MirOS Manual: perlport(1)


PERLPORT(1)     Perl Programmers Reference Guide      PERLPORT(1)

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 consti-
     tutes 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 impor-
     tant that the task that you are coding have the full gen-
     erality 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 dif-
         ferent 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 signi-
         ficant issues in writing portable code, and this docu-
         ment 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, Win-
     dows, Mac OS, VMS, etc.), consider writing platform-specific
     code.

     When the code will run on only two or three operating sys-
     tems, 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 IMPLEMENTA-
     TIONS").

     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 con-
     sidered 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 Mac-
     Perl, "\n" always means "\015".  In DOSish perls, "\n" usu-
     ally 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.

     A common cause of unportable programs is the misuse of
     chop() to trim newlines:

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         # XXX UNPORTABLE!
         while(<FILE>) {
             chop;
             @array = split(/:/);
             #...
         }

     You can get away with this on Unix and Mac OS (they have a
     single character end-of-line), but the same program will
     break under DOSish perls because you're only chop()ing half
     the end-of-line.  Instead, chomp() should be used to trim
     newlines.  The Dunce::Files module can help audit your code
     for misuses of chop().

     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().

     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 specif-
     ically, and the values of the logical "\n" and "\r" (car-
     riage 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>) {
             # ...
         }

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     Because both CRLF and LF end in LF, the input record separa-
     tor 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 func-
     tion that fetches a web page--should sometimes translate
     newlines before returning the data, if they've 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:

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         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 pro-
     grams when they attempt to transfer numbers in binary format
     from one CPU architecture to another, usually either "live"
     via network connection, or by storing the numbers to secon-
     dary 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 5.8.5, 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/;

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     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 plat-
     forms support the notion of a "path" to 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 lim-
     its 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 separa-
     tor.  The native pathname characters greater-than,
     less-than, number-sign, and percent-sign are always

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     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.

         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 hard-
     coded. Making them user-supplied or read from a configura-
     tion 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 distribu-
     tion, 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 sin-
     gle 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 con-
     tain the encrypted passwords, because the system is using

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     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 con-
     vention, 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 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) 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

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     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 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 filesys-
     tem 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 writ-
     ing, 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

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     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.

     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 pro-
     gram 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 expres-
     sion used below would then have to deal with a possible
     trailing version number in the VMS file name.

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     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:

       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 com-
     mand) 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.

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     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 sup-
     ported on most platforms (though many of them do not support
     any type of forking).  The problem with using them arises
     from what you invoke them on.  External tools are often
     named differently on different platforms, may not be avail-
     able 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 sys-
     tems, and even some Unix systems that may not have sendmail
     installed.  If a portable solution is needed, see the vari-
     ous 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()".

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     The rule of thumb for portable code is: Do it all in port-
     able 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 rea-
     sonable 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 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 con-
     trolled 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 abbrevia-
     tions (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 unambigu-
     ous format like the exact number of minutes offset from UTC,
     or the POSIX timezone format.

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     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.

         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

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     bit more portable, or at least more convenient and native-
     friendly for non-English users.  The system affects charac-
     ter 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 informa-
     tion.

     If you want to use non-ASCII bytes (outside the bytes
     0x00..0x7f) in the "source code" of your code, to be port-
     able 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 embed-
     ding 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 they are in some particular legacy encoding
     (ether single-byte or something more complicated), you can
     use the "encoding" pragma.  (If you want to write your code
     in UTF-8, you can use either the "utf8" pragma, or the
     "encoding" pragma.) The "bytes" and "utf8" pragmata are
     available since Perl 5.6.0, and the "encoding" pragma since
     Perl 5.8.0.

     System Resources

     If your code is destined for systems with severely con-
     strained (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 peo-
     ple.  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.

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     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 plat-
     forms).

     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 permis-
     sions check and the actual operation. Just try the opera-
     tion.)

     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.)

     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 differen-
     tiate platforms, as described in "PLATFORMS".

