NAME
    perlport - Writing portable Perl

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

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

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

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

    Be aware of two important points:

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

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

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

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

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

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

ISSUES
  Newlines
    In most operating systems, lines in files are terminated by newlines.
    Just what is used as a newline may vary from OS to OS. Unix
    traditionally uses "\012", one type of DOSish I/O uses "\015\012",
    Mac OS uses "\015", and z/OS uses "\025".

    Perl uses "\n" to represent the "logical" newline, where what is logical
    may depend on the platform in use. In MacPerl, "\n" always means "\015".
    On EBCDIC platforms, "\n" could be "\025" or "\045". In DOSish perls,
    "\n" usually means "\012", but when accessing a file in "text" mode,
    perl uses the ":crlf" layer that translates it to (or from) "\015\012",
    depending on whether you're reading or writing. Unix does the same thing
    on ttys in canonical mode. "\015\012" is commonly referred to as CRLF.

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

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

    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 safely.

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

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

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

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

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

        while (<$socket>) {  # NOT ADVISABLE!
            # ...
        }

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

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

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

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

    Similarly, functions that return text data--such as a function that
    fetches a web page--should sometimes translate newlines before returning
    the data, if they've not yet been translated to the local newline
    representation. A single line of code will often suffice:

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

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

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

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

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

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

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

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

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

    Conflicting storage orders make an 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 5.10.0, you can also use the ">" and "<" modifiers to force
    big- or little-endian byte-order. This is useful if you want to store
    signed integers or 64-bit integers, for example.

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

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

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

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

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

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

  Files and Filesystems
    Most platforms these days structure files in a hierarchical fashion. So,
    it is reasonably safe to assume that all platforms support the notion of
    a "path" to 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 9 and earlier used ":" as a path separator instead of "/".

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

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

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

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

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

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

    The "File::Spec" modules provide methods to manipulate path
    specifications and return the results in native format for each
    platform. This is often unnecessary as Unix-style paths are understood
    by Perl on every supported platform, but if you need to produce native
    paths for a native utility that does not understand Unix syntax, or if
    you are operating on paths or path components in unknown (and thus
    possibly native) syntax, "File::Spec" is your friend. Here are two brief
    examples:

        use File::Spec::Functions;
        chdir(updir());        # go up one directory

        # Concatenate a path from its components
        my $file = catfile(updir(), 'temp', 'file.txt');
        # on Unix:    '../temp/file.txt'
        # on Win32:   '..\temp\file.txt'
        # on VMS:     '[-.temp]file.txt'

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

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

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

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

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

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

    Likewise, when using the "AutoSplit" module, try to keep your functions
    to 8.3 naming and case-insensitive conventions; or, at the least, make
    it so the resulting files have a unique (case-insensitively) first 8
    characters.

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

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

    Don't assume ">" won't be the first character of a filename. Always use
    the three-arg version of "open":

        open my $fh, '<', $existing_file) or die $!;

    Two-arg "open" is magic and can translate characters like ">", "<", and
    "|" in filenames, which is usually the wrong thing to do. "sysopen" and
    three-arg "open" don't have this problem.

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

    Don't assume that in pathnames you can collapse two leading slashes "//"
    into one: some networking and clustering filesystems have special
    semantics for that. Let the operating system 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 s 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 S T U V W X Y Z
     0 1 2 3 4 5 6 7 8 9
     . _ -

    and "-" 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 filesystem metainformation
    like file permissions or owners. Remember to "close" files when you are
    done with them. Don't "unlink" or "rename" an open file. Don't "tie" or
    "open" a file already tied or opened; "untie" or "close" it first.

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

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

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

        1 while unlink "file";

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

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

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

    On VMS by default, changes to the %ENV hash persist after perl exits.
    Subsequent invocations of perl in the same process can inadvertently
    inherit environment settings that were meant to be temporary.

    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
    string values. Users may switch their locales causing error messages to
    be translated into their languages. If you can trust a POSIXish
    environment, you can portably use the symbols defined by the "Errno"
    module, like "ENOENT". And don't trust on the values of $! at all except
    immediately after a failed system call.

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

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

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

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

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

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

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

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

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

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

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

    Don't assume a particular network device name.

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

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

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

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

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

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

    Commands that launch external processes are generally supported on most
    platforms (though many of them do not support any type of forking). The
    problem with using them arises from what you invoke them on. External
    tools are often named differently on different platforms, may not be
    available in the same location, might accept different arguments, can
    behave differently, and often present their results in a
    platform-dependent way. Thus, you should seldom depend on them to
    produce consistent results. (Then again, if you're calling "netstat -a",
    you probably don't expect it to run on both Unix and CP/M.)

