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NAME
       perlport - Writing portable Perl

DESCRIPTION
       Perl runs on numerous operating systems.  While most of
       them share much in common, they also have their own unique
       features.

       This document is meant to help you to find out what
       constitutes portable Perl code.  That way once you make a
       decision to write portably, you know where the lines are
       drawn, and you can stay within them.

       There is a tradeoff between taking full advantage of one
       particular type of computer and taking advantage of a full
       range of them.  Naturally, as you broaden your range and
       become more diverse, the common factors drop, and you are
       left with an increasingly smaller area of common ground in
       which you can operate to accomplish a particular task.
       Thus, when you begin attacking a problem, it is important
       to consider under which part of the tradeoff curve you
       want to operate.  Specifically, you must decide whether it
       is important that the task that you are coding have the
       full generality of being portable, or whether to just get
       the job done right now.  This is the hardest choice to be
       made.  The rest is easy, because Perl provides many
       choices, whichever way you want to approach your problem.

       Looking at it another way, writing portable code is
       usually about willfully limiting your available choices.
       Naturally, it takes discipline and sacrifice to do that.
       The product of portability and convenience may be a
       constant.  You have been warned.

       Be aware of two important points:

       Not all Perl programs have to be portable
           There is no reason you should not use Perl as a
           language to glue Unix tools together, or to prototype
           a Macintosh application, or to manage the Windows
           registry.  If it makes no sense to aim for portability
           for one reason or another in a given program, then
           don't bother.

       Nearly all of Perl already is portable
           Don't be fooled into thinking that it is hard to
           create portable Perl code.  It isn't.  Perl tries its
           level-best to bridge the gaps between what's available
           on different platforms, and all the means available to
           use those features.  Thus almost all Perl code runs on
           any machine without modification.  But there are some
           significant issues in writing portable code, and this
           document is entirely about those issues.




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       Here's the general rule: When you approach a task commonly
       done using a whole range of platforms, think about writing
       portable code.  That way, you don't sacrifice much by way
       of the implementation choices you can avail yourself of,
       and at the same time you can give your users lots of
       platform choices.  On the other hand, when you have to
       take advantage of some unique feature of a particular
       platform, as is often the case with systems programming
       (whether for Unix, Windows, Mac OS, VMS, etc.), consider
       writing platform-specific code.

       When the code will run on only two or three operating
       systems, you may need to consider only the differences of
       those particular systems.  The important thing is to
       decide where the code will run and to be deliberate in
       your decision.

       The material below is separated into three main sections:
       main issues of portability ("ISSUES"), platform-specific
       issues ("PLATFORMS"), and built-in perl functions that
       behave differently on various ports ("FUNCTION
       IMPLEMENTATIONS").

       This information should not be considered complete; it
       includes possibly transient information about
       idiosyncrasies of some of the ports, almost all of which
       are in a state of constant evolution.  Thus, this material
       should be considered a perpetual work in progress ("<IMG
       SRC="yellow_sign.gif" ALT="Under Construction">").

ISSUES
   Newlines
       In most operating systems, lines in files are terminated
       by newlines.  Just what is used as a newline may vary from
       OS to OS.  Unix traditionally uses "\012", one type of
       DOSish I/O uses "\015\012", and Mac OS uses "\015".

       Perl uses "\n" to represent the "logical" newline, where
       what is logical may depend on the platform in use.  In
       MacPerl, "\n" always means "\015".  In DOSish perls, "\n"
       usually means "\012", but when accessing a file in "text"
       mode, STDIO translates it to (or from) "\015\012",
       depending on whether you're reading or writing.  Unix does
       the same thing on ttys in canonical mode.  "\015\012" is
       commonly referred to as CRLF.

       To trim trailing newlines from text lines use chomp().
       With default settings that function looks for a trailing
       "\n" character and thus trims in a portable way.

       When dealing with binary files (or text files in binary
       mode) be sure to explicitly set $/ to the appropriate
       value for your file format before using chomp().




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       Because of the "text" mode translation, DOSish perls have
       limitations in using "seek" and "tell" on a file accessed
       in "text" mode.  Stick to "seek"-ing to locations you got
       from "tell" (and no others), and you are usually free to
       use "seek" and "tell" even in "text" mode.  Using "seek"
       or "tell" or other file operations may be non-portable.
       If you use "binmode" on a file, however, you can usually
       "seek" and "tell" with arbitrary values in safety.

       A common misconception in socket programming is that "\n"
       eq "\012" everywhere.  When using protocols such as common
       Internet protocols, "\012" and "\015" are called for
       specifically, and the values of the logical "\n" and "\r"
       (carriage return) are not reliable.

           print SOCKET "Hi there, client!\r\n";      # WRONG
           print SOCKET "Hi there, client!\015\012";  # RIGHT

       However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can
       be tedious and unsightly, as well as confusing to those
       maintaining the code.  As such, the Socket module supplies
       the Right Thing for those who want it.

           use Socket qw(:DEFAULT :crlf);
           print SOCKET "Hi there, client!$CRLF"      # RIGHT

       When reading from a socket, remember that the default
       input record separator $/ is "\n", but robust socket code
       will recognize as either "\012" or "\015\012" as end of
       line:

           while (<SOCKET>) {
               # ...
           }

       Because both CRLF and LF end in LF, the input record
       separator can be set to LF and any CR stripped later.
       Better to write:

           use Socket qw(:DEFAULT :crlf);
           local($/) = LF;      # not needed if $/ is already \012

           while (<SOCKET>) {
               s/$CR?$LF/\n/;   # not sure if socket uses LF or CRLF, OK
           #   s/\015?\012/\n/; # same thing
           }

       This example is preferred over the previous one--even for
       Unix platforms--because now any "\015"'s ("\cM"'s) are
       stripped out (and there was much rejoicing).

       Similarly, functions that return text data--such as a
       function that fetches a web page--should sometimes
       translate newlines before returning the data, if they've



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       not yet been translated to the local newline
       representation.  A single line of code will often suffice:

           $data =~ s/\015?\012/\n/g;
           return $data;

       Some of this may be confusing.  Here's a handy reference
       to the ASCII CR and LF characters.  You can print it out
       and stick it in your wallet.

           LF  eq  \012  eq  \x0A  eq  \cJ  eq  chr(10)  eq  ASCII 10
           CR  eq  \015  eq  \x0D  eq  \cM  eq  chr(13)  eq  ASCII 13

                    | Unix | DOS  | Mac  |
               ---------------------------
               \n   |  LF  |  LF  |  CR  |
               \r   |  CR  |  CR  |  LF  |
               \n * |  LF  | CRLF |  CR  |
               \r * |  CR  |  CR  |  LF  |
               ---------------------------
               * text-mode STDIO

       The Unix column assumes that you are not accessing a
       serial line (like a tty) in canonical mode.  If you are,
       then CR on input becomes "\n", and "\n" on output becomes
       CRLF.

       These are just the most common definitions of "\n" and
       "\r" in Perl.  There may well be others.  For example, on
       an EBCDIC implementation such as z/OS (OS/390) or OS/400
       (using the ILE, the PASE is ASCII-based) the above
       material is similar to "Unix" but the code numbers change:

           LF  eq  \025  eq  \x15  eq  \cU  eq  chr(21)  eq  CP-1047 21
           LF  eq  \045  eq  \x25  eq           chr(37)  eq  CP-0037 37
           CR  eq  \015  eq  \x0D  eq  \cM  eq  chr(13)  eq  CP-1047 13
           CR  eq  \015  eq  \x0D  eq  \cM  eq  chr(13)  eq  CP-0037 13

                    | z/OS | OS/400 |
               ----------------------
               \n   |  LF  |  LF    |
               \r   |  CR  |  CR    |
               \n * |  LF  |  LF    |
               \r * |  CR  |  CR    |
               ----------------------
               * text-mode STDIO

   Numbers endianness and Width
       Different CPUs store integers and floating point numbers
       in different orders (called endianness) and widths (32-bit
       and 64-bit being the most common today).  This affects
       your programs when they attempt to transfer numbers in
       binary format from one CPU architecture to another,
       usually either "live" via network connection, or by



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       storing the numbers to secondary storage such as a disk
       file or tape.

       Conflicting storage orders make utter mess out of the
       numbers.  If a little-endian host (Intel, VAX) stores
       0x12345678 (305419896 in decimal), a big-endian host
       (Motorola, Sparc, PA) reads it as 0x78563412 (2018915346
       in decimal).  Alpha and MIPS can be either: Digital/Compaq
       used/uses them in little-endian mode; SGI/Cray uses them
       in big-endian mode.  To avoid this problem in network
       (socket) connections use the "pack" and "unpack" formats
       "n" and "N", the "network" orders.  These are guaranteed
       to be portable.

       As of perl 5.9.2, you can also use the ">" and "<"
       modifiers to force big- or little-endian byte-order.  This
       is useful if you want to store signed integers or 64-bit
       integers, for example.

       You can explore the endianness of your platform by
       unpacking a data structure packed in native format such
       as:

           print unpack("h*", pack("s2", 1, 2)), "\n";
           # '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
           # '00100020' on e.g. Motorola 68040

       If you need to distinguish between endian architectures
       you could use either of the variables set like so:

           $is_big_endian   = unpack("h*", pack("s", 1)) =~ /01/;
           $is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;

       Differing widths can cause truncation even between
       platforms of equal endianness.  The platform of shorter
       width loses the upper parts of the number.  There is no
       good solution for this problem except to avoid
       transferring or storing raw binary numbers.

       One can circumnavigate both these problems in two ways.
       Either transfer and store numbers always in text format,
       instead of raw binary, or else consider using modules like
       Data::Dumper (included in the standard distribution as of
       Perl 5.005) and Storable (included as of perl 5.8).
       Keeping all data as text significantly simplifies matters.

       The v-strings are portable only up to v2147483647
       (0x7FFFFFFF), that's how far EBCDIC, or more precisely
       UTF-EBCDIC will go.

   Files and Filesystems
       Most platforms these days structure files in a
       hierarchical fashion.  So, it is reasonably safe to assume
       that all platforms support the notion of a "path" to



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       uniquely identify a file on the system.  How that path is
       really written, though, differs considerably.

