3 perlport - Writing portable Perl
8 Perl runs on a variety of operating systems. While most of them share
9 a lot in common, they also have their own very particular and unique
12 This document is meant to help you to find out what constitutes portable
13 Perl code, so that once you have made your decision to write portably,
14 you know where the lines are drawn, and you can stay within them.
16 There is a tradeoff between taking full advantage of one particular type
17 of computer, and taking advantage of a full range of them. Naturally,
18 as you make your range bigger (and thus more diverse), the common
19 denominators drop, and you are left with fewer areas of common ground in
20 which you can operate to accomplish a particular task. Thus, when you
21 begin attacking a problem, it is important to consider which part of the
22 tradeoff curve you want to operate under. Specifically, whether it is
23 important to you that the task that you are coding needs the full
24 generality of being portable, or if it is sufficient to just get the job
25 done. This is the hardest choice to be made. The rest is easy, because
26 Perl provides lots of choices, whichever way you want to approach your
29 Looking at it another way, writing portable code is usually about
30 willfully limiting your available choices. Naturally, it takes discipline
33 Be aware of two important points:
38 =item Not all Perl programs have to be portable
40 There is no reason why you should not use Perl as a language to glue Unix
41 tools together, or to prototype a Macintosh application, or to manage the
42 Windows registry. If it makes no sense to aim for portability for one
43 reason or another in a given program, then don't bother.
45 =item The vast majority of Perl I<is> portable
47 Don't be fooled into thinking that it is hard to create portable Perl
48 code. It isn't. Perl tries its level-best to bridge the gaps between
49 what's available on different platforms, and all the means available to
50 use those features. Thus almost all Perl code runs on any machine
51 without modification. But there are some significant issues in
52 writing portable code, and this document is entirely about those issues.
57 Here's the general rule: When you approach a task that is commonly done
58 using a whole range of platforms, think in terms of writing portable
59 code. That way, you don't sacrifice much by way of the implementation
60 choices you can avail yourself of, and at the same time you can give
61 your users lots of platform choices. On the other hand, when you have to
62 take advantage of some unique feature of a particular platform, as is
63 often the case with systems programming (whether for Unix, Windows,
64 S<Mac OS>, VMS, etc.), consider writing platform-specific code.
66 When the code will run on only two or three operating systems, then you
67 may only need to consider the differences of those particular systems.
68 The important thing is to decide where the code will run, and to be
69 deliberate in your decision.
71 The material below is separated into three main sections: main issues of
72 portability (L<"ISSUES">, platform-specific issues (L<"PLATFORMS">, and
73 builtin perl functions that behave differently on various ports
74 (L<"FUNCTION IMPLEMENTATIONS">.
76 This information should not be considered complete; it includes possibly
77 transient information about idiosyncrasies of some of the ports, almost
78 all of which are in a state of constant evolution. Thus this material
79 should be considered a perpetual work in progress
80 (E<lt>IMG SRC="yellow_sign.gif" ALT="Under Construction"E<gt>).
87 In most operating systems, lines in files are terminated by newlines.
88 Just what is used as a newline may vary from OS to OS. Unix
89 traditionally uses C<\012>, one kind of Windows I/O uses C<\015\012>,
90 and S<Mac OS> uses C<\015>.
92 Perl uses C<\n> to represent the "logical" newline, where what
93 is logical may depend on the platform in use. In MacPerl, C<\n>
94 always means C<\015>. In DOSish perls, C<\n> usually means C<\012>, but
95 when accessing a file in "text" mode, STDIO translates it to (or from)
96 C<\015\012>. C<\015\012> is commonly referred to as CRLF.
98 Due to the "text" mode translation, DOSish perls have limitations
99 of using C<seek> and C<tell> when a file is being accessed in "text"
100 mode. Specifically, if you stick to C<seek>-ing to locations you got
101 from C<tell> (and no others), you are usually free to use C<seek> and
102 C<tell> even in "text" mode. In general, using C<seek> or C<tell> or
103 other file operations that count bytes instead of characters, without
104 considering the length of C<\n>, may be non-portable. If you use
105 C<binmode> on a file, however, you can usually use C<seek> and C<tell>
106 with arbitrary values quite safely.
