            The "io" options mean that any subsequent open() (or
            similar I/O operations) will have the ":utf8" PerlIO
            layer implicitly applied to them, in other words,
            UTF-8 is expected from any input stream, and UTF-8 is
            produced to any output stream.  This is just the
            default, with explicit layers in open() and with
            binmode() one can manipulate streams as usual.

            "-C" on its own (not followed by any number or option
            list), or the empty string "" for the "PERL_UNICODE"
            environment variable, has the same effect as "-CSDL".
            In other words, the standard I/O handles and the
            default "open()" layer are UTF-8-fied but only if the
            locale environment variables indicate a UTF-8 locale.
            This behaviour follows the implicit (and problematic)
            UTF-8 behaviour of Perl 5.8.0.

            You can use "-C0" (or "0" for "PERL_UNICODE") to
            explicitly disable all the above Unicode features.

            The read-only magic variable "${^UNICODE}" reflects



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            the numeric value of this setting.  This is variable
            is set during Perl startup and is thereafter read-
            only.  If you want runtime effects, use the three-arg
            open() (see "open" in perlfunc), the two-arg
            binmode() (see "binmode" in perlfunc), and the "open"
            pragma (see open).

            (In Perls earlier than 5.8.1 the "-C" switch was a
            Win32-only switch that enabled the use of Unicode-
            aware "wide system call" Win32 APIs.  This feature
            was practically unused, however, and the command line
            switch was therefore "recycled".)

            Note: Since perl 5.10.1, if the -C option is used on
            the #! line, it must be specified on the command line
            as well, since the standard streams are already set
            up at this point in the execution of the perl
            interpreter.  You can also use binmode() to set the
            encoding of an I/O stream.

       -c   causes Perl to check the syntax of the program and
            then exit without executing it.  Actually, it will
            execute "BEGIN", "UNITCHECK", "CHECK", and "use"
            blocks, because these are considered as occurring
            outside the execution of your program.  "INIT" and
            "END" blocks, however, will be skipped.

       -d
       -dt  runs the program under the Perl debugger.  See
            perldebug.  If t is specified, it indicates to the
            debugger that threads will be used in the code being
            debugged.

       -d:foo[=bar,baz]
       -dt:foo[=bar,baz]
            runs the program under the control of a debugging,
            profiling, or tracing module installed as Devel::foo.
            E.g., -d:DProf executes the program using the
            Devel::DProf profiler.  As with the -M flag, options
            may be passed to the Devel::foo package where they
            will be received and interpreted by the
            Devel::foo::import routine.  The comma-separated list
            of options must follow a "=" character.  If t is
            specified, it indicates to the debugger that threads
            will be used in the code being debugged.  See
            perldebug.

       -Dletters
       -Dnumber
            sets debugging flags.  To watch how it executes your
            program, use -Dtls.  (This works only if debugging is
            compiled into your Perl.)  Another nice value is -Dx,
            which lists your compiled syntax tree.  And -Dr
            displays compiled regular expressions; the format of



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            the output is explained in perldebguts.

            As an alternative, specify a number instead of list
            of letters (e.g., -D14 is equivalent to -Dtls):

                    1  p  Tokenizing and parsing (with v, displays parse stack)
                    2  s  Stack snapshots (with v, displays all stacks)
                    4  l  Context (loop) stack processing
                    8  t  Trace execution
                   16  o  Method and overloading resolution
                   32  c  String/numeric conversions
                   64  P  Print profiling info, preprocessor command for -P, source file input state
                  128  m  Memory and SV allocation
                  256  f  Format processing
                  512  r  Regular expression parsing and execution
                 1024  x  Syntax tree dump
                 2048  u  Tainting checks
                 4096  U  Unofficial, User hacking (reserved for private, unreleased use)
                 8192  H  Hash dump -- usurps values()
                16384  X  Scratchpad allocation
                32768  D  Cleaning up
                65536  S  Thread synchronization
               131072  T  Tokenising
               262144  R  Include reference counts of dumped variables (eg when using -Ds)
               524288  J  Do not s,t,P-debug (Jump over) opcodes within package DB
              1048576  v  Verbose: use in conjunction with other flags
              2097152  C  Copy On Write
              4194304  A  Consistency checks on internal structures
              8388608  q  quiet - currently only suppresses the "EXECUTING" message

            All these flags require -DDEBUGGING when you compile
            the Perl executable (but see Devel::Peek, re which
            may change this).  See the INSTALL file in the Perl
            source distribution for how to do this.  This flag is
            automatically set if you include -g option when
            "Configure" asks you about optimizer/debugger flags.

