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perlport



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 con­
       stitutes portable Perl code.  That way once you make a
       decision to write portably, you know where the lines are
       drawn, and you can stay within them.

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

       Looking at it another way, writing portable code is usu­
       ally about willfully limiting your available choices.
       Naturally, it takes discipline and sacrifice to do that.
       The product of portability and convenience may be a con­
       stant.  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 lan­
           guage to glue Unix tools together, or to prototype a
           Macintosh application, or to manage the Windows reg­
           istry.  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 cre­
           ate 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
       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 idiosyn­
       crasies of some of the ports, almost all of which are in a
       state of constant evolution.  Thus, this material should
       be considered a perpetual work in progress ("<IMG
       SRC="yellow_sign.gif" ALT="Under Construction">").


ISSUES

       Newlines

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

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

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

           # 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().
       (carriage return) are not reliable.

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

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

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

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

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

       Because both CRLF and LF end in LF, the input record sepa­
       rator 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 trans­
       late 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
               * 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 mate­
       rial 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, usu­
       ally either "live" via network connection, or by storing
       the numbers to secondary storage such as a disk file or
       tape.

       Conflicting storage orders make utter mess out of the num­
       bers.  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.

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

       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).  Keep­
       ing 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 hierarchi­
       cal fashion.  So, it is reasonably safe to assume that all
       platforms support the notion of a "path" to uniquely iden­
       tify a file on the system.  How that path is really writ­
       ten, though, differs considerably.

       Although similar, file path specifications differ between
       Unix, Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and proba­
       bly 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 idiosyn­
       cratic ways (such as having several root directories and
       various "unrooted" device files such NIL: and LPT:).

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

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

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

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

       VOS perl can emulate Unix filenames with "/" as path sepa­
       rator.  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
       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
       hardcoded.  Making them user-supplied or read from a con­
       figuration 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 separa­
       tor 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
       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 plat­
       forms 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.
       name.  Always use "<" explicitly to open a file for read­
       ing, 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 sepa­
       rating 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 lead­
       ing slashes "//" into one: some networking and clustering
       filesystems have special semantics for that.  Let the
       operating system to sort it out.

       The portable filename characters as defined by ANSI C are

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

       and the "-" shouldn't be the first character.  If you want
       to be hypercorrect, stay case-insensitive and within the
       8.3 naming convention (all the files and directories have
       to be unique within one directory if their names are low­
       ercased 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 usu­
       ally 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 own­
       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 say­
       ing "%ENV = ();", or, if you really have to, make it con­
       ditional 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", "read­
       dir", and "closedir" instead.

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

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

       Command names versus file pathnames

       Don't assume that the name used to invoke a command or
       program with "system" or "exec" can also be used to test
       for the existence of the file that holds the executable
       code for that command or program.  First, many systems
       have "internal" commands that are built-in to the shell or
       OS and while these commands can be invoked, there is no
       corresponding file.  Second, some operating systems (e.g.,
       Cygwin, DJGPP, OS/2, and VOS) have required suffixes for
       executable files; these suffixes are generally permitted
       on the command name but are not required.  Thus, a command
       like "perl" might exist in a file named "perl",
         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
       command) returns either a fully qualified hostname or a
       non-qualified hostname: it all depends on how the system
       had been configured.  Also remember things like DHCP and
       NAT-- the hostname you get back might not be very useful.

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

       results in a platform-dependent way.  Thus, you should
       seldom depend on them to produce consistent results. (Then
       again, if you're calling netstat -a, you probably don't
       expect it to run on both Unix and CP/M.)

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

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

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

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

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

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

       External Subroutines (XS)

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

       A different type of portability issue arises when writing
       XS code: availability of a C compiler on the end-user's
       system.  C brings with it its own portability issues, and
       NBDM_File and DB_File are available.

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

       Time and Date

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

       Don't assume that the epoch starts at 00:00:00, January 1,
       1970, because that is OS- and implementation-specific.  It
       is better to store a date in an unambiguous representa­
       tion.  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 rep­
       resentation (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".