108 A common misconception in socket programming is that C<\n> eq C<\012>
109 everywhere. When using protocols such as common Internet protocols,
110 C<\012> and C<\015> are called for specifically, and the values of
111 the logical C<\n> and C<\r> (carriage return) are not reliable.
113 print SOCKET "Hi there, client!\r\n"; # WRONG
114 print SOCKET "Hi there, client!\015\012"; # RIGHT
116 However, using C<\015\012> (or C<\cM\cJ>, or C<\x0D\x0A>) can be tedious
117 and unsightly, as well as confusing to those maintaining the code. As
118 such, the Socket module supplies the Right Thing for those who want it.
120 use Socket qw(:DEFAULT :crlf);
121 print SOCKET "Hi there, client!$CRLF" # RIGHT
123 When reading from a socket, remember that the default input record
124 separator C<$/> is C<\n>, but code like this should recognize C<$/> as
125 C<\012> or C<\015\012>:
131 Since both CRLF and LF end in LF, the input record separator can
132 be set to LF, and the CR can be stripped later, if present. Better:
134 use Socket qw(:DEFAULT :crlf);
135 local($/) = LF; # not needed if $/ is already \012
138 s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
139 # s/\015?\012/\n/; # same thing
142 And this example is actually better than the previous one even for Unix
143 platforms, because now any C<\015>'s (C<\cM>'s) are stripped out
144 (and there was much rejoicing).
146 Similarly, functions that return text data--such as a function that
147 fetches a web page--should, in some cases, translate newlines before
148 returning the data, if they've not yet been trsnalted to the local
149 newline. Often one line of code will suffice:
151 $data =~ s/\015?\012/\n/g;
154 Some of this may be confusing. Here's a handy reference to the ASCII CR
155 and LF characters. You can print it out and stick it in your wallet.
157 LF == \012 == \x0A == \cJ == ASCII 10
158 CR == \015 == \x0D == \cM == ASCII 13
161 ---------------------------
164 \n * | LF | CRLF | CR |
165 \r * | CR | CR | LF |
166 ---------------------------
169 These are just the most common definitions of C<\n> and C<\r> in Perl.
170 There may well be others.
173 =head2 Numbers endianness and Width
175 Different CPUs store integers and floating point numbers in different
176 orders (called I<endianness>) and widths (32-bit and 64-bit being the
177 most common). This affects your programs if they attempt to transfer
178 numbers in binary format from one CPU architecture to another over some
179 channel, usually either "live" via network connection, or by storing the
180 numbers to secondary storage such as a disk file.
182 Conflicting storage orders make utter mess out of the numbers: if a
183 little-endian host (Intel, Alpha) stores 0x12345678 (305419896 in
184 decimal), a big-endian host (Motorola, MIPS, Sparc, PA) reads it as
185 0x78563412 (2018915346 in decimal). To avoid this problem in network
186 (socket) connections use the C<pack> and C<unpack> formats C<n>
187 and C<N>, the "network" orders. They are guaranteed to be portable.
189 Different widths can cause truncation even between platforms of equal
190 endianness: the platform of shorter width loses the upper parts of the
191 number. There is no good solution for this problem except to avoid
192 transferring or storing raw binary numbers.
194 One can circumnavigate both these problems in two ways: either
195 transfer and store numbers always in text format, instead of raw
196 binary, or consider using modules like Data::Dumper (included in
197 the standard distribution as of Perl 5.005) and Storable.
200 =head2 Files and Filesystems
202 Most platforms these days structure files in a hierarchical fashion.
203 So, it is reasonably safe to assume that any platform supports the
204 notion of a "path" to uniquely identify a file on the system. How
205 that path is actually written differs.
207 While they are similar, file path specifications differ between Unix,
208 Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS> and probably others.