     Be careful in the tests you supply with your module or pro-
     grams. 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

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     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 develop-
     ers 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:

     +   Mailing list: cpan-testers@perl.org

     +   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.

     Unix

     Perl works on a bewildering variety of Unix and Unix-like
     platforms (see e.g. most of the files in the hints/ direc-
     tory 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:

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         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
         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 run-
     ning under systems like PC-DOS, MS-DOS, OS/2, and most Win-
     dows 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 be aware that
     each of these file specifications may have subtle differ-
     ences:

         $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

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     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 "open-
     dir".

     DOS also treats several filenames as special, such as AUX,
     PRN, NUL, CON, COM1, LPT1, LPT2, etc.  Unfortunately, some-
     times 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 vari-
     ous 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 port-
     able 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:

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

     +   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.

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

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

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

     +   The Cygwin environment for Win32; README.cygwin

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         (installed

         as perlcygwin), http://www.cygwin.com/

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

     +   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:

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         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 "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:

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

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

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

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

     VMS

     Perl on VMS is discussed in perlvms in the perl distribu-
     tion. 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:

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

     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>;".

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

     VMS's RMS filesystem is case-insensitive and does not
     preserve case. "readdir" returns lowercased filenames, but
     specifying a file for opening remains case-insensitive.
     Files without extensions have a trailing period on them, so
     doing a "readdir" with a file named A.;5 will return a.
     (though that file could be opened with "open(FH, 'A')").

     RMS had an eight level limit on directory depths from any
     rooted logical (allowing 16 levels overall) prior to VMS
     7.2.  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/".

     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.

     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

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     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 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";

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

     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:

     +   README.vms (installed as README_vms), perlvms

     +   vmsperl list, majordomo@perl.org

         (Put the words "subscribe vmsperl" in message body.)

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

     VOS

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

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

     or even a mixture of both as in:

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         C<< $ 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 pro-
     cessed.  Such files must be renamed before they can be pro-
     cessed by Perl.  Note that VOS limits file names to 32 or
     fewer characters.

     Perl on VOS can be built using two different compilers and
     two different versions of the POSIX runtime.  The recom-
     mended method for building full Perl is with the GNU C com-
     piler and the generally-available version of VOS POSIX sup-
     port.  See README.vos (installed as perlvos) for restric-
     tions that apply when Perl is built using the VOS Standard C
     compiler or the alpha version of VOS POSIX support.

     The value of $^O on VOS is "VOS".  To determine the archi-
     tecture 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;
         }

         if (grep(/860/, @INC)) {
             print "This box is a Stratus XA/R!\n";

         } elsif (grep(/7100/, @INC)) {
             print "This box is a Stratus HP 7100 or 8xxx!\n";

         } elsif (grep(/8000/, @INC)) {
             print "This box is a Stratus HP 8xxx!\n";

         } else {
             print "This box is a Stratus 68K!\n";
         }

     Also see:

     +   README.vos (installed as perlvos)

     +   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

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PERLPORT(1)     Perl Programmers Reference Guide      PERLPORT(1)

         letter with "subscribe Info-Stratus" in the message body
         to majordomo@list.stratagy.com.

     +   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 sys-
     tems).  On the mainframe perl currently works under the
     "Unix system services for OS/390" (formerly known as OpenEd-
     ition), 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 sim-
     ple 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

     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

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     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:

     +   perlos390, README.os390, perlbs2000, README.vmesa, per-
         lebcdic.

     +   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.

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

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     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 direc-
     tory 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 limita-
     tions.

     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$Path"
     until a name is made that points to an object on disk. Writ-
     ing to a new file "System:Modules" would be allowed only if
     "System$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 charac-
     ters, 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 "read-
     dir" 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 environ-
     ment variables are of the form "Program$Name".  Each
     filesystem maintains a current directory, and the current
     filesystem's current directory is the global current direc-
     tory.  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 prob-
     lems, too: `` command output capture has to perform a guess-
     ing 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 shout-
     ing).