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

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

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

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

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

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

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

    A different type of portability issue arises when writing XS code:
    availability of a C compiler on the end-user's 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 "NDBM_File" and "DB_File" are available.

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

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

    Don't assume that the epoch starts at 00:00:00, January 1, 1970, because
    that is OS- and implementation-specific. It is better to store a date in
    an unambiguous representation. The ISO 8601 standard defines YYYY-MM-DD
    as the date format, or YYYY-MM-DDTHH:MM:SS (that's a literal "T"
    separating the date from the time). Please do use the ISO 8601 instead
    of making us 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 "Time::Piece"
    (see "Date Parsing" in Time::Piece) or "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.

        use Time::Local qw(timegm);
        my $offset = timegm(0, 0, 0, 1, 0, 70);

    The value for $offset in Unix will be 0, but in Mac OS Classic 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.

  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)". However, starting
    in Perl v5.22, regular expression pattern bracketed character class
    ranges specified like "qr/[\N{U+HH}-\N{U+HH}]/" are portable, and
    starting in Perl v5.24, the same ranges are portable in "tr///". You can
    portably use symbolic character classes like "[:print:]".

    Do not assume that the alphabetic characters are encoded contiguously
    (in the numeric sense). There may be gaps. Special coding in Perl,
    however, guarantees that all subsets of "qr/[A-Z]/", "qr/[a-z]/", and
    "qr/[0-9]/" behave as expected. "tr///" behaves the same for these
    ranges. In patterns, any ranges specified with end points using the
    "\N{...}" notations ensures character set portability, but it is a bug
    in Perl v5.22 that this isn't true of "tr///", fixed in v5.24.

    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 ä comes before "b". Unicode::Collate can be used to
    sort this all out.

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

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

    By default Perl assumes your source code is written in an 8-bit ASCII
    superset. To embed Unicode characters in your strings and regexes, you
    can use the "\x{HH}" or (more portably) "\N{U+HH}" notations. You can
    also use the "utf8" pragma and write your code in UTF-8, which lets you
    use Unicode characters directly (not just in quoted constructs but also
    in identifiers).

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

        my @lines = <$very_large_file>;            # bad

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

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

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

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

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

    Don't assume the Unix user and group semantics: especially, don't expect
    $< and $> (or $( 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 differentiate platforms, as described in "PLATFORMS".

    Beware of the "else syndrome":

      if ($^O eq 'MSWin32') {
        # code that assumes Windows
      } else {
        # code that assumes Linux
      }

    The "else" branch should be used for the really ultimate fallback, not
    for code specific to some platform.

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

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

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

    Also see:

    *   Mailing list: cpan-testers-discuss@perl.org

    *   Testing results: <http://www.cpantesters.org/>

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

        uname         $^O        $Config{archname}
        --------------------------------------------
        AIX           aix        aix
        BSD/OS        bsdos      i386-bsdos
        Darwin        darwin     darwin
        DYNIX/ptx     dynixptx   i386-dynixptx
        FreeBSD       freebsd    freebsd-i386
        Haiku         haiku      BePC-haiku
        Linux         linux      arm-linux
        Linux         linux      armv5tel-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
        NeXT 3        next       next-fat
        NeXT 4        next       OPENSTEP-Mach
        openbsd       openbsd    i386-openbsd
        OSF1          dec_osf    alpha-dec_osf
        reliantunix-n svr4       RM400-svr4
        SCO_SV        sco_sv     i386-sco_sv
        SINIX-N       svr4       RM400-svr4
        sn4609        unicos     CRAY_C90-unicos
        sn6521        unicosmk   t3e-unicosmk
        sn9617        unicos     CRAY_J90-unicos
        SunOS         solaris    sun4-solaris
        SunOS         solaris    i86pc-solaris
        SunOS4        sunos      sun4-sunos

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

  DOS and Derivatives
    Perl has long been ported to Intel-style microcomputers running under
    systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
    bring yourself to mention (except for Windows CE, if you count that).
    Users familiar with *COMMAND.COM* or *CMD.EXE* style shells should be
    aware that each of these file specifications may have subtle
    differences:

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

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

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

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

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

    Newline ("\n") is translated as "\015\012" by the I/O system when
    reading from and writing to files (see "Newlines").
    "binmode($filehandle)" will keep "\n" translated as "\012" for that
    filehandle. "binmode" should always be used for code that deals with
    binary data. That's assuming you realize in advance that your data is in
    binary. General-purpose programs should often assume nothing about their
    data.