       Although similar, file path specifications differ between
       Unix, Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and
       probably others.  Unix, for example, is one of the few
       OSes that has the elegant idea of a single root directory.

       DOS, OS/2, VMS, VOS, and Windows can work similarly to
       Unix with "/" as path separator, or in their own
       idiosyncratic ways (such as having several root
       directories and various "unrooted" device files such NIL:
       and LPT:).

       Mac OS uses ":" as a path separator instead of "/".

       The filesystem may support neither hard links ("link") nor
       symbolic links ("symlink", "readlink", "lstat").

       The filesystem may support neither access timestamp nor
       change timestamp (meaning that about the only portable
       timestamp is the modification timestamp), or one second
       granularity of any timestamps (e.g. the FAT filesystem
       limits the time granularity to two seconds).

       The "inode change timestamp" (the "-C" filetest) may
       really be the "creation timestamp" (which it is not in
       UNIX).

       VOS perl can emulate Unix filenames with "/" as path
       separator.  The native pathname characters greater-than,
       less-than, number-sign, and percent-sign are always
       accepted.

       RISC OS perl can emulate Unix filenames with "/" as path
       separator, or go native and use "." for path separator and
       ":" to signal filesystems and disk names.

       Don't assume UNIX filesystem access semantics: that read,
       write, and execute are all the permissions there are, and
       even if they exist, that their semantics (for example what
       do r, w, and x mean on a directory) are the UNIX ones.
       The various UNIX/POSIX compatibility layers usually try to
       make interfaces like chmod() work, but sometimes there
       simply is no good mapping.

       If all this is intimidating, have no (well, maybe only a
       little) fear.  There are modules that can help.  The
       File::Spec modules provide methods to do the Right Thing
       on whatever platform happens to be running the program.







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           use File::Spec::Functions;
           chdir(updir());        # go up one directory
           $file = catfile(curdir(), 'temp', 'file.txt');
           # on Unix and Win32, './temp/file.txt'
           # on Mac OS, ':temp:file.txt'
           # on VMS, '[.temp]file.txt'

       File::Spec is available in the standard distribution as of
       version 5.004_05.  File::Spec::Functions is only in
       File::Spec 0.7 and later, and some versions of perl come
       with version 0.6.  If File::Spec is not updated to 0.7 or
       later, you must use the object-oriented interface from
       File::Spec (or upgrade File::Spec).

       In general, production code should not have file paths
       hardcoded.  Making them user-supplied or read from a
       configuration file is better, keeping in mind that file
       path syntax varies on different machines.

       This is especially noticeable in scripts like Makefiles
       and test suites, which often assume "/" as a path
       separator for subdirectories.

       Also of use is File::Basename from the standard
       distribution, which splits a pathname into pieces (base
       filename, full path to directory, and file suffix).

       Even when on a single platform (if you can call Unix a
       single platform), remember not to count on the existence
       or the contents of particular system-specific files or
       directories, like /etc/passwd, /etc/sendmail.conf,
       /etc/resolv.conf, or even /tmp/.  For example, /etc/passwd
       may exist but not contain the encrypted passwords, because
       the system is using some form of enhanced security.  Or it
       may not contain all the accounts, because the system is
       using NIS.  If code does need to rely on such a file,
       include a description of the file and its format in the
       code's documentation, then make it easy for the user to
       override the default location of the file.

       Don't assume a text file will end with a newline.  They
       should, but people forget.

       Do not have two files or directories of the same name with
       different case, like test.pl and Test.pl, as many
       platforms have case-insensitive (or at least case-
       forgiving) filenames.  Also, try not to have non-word
       characters (except for ".") in the names, and keep them to
       the 8.3 convention, for maximum portability, onerous a
       burden though this may appear.

       Likewise, when using the AutoSplit module, try to keep
       your functions to 8.3 naming and case-insensitive
       conventions; or, at the least, make it so the resulting



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       files have a unique (case-insensitively) first 8
       characters.

       Whitespace in filenames is tolerated on most systems, but
       not all, and even on systems where it might be tolerated,
       some utilities might become confused by such whitespace.

       Many systems (DOS, VMS ODS-2) cannot have more than one
       "." in their filenames.

       Don't assume ">" won't be the first character of a
       filename.  Always use "<" explicitly to open a file for
       reading, or even better, use the three-arg version of
       open, unless you want the user to be able to specify a
       pipe open.

           open(FILE, '<', $existing_file) or die $!;

       If filenames might use strange characters, it is safest to
       open it with "sysopen" instead of "open".  "open" is magic
       and can translate characters like ">", "<", and "|", which
       may be the wrong thing to do.  (Sometimes, though, it's
       the right thing.)  Three-arg open can also help protect
       against this translation in cases where it is undesirable.

       Don't use ":" as a part of a filename since many systems
       use that for their own semantics (Mac OS Classic for
       separating pathname components, many networking schemes
       and utilities for separating the nodename and the
       pathname, and so on).  For the same reasons, avoid "@",
       ";" and "|".

       Don't assume that in pathnames you can collapse two
       leading slashes "//" into one: some networking and
       clustering filesystems have special semantics for that.
       Let the operating system to sort it out.

       The portable filename characters as defined by ANSI C are

        a b c d e f g h i j k l m n o p q r t u v w x y z
        A B C D E F G H I J K L M N O P Q R T U V W X Y Z
        0 1 2 3 4 5 6 7 8 9
        . _ -

       and the "-" shouldn't be the first character.  If you want
       to be hypercorrect, stay case-insensitive and within the
       8.3 naming convention (all the files and directories have
       to be unique within one directory if their names are
       lowercased and truncated to eight characters before the
       ".", if any, and to three characters after the ".", if
       any).  (And do not use "."s in directory names.)

   System Interaction
       Not all platforms provide a command line.  These are



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       usually platforms that rely primarily on a Graphical User
       Interface (GUI) for user interaction.  A program requiring
       a command line interface might not work everywhere.  This
       is probably for the user of the program to deal with, so
       don't stay up late worrying about it.

       Some platforms can't delete or rename files held open by
       the system, this limitation may also apply to changing
       filesystem metainformation like file permissions or
       owners.  Remember to "close" files when you are done with
       them.  Don't "unlink" or "rename" an open file.  Don't
       "tie" or "open" a file already tied or opened; "untie" or
       "close" it first.

       Don't open the same file more than once at a time for
       writing, as some operating systems put mandatory locks on
       such files.

       Don't assume that write/modify permission on a directory
       gives the right to add or delete files/directories in that
       directory.  That is filesystem specific: in some
       filesystems you need write/modify permission also (or even
       just) in the file/directory itself.  In some filesystems
       (AFS, DFS) the permission to add/delete directory entries
       is a completely separate permission.

       Don't assume that a single "unlink" completely gets rid of
       the file: some filesystems (most notably the ones in VMS)
       have versioned filesystems, and unlink() removes only the
       most recent one (it doesn't remove all the versions
       because by default the native tools on those platforms
       remove just the most recent version, too).  The portable
       idiom to remove all the versions of a file is

           1 while unlink "file";

       This will terminate if the file is undeleteable for some
       reason (protected, not there, and so on).

       Don't count on a specific environment variable existing in
       %ENV.  Don't count on %ENV entries being case-sensitive,
       or even case-preserving.  Don't try to clear %ENV by
       saying "%ENV = ();", or, if you really have to, make it
       conditional on "$^O ne 'VMS'" since in VMS the %ENV table
       is much more than a per-process key-value string table.

       On VMS, some entries in the %ENV hash are dynamically
       created when their key is used on a read if they did not
       previously exist.  The values for $ENV{HOME}, $ENV{TERM},
       $ENV{HOME}, and $ENV{USER}, are known to be dynamically
       generated.  The specific names that are dynamically
       generated may vary with the version of the C library on
       VMS, and more may exist than is documented.




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       On VMS by default, changes to the %ENV hash are persistent
       after the process exits.  This can cause unintended
       issues.

       Don't count on signals or %SIG for anything.

       Don't count on filename globbing.  Use "opendir",
       "readdir", and "closedir" instead.

       Don't count on per-program environment variables, or per-
       program current directories.

       Don't count on specific values of $!, neither numeric nor
       especially the strings values-- users may switch their
       locales causing error messages to be translated into their
       languages.  If you can trust a POSIXish environment, you
       can portably use the symbols defined by the Errno module,
       like ENOENT.  And don't trust on the values of $!  at all
       except immediately after a failed system call.

   Command names versus file pathnames
       Don't assume that the name used to invoke a command or
       program with "system" or "exec" can also be used to test
       for the existence of the file that holds the executable
       code for that command or program.  First, many systems
       have "internal" commands that are built-in to the shell or
       OS and while these commands can be invoked, there is no
       corresponding file.  Second, some operating systems (e.g.,
       Cygwin, DJGPP, OS/2, and VOS) have required suffixes for
       executable files; these suffixes are generally permitted
       on the command name but are not required.  Thus, a command
       like "perl" might exist in a file named "perl",
       "perl.exe", or "perl.pm", depending on the operating
       system.  The variable "_exe" in the Config module holds
       the executable suffix, if any.  Third, the VMS port
       carefully sets up $^X and $Config{perlpath} so that no
       further processing is required.  This is just as well,
       because the matching regular expression used below would
       then have to deal with a possible trailing version number
       in the VMS file name.

       To convert $^X to a file pathname, taking account of the
       requirements of the various operating system
       possibilities, say:

         use Config;
         $thisperl = $^X;
         if ($^O ne 'VMS')
            {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}

       To convert $Config{perlpath} to a file pathname, say:






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         use Config;
         $thisperl = $Config{perlpath};
         if ($^O ne 'VMS')
            {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}

   Networking
       Don't assume that you can reach the public Internet.

       Don't assume that there is only one way to get through
       firewalls to the public Internet.

       Don't assume that you can reach outside world through any
       other port than 80, or some web proxy.  ftp is blocked by
       many firewalls.

       Don't assume that you can send email by connecting to the
       local SMTP port.