            If you're just trying to get a print out of each line
            of Perl code as it executes, the way that "sh -x"
            provides for shell scripts, you can't use Perl's -D
            switch.  Instead do this

              # If you have "env" utility
              env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program

              # Bourne shell syntax
              $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program

              # csh syntax
              % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)

            See perldebug for details and variations.





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       -e commandline
            may be used to enter one line of program.  If -e is
            given, Perl will not look for a filename in the
            argument list.  Multiple -e commands may be given to
            build up a multi-line script.  Make sure to use
            semicolons where you would in a normal program.

       -E commandline
            behaves just like -e, except that it implicitly
            enables all optional features (in the main
            compilation unit). See feature.

       -f   Disable executing $Config{sitelib}/sitecustomize.pl
            at startup.

            Perl can be built so that it by default will try to
            execute $Config{sitelib}/sitecustomize.pl at startup
            (in a BEGIN block).  This is a hook that allows the
            sysadmin to customize how perl behaves.  It can for
            instance be used to add entries to the @INC array to
            make perl find modules in non-standard locations.

       -Fpattern
            specifies the pattern to split on if -a is also in
            effect.  The pattern may be surrounded by "//", "",
            or '', otherwise it will be put in single quotes. You
            can't use literal whitespace in the pattern.

       -h   prints a summary of the options.

       -i[extension]
            specifies that files processed by the "<>" construct
            are to be edited in-place.  It does this by renaming
            the input file, opening the output file by the
            original name, and selecting that output file as the
            default for print() statements.  The extension, if
            supplied, is used to modify the name of the old file
            to make a backup copy, following these rules:

            If no extension is supplied, no backup is made and
            the current file is overwritten.

            If the extension doesn't contain a "*", then it is
            appended to the end of the current filename as a
            suffix.  If the extension does contain one or more
            "*" characters, then each "*" is replaced with the
            current filename.  In Perl terms, you could think of
            this as:

                ($backup = $extension) =~ s/\*/$file_name/g;

            This allows you to add a prefix to the backup file,
            instead of (or in addition to) a suffix:




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                $ perl -pi'orig_*' -e 's/bar/baz/' fileA    # backup to 'orig_fileA'

            Or even to place backup copies of the original files
            into another directory (provided the directory
            already exists):

                $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'

            These sets of one-liners are equivalent:

                $ perl -pi -e 's/bar/baz/' fileA            # overwrite current file
                $ perl -pi'*' -e 's/bar/baz/' fileA         # overwrite current file

                $ perl -pi'.orig' -e 's/bar/baz/' fileA     # backup to 'fileA.orig'
                $ perl -pi'*.orig' -e 's/bar/baz/' fileA    # backup to 'fileA.orig'

            From the shell, saying

                $ perl -p -i.orig -e "s/foo/bar/; ... "

            is the same as using the program:

                #!/usr/bin/perl -pi.orig
                s/foo/bar/;

            which is equivalent to

                #!/usr/bin/perl
                $extension = '.orig';
                LINE: while (<>) {
                    if ($ARGV ne $oldargv) {
                        if ($extension !~ /\*/) {
                            $backup = $ARGV . $extension;
                        }
                        else {
                            ($backup = $extension) =~ s/\*/$ARGV/g;
                        }
                        rename($ARGV, $backup);
                        open(ARGVOUT, ">$ARGV");
                        select(ARGVOUT);
                        $oldargv = $ARGV;
                    }
                    s/foo/bar/;
                }
                continue {
                    print;  # this prints to original filename
                }
                select(STDOUT);

            except that the -i form doesn't need to compare $ARGV
            to $oldargv to know when the filename has changed.
            It does, however, use ARGVOUT for the selected
            filehandle.  Note that STDOUT is restored as the
            default output filehandle after the loop.



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            As shown above, Perl creates the backup file whether
            or not any output is actually changed.  So this is
            just a fancy way to copy files:

                $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
            or
                $ perl -p -i'.orig' -e 1 file1 file2 file3...

            You can use "eof" without parentheses to locate the
            end of each input file, in case you want to append to
            each file, or reset line numbering (see example in
            "eof" in perlfunc).

            If, for a given file, Perl is unable to create the
            backup file as specified in the extension then it
            will skip that file and continue on with the next one
            (if it exists).