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

        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 Vista  MSWin32   MSWin32-x86        2     6 00
        Windows 7      MSWin32   MSWin32-x86        2     6 01
        Windows 7      MSWin32   MSWin32-x64        2     6 01
        Windows 2008   MSWin32   MSWin32-x86        2     6 01
        Windows 2008   MSWin32   MSWin32-x64        2     6 01
        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()|Win32/Win32::IsWinNT()",
    "Win32::IsWin95()|Win32/Win32::IsWin95()", and "Win32::GetOSName()"; try
    "perldoc Win32". The very portable "POSIX::uname()" will work too:

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

    Errors set by Winsock functions are now put directly into $^E, and the
    relevant "WSAE*" error codes are now exported from the Errno and POSIX
    modules for testing this against.

    The previous behavior of putting the errors (converted to POSIX-style
    "E*" error codes since Perl 5.20.0) into $! was buggy due to the
    non-equivalence of like-named Winsock and POSIX error constants, a
    relationship between which has unfortunately been established in one way
    or another since Perl 5.8.0.

    The new behavior provides a much more robust solution for checking
    Winsock errors in portable software without accidentally matching POSIX
    tests that were intended for other OSes and may have different meanings
    for Winsock.

    The old behavior is currently retained, warts and all, for backwards
    compatibility, but users are encouraged to change any code that tests $!
    against "E*" constants for Winsock errors to instead test $^E against
    "WSAE*" constants. After a suitable deprecation period, which started
    with Perl 5.24, the old behavior may be removed, leaving $! unchanged
    after Winsock function calls, to avoid any possible confusion over which
    error variable to check.

    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,
        <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 (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

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

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

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

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

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

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

        print "Hello from Perl!\n";

        __END__
        $ endif

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

    The VMS operating system has two filesystems, designated by their
    on-disk structure (ODS) level: ODS-2 and its successor ODS-5. The
    initial port of Perl to VMS pre-dates ODS-5, but all current testing and
    development assumes ODS-5 and its capabilities, including case
    preservation, extended characters in filespecs, and names up to 8192
    bytes long.

    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

    In general, the easiest path to portability is always to specify
    filenames in Unix format unless they will need to be processed by native
    commands or utilities. Because of this latter consideration, the
    File::Spec module by default returns native format specifications
    regardless of input format. This default may be reversed so that
    filenames are always reported in Unix format by specifying the
    "DECC$FILENAME_UNIX_REPORT" feature logical in the environment.

    The file type, or extension, is always present in a VMS-format file
    specification even if it's zero-length. This means that, by default,
    "readdir" will return a trailing dot on a file with no extension, so
    where you would see "a" on Unix you'll see "a." on VMS. However, the
    trailing dot may be suppressed by enabling the
    "DECC$READDIR_DROPDOTNOTYPE" feature in the environment (see the CRTL
    documentation on feature logical names).

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

    The value of $^O on OpenVMS is "VMS". To determine the architecture that
    you are running on refer to $Config{archname}.

    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, vmsperl-subscribe@perl.org

    *   vmsperl on the web, <http://www.sidhe.org/vmsperl/index.html>

    *   VMS Software Inc. web site, <http://www.vmssoftware.com>

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

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

    or even a mixture of both as in:

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

    Even though VOS allows the slash character to appear in object names,
    because the VOS port of Perl interprets it as a pathname delimiting
    character, VOS files, directories, or links whose names contain a slash
    character cannot be processed. Such files must be renamed before they
    can be processed by Perl.

    Older releases of VOS (prior to OpenVOS Release 17.0) limit file names
    to 32 or fewer characters, prohibit file names from starting with a "-"
    character, and prohibit file names from containing " " (space) or any
    character from the set "!#%&'()*;<=>?".

    Newer releases of VOS (OpenVOS Release 17.0 or later) support a feature
    known as extended names. On these releases, file names can contain up to
    255 characters, are prohibited from starting with a "-" character, and
    the set of prohibited characters is reduced to "#%*<>?". There are
    restrictions involving spaces and apostrophes: these characters must not
    begin or end a name, nor can they immediately precede or follow a
    period. Additionally, a space must not immediately precede another space
    or hyphen. Specifically, the following character combinations are
    prohibited: space-space, space-hyphen, period-space, space-period,
    period-apostrophe, apostrophe-period, leading or trailing space, and
    leading or trailing apostrophe. Although an extended file name is
    limited to 255 characters, a path name is still limited to 256
    characters.