       Don't assume that you can reach yourself or any node by
       the name 'localhost'.  The same goes for '127.0.0.1'.  You
       will have to try both.

       Don't assume that the host has only one network card, or
       that it can't bind to many virtual IP addresses.

       Don't assume a particular network device name.

       Don't assume a particular set of ioctl()s will work.

       Don't assume that you can ping hosts and get replies.

       Don't assume that any particular port (service) will
       respond.

       Don't assume that Sys::Hostname (or any other API or
       command) returns either a fully qualified hostname or a
       non-qualified hostname: it all depends on how the system
       had been configured.  Also remember things like DHCP and
       NAT-- the hostname you get back might not be very useful.

       All the above "don't":s may look daunting, and they are --
       but the key is to degrade gracefully if one cannot reach
       the particular network service one wants.  Croaking or
       hanging do not look very professional.

   Interprocess Communication (IPC)
       In general, don't directly access the system in code meant
       to be portable.  That means, no "system", "exec", "fork",
       "pipe", "``", "qx//", "open" with a "|", nor any of the
       other things that makes being a perl hacker worth being.

       Commands that launch external processes are generally
       supported on most platforms (though many of them do not
       support any type of forking).  The problem with using them



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       arises from what you invoke them on.  External tools are
       often named differently on different platforms, may not be
       available in the same location, might accept different
       arguments, can behave differently, and often present their
       results in a platform-dependent way.  Thus, you should
       seldom depend on them to produce consistent results. (Then
       again, if you're calling netstat -a, you probably don't
       expect it to run on both Unix and CP/M.)

       One especially common bit of Perl code is opening a pipe
       to sendmail:

           open(MAIL, '|/usr/lib/sendmail -t')
               or die "cannot fork sendmail: $!";

       This is fine for systems programming when sendmail is
       known to be available.  But it is not fine for many non-
       Unix systems, and even some Unix systems that may not have
       sendmail installed.  If a portable solution is needed, see
       the various distributions on CPAN that deal with it.
       Mail::Mailer and Mail::Send in the MailTools distribution
       are commonly used, and provide several mailing methods,
       including mail, sendmail, and direct SMTP (via Net::SMTP)
       if a mail transfer agent is not available.  Mail::Sendmail
       is a standalone module that provides simple, platform-
       independent mailing.

       The Unix System V IPC ("msg*(), sem*(), shm*()") is not
       available even on all Unix platforms.

       Do not use either the bare result of "pack("N", 10, 20,
       30, 40)" or bare v-strings (such as "v10.20.30.40") to
       represent IPv4 addresses: both forms just pack the four
       bytes into network order.  That this would be equal to the
       C language "in_addr" struct (which is what the socket code
       internally uses) is not guaranteed.  To be portable use
       the routines of the Socket extension, such as
       "inet_aton()", "inet_ntoa()", and "sockaddr_in()".

       The rule of thumb for portable code is: Do it all in
       portable Perl, or use a module (that may internally
       implement it with platform-specific code, but expose a
       common interface).

   External Subroutines (XS)
       XS code can usually be made to work with any platform, but
       dependent libraries, header files, etc., might not be
       readily available or portable, or the XS code itself might
       be platform-specific, just as Perl code might be.  If the
       libraries and headers are portable, then it is normally
       reasonable to make sure the XS code is portable, too.

       A different type of portability issue arises when writing
       XS code: availability of a C compiler on the end-user's



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       system.  C brings with it its own portability issues, and
       writing XS code will expose you to some of those.  Writing
       purely in Perl is an easier way to achieve portability.

   Standard Modules
       In general, the standard modules work across platforms.
       Notable exceptions are the CPAN module (which currently
       makes connections to external programs that may not be
       available), platform-specific modules (like
       ExtUtils::MM_VMS), and DBM modules.

       There is no one DBM module available on all platforms.
       SDBM_File and the others are generally available on all
       Unix and DOSish ports, but not in MacPerl, where only
       NBDM_File and DB_File are available.

       The good news is that at least some DBM module should be
       available, and AnyDBM_File will use whichever module it
       can find.  Of course, then the code needs to be fairly
       strict, dropping to the greatest common factor (e.g., not
       exceeding 1K for each record), so that it will work with
       any DBM module.  See AnyDBM_File for more details.

   Time and Date
       The system's notion of time of day and calendar date is
       controlled in widely different ways.  Don't assume the
       timezone is stored in $ENV{TZ}, and even if it is, don't
       assume that you can control the timezone through that
       variable.  Don't assume anything about the three-letter
       timezone abbreviations (for example that MST would be the
       Mountain Standard Time, it's been known to stand for
       Moscow Standard Time).  If you need to use timezones,
       express them in some unambiguous format like the exact
       number of minutes offset from UTC, or the POSIX timezone
       format.

       Don't assume that the epoch starts at 00:00:00, January 1,
       1970, because that is OS- and implementation-specific.  It
       is better to store a date in an unambiguous
       representation.  The ISO 8601 standard defines YYYY-MM-DD
       as the date format, or YYYY-MM-DDTHH-MM-SS (that's a
       literal "T" separating the date from the time).  Please do
       use the ISO 8601 instead of making us to guess what date
       02/03/04 might be.  ISO 8601 even sorts nicely as-is.  A
       text representation (like "1987-12-18") can be easily
       converted into an OS-specific value using a module like
       Date::Parse.  An array of values, such as those returned
       by "localtime", can be converted to an OS-specific
       representation using Time::Local.

       When calculating specific times, such as for tests in time
       or date modules, it may be appropriate to calculate an
       offset for the epoch.




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           require Time::Local;
           $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);

       The value for $offset in Unix will be 0, but in Mac OS
       will be some large number.  $offset can then be added to a
       Unix time value to get what should be the proper value on
       any system.

       On Windows (at least), you shouldn't pass a negative value
       to "gmtime" or "localtime".

   Character sets and character encoding
       Assume very little about character sets.

       Assume nothing about numerical values ("ord", "chr") of
       characters.  Do not use explicit code point ranges (like
       \xHH-\xHH); use for example symbolic character classes
       like "[:print:]".

       Do not assume that the alphabetic characters are encoded
       contiguously (in the numeric sense).  There may be gaps.

       Do not assume anything about the ordering of the
       characters.  The lowercase letters may come before or
       after the uppercase letters; the lowercase and uppercase
       may be interlaced so that both "a" and "A" come before
       "b"; the accented and other international characters may
       be interlaced so that ae comes before "b".

   Internationalisation
       If you may assume POSIX (a rather large assumption), you
       may read more about the POSIX locale system from
       perllocale.  The locale system at least attempts to make
       things a little bit more portable, or at least more
       convenient and native-friendly for non-English users.  The
       system affects character sets and encoding, and date and
       time formatting--amongst other things.

       If you really want to be international, you should
       consider Unicode.  See perluniintro and perlunicode for
       more information.

       If you want to use non-ASCII bytes (outside the bytes
       0x00..0x7f) in the "source code" of your code, to be
       portable you have to be explicit about what bytes they
       are.  Someone might for example be using your code under a
       UTF-8 locale, in which case random native bytes might be
       illegal ("Malformed UTF-8 ...")  This means that for
       example embedding ISO 8859-1 bytes beyond 0x7f into your
       strings might cause trouble later.  If the bytes are
       native 8-bit bytes, you can use the "bytes" pragma.  If
       the bytes are in a string (regular expression being a
       curious string), you can often also use the "\xHH"
       notation instead of embedding the bytes as-is.  (If you



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       want to write your code in UTF-8, you can use the "utf8".)
       The "bytes" and "utf8" pragmata are available since Perl
       5.6.0.

   System Resources
       If your code is destined for systems with severely
       constrained (or missing!) virtual memory systems then you
       want to be especially mindful of avoiding wasteful
       constructs such as:

           # NOTE: this is no longer "bad" in perl5.005
           for (0..10000000) {}                       # bad
           for (my $x = 0; $x <= 10000000; ++$x) {}   # good

           @lines = <VERY_LARGE_FILE>;                # bad

           while (<FILE>) {$file .= $_}               # sometimes bad
           $file = join('', <FILE>);                  # better

       The last two constructs may appear unintuitive to most
       people.  The first repeatedly grows a string, whereas the
       second allocates a large chunk of memory in one go.  On
       some systems, the second is more efficient that the first.

   Security
       Most multi-user platforms provide basic levels of
       security, usually implemented at the filesystem level.
       Some, however, do not-- unfortunately.  Thus the notion of
       user id, or "home" directory, or even the state of being
       logged-in, may be unrecognizable on many platforms.  If
       you write programs that are security-conscious, it is
       usually best to know what type of system you will be
       running under so that you can write code explicitly for
       that platform (or class of platforms).

       Don't assume the UNIX filesystem access semantics: the
       operating system or the filesystem may be using some ACL
       systems, which are richer languages than the usual rwx.
       Even if the rwx exist, their semantics might be different.

       (From security viewpoint testing for permissions before
       attempting to do something is silly anyway: if one tries
       this, there is potential for race conditions-- someone or
       something might change the permissions between the
       permissions check and the actual operation.  Just try the
       operation.)

       Don't assume the UNIX user and group semantics:
       especially, don't expect the $< and $> (or the $( and $))
       to work for switching identities (or memberships).

       Don't assume set-uid and set-gid semantics. (And even if
       you do, think twice: set-uid and set-gid are a known can
       of security worms.)



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   Style
       For those times when it is necessary to have platform-
       specific code, consider keeping the platform-specific code
       in one place, making porting to other platforms easier.
       Use the Config module and the special variable $^O to
       differentiate platforms, as described in "PLATFORMS".

       Be careful in the tests you supply with your module or
       programs.  Module code may be fully portable, but its
       tests might not be.  This often happens when tests spawn
       off other processes or call external programs to aid in
       the testing, or when (as noted above) the tests assume
       certain things about the filesystem and paths.  Be careful
       not to depend on a specific output style for errors, such
       as when checking $! after a failed system call.  Using $!
       for anything else than displaying it as output is doubtful
       (though see the Errno module for testing reasonably
       portably for error value). Some platforms expect a certain
       output format, and Perl on those platforms may have been
       adjusted accordingly.  Most specifically, don't anchor a
       regex when testing an error value.