            For a discussion of issues surrounding file
            permissions and -i, see "Why does Perl let me delete
            read-only files?  Why does -i clobber protected
            files?  Isn't this a bug in Perl?" in perlfaq5.

            You cannot use -i to create directories or to strip
            extensions from files.

            Perl does not expand "~" in filenames, which is good,
            since some folks use it for their backup files:

                $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...

            Note that because -i renames or deletes the original
            file before creating a new file of the same name,
            UNIX-style soft and hard links will not be preserved.

            Finally, the -i switch does not impede execution when
            no files are given on the command line.  In this
            case, no backup is made (the original file cannot, of
            course, be determined) and processing proceeds from
            STDIN to STDOUT as might be expected.

       -Idirectory
            Directories specified by -I are prepended to the
            search path for modules (@INC), and also tells the C
            preprocessor where to search for include files.  The
            C preprocessor is invoked with -P; by default it
            searches /usr/include and /usr/lib/perl.

       -l[octnum]
            enables automatic line-ending processing.  It has two
            separate effects.  First, it automatically chomps $/
            (the input record separator) when used with -n or -p.
            Second, it assigns "$\" (the output record separator)
            to have the value of octnum so that any print



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            statements will have that separator added back on.
            If octnum is omitted, sets "$\" to the current value
            of $/.  For instance, to trim lines to 80 columns:

                perl -lpe 'substr($_, 80) = ""'

            Note that the assignment "$\ = $/" is done when the
            switch is processed, so the input record separator
            can be different than the output record separator if
            the -l switch is followed by a -0 switch:

                gnufind / -print0 | perl -ln0e 'print "found $_" if -p'

            This sets "$\" to newline and then sets $/ to the
            null character.

       -m[-]module
       -M[-]module
       -M[-]'module ...'
       -[mM][-]module=arg[,arg]...
            -mmodule executes "use" module "();" before executing
            your program.

            -Mmodule executes "use" module ";" before executing
            your program.  You can use quotes to add extra code
            after the module name, e.g., '-Mmodule qw(foo bar)'.

            If the first character after the -M or -m is a dash
            ("-") then the 'use' is replaced with 'no'.

            A little builtin syntactic sugar means you can also
            say -mmodule=foo,bar or -Mmodule=foo,bar as a
            shortcut for '-Mmodule qw(foo bar)'.  This avoids the
            need to use quotes when importing symbols.  The
            actual code generated by -Mmodule=foo,bar is "use
            module split(/,/,q{foo,bar})".  Note that the "="
            form removes the distinction between -m and -M.

            A consequence of this is that -MFoo=number never does
            a version check (unless "Foo::import()" itself is set
            up to do a version check, which could happen for
            example if Foo inherits from Exporter.)

       -n   causes Perl to assume the following loop around your
            program, which makes it iterate over filename
            arguments somewhat like sed -n or awk:

              LINE:
                while (<>) {
                    ...             # your program goes here
                }

            Note that the lines are not printed by default.  See
            -p to have lines printed.  If a file named by an



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            argument cannot be opened for some reason, Perl warns
            you about it and moves on to the next file.

            Also note that "<>" passes command line arguments to
            "open" in perlfunc, which doesn't necessarily
            interpret them as file names.  See  perlop for
            possible security implications.

            Here is an efficient way to delete all files that
            haven't been modified for at least a week:

                find . -mtime +7 -print | perl -nle unlink

            This is faster than using the -exec switch of find
            because you don't have to start a process on every
            filename found.  It does suffer from the bug of
            mishandling newlines in pathnames, which you can fix
            if you follow the example under -0.

            "BEGIN" and "END" blocks may be used to capture
            control before or after the implicit program loop,
            just as in awk.

       -p   causes Perl to assume the following loop around your
            program, which makes it iterate over filename
            arguments somewhat like sed:

              LINE:
                while (<>) {
                    ...             # your program goes here
                } continue {
                    print or die "-p destination: $!\n";
                }

            If a file named by an argument cannot be opened for
            some reason, Perl warns you about it, and moves on to
            the next file.  Note that the lines are printed
            automatically.  An error occurring during printing is
            treated as fatal.  To suppress printing use the -n
            switch.  A -p overrides a -n switch.

            "BEGIN" and "END" blocks may be used to capture
            control before or after the implicit loop, just as in
            awk.

       -P   NOTE: Use of -P is strongly discouraged because of
            its inherent problems, including poor portability. It
            is deprecated and will be removed in a future version
            of Perl.