209 Unix, for example, is one of the few OSes that has the idea of a single
212 DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with C</>
213 as path separator, or in their own idiosyncratic ways (such as having
214 several root directories and various "unrooted" device files such NIL:
217 S<Mac OS> uses C<:> as a path separator instead of C</>.
219 The filesystem may support neither hard links (C<link>) nor
220 symbolic links (C<symlink>, C<readlink>, C<lstat>).
222 The filesystem may support neither access timestamp nor change
223 timestamp (meaning that about the only portable timestamp is the
224 modification timestamp), or one second granularity of any timestamps
225 (e.g. the FAT filesystem limits the time granularity to two seconds).
227 VOS perl can emulate Unix filenames with C</> as path separator. The
228 native pathname characters greater-than, less-than, number-sign, and
229 percent-sign are always accepted.
231 S<RISC OS> perl can emulate Unix filenames with C</> as path
232 separator, or go native and use C<.> for path separator and C<:> to
233 signal filesystems and disk names.
235 If all this is intimidating, have no (well, maybe only a little) fear.
236 There are modules that can help. The File::Spec modules provide
237 methods to do the Right Thing on whatever
238 platform happens to be running the program.
240 use File::Spec::Functions;
241 chdir(updir()); # go up one directory
242 $file = catfile(curdir(), 'temp', 'file.txt');
243 # on Unix and Win32, './temp/file.txt'
244 # on Mac OS, ':temp:file.txt'
246 File::Spec is available in the standard distribution, as of version
249 In general, production code should not have file paths hardcoded; making
250 them user supplied or from a configuration file is better, keeping in mind
251 that file path syntax varies on different machines.
253 This is especially noticeable in scripts like Makefiles and test suites,
254 which often assume C</> as a path separator for subdirectories.
256 Also of use is File::Basename, from the standard distribution, which
257 splits a pathname into pieces (base filename, full path to directory,
260 Even when on a single platform (if you can call UNIX a single platform),
261 remember not to count on the existence or the contents of
262 system-specific files or directories, like F</etc/passwd>,
263 F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
264 example, F</etc/passwd> may exist but it may not contain the encrypted
265 passwords because the system is using some form of enhanced security,
266 or it may not contain all the accounts because the system is using NIS.
267 If code does need to rely on such a file, include a description of the
268 file and its format in the code's documentation, and make it easy for
269 the user to override the default location of the file.
271 Don't assume a text file will end with a newline.
273 Do not have two files of the same name with different case, like
274 F<test.pl> and F<Test.pl>, as many platforms have case-insensitive
275 filenames. Also, try not to have non-word characters (except for C<.>)
276 in the names, and keep them to the 8.3 convention, for maximum
279 Likewise, if using the AutoSplit module, try to keep the split functions to
280 8.3 naming and case-insensitive conventions; or, at the very least,
281 make it so the resulting files have a unique (case-insensitively)
284 There certainly can be whitespace in filenames on most systems, but
285 some may not allow it. Many systems (DOS, VMS) cannot have more than
286 one C<.> in their filenames.
288 Don't assume C<E<gt>> won't be the first character of a filename.
289 Always use C<E<lt>> explicitly to open a file for reading.
291 open(FILE, "< $existing_file") or die $!;
293 If filenames might use strange characters, it is safest to open it
294 with C<sysopen> instead of C<open>. C<open> is magic and can
295 translate characters like C<E<gt>>, C<E<lt>>, and C<|>, which may
296 be the wrong thing to do.
299 =head2 System Interaction
301 Not all platforms provide for the notion of a command line, necessarily.
302 These are usually platforms that rely on a Graphical User Interface (GUI)
303 for user interaction. So a program requiring command lines might not work
304 everywhere. But this is probably for the user of the program to deal
305 with, so don't stay up late worrying about it.
307 Some platforms can't delete or rename files that are being held open by
308 the system. Remember to C<close> files when you are done with them.
309 Don't C<unlink> or C<rename> an open file. Don't C<tie> or C<open> a
310 file that is already tied or opened; C<untie> or C<close> first.
312 Don't open the same file more than once at a time for writing, as some
313 operating systems put mandatory locks on such files.