    The value of $^O on VOS is "vos". To determine the architecture that you
    are running on refer to $Config{archname}.

    Also see:

    *   README.vos (installed as perlvos)

    *   The VOS mailing list.

        There is no specific mailing list for Perl on VOS. You can contact
        the Stratus Technologies Customer Assistance Center (CAC) for your
        region, or you can use the contact information located in the
        distribution files on the Stratus Anonymous FTP site.

    *   Stratus Technologies on the web at <http://www.stratus.com>

    *   VOS Open-Source Software on the web at
        <http://ftp.stratus.com/pub/vos/vos.html>

  EBCDIC Platforms
    v5.22 core Perl runs on z/OS (formerly OS/390). Theoretically it could
    run on the successors of OS/400 on AS/400 minicomputers as well as
    VM/ESA, and BS2000 for S/390 Mainframes. Such computers use EBCDIC
    character sets internally (usually Character Code Set ID 0037 for OS/400
    and either 1047 or POSIX-BC for S/390 systems).

    The rest of this section may need updating, but we don't know what it
    should say. Please email comments to perlbug@perl.org
    <mailto:perlbug@perl.org>.

    On the mainframe Perl currently works under the "Unix system services
    for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or the
    BS200 POSIX-BC system (BS2000 is supported in Perl 5.6 and greater). See
    perlos390 for details. Note that for OS/400 there is also a port of Perl
    5.8.1/5.10.0 or later to the PASE which is ASCII-based (as opposed to
    ILE which is EBCDIC-based), see perlos400.

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

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

        print "Hello from perl!\n";

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

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

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

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

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

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

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

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

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

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

        if ("\t" eq "\005")  { 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, perlos400, perlbs2000, perlebcdic.

    *   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.

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

    Native filenames are of the form

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

    where

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

    The default filename translation is roughly "tr|/.|./|", swapping dots
    and slahes.

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

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

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

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

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

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

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

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

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

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

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

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

        OS            $^O        $Config{archname}
        ------------------------------------------
        Amiga DOS     amigaos    m68k-amigos

    See also:

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

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

    *   Plan 9, README.plan9

FUNCTION IMPLEMENTATIONS
    Listed below are functions that are either completely unimplemented or
    else have been implemented differently on various platforms. Preceding
    each description will be, in parentheses, a list of platforms that the
    description applies to.

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

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

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

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

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

            (RISC 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.

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

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

            (VMS, RISC OS) "-p" is not particularly meaningful.

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

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

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

    alarm   (Win32) Emulated using timers that must be explicitly polled
            whenever Perl wants to dispatch "safe signals" and therefore
            cannot interrupt blocking system calls.

    atan2   (Tru64, HP-UX 10.20) 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.

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

    binmode (RISC OS) Meaningless.

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

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

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

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

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

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

            (Android) Setting the exec bit on some locations (generally
            /sdcard) will return true but not actually set the bit.

    chown   (Plan 9, RISC OS) Not implemented.

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

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

    chroot  (Win32, VMS, Plan 9, RISC OS, VOS) Not implemented.

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

            (Android) Not implemented.

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

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

    dump    (RISC OS) Not useful.

            (Cygwin, Win32) Not supported.

            (VMS) Invokes VMS debugger.

    exec    (Win32) "exec LIST" without the use of indirect object syntax
            ("exec PROGRAM LIST") may fall back to trying the shell if the
            first "spawn()" fails.

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

            (Symbian OS) Not supported.

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

            (Solaris) "exit" resets file pointers, which is a problem when
            called from a child process (created by "fork") in "BEGIN". A
            workaround is to use "POSIX::_exit".

                exit unless $Config{archname} =~ /\bsolaris\b/;
                require POSIX;
                POSIX::_exit(0);

    fcntl   (Win32) Not implemented.

            (VMS) Some functions available based on the version of VMS.

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

    fork    (AmigaOS, RISC OS, VMS) Not implemented.

            (Win32) Emulated using multiple interpreters. See perlfork.

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

    getlogin
            (RISC OS) Not implemented.

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

    getppid (Win32, RISC OS) Not implemented.

    getpriority
            (Win32, VMS, RISC OS, VOS) Not implemented.

    getpwnam
            (Win32) Not implemented.

            (RISC OS) Not useful.

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

    getnetbyname
            (Android, Win32, Plan 9) Not implemented.

    getpwuid
            (Win32) Not implemented.