            This option causes your program to be run through the
            C preprocessor before compilation by Perl.  Because
            both comments and cpp directives begin with the #
            character, you should avoid starting comments with



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            any words recognized by the C preprocessor such as
            "if", "else", or "define".

            If you're considering using "-P", you might also want
            to look at the Filter::cpp module from CPAN.

            The problems of -P include, but are not limited to:

            o         The "#!" line is stripped, so any switches
                      there don't apply.

            o         A "-P" on a "#!" line doesn't work.

            o         All lines that begin with (whitespace and)
                      a "#" but do not look like cpp commands,
                      are stripped, including anything inside
                      Perl strings, regular expressions, and
                      here-docs .

            o         In some platforms the C preprocessor knows
                      too much: it knows about the C++ -style
                      until-end-of-line comments starting with
                      "//".  This will cause problems with common
                      Perl constructs like

                          s/foo//;

                      because after -P this will became illegal
                      code

                          s/foo

                      The workaround is to use some other quoting
                      separator than "/", like for example "!":

                          s!foo!!;

            o         It requires not only a working C
                      preprocessor but also a working sed.  If
                      not on UNIX, you are probably out of luck
                      on this.

            o         Script line numbers are not preserved.

            o         The "-x" does not work with "-P".

       -s   enables rudimentary switch parsing for switches on
            the command line after the program name but before
            any filename arguments (or before an argument of --).
            Any switch found there is removed from @ARGV and sets
            the corresponding variable in the Perl program.  The
            following program prints "1" if the program is
            invoked with a -xyz switch, and "abc" if it is
            invoked with -xyz=abc.



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                #!/usr/bin/perl -s
                if ($xyz) { print "$xyz\n" }

            Do note that a switch like --help creates the
            variable ${-help}, which is not compliant with
            "strict refs".  Also, when using this option on a
            script with warnings enabled you may get a lot of
            spurious "used only once" warnings.

       -S   makes Perl use the PATH environment variable to
            search for the program (unless the name of the
            program contains directory separators).

            On some platforms, this also makes Perl append
            suffixes to the filename while searching for it.  For
            example, on Win32 platforms, the ".bat" and ".cmd"
            suffixes are appended if a lookup for the original
            name fails, and if the name does not already end in
            one of those suffixes.  If your Perl was compiled
            with DEBUGGING turned on, using the -Dp switch to
            Perl shows how the search progresses.

            Typically this is used to emulate #! startup on
            platforms that don't support #!.  Its also convenient
            when debugging a script that uses #!, and is thus
            normally found by the shell's $PATH search mechanism.

            This example works on many platforms that have a
            shell compatible with Bourne shell:

                #!/usr/bin/perl
                eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
                        if $running_under_some_shell;

            The system ignores the first line and feeds the
            program to /bin/sh, which proceeds to try to execute
            the Perl program as a shell script.  The shell
            executes the second line as a normal shell command,
            and thus starts up the Perl interpreter.  On some
            systems $0 doesn't always contain the full pathname,
            so the -S tells Perl to search for the program if
            necessary.  After Perl locates the program, it parses
            the lines and ignores them because the variable
            $running_under_some_shell is never true.  If the
            program will be interpreted by csh, you will need to
            replace "${1+"$@"}" with $*, even though that doesn't
            understand embedded spaces (and such) in the argument
            list.  To start up sh rather than csh, some systems
            may have to replace the #! line with a line
            containing just a colon, which will be politely
            ignored by Perl.  Other systems can't control that,
            and need a totally devious construct that will work
            under any of csh, sh, or Perl, such as the following:




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                    eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
                    & eval 'exec /usr/bin/perl -wS $0 $argv:q'
                            if $running_under_some_shell;

            If the filename supplied contains directory
            separators (i.e., is an absolute or relative
            pathname), and if that file is not found, platforms
            that append file extensions will do so and try to
            look for the file with those extensions added, one by
            one.

            On DOS-like platforms, if the program does not
            contain directory separators, it will first be
            searched for in the current directory before being
            searched for on the PATH.  On Unix platforms, the
            program will be searched for strictly on the PATH.

       -t   Like -T, but taint checks will issue warnings rather
            than fatal errors.  These warnings can be controlled
            normally with "no warnings qw(taint)".

            NOTE: this is not a substitute for -T. This is meant
            only to be used as a temporary development aid while
            securing legacy code: for real production code and
            for new secure code written from scratch always use
            the real -T.