315 Don't count on a specific environment variable existing in C<%ENV>.
316 Don't count on C<%ENV> entries being case-sensitive, or even
319 Don't count on signals for anything.
321 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
324 Don't count on per-program environment variables, or per-program current
327 Don't count on specific values of C<$!>.
330 =head2 Interprocess Communication (IPC)
332 In general, don't directly access the system in code that is meant to be
333 portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>, C<``>,
334 C<qx//>, C<open> with a C<|>, nor any of the other things that makes being
335 a Unix perl hacker worth being.
337 Commands that launch external processes are generally supported on
338 most platforms (though many of them do not support any type of forking),
339 but the problem with using them arises from what you invoke with them.
340 External tools are often named differently on different platforms, often
341 not available in the same location, often accept different arguments,
342 often behave differently, and often represent their results in a
343 platform-dependent way. Thus you should seldom depend on them to produce
346 The UNIX System V IPC (msg*(), sem*(), shm*()) is not available
347 even in all UNIX platforms.
349 One especially common bit of Perl code is opening a pipe to sendmail:
351 open(MAIL, '| /usr/lib/sendmail -t') or die $!;
353 This is fine for systems programming when sendmail is known to be
354 available. But it is not fine for many non-Unix systems, and even
355 some Unix systems that may not have sendmail installed. If a portable
356 solution is needed, see the various distributions on CPAN that deal with
357 it. Mail::Mailer and Mail::Send in the MailTools distribution
358 are commonly used, and provide several mailing methods, including mail,
359 sendmail, and direct SMTP (via Net::SMTP) if a mail transfer agent is
360 not available. Mail::Sendmail is a standalone module that provides
361 simple, platform-independent mailing.
363 The rule of thumb for portable code is: Do it all in portable Perl, or
364 use a module (that may internally implement it with platform-specific
365 code, but expose a common interface).
368 =head2 External Subroutines (XS)
370 XS code, in general, can be made to work with any platform; but dependent
371 libraries, header files, etc., might not be readily available or
372 portable, or the XS code itself might be platform-specific, just as Perl
373 code might be. If the libraries and headers are portable, then it is
374 normally reasonable to make sure the XS code is portable, too.
376 There is a different kind of portability issue with writing XS
377 code: availability of a C compiler on the end-user's system. C brings
378 with it its own portability issues, and writing XS code will expose you to
379 some of those. Writing purely in perl is a comparatively easier way to
383 =head2 Standard Modules
385 In general, the standard modules work across platforms. Notable
386 exceptions are the CPAN module (which currently makes connections to external
387 programs that may not be available), platform-specific modules (like
388 ExtUtils::MM_VMS), and DBM modules.
390 There is no one DBM module that is available on all platforms.
391 SDBM_File and the others are generally available on all Unix and DOSish
392 ports, but not in MacPerl, where only NBDM_File and DB_File are
395 The good news is that at least some DBM module should be available, and
396 AnyDBM_File will use whichever module it can find. Of course, then
397 the code needs to be fairly strict, dropping to the lowest common
398 denominator (e.g., not exceeding 1K for each record), so that it will
399 work with any DBM module. See L<AnyDBM_File> for more details.
404 The system's notion of time of day and calendar date is controlled in
405 widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>,
406 and even if it is, don't assume that you can control the timezone through
409 Don't assume that the epoch starts at 00:00:00, January 1, 1970,
410 because that is OS- and implementation-specific. It is better to store a date
411 in an unambiguous representation. The ISO-8601 standard defines
412 "YYYY-MM-DD" as the date format. A text representation (like "1987-12-18")
413 can be easily converted into an OS-specific value using a module like
414 Date::Parse. An array of values, such as those returned by
415 C<localtime>, can be converted to an OS-specific representation using
419 =head2 Character sets and character encoding
421 Assume very little about character sets. Do not assume anything about
422 the numerical values (C<ord>, C<chr>) of characters. Do not
423 assume that the alphabetic characters are encoded contiguously (in
424 numerical sense). Do not assume anything about the ordering of the
425 characters. The lowercase letters may come before or after the
426 uppercase letters, the lowercase and uppercase may be interlaced so
427 that both 'a' and 'A' come before the 'b', the accented and other
428 international characters may be interlaced so that E<auml> comes
432 =head2 Internationalisation
434 If you may assume POSIX (a rather large assumption, that in practice
435 means UNIX), you may read more about the POSIX locale system (see
436 L<perllocale>. The locale system at least attempts to make things a
437 little bit more portable, or at least more convenient and
438 native-friendly for non-English users. The system affects character
439 sets and encoding, and date and time formatting, among other things.