            (RISC OS) Not useful.

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

    getnetbyaddr
            (Android, Win32, Plan 9) Not implemented.

    getprotobynumber
            (Android) Not implemented.

    getpwent
            (Android, Win32) Not implemented.

    getgrent
            (Android, Win32, VMS) Not implemented.

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

    gethostent
            (Win32) Not implemented.

    getnetent
            (Android, Win32, Plan 9) Not implemented.

    getprotoent
            (Android, Win32, Plan 9) Not implemented.

    getservent
            (Win32, Plan 9) Not implemented.

    seekdir (Android) Not implemented.

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

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

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

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

    endpwent
            (Win32) Not implemented.

            (Android) Either not implemented or a no-op.

    endgrent
            (Android, RISC OS, VMS, Win32) Not implemented.

    endhostent
            (Android, Win32) Not implemented.

    endnetent
            (Android, Win32, Plan 9) Not implemented.

    endprotoent
            (Android, Win32, Plan 9) Not implemented.

    endservent
            (Plan 9, Win32) Not implemented.

    getsockopt
            (Plan 9) Not implemented.

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

    gmtime  In theory, "gmtime" is reliable from -2**63 to 2**63-1. However,
            because work-arounds in the implementation use floating point
            numbers, it will become inaccurate as the time gets larger. This
            is a bug and will be fixed in the future.

            (VOS) Time values are 32-bit quantities.

    ioctl   (VMS) Not implemented.

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

            (RISC OS) Available only for socket handles.

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

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

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

            (VMS) A pid of -1 indicating all processes on the system is not
            currently supported.

    link    (RISC OS, VOS) Not implemented.

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

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

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

    localtime
            "localtime" has the same range as "gmtime", but because time
            zone rules change, its accuracy for historical and future times
            may degrade but usually by no more than an hour.

    lstat   (RISC OS) Not implemented.

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

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

    open    (Win32, RISC OS) Open modes "|-" and "-|" are unsupported.

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

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

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

    rewinddir
            (Win32) Will not cause "readdir" to re-read the directory
            stream. The entries already read before the "rewinddir" call
            will just be returned again from a cache buffer.

    select  (Win32, VMS) Only implemented on sockets.

            (RISC OS) Only reliable on sockets.

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

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

    setgrent
            (Android, VMS, Win32, RISC OS) Not implemented.

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

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

    setpwent
            (Android, Win32, RISC OS) Not implemented.

    setsockopt
            (Plan 9) Not implemented.

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

    sleep   (Win32) Emulated using synchronization functions such that it
            can be interrupted by "alarm", and limited to a maximum of
            4294967 seconds, approximately 49 days.

    socketpair
            (RISC OS) Not implemented.

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

    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.

            (Mac OS X) "ctime" not supported on UFS.

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

            (Win32) "dev" and "ino" are not meaningful.

            (VMS) "dev" and "ino" are not necessarily reliable.

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

            (OS/2) "dev", "rdev", "blksize", and "blocks" are not available.
            "ino" is not meaningful and will differ between stat calls on
            the same file.

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

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

    symlink (Win32, RISC OS) Not implemented.

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

    syscall (Win32, VMS, RISC OS, VOS) Not implemented.

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

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

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

            (Win32) "system LIST" without the use of indirect object syntax
            ("system PROGRAM LIST") may fall back to trying the shell if the
            first "spawn()" fails.

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

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

    telldir (Android) Not implemented.

    times   (Win32) "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.

            (RISC OS) Not useful.

    truncate
            (Older versions of VMS) Not implemented.

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

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

    umask   Returns "undef" where unavailable.

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

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

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

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

            (RISC OS) Not useful.

Supported Platforms
    The following platforms are known to build Perl 5.12 (as of April 2010,
    its release date) from the standard source code distribution available
    at <http://www.cpan.org/src>

    Linux (x86, ARM, IA64)
    HP-UX
    AIX
    Win32

        Windows 2000
        Windows XP
        Windows Server 2003
        Windows Vista
        Windows Server 2008
        Windows 7

    Cygwin
        Some tests are known to fail:

        *   ext/XS-APItest/t/call_checker.t - see
            <https://rt.perl.org/Ticket/Display.html?id=78502>

        *   dist/I18N-Collate/t/I18N-Collate.t

        *   ext/Win32CORE/t/win32core.t - may fail on recent cygwin
            installs.