       -T   forces "taint" checks to be turned on so you can test
            them.  Ordinarily these checks are done only when
            running setuid or setgid.  It's a good idea to turn
            them on explicitly for programs that run on behalf of
            someone else whom you might not necessarily trust,
            such as CGI programs or any internet servers you
            might write in Perl.  See perlsec for details.  For
            security reasons, this option must be seen by Perl
            quite early; usually this means it must appear early
            on the command line or in the #! line for systems
            which support that construct.

       -u   This obsolete switch causes Perl to dump core after
            compiling your program.  You can then in theory take
            this core dump and turn it into an executable file by
            using the undump program (not supplied).  This speeds
            startup at the expense of some disk space (which you
            can minimize by stripping the executable).  (Still, a
            "hello world" executable comes out to about 200K on
            my machine.)  If you want to execute a portion of
            your program before dumping, use the dump() operator
            instead.  Note: availability of undump is platform
            specific and may not be available for a specific port
            of Perl.

       -U   allows Perl to do unsafe operations.  Currently the
            only "unsafe" operations are attempting to unlink



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            directories while running as superuser, and running
            setuid programs with fatal taint checks turned into
            warnings.  Note that the -w switch (or the $^W
            variable) must be used along with this option to
            actually generate the taint-check warnings.

       -v   prints the version and patchlevel of your perl
            executable.

       -V   prints summary of the major perl configuration values
            and the current values of @INC.

       -V:configvar
            Prints to STDOUT the value of the named configuration
            variable(s), with multiples when your configvar
            argument looks like a regex (has non-letters).  For
            example:

                $ perl -V:libc
                    libc='/lib/libc-2.2.4.so';
                $ perl -V:lib.
                    libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
                    libc='/lib/libc-2.2.4.so';
                $ perl -V:lib.*
                    libpth='/usr/local/lib /lib /usr/lib';
                    libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
                    lib_ext='.a';
                    libc='/lib/libc-2.2.4.so';
                    libperl='libperl.a';
                    ....

            Additionally, extra colons can be used to control
            formatting.  A trailing colon suppresses the linefeed
            and terminator ';', allowing you to embed queries
            into shell commands.  (mnemonic: PATH separator ':'.)

                $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
                compression-vars:  zcat='' zip='zip'  are here !

            A leading colon removes the 'name=' part of the
            response, this allows you to map to the name you
            need.  (mnemonic: empty label)

                $ echo "goodvfork="`./perl -Ilib -V::usevfork`
                goodvfork=false;

            Leading and trailing colons can be used together if
            you need positional parameter values without the
            names.  Note that in the case below, the PERL_API
            params are returned in alphabetical order.

                $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
                building_on 'linux' '5' '1' '9' now




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       -w   prints warnings about dubious constructs, such as
            variable names that are mentioned only once and
            scalar variables that are used before being set,
            redefined subroutines, references to undefined
            filehandles or filehandles opened read-only that you
            are attempting to write on, values used as a number
            that don't look like numbers, using an array as
            though it were a scalar, if your subroutines recurse
            more than 100 deep, and innumerable other things.

            This switch really just enables the internal $^W
            variable.  You can disable or promote into fatal
            errors specific warnings using "__WARN__" hooks, as
            described in perlvar and "warn" in perlfunc.  See
            also perldiag and perltrap.  A new, fine-grained
            warning facility is also available if you want to
            manipulate entire classes of warnings; see warnings
            or perllexwarn.

       -W   Enables all warnings regardless of "no warnings" or
            $^W.  See perllexwarn.

       -X   Disables all warnings regardless of "use warnings" or
            $^W.  See perllexwarn.

       -x
       -xdirectory
            tells Perl that the program is embedded in a larger
            chunk of unrelated ASCII text, such as in a mail
            message.  Leading garbage will be discarded until the
            first line that starts with #! and contains the
            string "perl".  Any meaningful switches on that line
            will be applied.

            All references to line numbers by the program
            (warnings, errors, ...)  will treat the #! line as
            the first line.  Thus a warning on the 2nd line of
            the program (which is on the 100th line in the file)
            will be reported as line 2, and not as line 100.
            This can be overridden by using the #line directive.
            (See "Plain-Old-Comments-(Not!)" in perlsyn)

            If a directory name is specified, Perl will switch to
            that directory before running the program.  The -x
            switch controls only the disposal of leading garbage.
            The program must be terminated with "__END__" if
            there is trailing garbage to be ignored (the program
            can process any or all of the trailing garbage via
            the DATA filehandle if desired).

            The directory, if specified, must appear immediately
            following the -x with no intervening whitespace.