CPAN Testers
       Modules uploaded to CPAN are tested by a variety of
       volunteers on different platforms.  These CPAN testers are
       notified by mail of each new upload, and reply to the list
       with PASS, FAIL, NA (not applicable to this platform), or
       UNKNOWN (unknown), along with any relevant notations.

       The purpose of the testing is twofold: one, to help
       developers fix any problems in their code that crop up
       because of lack of testing on other platforms; two, to
       provide users with information about whether a given
       module works on a given platform.

       Also see:

       o   Mailing list: cpan-testers@perl.org

       o   Testing results: http://testers.cpan.org/

PLATFORMS
       As of version 5.002, Perl is built with a $^O variable
       that indicates the operating system it was built on.  This
       was implemented to help speed up code that would otherwise
       have to "use Config" and use the value of $Config{osname}.
       Of course, to get more detailed information about the
       system, looking into %Config is certainly recommended.

       %Config cannot always be trusted, however, because it was
       built at compile time.  If perl was built in one place,
       then transferred elsewhere, some values may be wrong.  The
       values may even have been edited after the fact.




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   Unix
       Perl works on a bewildering variety of Unix and Unix-like
       platforms (see e.g. most of the files in the hints/
       directory in the source code kit).  On most of these
       systems, the value of $^O (hence $Config{'osname'}, too)
       is determined either by lowercasing and stripping
       punctuation from the first field of the string returned by
       typing "uname -a" (or a similar command) at the shell
       prompt or by testing the file system for the presence of
       uniquely named files such as a kernel or header file.
       Here, for example, are a few of the more popular Unix
       flavors:

           uname         $^O        $Config{'archname'}
           --------------------------------------------
           AIX           aix        aix
           BSD/OS        bsdos      i386-bsdos
           Darwin        darwin     darwin
           dgux          dgux       AViiON-dgux
           DYNIX/ptx     dynixptx   i386-dynixptx
           FreeBSD       freebsd    freebsd-i386
           Haiku         haiku      BePC-haiku
           Linux         linux      arm-linux
           Linux         linux      i386-linux
           Linux         linux      i586-linux
           Linux         linux      ppc-linux
           HP-UX         hpux       PA-RISC1.1
           IRIX          irix       irix
           Mac OS X      darwin     darwin
           MachTen PPC   machten    powerpc-machten
           NeXT 3        next       next-fat
           NeXT 4        next       OPENSTEP-Mach
           openbsd       openbsd    i386-openbsd
           OSF1          dec_osf    alpha-dec_osf
           reliantunix-n svr4       RM400-svr4
           SCO_SV        sco_sv     i386-sco_sv
           SINIX-N       svr4       RM400-svr4
           sn4609        unicos     CRAY_C90-unicos
           sn6521        unicosmk   t3e-unicosmk
           sn9617        unicos     CRAY_J90-unicos
           SunOS         solaris    sun4-solaris
           SunOS         solaris    i86pc-solaris
           SunOS4        sunos      sun4-sunos

       Because the value of $Config{archname} may depend on the
       hardware architecture, it can vary more than the value of
       $^O.

   DOS and Derivatives
       Perl has long been ported to Intel-style microcomputers
       running under systems like PC-DOS, MS-DOS, OS/2, and most
       Windows platforms you can bring yourself to mention
       (except for Windows CE, if you count that).  Users
       familiar with COMMAND.COM or CMD.EXE style shells should



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       be aware that each of these file specifications may have
       subtle differences:

           $filespec0 = "c:/foo/bar/file.txt";
           $filespec1 = "c:\\foo\\bar\\file.txt";
           $filespec2 = 'c:\foo\bar\file.txt';
           $filespec3 = 'c:\\foo\\bar\\file.txt';

       System calls accept either "/" or "\" as the path
       separator.  However, many command-line utilities of DOS
       vintage treat "/" as the option prefix, so may get
       confused by filenames containing "/".  Aside from calling
       any external programs, "/" will work just fine, and
       probably better, as it is more consistent with popular
       usage, and avoids the problem of remembering what to
       backwhack and what not to.

       The DOS FAT filesystem can accommodate only "8.3" style
       filenames.  Under the "case-insensitive, but case-
       preserving" HPFS (OS/2) and NTFS (NT) filesystems you may
       have to be careful about case returned with functions like
       "readdir" or used with functions like "open" or "opendir".

       DOS also treats several filenames as special, such as AUX,
       PRN, NUL, CON, COM1, LPT1, LPT2, etc.  Unfortunately,
       sometimes these filenames won't even work if you include
       an explicit directory prefix.  It is best to avoid such
       filenames, if you want your code to be portable to DOS and
       its derivatives.  It's hard to know what these all are,
       unfortunately.

       Users of these operating systems may also wish to make use
       of scripts such as pl2bat.bat or pl2cmd to put wrappers
       around your scripts.

       Newline ("\n") is translated as "\015\012" by STDIO when
       reading from and writing to files (see "Newlines").
       "binmode(FILEHANDLE)" will keep "\n" translated as "\012"
       for that filehandle.  Since it is a no-op on other
       systems, "binmode" should be used for cross-platform code
       that deals with binary data.  That's assuming you realize
       in advance that your data is in binary.  General-purpose
       programs should often assume nothing about their data.

       The $^O variable and the $Config{archname} values for
       various DOSish perls are as follows:











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            OS            $^O      $Config{archname}   ID    Version
            --------------------------------------------------------
            MS-DOS        dos        ?
            PC-DOS        dos        ?
            OS/2          os2        ?
            Windows 3.1   ?          ?                 0      3 01
            Windows 95    MSWin32    MSWin32-x86       1      4 00
            Windows 98    MSWin32    MSWin32-x86       1      4 10
            Windows ME    MSWin32    MSWin32-x86       1      ?
            Windows NT    MSWin32    MSWin32-x86       2      4 xx
            Windows NT    MSWin32    MSWin32-ALPHA     2      4 xx
            Windows NT    MSWin32    MSWin32-ppc       2      4 xx
            Windows 2000  MSWin32    MSWin32-x86       2      5 00
            Windows XP    MSWin32    MSWin32-x86       2      5 01
            Windows 2003  MSWin32    MSWin32-x86       2      5 02
            Windows CE    MSWin32    ?                 3
            Cygwin        cygwin     cygwin

       The various MSWin32 Perl's can distinguish the OS they are
       running on via the value of the fifth element of the list
       returned from Win32::GetOSVersion().  For example:

           if ($^O eq 'MSWin32') {
               my @os_version_info = Win32::GetOSVersion();
               print +('3.1','95','NT')[$os_version_info[4]],"\n";
           }

       There are also Win32::IsWinNT() and Win32::IsWin95(), try
       "perldoc Win32", and as of libwin32 0.19 (not part of the
       core Perl distribution) Win32::GetOSName().  The very
       portable POSIX::uname() will work too:

           c:\> perl -MPOSIX -we "print join '|', uname"
           Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86

       Also see:

       o   The djgpp environment for DOS,
           http://www.delorie.com/djgpp/ and perldos.

       o   The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
           http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html
           or ftp://hobbes.nmsu.edu/pub/os2/dev/emx/  Also
           perlos2.

       o   Build instructions for Win32 in perlwin32, or under
           the Cygnus environment in perlcygwin.

       o   The "Win32::*" modules in Win32.

       o   The ActiveState Pages, http://www.activestate.com/

       o   The Cygwin environment for Win32; README.cygwin
           (installed as perlcygwin), http://www.cygwin.com/



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       o   The U/WIN environment for Win32,
           http://www.research.att.com/sw/tools/uwin/

       o   Build instructions for OS/2, perlos2

   Mac OS
       Any module requiring XS compilation is right out for most
       people, because MacPerl is built using non-free (and non-
       cheap!) compilers.  Some XS modules that can work with
       MacPerl are built and distributed in binary form on CPAN.

       Directories are specified as:

           volume:folder:file              for absolute pathnames
           volume:folder:                  for absolute pathnames
           :folder:file                    for relative pathnames
           :folder:                        for relative pathnames
           :file                           for relative pathnames
           file                            for relative pathnames

       Files are stored in the directory in alphabetical order.
       Filenames are limited to 31 characters, and may include
       any character except for null and ":", which is reserved
       as the path separator.

       Instead of "flock", see "FSpSetFLock" and "FSpRstFLock" in
       the Mac::Files module, or "chmod(0444, ...)" and
       "chmod(0666, ...)".

       In the MacPerl application, you can't run a program from
       the command line; programs that expect @ARGV to be
       populated can be edited with something like the following,
       which brings up a dialog box asking for the command line
       arguments.

           if (!@ARGV) {
               @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
           }

       A MacPerl script saved as a "droplet" will populate @ARGV
       with the full pathnames of the files dropped onto the
       script.

       Mac users can run programs under a type of command line
       interface under MPW (Macintosh Programmer's Workshop, a
       free development environment from Apple).  MacPerl was
       first introduced as an MPW tool, and MPW can be used like
       a shell:

           perl myscript.plx some arguments

       ToolServer is another app from Apple that provides access
       to MPW tools from MPW and the MacPerl app, which allows
       MacPerl programs to use "system", backticks, and piped



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       "open".

       "Mac OS" is the proper name for the operating system, but
       the value in $^O is "MacOS".  To determine architecture,
       version, or whether the application or MPW tool version is
       running, check:

           $is_app    = $MacPerl::Version =~ /App/;
           $is_tool   = $MacPerl::Version =~ /MPW/;
           ($version) = $MacPerl::Version =~ /^(\S+)/;
           $is_ppc    = $MacPerl::Architecture eq 'MacPPC';
           $is_68k    = $MacPerl::Architecture eq 'Mac68K';

       Mac OS X, based on NeXT's OpenStep OS, runs MacPerl
       natively, under the "Classic" environment.  There is no
       "Carbon" version of MacPerl to run under the primary Mac
       OS X environment.  Mac OS X and its Open Source version,
       Darwin, both run Unix perl natively.