       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 inter­
       laced 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 perllo­
       cale.  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 con­
       sider Unicode.  See perluniintro and perlunicode for more
       information.

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

       logged-in, may be unrecognizable on many platforms.  If
       you write programs that are security-conscious, it is usu­
       ally best to know what type of system you will be running
       under so that you can write code explicitly for that plat­
       form (or class of platforms).

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

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

       Don't assume the UNIX user and group semantics: espe­
       cially, 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-spe­
       cific 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 differ­
       entiate platforms, as described in "PLATFORMS".

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


CPAN Testers

       Modules uploaded to CPAN are tested by a variety of volun­
       teers on different platforms.  These CPAN testers are
       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 sys­
       tem, 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 deter­
       mined 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 test­
       ing the file system for the presence of uniquely named
       files such as a kernel or header file.  Here, for example,
       are a few of the more popular Unix flavors:

           uname         $^O        $Config{'archname'}
           --------------------------------------------
           AIX           aix        aix
           BSD/OS        bsdos      i386-bsdos
           Darwin        darwin     darwin
           dgux          dgux       AViiON-dgux
           DYNIX/ptx     dynixptx   i386-dynixptx
           FreeBSD       freebsd    freebsd-i386
           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

       iar with COMMAND.COM or CMD.EXE style shells should be
       aware that each of these file specifications may have sub­
       tle differences:

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

       System calls accept either "/" or "\" as the path separa­
       tor.  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-preserv­
       ing" HPFS (OS/2) and NTFS (NT) filesystems you may have to
       be careful about case returned with functions like "read­
       dir" or used with functions like "open" or "opendir".

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

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

       Newline ("\n") is translated as "\015\012" by STDIO when
       reading from and writing to files (see "Newlines").  "bin­
       mode(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 pro­
       grams should often assume nothing about their data.

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

            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 xx
            Windows XP    MSWin32    MSWin32-x86       2      ?
            Windows CE    MSWin32    ?                 3
            Cygwin        cygwin     ?

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

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

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

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

       Also see:

       ·   The djgpp environment for DOS, http://www.delo­
           rie.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 per­
           los2.

       ·   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

           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 popu­
       lated can be edited with something like the following,
       which brings up a dialog box asking for the command line
       arguments.

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

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

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

           perl myscript.plx some arguments

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

           $ 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
       maximum length for extensions is also 39 characters.  Ver­
       sion is a number from 1 to 32767.  Valid characters are
       "/[A-Z0-9$_-]/".

       VMS's RMS filesystem is case-insensitive and does not pre­
       serve 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
       "\012", "\015\012", "\000", "\040", or nothing depending
       on the file organiztion 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 sup­
       ported.

       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$TIME­
       ZONE_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 distri­
       bution (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:
       compiler and the generally-available version of VOS POSIX
       support.  See README.vos (installed as perlvos) for
       restrictions that apply when Perl is built using the VOS
       Standard C compiler or the alpha version of VOS POSIX sup­
       port.

       The value of $^O on VOS is "VOS".  To determine the archi­
       tecture that you are running on without resorting to load­
       ing 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 news­
           group, or subscribe to the general Stratus mailing
           list.  Send a letter with "subscribe Info-Stratus" in
           the message body to majordomo@list.stratagy.com.

       ·   VOS Perl on the web at http://ftp.stra­
           tus.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
       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-fid­
       dling 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 cor­
       rectly 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):

       ·   *

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

       ·   The perl-mvs@perl.org list is for discussion of port­
           ing 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 emu­
       lation 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 cur­
       rently has a name length limit of 10 characters, with up
       to 77 items in a directory, but other filesystems may not
       impose such limitations.

       Native filenames are of the form

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

       where

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

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

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

       Because "." was in use as a directory separator and file­
       names could not be assumed to be unique after 10 charac­
       ters, Acorn implemented the C compiler to strip the trail­
       ing ".c" ".h" ".s" and ".o" suffix from filenames speci­
       fied in source code and store the respective files in sub­
       directories 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 trans­
       parent, 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 trans­
       lated to "/".