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ENVIRONMENT
       HOME        Used if chdir has no argument.

       LOGDIR      Used if chdir has no argument and HOME is not
                   set.

       PATH        Used in executing subprocesses, and in finding
                   the program if -S is used.

       PERL5LIB    A list of directories in which to look for
                   Perl library files before looking in the
                   standard library and the current directory.
                   Any architecture-specific directories under
                   the specified locations are automatically
                   included if they exist (this lookup being done
                   at interpreter startup time.)

                   If PERL5LIB is not defined, PERLLIB is used.
                   Directories are separated (like in PATH) by a
                   colon on unixish platforms and by a semicolon
                   on Windows (the proper path separator being
                   given by the command "perl -V:path_sep").

                   When running taint checks (either because the
                   program was running setuid or setgid, or the
                   -T or -t switch was specified), neither
                   variable is used. The program should instead
                   say:

                       use lib "/my/directory";

       PERL5OPT    Command-line options (switches).  Switches in
                   this variable are taken as if they were on
                   every Perl command line.  Only the
                   -[CDIMUdmtw] switches are allowed.  When
                   running taint checks (because the program was
                   running setuid or setgid, or the -T switch was
                   used), this variable is ignored.  If PERL5OPT
                   begins with -T, tainting will be enabled, and
                   any subsequent options ignored.

       PERLIO      A space (or colon) separated list of PerlIO
                   layers. If perl is built to use PerlIO system
                   for IO (the default) these layers effect
                   perl's IO.

                   It is conventional to start layer names with a
                   colon e.g. ":perlio" to emphasise their
                   similarity to variable "attributes". But the
                   code that parses layer specification strings
                   (which is also used to decode the PERLIO
                   environment variable) treats the colon as a
                   separator.




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                   An unset or empty PERLIO is equivalent to the
                   default set of layers for your platform, for
                   example ":unix:perlio" on UNIX-like systems
                   and ":unix:crlf" on Windows and other DOS-like
                   systems.

                   The list becomes the default for all perl's
                   IO. Consequently only built-in layers can
                   appear in this list, as external layers (such
                   as :encoding()) need IO in  order to load
                   them!. See "open pragma" for how to add
                   external encodings as defaults.

                   The layers that it makes sense to include in
                   the PERLIO environment variable are briefly
                   summarised below. For more details see PerlIO.

                   :bytes  A pseudolayer that turns off the
                           ":utf8" flag for the layer below.
                           Unlikely to be useful on its own in
                           the global PERLIO environment
                           variable.  You perhaps were thinking
                           of ":crlf:bytes" or ":perlio:bytes".

                   :crlf   A layer which does CRLF to "\n"
                           translation distinguishing "text" and
                           "binary" files in the manner of MS-DOS
                           and similar operating systems.  (It
                           currently does not mimic MS-DOS as far
                           as treating of Control-Z as being an
                           end-of-file marker.)

                   :mmap   A layer which implements "reading" of
                           files by using "mmap()" to make
                           (whole) file appear in the process's
                           address space, and then using that as
                           PerlIO's "buffer".

                   :perlio This is a re-implementation of "stdio-
                           like" buffering written as a PerlIO
                           "layer".  As such it will call
                           whatever layer is below it for its
                           operations (typically ":unix").

                   :pop    An experimental pseudolayer that
                           removes the topmost layer.  Use with
                           the same care as is reserved for
                           nitroglycerin.

                   :raw    A pseudolayer that manipulates other
                           layers.  Applying the ":raw" layer is
                           equivalent to calling "binmode($fh)".
                           It makes the stream pass each byte as-
                           is without any translation.  In



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                           particular CRLF translation, and/or
                           :utf8 intuited from locale are
                           disabled.

                           Unlike in the earlier versions of Perl
                           ":raw" is not just the inverse of
                           ":crlf" - other layers which would
                           affect the binary nature of the stream
                           are also removed or disabled.

                   :stdio  This layer provides PerlIO interface
                           by wrapping system's ANSI C "stdio"
                           library calls. The layer provides both
                           buffering and IO.  Note that ":stdio"
                           layer does not do CRLF translation
                           even if that is platforms normal
                           behaviour. You will need a ":crlf"
                           layer above it to do that.

                   :unix   Low level layer which calls "read",
                           "write" and "lseek" etc.