       Also see:

       o   MacPerl Development, http://dev.macperl.org/ .

       o   The MacPerl Pages, http://www.macperl.com/ .

       o   The MacPerl mailing lists, http://lists.perl.org/ .

       o   MPW,
           ftp://ftp.apple.com/developer/Tool_Chest/Core_Mac_OS_Tools/

   VMS
       Perl on VMS is discussed in perlvms in the perl
       distribution.

       The official name of VMS as of this writing is OpenVMS.

       Perl on VMS can accept either VMS- or Unix-style file
       specifications as in either of the following:

           $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
           $ perl -ne "print if /perl_setup/i" /sys$login/login.com

       but not a mixture of both as in:

           $ perl -ne "print if /perl_setup/i" sys$login:/login.com
           Can't open sys$login:/login.com: file specification syntax error

       Interacting with Perl from the Digital Command Language
       (DCL) shell often requires a different set of quotation
       marks than Unix shells do.  For example:

           $ perl -e "print ""Hello, world.\n"""
           Hello, world.




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       There are several ways to wrap your perl scripts in DCL
       .COM files, if you are so inclined.  For example:

           $ write sys$output "Hello from DCL!"
           $ if p1 .eqs. ""
           $ then perl -x 'f$environment("PROCEDURE")
           $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
           $ deck/dollars="__END__"
           #!/usr/bin/perl

           print "Hello from Perl!\n";

           __END__
           $ endif

       Do take care with "$ ASSIGN/nolog/user SYS$COMMAND:
       SYS$INPUT" if your perl-in-DCL script expects to do things
       like "$read = <STDIN>;".

       The VMS operating system has two filesystems, known as
       ODS-2 and ODS-5.

       For ODS-2, filenames are in the format
       "name.extension;version".  The maximum length for
       filenames is 39 characters, and the maximum length for
       extensions is also 39 characters.  Version is a number
       from 1 to 32767.  Valid characters are "/[A-Z0-9$_-]/".

       The ODS-2 filesystem is case-insensitive and does not
       preserve case.  Perl simulates this by converting all
       filenames to lowercase internally.

       For ODS-5, filenames may have almost any character in them
       and can include Unicode characters.  Characters that could
       be misinterpreted by the DCL shell or file parsing
       utilities need to be prefixed with the "^" character, or
       replaced with hexadecimal characters prefixed with the "^"
       character.  Such prefixing is only needed with the
       pathnames are in VMS format in applications.  Programs
       that can accept the UNIX format of pathnames do not need
       the escape characters.  The maximum length for filenames
       is 255 characters.  The ODS-5 file system can handle both
       a case preserved and a case sensitive mode.

       ODS-5 is only available on the OpenVMS for 64 bit
       platforms.

       Support for the extended file specifications is being done
       as optional settings to preserve backward compatibility
       with Perl scripts that assume the previous VMS
       limitations.

       In general routines on VMS that get a UNIX format file
       specification should return it in a UNIX format, and when



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       they get a VMS format specification they should return a
       VMS format unless they are documented to do a conversion.

       For routines that generate return a file specification,
       VMS allows setting if the C library which Perl is built on
       if it will be returned in VMS format or in UNIX format.

       With the ODS-2 file system, there is not much difference
       in syntax of filenames without paths for VMS or UNIX.
       With the extended character set available with ODS-5 there
       can be a significant difference.

       Because of this, existing Perl scripts written for VMS
       were sometimes treating VMS and UNIX filenames
       interchangeably.  Without the extended character set
       enabled, this behavior will mostly be maintained for
       backwards compatibility.

       When extended characters are enabled with ODS-5, the
       handling of UNIX formatted file specifications is to that
       of a UNIX system.

       VMS file specifications without extensions have a trailing
       dot.  An equivalent UNIX file specification should not
       show the trailing dot.

       The result of all of this, is that for VMS, for portable
       scripts, you can not depend on Perl to present the
       filenames in lowercase, to be case sensitive, and that the
       filenames could be returned in either UNIX or VMS format.

       And if a routine returns a file specification, unless it
       is intended to convert it, it should return it in the same
       format as it found it.

       "readdir" by default has traditionally returned lowercased
       filenames.  When the ODS-5 support is enabled, it will
       return the exact case of the filename on the disk.

       Files without extensions have a trailing period on them,
       so doing a "readdir" in the default mode with a file named
       A.;5 will return a. when VMS is (though that file could be
       opened with "open(FH, 'A')").

       With support for extended file specifications and if
       "opendir" was given a UNIX format directory, a file named
       A.;5 will return a and optionally in the exact case on the
       disk.  When "opendir" is given a VMS format directory,
       then "readdir" should return a., and again with the
       optionally the exact case.

       RMS had an eight level limit on directory depths from any
       rooted logical (allowing 16 levels overall) prior to VMS
       7.2, and even with versions of VMS on VAX up through 7.3.



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       Hence "PERL_ROOT:[LIB.2.3.4.5.6.7.8]" is a valid directory
       specification but "PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]" is
       not.  Makefile.PL authors might have to take this into
       account, but at least they can refer to the former as
       "/PERL_ROOT/lib/2/3/4/5/6/7/8/".

       Pumpkings and module integrators can easily see whether
       files with too many directory levels have snuck into the
       core by running the following in the top-level source
       directory:

          $ perl -ne "$_=~s/\s+.*//; print if scalar(split /\//) > 8;" < MANIFEST

       The VMS::Filespec module, which gets installed as part of
       the build process on VMS, is a pure Perl module that can
       easily be installed on non-VMS platforms and can be
       helpful for conversions to and from RMS native formats.
       It is also now the only way that you should check to see
       if VMS is in a case sensitive mode.

       What "\n" represents depends on the type of file opened.
       It usually represents "\012" but it could also be "\015",
       "\012", "\015\012", "\000", "\040", or nothing depending
       on the file organization and record format.  The
       VMS::Stdio module provides access to the special fopen()
       requirements of files with unusual attributes on VMS.

       TCP/IP stacks are optional on VMS, so socket routines
       might not be implemented.  UDP sockets may not be
       supported.

       The TCP/IP library support for all current versions of VMS
       is dynamically loaded if present, so even if the routines
       are configured, they may return a status indicating that
       they are not implemented.

       The value of $^O on OpenVMS is "VMS".  To determine the
       architecture that you are running on without resorting to
       loading all of %Config you can examine the content of the
       @INC array like so:

           if (grep(/VMS_AXP/, @INC)) {
               print "I'm on Alpha!\n";

           } elsif (grep(/VMS_VAX/, @INC)) {
               print "I'm on VAX!\n";

           } elsif (grep(/VMS_IA64/, @INC)) {
               print "I'm on IA64!\n";

           } else {
               print "I'm not so sure about where $^O is...\n";
           }




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       In general, the significant differences should only be if
       Perl is running on VMS_VAX or one of the 64 bit OpenVMS
       platforms.

       On VMS, perl determines the UTC offset from the
       "SYS$TIMEZONE_DIFFERENTIAL" logical name.  Although the
       VMS epoch began at 17-NOV-1858 00:00:00.00, calls to
       "localtime" are adjusted to count offsets from 01-JAN-1970
       00:00:00.00, just like Unix.

       Also see:

       o   README.vms (installed as README_vms), perlvms

       o   vmsperl list, vmsperl-subscribe@perl.org

       o   vmsperl on the web,
           http://www.sidhe.org/vmsperl/index.html

   VOS
       Perl on VOS is discussed in README.vos in the perl
       distribution (installed as perlvos).  Perl on VOS can
       accept either VOS- or Unix-style file specifications as in
       either of the following:

           $ perl -ne "print if /perl_setup/i" >system>notices
           $ perl -ne "print if /perl_setup/i" /system/notices

       or even a mixture of both as in:

           $ perl -ne "print if /perl_setup/i" >system/notices

       Even though VOS allows the slash character to appear in
       object names, because the VOS port of Perl interprets it
       as a pathname delimiting character, VOS files,
       directories, or links whose names contain a slash
       character cannot be processed.  Such files must be renamed
       before they can be processed by Perl.  Note that VOS
       limits file names to 32 or fewer characters, file names
       cannot start with a "-" character, or contain any
       character matching "tr/ !%&'()*+;<>?//"

       The value of $^O on VOS is "VOS".  To determine the
       architecture that you are running on without resorting to
       loading all of %Config you can examine the content of the
       @INC array like so:

           if ($^O =~ /VOS/) {
               print "I'm on a Stratus box!\n";
           } else {
               print "I'm not on a Stratus box!\n";
               die;
           }




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       Also see:

       o   README.vos (installed as perlvos)

       o   The VOS mailing list.

           There is no specific mailing list for Perl on VOS.
           You can post comments to the comp.sys.stratus
           newsgroup, or subscribe to the general Stratus mailing
           list.  Send a letter with "subscribe Info-Stratus" in
           the message body to majordomo@list.stratagy.com.

       o   VOS Perl on the web at
           http://ftp.stratus.com/pub/vos/posix/posix.html

   EBCDIC Platforms
       Recent versions of Perl have been ported to platforms such
       as OS/400 on AS/400 minicomputers as well as OS/390,
       VM/ESA, and BS2000 for S/390 Mainframes.  Such computers
       use EBCDIC character sets internally (usually Character
       Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC
       for S/390 systems).  On the mainframe perl currently works
       under the "Unix system services for OS/390" (formerly
       known as OpenEdition), VM/ESA OpenEdition, or the BS200
       POSIX-BC system (BS2000 is supported in perl 5.6 and
       greater).  See perlos390 for details.  Note that for
       OS/400 there is also a port of Perl 5.8.1/5.9.0 or later
       to the PASE which is ASCII-based (as opposed to ILE which
       is EBCDIC-based), see perlos400.

       As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA
       these Unix sub-systems do not support the "#!" shebang
       trick for script invocation.  Hence, on OS/390 and VM/ESA
       perl scripts can be executed with a header similar to the
       following simple script:

           : # use perl
               eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
                   if 0;
           #!/usr/local/bin/perl     # just a comment really

           print "Hello from perl!\n";

       OS/390 will support the "#!" shebang trick in release 2.8
       and beyond.  Calls to "system" and backticks can use POSIX
       shell syntax on all S/390 systems.