     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 informa-
     tion, 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:

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

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

     +   Be OS, README.beos

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

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

     +   Plan 9, README.plan9

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FUNCTION IMPLEMENTATIONS

     Listed below are functions that are either completely unim-
     plemented or else have been implemented differently on vari-
     ous 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 docu-
     mentation 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)

             "-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 particu-
             larly meaningful. (Win32, VMS, RISC OS)

             "-d" is true if passed a device spec without an

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             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 Y,X
             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>.

     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 per-
             mission is mapped to locking/unlocking the file.
             (Mac OS)

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             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)

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

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

     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)

             Not implemented. (VOS)

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

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

     dump    Not useful. (Mac OS, RISC OS)

             Not implemented. (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. (VMS)

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     fcntl   Not implemented. (Win32, VMS)

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

             Available only on Windows NT (not on Windows 95).
             (Win32)

     fork    Not implemented. (Mac OS, AmigaOS, RISC OS, VOS,
             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, VOS)

     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)

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     getservbyport
             Not implemented. (Mac OS)

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

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

     gethostbyname
             "gethostbyname('localhost')" does not work every-
             where: you may have to use "gethost-
             byname('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

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

     endservent
             Not implemented. (Plan 9, Win32)

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

     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 check-
             ing. (RISC OS)

             "kill()" doesn't have the semantics of "raise()",
             i.e. it doesn't send a signal to the identified pro-
             cess 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)

     link    Not implemented. (Mac OS, MPE/iX, VMS, 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 (Windows NT and
             Windows 2000) under NTFS only.

     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

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             may result in unexpected behavior depending on your
             operating system's implementation of localtime().

     lstat   Not implemented. (VMS, 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 out-
             put 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 dif-
             ferent 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)

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

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

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

     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. (Win32, VMS, RISC OS, VOS, VM/ESA)

     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 modifica-
             tion time.  Device and inode are not necessarily
             reliable.  (RISC OS)

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

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

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

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

     system  In general, do not assume the UNIX/POSIX semantics
             that you can shift $? right by eight to get the exit
             value, or that "$? & 127" would give you the number
             of the signal that terminated the program, or that
             "$? & 128" would test true if the program was ter-
             minated by a coredump.  Instead, use the POSIX W*()
             interfaces: for example, use WIFEXITED($?) and WEX-
             ITVALUE($?) to test for a normal exit and the exit
             value, WIFSIGNALED($?) and WTERMSIG($?) for a signal
             exit and the signal.  Core dumping is not a portable
             concept, so there's no portable way to test for
             that.

             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 subpro-
             cess 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 emula-
             tion of the stdin, stdout, stderr in force in the
             parent, providing the child program uses a compati-
             ble version of the emulation library. scalar will
             call the native command line direct and no such emu-
             lation 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

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             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'"). 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 zero-length 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)

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

     wait

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     waitpid Not implemented. (Mac OS, VOS)

             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 September 2003 (the Perl release 5.8.1), the following
     platforms are able to build Perl from the standard source
     code distribution available at
     http://www.cpan.org/src/index.html

perl v5.8.8                2006-06-30                          41

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             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
             LynxOS
             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)
             SVR4
             Tru64 UNIX      (formerly DEC OSF/1, Digital UNIX)
             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 5.8.1 release.  There is a very
     good chance that many of these will work fine with the
     5.8.1.

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             DomainOS
             Hurd
             MachTen
             PowerMAX
             SCO SV
             Unixware
             Windows 3.1

     Known to be broken for 5.8.0 and 5.8.1 (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
             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

perl v5.8.8                2006-06-30                          43

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     The following platforms have their own source code distribu-
     tions 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 distribu-
     tions.

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, perlso-
     laris, perltru64, perlunicode, perlvmesa, perlvms, perlvos,
     perlwin32, and Win32.

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>,

perl v5.8.8                2006-06-30                          44

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     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>.

perl v5.8.8                2006-06-30                          45

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