                   :utf8   A pseudolayer that turns on a flag on
                           the layer below to tell perl that
                           output should be in utf8 and that
                           input should be regarded as already in
                           valid utf8 form. It does not check for
                           validity and as such should be handled
                           with caution for input. Generally
                           ":encoding(utf8)" is the best option
                           when reading UTF-8 encoded data.

                   :win32  On Win32 platforms this experimental
                           layer uses native "handle" IO rather
                           than unix-like numeric file descriptor
                           layer. Known to be buggy in this
                           release.

                   On all platforms the default set of layers
                   should give acceptable results.

                   For UNIX platforms that will equivalent of
                   "unix perlio" or "stdio".  Configure is setup
                   to prefer "stdio" implementation if system's
                   library provides for fast access to the
                   buffer, otherwise it uses the "unix perlio"
                   implementation.

                   On Win32 the default in this release is "unix
                   crlf". Win32's "stdio" has a number of
                   bugs/mis-features for perl IO which are
                   somewhat C compiler vendor/version dependent.
                   Using our own "crlf" layer as the buffer
                   avoids those issues and makes things more



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                   uniform.  The "crlf" layer provides CRLF
                   to/from "\n" conversion as well as buffering.

                   This release uses "unix" as the bottom layer
                   on Win32 and so still uses C compiler's
                   numeric file descriptor routines. There is an
                   experimental native "win32" layer which is
                   expected to be enhanced and should eventually
                   be the default under Win32.

                   The PERLIO environment variable is completely
                   ignored when perl is run in taint mode.

       PERLIO_DEBUG
                   If set to the name of a file or device then
                   certain operations of PerlIO sub-system will
                   be logged to that file (opened as append).
                   Typical uses are UNIX:

                      PERLIO_DEBUG=/dev/tty perl script ...

                   and Win32 approximate equivalent:

                      set PERLIO_DEBUG=CON
                      perl script ...

                   This functionality is disabled for setuid
                   scripts and for scripts run with -T.

       PERLLIB     A list of directories in which to look for
                   Perl library files before looking in the
                   standard library and the current directory.
                   If PERL5LIB is defined, PERLLIB is not used.

                   The PERLLIB environment variable is completely
                   ignored when perl is run in taint mode.

       PERL5DB     The command used to load the debugger code.
                   The default is:

                           BEGIN { require 'perl5db.pl' }

                   The PERL5DB environment variable only used
                   when perl is started with a bare -d switch.

       PERL5DB_THREADED
                   If set to a true value, indicates to the
                   debugger that the code being debugged uses
                   threads.

       PERL5SHELL (specific to the Win32 port)
                   May be set to an alternative shell that perl
                   must use internally for executing "backtick"
                   commands or system().  Default is "cmd.exe



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                   /x/d/c" on WindowsNT and "command.com /c" on
                   Windows95.  The value is considered to be
                   space-separated.  Precede any character that
                   needs to be protected (like a space or
                   backslash) with a backslash.

                   Note that Perl doesn't use COMSPEC for this
                   purpose because COMSPEC has a high degree of
                   variability among users, leading to
                   portability concerns.  Besides, perl can use a
                   shell that may not be fit for interactive use,
                   and setting COMSPEC to such a shell may
                   interfere with the proper functioning of other
                   programs (which usually look in COMSPEC to
                   find a shell fit for interactive use).

                   Before Perl 5.10.0 and 5.8.8, PERL5SHELL was
                   not taint checked when running external
                   commands.  It is recommended that you
                   explicitly set (or delete) $ENV{PERL5SHELL}
                   when running in taint mode under Windows.

       PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
                   Set to 1 to allow the use of non-IFS
                   compatible LSP's.  Perl normally searches for
                   an IFS-compatible LSP because this is required
                   for its emulation of Windows sockets as real
                   filehandles.  However, this may cause problems
                   if you have a firewall such as McAfee Guardian
                   which requires all applications to use its LSP
                   which is not IFS-compatible, because clearly
                   Perl will normally avoid using such an LSP.
                   Setting this environment variable to 1 means
                   that Perl will simply use the first suitable
                   LSP enumerated in the catalog, which keeps
                   McAfee Guardian happy (and in that particular
                   case Perl still works too because McAfee
                   Guardian's LSP actually plays some other games
                   which allow applications requiring IFS
                   compatibility to work).

       PERL_DEBUG_MSTATS
                   Relevant only if perl is compiled with the
                   malloc included with the perl distribution
                   (that is, if "perl -V:d_mymalloc" is
                   'define').  If set, this causes memory
                   statistics to be dumped after execution.  If
                   set to an integer greater than one, also
                   causes memory statistics to be dumped after
                   compilation.