       On the AS/400, if PERL5 is in your library list, you may
       need to wrap your perl scripts in a CL procedure to invoke
       them like so:

           BEGIN
             CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
           ENDPGM



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       This will invoke the perl script hello.pl in the root of
       the QOpenSys file system.  On the AS/400 calls to "system"
       or backticks must use CL syntax.

       On these platforms, bear in mind that the EBCDIC character
       set may have an effect on what happens with some perl
       functions (such as "chr", "pack", "print", "printf",
       "ord", "sort", "sprintf", "unpack"), as well as bit-
       fiddling with ASCII constants using operators like "^",
       "&" and "|", not to mention dealing with socket interfaces
       to ASCII computers (see "Newlines").

       Fortunately, most web servers for the mainframe will
       correctly translate the "\n" in the following statement to
       its ASCII equivalent ("\r" is the same under both Unix and
       OS/390 & VM/ESA):

           print "Content-type: text/html\r\n\r\n";

       The values of $^O on some of these platforms includes:

           uname         $^O        $Config{'archname'}
           --------------------------------------------
           OS/390        os390      os390
           OS400         os400      os400
           POSIX-BC      posix-bc   BS2000-posix-bc
           VM/ESA        vmesa      vmesa

       Some simple tricks for determining if you are running on
       an EBCDIC platform could include any of the following
       (perhaps all):

           if ("\t" eq "\05")   { print "EBCDIC may be spoken here!\n"; }

           if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }

           if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }

       One thing you may not want to rely on is the EBCDIC
       encoding of punctuation characters since these may differ
       from code page to code page (and once your module or
       script is rumoured to work with EBCDIC, folks will want it
       to work with all EBCDIC character sets).

       Also see:

       o   perlos390, README.os390, perlbs2000, README.vmesa,
           perlebcdic.

       o   The perl-mvs@perl.org list is for discussion of
           porting issues as well as general usage issues for all
           EBCDIC Perls.  Send a message body of "subscribe perl-
           mvs" to majordomo@perl.org.




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       o   AS/400 Perl information at
           http://as400.rochester.ibm.com/ as well as on CPAN in
           the ports/ directory.

   Acorn RISC OS
       Because Acorns use ASCII with newlines ("\n") in text
       files as "\012" like Unix, and because Unix filename
       emulation is turned on by default, most simple scripts
       will probably work "out of the box".  The native
       filesystem is modular, and individual filesystems are free
       to be case-sensitive or insensitive, and are usually case-
       preserving.  Some native filesystems have name length
       limits, which file and directory names are silently
       truncated to fit.  Scripts should be aware that the
       standard filesystem currently has a name length limit of
       10 characters, with up to 77 items in a directory, but
       other filesystems may not impose such limitations.

       Native filenames are of the form

           Filesystem#Special_Field::DiskName.$.Directory.Directory.File

       where

           Special_Field is not usually present, but may contain . and $ .
           Filesystem =~ m|[A-Za-z0-9_]|
           DsicName   =~ m|[A-Za-z0-9_/]|
           $ represents the root directory
           . is the path separator
           @ is the current directory (per filesystem but machine global)
           ^ is the parent directory
           Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|

       The default filename translation is roughly "tr|/.|./|;"

       Note that ""ADFS::HardDisk.$.File" ne
       'ADFS::HardDisk.$.File'" and that the second stage of "$"
       interpolation in regular expressions will fall foul of the
       $. if scripts are not careful.

       Logical paths specified by system variables containing
       comma-separated search lists are also allowed; hence
       "System:Modules" is a valid filename, and the filesystem
       will prefix "Modules" with each section of "System$Path"
       until a name is made that points to an object on disk.
       Writing to a new file "System:Modules" would be allowed
       only if "System$Path" contains a single item list.  The
       filesystem will also expand system variables in filenames
       if enclosed in angle brackets, so "<System$Dir>.Modules"
       would look for the file "$ENV{'System$Dir'} . 'Modules'".
       The obvious implication of this is that fully qualified
       filenames can start with "<>" and should be protected when
       "open" is used for input.




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       Because "." was in use as a directory separator and
       filenames could not be assumed to be unique after 10
       characters, Acorn implemented the C compiler to strip the
       trailing ".c" ".h" ".s" and ".o" suffix from filenames
       specified in source code and store the respective files in
       subdirectories named after the suffix.  Hence files are
       translated:

           foo.h           h.foo
           C:foo.h         C:h.foo        (logical path variable)
           sys/os.h        sys.h.os       (C compiler groks Unix-speak)
           10charname.c    c.10charname
           10charname.o    o.10charname
           11charname_.c   c.11charname   (assuming filesystem truncates at 10)

       The Unix emulation library's translation of filenames to
       native assumes that this sort of translation is required,
       and it allows a user-defined list of known suffixes that
       it will transpose in this fashion.  This may seem
       transparent, but consider that with these rules
       "foo/bar/baz.h" and "foo/bar/h/baz" both map to
       "foo.bar.h.baz", and that "readdir" and "glob" cannot and
       do not attempt to emulate the reverse mapping.  Other
       "."'s in filenames are translated to "/".

       As implied above, the environment accessed through %ENV is
       global, and the convention is that program specific
       environment variables are of the form "Program$Name".
       Each filesystem maintains a current directory, and the
       current filesystem's current directory is the global
       current directory.  Consequently, sociable programs don't
       change the current directory but rely on full pathnames,
       and programs (and Makefiles) cannot assume that they can
       spawn a child process which can change the current
       directory without affecting its parent (and everyone else
       for that matter).

       Because native operating system filehandles are global and
       are currently allocated down from 255, with 0 being a
       reserved value, the Unix emulation library emulates Unix
       filehandles.  Consequently, you can't rely on passing
       "STDIN", "STDOUT", or "STDERR" to your children.

       The desire of users to express filenames of the form
       "<Foo$Dir>.Bar" on the command line unquoted causes
       problems, too: "``" command output capture has to perform
       a guessing game.  It assumes that a string
       "<[^<>]+\$[^<>]>" is a reference to an environment
       variable, whereas anything else involving "<" or ">" is
       redirection, and generally manages to be 99% right.  Of
       course, the problem remains that scripts cannot rely on
       any Unix tools being available, or that any tools found
       have Unix-like command line arguments.




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       Extensions and XS are, in theory, buildable by anyone
       using free tools.  In practice, many don't, as users of
       the Acorn platform are used to binary distributions.
       MakeMaker does run, but no available make currently copes
       with MakeMaker's makefiles; even if and when this should
       be fixed, the lack of a Unix-like shell will cause
       problems with makefile rules, especially lines of the form
       "cd sdbm && make all", and anything using quoting.

       "RISC OS" is the proper name for the operating system, but
       the value in $^O is "riscos" (because we don't like
       shouting).

   Other perls
       Perl has been ported to many platforms that do not fit
       into any of the categories listed above.  Some, such as
       AmigaOS, Atari MiNT, BeOS, HP MPE/iX, QNX, Plan 9, and
       VOS, have been well-integrated into the standard Perl
       source code kit.  You may need to see the ports/ directory
       on CPAN for information, and possibly binaries, for the
       likes of: aos, Atari ST, lynxos, riscos, Novell Netware,
       Tandem Guardian, etc.  (Yes, we know that some of these
       OSes may fall under the Unix category, but we are not a
       standards body.)

       Some approximate operating system names and their $^O
       values in the "OTHER" category include:

           OS            $^O        $Config{'archname'}
           ------------------------------------------
           Amiga DOS     amigaos    m68k-amigos
           BeOS          beos
           MPE/iX        mpeix      PA-RISC1.1

       See also:

       o   Amiga, README.amiga (installed as perlamiga).

       o   Atari, README.mint and Guido Flohr's web page
           http://stud.uni-sb.de/~gufl0000/

       o   Be OS, README.beos

       o   HP 300 MPE/iX, README.mpeix and Mark Bixby's web page
           http://www.bixby.org/mark/perlix.html

       o   A free perl5-based PERL.NLM for Novell Netware is
           available in precompiled binary and source code form
           from http://www.novell.com/ as well as from CPAN.

       o   Plan 9, README.plan9

FUNCTION IMPLEMENTATIONS
       Listed below are functions that are either completely



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       unimplemented or else have been implemented differently on
       various platforms.  Following each description will be, in
       parentheses, a list of platforms that the description
       applies to.

       The list may well be incomplete, or even wrong in some
       places.  When in doubt, consult the platform-specific
       README files in the Perl source distribution, and any
       other documentation resources accompanying a given port.

       Be aware, moreover, that even among Unix-ish systems there
       are variations.

       For many functions, you can also query %Config, exported
       by default from the Config module.  For example, to check
       whether the platform has the "lstat" call, check
       $Config{d_lstat}.  See Config for a full description of
       available variables.

   Alphabetical Listing of Perl Functions
       -X      "-r", "-w", and "-x" have a limited meaning only;
               directories and applications are executable, and
               there are no uid/gid considerations.  "-o" is not
               supported.  (Mac OS)

               "-w" only inspects the read-only file attribute
               (FILE_ATTRIBUTE_READONLY), which determines
               whether the directory can be deleted, not whether
               it can be written to. Directories always have read
               and write access unless denied by discretionary
               access control lists (DACLs).  (Win32)

               "-r", "-w", "-x", and "-o" tell whether the file
               is accessible, which may not reflect UIC-based
               file protections.  (VMS)

               "-s" returns the size of the data fork, not the
               total size of data fork plus resource fork.
               (Mac OS).