       As implied above, the environment accessed through %ENV is
       global, and the convention is that program specific envi­
       ronment 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 pro­
       grams (and Makefiles) cannot assume that they can spawn a
       child process which can change the current directory with­
       out affecting its parent (and everyone else for that mat­
       ter).

       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
       guessing game.  It assumes that a string "<[^<>]+\$[^<>]>"
       is a reference to an environment variable, whereas any­
       thing else involving "<" or ">" is redirection, and gener­
       ally 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

       Other perls

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

       Some approximate operating system names and their $^O val­
       ues 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
           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.  Following each description will be, in
       parentheses, a list of platforms that the description
       applies to.

       The list may well be incomplete, or even wrong in some
       places.  When in doubt, consult the platform-specific
       README files in the Perl source distribution, and any
       other documentation resources accompanying a given port.
       -X EXPR
       -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 partic­
               ularly meaningful.  (Win32, VMS, RISC OS)

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

               "-T" and "-B" are implemented, but might misclas­
               sify 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 exe­
               cutable file type.  (RISC OS)

       alarm SECONDS
       alarm   Not implemented. (Win32)

       binmode FILEHANDLE
               Meaningless.  (Mac OS, RISC OS)

               Reopens file and restores pointer; if function
               fails, underlying filehandle may be closed, or
               Only good for changing "owner" and "other" read-
               write access. (RISC OS)

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

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

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

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

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

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

               Not implemented. (VOS)

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

       dbmopen HASH,DBNAME,MODE
               Not implemented. (VMS, Plan 9, VOS)

       dump LABEL
               Not useful. (Mac OS, RISC OS)

               Not implemented. (Win32)

               Invokes VMS debugger. (VMS)

       exec LIST
               Not implemented. (Mac OS)

               Implemented via Spawn. (VM/ESA)

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

       exit EXPR
       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

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

               Emulated using multiple interpreters.  See perl­
               fork.  (Win32)

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

       getlogin
               Not implemented. (Mac OS, RISC OS)

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

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

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

       getpwnam NAME
               Not implemented. (Mac OS, Win32)

               Not useful. (RISC OS)

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

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

       getpwuid UID
               Not implemented. (Mac OS, Win32)

               Not useful. (RISC OS)

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

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

       getprotobynumber NUMBER
               Not implemented. (Mac OS)

       getservbyport PORT,PROTO
               Not implemented. (Mac OS)

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

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

       getservent
               Not implemented. (Win32, Plan 9)

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

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

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

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

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

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

       endhostent
               Not implemented. (Mac OS, Win32)

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

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

       endservent
               Not implemented. (Plan 9, Win32)

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

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

       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)
               "kill($sig, $pid)" terminates the process identi­
               fied 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 OLDFILE,NEWFILE
               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.

       lstat FILEHANDLE
       lstat EXPR
       lstat   Not implemented. (VMS, RISC OS)

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

       msgctl ID,CMD,ARG
       msgget KEY,FLAGS
       msgsnd ID,MSG,FLAGS
       msgrcv ID,VAR,SIZE,TYPE,FLAGS
               Not implemented. (Mac OS, Win32, VMS, Plan 9,
               RISC OS, VOS)

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

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

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

       pipe READHANDLE,WRITEHANDLE
               Very limited functionality. (MiNT)

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

       select RBITS,WBITS,EBITS,TIMEOUT
               Only implemented on sockets. (Win32, VMS)


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

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

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

       setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
               Not implemented. (Plan 9)

       shmctl ID,CMD,ARG
       shmget KEY,SIZE,FLAGS
       shmread ID,VAR,POS,SIZE
       shmwrite ID,STRING,POS,SIZE
               Not implemented. (Mac OS, Win32, VMS, RISC OS,
               VOS)

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

       socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
               Not implemented. (Win32, VMS, RISC OS, VOS,
               VM/ESA)

       stat FILEHANDLE
       stat EXPR
       stat    Platforms that do not have rdev, blksize, or
               blocks will return these as '', so numeric compar­
               ison 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 modifi­