       PERL_DESTRUCT_LEVEL
                   Relevant only if your perl executable was
                   built with -DDEBUGGING, this controls the



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                   behavior of global destruction of objects and
                   other references.  See "PERL_DESTRUCT_LEVEL"
                   in perlhack for more information.

       PERL_DL_NONLAZY
                   Set to one to have perl resolve all undefined
                   symbols when it loads a dynamic library.  The
                   default behaviour is to resolve symbols when
                   they are used.  Setting this variable is
                   useful during testing of extensions as it
                   ensures that you get an error on misspelled
                   function names even if the test suite doesn't
                   call it.

       PERL_ENCODING
                   If using the "encoding" pragma without an
                   explicit encoding name, the PERL_ENCODING
                   environment variable is consulted for an
                   encoding name.

       PERL_HASH_SEED
                   (Since Perl 5.8.1.)  Used to randomise perl's
                   internal hash function.  To emulate the
                   pre-5.8.1 behaviour, set to an integer (zero
                   means exactly the same order as 5.8.0).
                   "Pre-5.8.1" means, among other things, that
                   hash keys will always have the same ordering
                   between different runs of perl.

                   Most hashes return elements in the same order
                   as Perl 5.8.0 by default.  On a hash by hash
                   basis, if pathological data is detected during
                   a hash key insertion, then that hash will
                   switch to an alternative random hash seed.

                   The default behaviour is to randomise unless
                   the PERL_HASH_SEED is set.  If perl has been
                   compiled with "-DUSE_HASH_SEED_EXPLICIT", the
                   default behaviour is not to randomise unless
                   the PERL_HASH_SEED is set.

                   If PERL_HASH_SEED is unset or set to a non-
                   numeric string, perl uses the pseudorandom
                   seed supplied by the operating system and
                   libraries.

                   Please note that the hash seed is sensitive
                   information. Hashes are randomized to protect
                   against local and remote attacks against Perl
                   code. By manually setting a seed this
                   protection may be partially or completely
                   lost.

                   See "Algorithmic Complexity Attacks" in



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                   perlsec and "PERL_HASH_SEED_DEBUG" for more
                   information.

       PERL_HASH_SEED_DEBUG
                   (Since Perl 5.8.1.)  Set to one to display (to
                   STDERR) the value of the hash seed at the
                   beginning of execution.  This, combined with
                   "PERL_HASH_SEED" is intended to aid in
                   debugging nondeterministic behavior caused by
                   hash randomization.

                   Note that the hash seed is sensitive
                   information: by knowing it one can craft a
                   denial-of-service attack against Perl code,
                   even remotely, see "Algorithmic Complexity
                   Attacks" in perlsec for more information.  Do
                   not disclose the hash seed to people who don't
                   need to know it.  See also hash_seed() of
                   Hash::Util.

       PERL_ROOT (specific to the VMS port)
                   A translation concealed rooted logical name
                   that contains perl and the logical device for
                   the @INC path on VMS only.  Other logical
                   names that affect perl on VMS include PERLSHR,
                   PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL
                   but are optional and discussed further in
                   perlvms and in README.vms in the Perl source
                   distribution.

       PERL_SIGNALS
                   In Perls 5.8.1 and later.  If set to "unsafe"
                   the pre-Perl-5.8.0 signals behaviour
                   (immediate but unsafe) is restored.  If set to
                   "safe" the safe (or deferred) signals are
                   used.  See "Deferred Signals (Safe Signals)"
                   in perlipc.

       PERL_UNICODE
                   Equivalent to the -C command-line switch.
                   Note that this is not a boolean variable--
                   setting this to "1" is not the right way to
                   "enable Unicode" (whatever that would mean).
                   You can use "0" to "disable Unicode", though
                   (or alternatively unset PERL_UNICODE in your
                   shell before starting Perl).  See the
                   description of the "-C" switch for more
                   information.

       SYS$LOGIN (specific to the VMS port)
                   Used if chdir has no argument and HOME and
                   LOGDIR are not set.

       Perl also has environment variables that control how Perl



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       handles data specific to particular natural languages.
       See perllocale.

       Apart from these, Perl uses no other environment
       variables, except to make them available to the program
       being executed, and to child processes.  However, programs
       running setuid would do well to execute the following
       lines before doing anything else, just to keep people
       honest:

           $ENV{PATH}  = '/bin:/usr/bin';    # or whatever you need
           $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
           delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};












































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