               "-s" by name on an open file will return the space
               reserved on disk, rather than the current extent.
               "-s" on an open filehandle returns the current
               size.  (RISC OS)

               "-R", "-W", "-X", "-O" are indistinguishable from
               "-r", "-w", "-x", "-o". (Mac OS, Win32, VMS,
               RISC OS)

               "-b", "-c", "-k", "-g", "-p", "-u", "-A" are not
               implemented.  (Mac OS)

               "-g", "-k", "-l", "-p", "-u", "-A" are not
               particularly meaningful.  (Win32, VMS, RISC OS)



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               "-d" is true if passed a device spec without an
               explicit directory.  (VMS)

               "-T" and "-B" are implemented, but might
               misclassify Mac text files with foreign
               characters; this is the case will all platforms,
               but may affect Mac OS often.  (Mac OS)

               "-x" (or "-X") determine if a file ends in one of
               the executable suffixes.  "-S" is meaningless.
               (Win32)

               "-x" (or "-X") determine if a file has an
               executable file type.  (RISC OS)

       atan2   Due to issues with various CPUs, math libraries,
               compilers, and standards, results for "atan2()"
               may vary depending on any combination of the
               above.  Perl attempts to conform to the Open
               Group/IEEE standards for the results returned from
               "atan2()", but cannot force the issue if the
               system Perl is run on does not allow it.  (Tru64,
               HP-UX 10.20)

               The current version of the standards for "atan2()"
               is available at
               <http://www.opengroup.org/onlinepubs/009695399/functions/atan2.html>.

       binmode Meaningless.  (Mac OS, RISC OS)

               Reopens file and restores pointer; if function
               fails, underlying filehandle may be closed, or
               pointer may be in a different position.  (VMS)

               The value returned by "tell" may be affected after
               the call, and the filehandle may be flushed.
               (Win32)

       chmod   Only limited meaning.  Disabling/enabling write
               permission is mapped to locking/unlocking the
               file. (Mac OS)

               Only good for changing "owner" read-write access,
               "group", and "other" bits are meaningless. (Win32)

               Only good for changing "owner" and "other" read-
               write access. (RISC OS)

               Access permissions are mapped onto VOS access-
               control list changes. (VOS)

               The actual permissions set depend on the value of
               the "CYGWIN" in the SYSTEM environment settings.
               (Cygwin)



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       chown   Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

               Does nothing, but won't fail. (Win32)

               A little funky, because VOS's notion of ownership
               is a little funky (VOS).

       chroot  Not implemented. (Mac OS, Win32, VMS, Plan 9,
               RISC OS, VOS, VM/ESA)

       crypt   May not be available if library or source was not
               provided when building perl. (Win32)

       dbmclose
               Not implemented. (VMS, Plan 9, VOS)

       dbmopen Not implemented. (VMS, Plan 9, VOS)

       dump    Not useful. (Mac OS, RISC OS)

               Not supported. (Cygwin, Win32)

               Invokes VMS debugger. (VMS)

       exec    Not implemented. (Mac OS)

               Implemented via Spawn. (VM/ESA)

               Does not automatically flush output handles on
               some platforms.  (SunOS, Solaris, HP-UX)

       exit    Emulates UNIX exit() (which considers "exit 1" to
               indicate an error) by mapping the 1 to SS$_ABORT
               (44).  This behavior may be overridden with the
               pragma "use vmsish 'exit'".  As with the CRTL's
               exit() function, "exit 0" is also mapped to an
               exit status of SS$_NORMAL (1); this mapping cannot
               be overridden.  Any other argument to exit() is
               used directly as Perl's exit status.  On VMS,
               unless the future POSIX_EXIT mode is enabled, the
               exit code should always be a valid VMS exit code
               and not a generic number.  When the POSIX_EXIT
               mode is enabled, a generic number will be encoded
               in a method compatible with the C library
               _POSIX_EXIT macro so that it can be decoded by
               other programs, particularly ones written in C,
               like the GNV package.  (VMS)

       fcntl   Not implemented. (Win32) Some functions available
               based on the version of VMS. (VMS)

       flock   Not implemented (Mac OS, VMS, RISC OS, VOS).

               Available only on Windows NT (not on Windows 95).



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               (Win32)

       fork    Not implemented. (Mac OS, AmigaOS, RISC OS,
               VM/ESA, VMS)

               Emulated using multiple interpreters.  See
               perlfork.  (Win32)

               Does not automatically flush output handles on
               some platforms.  (SunOS, Solaris, HP-UX)

       getlogin
               Not implemented. (Mac OS, RISC OS)

       getpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getppid Not implemented. (Mac OS, Win32, RISC OS)

       getpriority
               Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS, VM/ESA)

       getpwnam
               Not implemented. (Mac OS, Win32)

               Not useful. (RISC OS)

       getgrnam
               Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getnetbyname
               Not implemented. (Mac OS, Win32, Plan 9)

       getpwuid
               Not implemented. (Mac OS, Win32)

               Not useful. (RISC OS)

       getgrgid
               Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getnetbyaddr
               Not implemented. (Mac OS, Win32, Plan 9)

       getprotobynumber
               Not implemented. (Mac OS)

       getservbyport
               Not implemented. (Mac OS)

       getpwent
               Not implemented. (Mac OS, Win32, VM/ESA)





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       getgrent
               Not implemented. (Mac OS, Win32, VMS, VM/ESA)

       gethostbyname
               "gethostbyname('localhost')" does not work
               everywhere: you may have to use
               "gethostbyname('127.0.0.1')". (Mac OS, Irix 5)

       gethostent
               Not implemented. (Mac OS, Win32)

       getnetent
               Not implemented. (Mac OS, Win32, Plan 9)

       getprotoent
               Not implemented. (Mac OS, Win32, Plan 9)

       getservent
               Not implemented. (Win32, Plan 9)

       sethostent
               Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setnetent
               Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setprotoent
               Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setservent
               Not implemented. (Plan 9, Win32, RISC OS)

       endpwent
               Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)

       endgrent
               Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA,
               VMS, Win32)

       endhostent
               Not implemented. (Mac OS, Win32)

       endnetent
               Not implemented. (Mac OS, Win32, Plan 9)

       endprotoent
               Not implemented. (Mac OS, Win32, Plan 9)

       endservent
               Not implemented. (Plan 9, Win32)

       getsockopt SOCKET,LEVEL,OPTNAME
               Not implemented. (Plan 9)




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       glob    This operator is implemented via the File::Glob
               extension on most platforms.  See File::Glob for
               portability information.

       gmtime  Same portability caveats as localtime.

       ioctl FILEHANDLE,FUNCTION,SCALAR
               Not implemented. (VMS)

               Available only for socket handles, and it does
               what the ioctlsocket() call in the Winsock API
               does. (Win32)

               Available only for socket handles. (RISC OS)

       kill    "kill(0, LIST)" is implemented for the sake of
               taint checking; use with other signals is
               unimplemented. (Mac OS)

               Not implemented, hence not useful for taint
               checking. (RISC OS)

               "kill()" doesn't have the semantics of "raise()",
               i.e. it doesn't send a signal to the identified
               process like it does on Unix platforms.  Instead
               "kill($sig, $pid)" terminates the process
               identified by $pid, and makes it exit immediately
               with exit status $sig.  As in Unix, if $sig is 0
               and the specified process exists, it returns true
               without actually terminating it. (Win32)

               "kill(-9, $pid)" will terminate the process
               specified by $pid and recursively all child
               processes owned by it.  This is different from the
               Unix semantics, where the signal will be delivered
               to all processes in the same process group as the
               process specified by $pid. (Win32)

               Is not supported for process identification number
               of 0 or negative numbers. (VMS)

       link    Not implemented. (Mac OS, MPE/iX, RISC OS)

               Link count not updated because hard links are not
               quite that hard (They are sort of half-way between
               hard and soft links). (AmigaOS)

               Hard links are implemented on Win32 under NTFS
               only. They are natively supported on Windows 2000
               and later.  On Windows NT they are implemented
               using the Windows POSIX subsystem support and the
               Perl process will need Administrator or Backup
               Operator privileges to create hard links.




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               Available on 64 bit OpenVMS 8.2 and later.  (VMS)

       localtime
               Because Perl currently relies on the native
               standard C localtime() function, it is only safe
               to use times between 0 and (2**31)-1.  Times
               outside this range may result in unexpected
               behavior depending on your operating system's
               implementation of localtime().

       lstat   Not implemented. (RISC OS)

               Return values (especially for device and inode)
               may be bogus. (Win32)

       msgctl
       msgget
       msgsnd
       msgrcv  Not implemented. (Mac OS, Win32, VMS, Plan 9,
               RISC OS, VOS)

       open    The "|" variants are supported only if ToolServer
               is installed.  (Mac OS)

               open to "|-" and "-|" are unsupported. (Mac OS,
               Win32, RISC OS)

               Opening a process does not automatically flush
               output handles on some platforms.  (SunOS,
               Solaris, HP-UX)

       pipe    Very limited functionality. (MiNT)

       readlink
               Not implemented. (Win32, VMS, RISC OS)

       rename  Can't move directories between directories on
               different logical volumes. (Win32)

       select  Only implemented on sockets. (Win32, VMS)

               Only reliable on sockets. (RISC OS)

               Note that the "select FILEHANDLE" form is
               generally portable.

       semctl
       semget
       semop   Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS)

       setgrent
               Not implemented. (Mac OS, MPE/iX, VMS, Win32,
               RISC OS, VOS)



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       setpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS)

       setpriority
               Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS)

       setpwent
               Not implemented. (Mac OS, MPE/iX, Win32, RISC OS,
               VOS)

       setsockopt
               Not implemented. (Plan 9)

       shmctl
       shmget
       shmread
       shmwrite
               Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS)

       sockatmark
               A relatively recent addition to socket functions,
               may not be implemented even in UNIX platforms.

       socketpair
               Not implemented. (RISC OS, VOS, VM/ESA)

               Available on 64 bit OpenVMS 8.2 and later.  (VMS)

       stat    Platforms that do not have rdev, blksize, or
               blocks will return these as '', so numeric
               comparison or manipulation of these fields may
               cause 'not numeric' warnings.

               mtime and atime are the same thing, and ctime is
               creation time instead of inode change time.
               (Mac OS).

               ctime not supported on UFS (Mac OS X).

               ctime is creation time instead of inode change
               time  (Win32).

               device and inode are not meaningful.  (Win32)

               device and inode are not necessarily reliable.
               (VMS)

               mtime, atime and ctime all return the last
               modification time.  Device and inode are not
               necessarily reliable.  (RISC OS)

               dev, rdev, blksize, and blocks are not available.