    Solaris (x86, SPARC)
    OpenVMS

        Alpha (7.2 and later)
        I64 (8.2 and later)

    Symbian
    NetBSD
    FreeBSD
    Debian GNU/kFreeBSD
    Haiku
    Irix (6.5. What else?)
    OpenBSD
    Dragonfly BSD
    Midnight BSD
    QNX Neutrino RTOS (6.5.0)
    MirOS BSD
    Stratus OpenVOS (17.0 or later)
        Caveats:

        time_t issues that may or may not be fixed

    Symbian (Series 60 v3, 3.2 and 5 - what else?)
    Stratus VOS / OpenVOS
    AIX
    Android
    FreeMINT
        Perl now builds with FreeMiNT/Atari. It fails a few tests, that
        needs some investigation.

        The FreeMiNT port uses GNU dld for loadable module capabilities. So
        ensure you have that library installed when building perl.

EOL Platforms
  (Perl 5.20)
    The following platforms were supported by a previous version of Perl but
    have been officially removed from Perl's source code as of 5.20:

    AT&T 3b1

  (Perl 5.14)
    The following platforms were supported up to 5.10. They may still have
    worked in 5.12, but supporting code has been removed for 5.14:

    Windows 95
    Windows 98
    Windows ME
    Windows NT4

  (Perl 5.12)
    The following platforms were supported by a previous version of Perl but
    have been officially removed from Perl's source code as of 5.12:

    Atari MiNT
    Apollo Domain/OS
    Apple Mac OS 8/9
    Tenon Machten

Supported Platforms (Perl 5.8)
    As of July 2002 (the Perl release 5.8.0), the following platforms were
    able to build Perl from the standard source code distribution available
    at <http://www.cpan.org/src/>

            AIX
            BeOS
            BSD/OS          (BSDi)
            Cygwin
            DG/UX
            DOS DJGPP       1)
            DYNIX/ptx
            EPOC R5
            FreeBSD
            HI-UXMPP        (Hitachi) (5.8.0 worked but we didn't know it)
            HP-UX
            IRIX
            Linux
            Mac OS Classic
            Mac OS X        (Darwin)
            MPE/iX
            NetBSD
            NetWare
            NonStop-UX
            ReliantUNIX     (formerly SINIX)
            OpenBSD
            OpenVMS         (formerly VMS)
            Open UNIX       (Unixware) (since Perl 5.8.1/5.9.0)
            OS/2
            OS/400          (using the PASE) (since Perl 5.8.1/5.9.0)
            PowerUX
            POSIX-BC        (formerly BS2000)
            QNX
            Solaris
            SunOS 4
            SUPER-UX        (NEC)
            Tru64 UNIX      (formerly DEC OSF/1, Digital UNIX)
            UNICOS
            UNICOS/mk
            UTS
            VOS / OpenVOS
            Win95/98/ME/2K/XP 2)
            WinCE
            z/OS            (formerly OS/390)
            VM/ESA

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

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

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

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

            AmigaOS 3

    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
            MPC
            NEWS-OS
            NextSTEP
            OpenSTEP
            Opus
            Plan 9
            RISC/os
            SCO ODT/OSR
            Stellar
            SVR2
            TI1500
            TitanOS
            Ultrix
            Unisys Dynix

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

                                    Perl release

            OS/400 (ILE)            5.005_02
            Tandem Guardian         5.004

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

                                    Perl release

            Acorn RISCOS            5.005_02
            AOS                     5.002
            LynxOS                  5.004_02

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

SEE ALSO
    perlaix, perlamiga, perlbs2000, perlce, perlcygwin, perldos, perlebcdic,
    perlfreebsd, perlhurd, perlhpux, perlirix, perlmacos, perlmacosx,
    perlnetware, perlos2, perlos390, perlos400, perlplan9, perlqnx,
    perlsolaris, perltru64, perlunicode, perlvms, perlvos, perlwin32, and
    Win32.

AUTHORS / CONTRIBUTORS
    Abigail <abigail@abigail.be>, 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. König <a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>, Andrew
    M. Langmead <aml@world.std.com>, Lukas Mai <l.mai@web.de>, 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>, André Pirard <A.Pirard@ulg.ac.be>, Peter
    Prymmer <pvhp@forte.com>, Hugo van der Sanden <hv@crypt0.demon.co.uk>,
    Gurusamy Sarathy <gsar@activestate.com>, Paul J. Schinder
    <schinder@pobox.com>, Michael G Schwern <schwern@pobox.com>, Dan
    Sugalski <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>, John
    Malmberg <wb8tyw@qsl.net>