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

       sysopen FILEHANDLE,FILENAME,MODE,PERMS
               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 LIST
               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 "$? & 128" would test true if the program
               was terminated by a coredump.  Instead, use the
               POSIX W*() interfaces: for example, use WIFEX­
               ITED($?) and WEXITVALUE($?) to test for a normal
               exit and the exit value, WIFSIGNALED($?) 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 sub­
               process 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 ter­
               minated by "\n" "\r" or "\0" to the spawned pro­
               gram.  Redirection such as "> foo" is performed
               (if at all) by the run time library of the spawned
               program.  "system" list will call the Unix emula­
               tion library's "exec" emulation, which attempts to
               provide emulation of the stdin, stdout, stderr in
               force in the parent, providing the child program
               uses a compatible version of the emulation
               library.  scalar will call the native command line
               direct and no such emulation of a child Unix pro­
               gram will exists.  Mileage will vary.  (RISC OS)
               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 FILEHANDLE,LENGTH
       truncate EXPR,LENGTH
               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 EXPR
       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 LIST
               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
               typically does not support an "access time" field,
               and it may limit timestamps to a granularity of
               two seconds. (Win32)

       wait
       waitpid PID,FLAGS
               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)


       v1.45, 20 December 1999
           Small changes from 5.005_63 distribution, more changes
           to EBCDIC info.

       v1.44, 19 July 1999
           A bunch of updates from Peter Prymmer for $^O values,
           endianness, File::Spec, VMS, BS2000, OS/400.

       v1.43, 24 May 1999
           Added a lot of cleaning up from Tom Christiansen.

       v1.42, 22 May 1999
           Added notes about tests, sprintf/printf, and epoch
           offsets.

       v1.41, 19 May 1999
           Lots more little changes to formatting and content.

           Added a bunch of $^O and related values for various
           platforms; fixed mail and web addresses, and added and
           changed miscellaneous notes.  (Peter Prymmer)

       v1.40, 11 April 1999
           Miscellaneous changes.

       v1.39, 11 February 1999
           Changes from Jarkko and EMX URL fixes Michael Schwern.
           Additional note about newlines added.

       v1.38, 31 December 1998
           More changes from Jarkko.

       v1.37, 19 December 1998
           More minor changes.  Merge two separate version 1.35
           documents.

       v1.36, 9 September 1998
           Updated for Stratus VOS.  Also known as version 1.35.

       v1.35, 13 August 1998
           Integrate more minor changes, plus addition of new
           sections under "ISSUES": "Numbers endianness and
           Width", "Character sets and character encoding",
           "Internationalisation".

       v1.33, 06 August 1998
           Integrate more minor changes.

       v1.32, 05 August 1998
           Integrate more minor changes.

               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
               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.

               DomainOS
               Hurd
               LynxOS
               MachTen

       either because the hardware/software platforms are rare or
       because we don't have an active champion on these plat­
       forms--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

       The following platforms have their own source code distri­
       butions 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

       netware, perlos2, perlos390, perlos400, perlplan9, per­
       lqnx, perlsolaris, perltru64, perlunicode, perlvmesa, per­
       lvms, perlvos, perlwin32, and Win32.


AUTHORS / CONTRIBUTORS

       Abigail <abigail@foad.org>, Charles Bailey <bailey@new­
       man.upenn.edu>, Graham Barr <gbarr@pobox.com>, Tom Chris­
       tiansen <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.tab­
       nsw.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-sim­
       mons.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@Com­
       puServe.COM>, Tom Phoenix <rootbeer@teleport.com>, Andre
       Pirard <A.Pirard@ulg.ac.be>, Peter Prymmer
       <pvhp@forte.com>, Hugo van der Sanden
       <hv@crypt0.demon.co.uk>, Gurusamy Sarathy <gsar@actives­
       tate.com>, Paul J. Schinder <schinder@pobox.com>, Michael
       G Schwern <schwern@pobox.com>, Dan Sugalski
       <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>.

perl v5.8.1                 2003-09-02                PERLPORT(1)
  




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