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               inode is not meaningful and will differ between
               stat calls on the same file.  (os2)

               some versions of cygwin when doing a stat("foo")
               and if not finding it may then attempt to
               stat("foo.exe") (Cygwin)

               On Win32 stat() needs to open the file to
               determine the link count and update attributes
               that may have been changed through hard links.
               Setting ${^WIN32_SLOPPY_STAT} to a true value
               speeds up stat() by not performing this operation.
               (Win32)

       symlink Not implemented. (Win32, RISC OS)

               Implemented on 64 bit VMS 8.3.  VMS requires the
               symbolic link to be in Unix syntax if it is
               intended to resolve to a valid path.

       syscall Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS, VM/ESA)

       sysopen The traditional "0", "1", and "2" MODEs are
               implemented with different numeric values on some
               systems.  The flags exported by "Fcntl" (O_RDONLY,
               O_WRONLY, O_RDWR) should work everywhere though.
               (Mac OS, OS/390, VM/ESA)

       system  Only implemented if ToolServer is installed.
               (Mac OS)

               As an optimization, may not call the command shell
               specified in $ENV{PERL5SHELL}.  "system(1, @args)"
               spawns an external process and immediately returns
               its process designator, without waiting for it to
               terminate.  Return value may be used subsequently
               in "wait" or "waitpid".  Failure to spawn() a
               subprocess is indicated by setting $? to "255 <<
               8".  $? is set in a way compatible with Unix (i.e.
               the exitstatus of the subprocess is obtained by
               "$? >> 8", as described in the documentation).
               (Win32)

               There is no shell to process metacharacters, and
               the native standard is to pass a command line
               terminated by "\n" "\r" or "\0" to the spawned
               program.  Redirection such as "> foo" is performed
               (if at all) by the run time library of the spawned
               program.  "system" list will call the Unix
               emulation library's "exec" emulation, which
               attempts to provide emulation of the stdin,
               stdout, stderr in force in the parent, providing
               the child program uses a compatible version of the



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               emulation library.  scalar will call the native
               command line direct and no such emulation of a
               child Unix program will exists.  Mileage will
               vary.  (RISC OS)

               Far from being POSIX compliant.  Because there may
               be no underlying /bin/sh tries to work around the
               problem by forking and execing the first token in
               its argument string.  Handles basic redirection
               ("<" or ">") on its own behalf. (MiNT)

               Does not automatically flush output handles on
               some platforms.  (SunOS, Solaris, HP-UX)

               The return value is POSIX-like (shifted up by 8
               bits), which only allows room for a made-up value
               derived from the severity bits of the native
               32-bit condition code (unless overridden by "use
               vmsish 'status'").  If the native condition code
               is one that has a POSIX value encoded, the POSIX
               value will be decoded to extract the expected exit
               value.  For more details see "$?" in perlvms.
               (VMS)

       times   Only the first entry returned is nonzero. (Mac OS)

               "cumulative" times will be bogus.  On anything
               other than Windows NT or Windows 2000, "system"
               time will be bogus, and "user" time is actually
               the time returned by the clock() function in the C
               runtime library. (Win32)

               Not useful. (RISC OS)

       truncate
               Not implemented. (Older versions of VMS)

               Truncation to same-or-shorter lengths only. (VOS)

               If a FILEHANDLE is supplied, it must be writable
               and opened in append mode (i.e., use "open(FH,
               '>>filename')" or
               "sysopen(FH,...,O_APPEND|O_RDWR)".  If a filename
               is supplied, it should not be held open elsewhere.
               (Win32)

       umask   Returns undef where unavailable, as of version
               5.005.

               "umask" works but the correct permissions are set
               only when the file is finally closed. (AmigaOS)

       utime   Only the modification time is updated. (BeOS,
               Mac OS, VMS, RISC OS)



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               May not behave as expected.  Behavior depends on
               the C runtime library's implementation of utime(),
               and the filesystem being used.  The FAT filesystem
               typically does not support an "access time" field,
               and it may limit timestamps to a granularity of
               two seconds. (Win32)

       wait
       waitpid Not implemented. (Mac OS)

               Can only be applied to process handles returned
               for processes spawned using "system(1, ...)" or
               pseudo processes created with "fork()". (Win32)

               Not useful. (RISC OS)

Supported Platforms
       As of July 2002 (the Perl release 5.8.0), the following
       platforms are able to build Perl from the standard source
       code distribution available at
       http://www.cpan.org/src/index.html

               AIX
               BeOS
               BSD/OS          (BSDi)
               Cygwin
               DG/UX
               DOS DJGPP       1)
               DYNIX/ptx
               EPOC R5
               FreeBSD
               HI-UXMPP        (Hitachi) (5.8.0 worked but we didn't know it)
               HP-UX
               IRIX
               Linux
               Mac OS Classic
               Mac OS X        (Darwin)
               MPE/iX
               NetBSD
               NetWare
               NonStop-UX
               ReliantUNIX     (formerly SINIX)
               OpenBSD
               OpenVMS         (formerly VMS)
               Open UNIX       (Unixware) (since Perl 5.8.1/5.9.0)
               OS/2
               OS/400          (using the PASE) (since Perl 5.8.1/5.9.0)
               PowerUX
               POSIX-BC        (formerly BS2000)
               QNX
               Solaris
               SunOS 4
               SUPER-UX        (NEC)
               Tru64 UNIX      (formerly DEC OSF/1, Digital UNIX)



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               UNICOS
               UNICOS/mk
               UTS
               VOS
               Win95/98/ME/2K/XP 2)
               WinCE
               z/OS            (formerly OS/390)
               VM/ESA

               1) in DOS mode either the DOS or OS/2 ports can be used
               2) compilers: Borland, MinGW (GCC), VC6

       The following platforms worked with the previous releases
       (5.6 and 5.7), but we did not manage either to fix or to
       test these in time for the 5.8.0 release.  There is a very
       good chance that many of these will work fine with the
       5.8.0.

               BSD/OS
               DomainOS
               Hurd
               LynxOS
               MachTen
               PowerMAX
               SCO SV
               SVR4
               Unixware
               Windows 3.1

       Known to be broken for 5.8.0 (but 5.6.1 and 5.7.2 can be
       used):

               AmigaOS

       The following platforms have been known to build Perl from
       source in the past (5.005_03 and earlier), but we haven't
       been able to verify their status for the current release,
       either because the hardware/software platforms are rare or
       because we don't have an active champion on these
       platforms--or both.  They used to work, though, so go
       ahead and try compiling them, and let perlbug@perl.org of
       any trouble.

               3b1
               A/UX
               ConvexOS
               CX/UX
               DC/OSx
               DDE SMES
               DOS EMX
               Dynix
               EP/IX
               ESIX
               FPS



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               GENIX
               Greenhills
               ISC
               MachTen 68k
               MiNT
               MPC
               NEWS-OS
               NextSTEP
               OpenSTEP
               Opus
               Plan 9
               RISC/os
               SCO ODT/OSR
               Stellar
               SVR2
               TI1500
               TitanOS
               Ultrix
               Unisys Dynix

       The following platforms have their own source code
       distributions and binaries available via
       http://www.cpan.org/ports/

                                       Perl release

               OS/400 (ILE)            5.005_02
               Tandem Guardian         5.004

       The following platforms have only binaries available via
       http://www.cpan.org/ports/index.html :

                                       Perl release

               Acorn RISCOS            5.005_02
               AOS                     5.002
               LynxOS                  5.004_02

       Although we do suggest that you always build your own Perl
       from the source code, both for maximal configurability and
       for security, in case you are in a hurry you can check
       http://www.cpan.org/ports/index.html for binary
       distributions.

SEE ALSO
       perlaix, perlamiga, perlapollo, perlbeos, perlbs2000,
       perlce, perlcygwin, perldgux, perldos, perlepoc,
       perlebcdic, perlfreebsd, perlhurd, perlhpux, perlirix,
       perlmachten, perlmacos, perlmacosx, perlmint, perlmpeix,
       perlnetware, perlos2, perlos390, perlos400, perlplan9,
       perlqnx, perlsolaris, perltru64, perlunicode, perlvmesa,
       perlvms, perlvos, perlwin32, and Win32.





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AUTHORS / CONTRIBUTORS
       Abigail <abigail@foad.org>, Charles Bailey
       <bailey@newman.upenn.edu>, Graham Barr <gbarr@pobox.com>,
       Tom Christiansen <tchrist@perl.com>, Nicholas Clark
       <nick@ccl4.org>, Thomas Dorner <Thomas.Dorner@start.de>,
       Andy Dougherty <doughera@lafayette.edu>, Dominic Dunlop
       <domo@computer.org>, Neale Ferguson
       <neale@vma.tabnsw.com.au>, David J. Fiander
       <davidf@mks.com>, Paul Green <Paul.Green@stratus.com>,
       M.J.T. Guy <mjtg@cam.ac.uk>, Jarkko Hietaniemi
       <jhi@iki.fi>, Luther Huffman <lutherh@stratcom.com>, Nick
       Ing-Simmons <nick@ing-simmons.net>, Andreas J. Koenig
       <a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>,
       Andrew M. Langmead <aml@world.std.com>, Larry Moore
       <ljmoore@freespace.net>, Paul Moore
       <Paul.Moore@uk.origin-it.com>, Chris Nandor
       <pudge@pobox.com>, Matthias Neeracher <neeracher@mac.com>,
       Philip Newton <pne@cpan.org>, Gary Ng
       <71564.1743@CompuServe.COM>, Tom Phoenix
       <rootbeer@teleport.com>, Andre Pirard
       <A.Pirard@ulg.ac.be>, Peter Prymmer <pvhp@forte.com>, Hugo
       van der Sanden <hv@crypt0.demon.co.uk>, Gurusamy Sarathy
       <gsar@activestate.com>, Paul J. Schinder
       <schinder@pobox.com>, Michael G Schwern
       <schwern@pobox.com>, Dan Sugalski <dan@sidhe.org>, Nathan
       Torkington <gnat@frii.com>.  John Malmberg
       <wb8tyw@qsl.net>






























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