442 =head2 System Resources
444 If your code is destined for systems with severely constrained (or
445 missing!) virtual memory systems then you want to be I<especially> mindful
446 of avoiding wasteful constructs such as:
448 # NOTE: this is no longer "bad" in perl5.005
449 for (0..10000000) {} # bad
450 for (my $x = 0; $x <= 10000000; ++$x) {} # good
452 @lines = <VERY_LARGE_FILE>; # bad
454 while (<FILE>) {$file .= $_} # sometimes bad
455 $file = join('', <FILE>); # better
457 The last two may appear unintuitive to most people. The first of those
458 two constructs repeatedly grows a string, while the second allocates a
459 large chunk of memory in one go. On some systems, the latter is more
460 efficient that the former.
465 Most multi-user platforms provide basic levels of security that is usually
466 felt at the file-system level. Other platforms usually don't
467 (unfortunately). Thus the notion of user id, or "home" directory, or even
468 the state of being logged-in, may be unrecognizable on many platforms. If
469 you write programs that are security-conscious, it is usually best to know
470 what type of system you will be operating under, and write code explicitly
471 for that platform (or class of platforms).
476 For those times when it is necessary to have platform-specific code,
477 consider keeping the platform-specific code in one place, making porting
478 to other platforms easier. Use the Config module and the special
479 variable C<$^O> to differentiate platforms, as described in
482 Be careful not to depend on a specific output style for errors,
483 such as when checking C<$@> after an C<eval>. Some platforms
484 expect a certain output format, and perl on those platforms may
485 have been adjusted accordingly. Most specifically, don't anchor
486 a regex when testing an error value.
488 $@ =~ /^I got an error!/ # may fail
489 $@ =~ /I got an error!/ # probably better
494 Modules uploaded to CPAN are tested by a variety of volunteers on
495 different platforms. These CPAN testers are notified by mail of each
496 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
497 this platform), or UNKNOWN (unknown), along with any relevant notations.
499 The purpose of the testing is twofold: one, to help developers fix any
500 problems in their code that crop up because of lack of testing on other
501 platforms; two, to provide users with information about whether or not
502 a given module works on a given platform.
506 =item Mailing list: cpan-testers@perl.org
508 =item Testing results: C<http://www.perl.org/cpan-testers/>
515 As of version 5.002, Perl is built with a C<$^O> variable that
516 indicates the operating system it was built on. This was implemented
517 to help speed up code that would otherwise have to C<use Config;> and
518 use the value of C<$Config{'osname'}>. Of course, to get
519 detailed information about the system, looking into C<%Config> is
520 certainly recommended.
522 C<%Config> cannot always be trusted, however,
523 because it is built at compile time, and if perl was built in once
524 place and transferred elsewhere, some values may be off, or the
525 values may have been edited after the fact.
530 Perl works on a bewildering variety of Unix and Unix-like platforms (see
531 e.g. most of the files in the F<hints/> directory in the source code kit).
532 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
533 too) is determined by lowercasing and stripping punctuation from the first
534 field of the string returned by typing C<uname -a> (or a similar command)
535 at the shell prompt. Here, for example, are a few of the more popular
538 uname $^O $Config{'archname'}
539 --------------------------------------------
541 BSD/OS bsdos i386-bsdos
542 dgux dgux AViiON-dgux
543 DYNIX/ptx dynixptx i386-dynixptx
544 FreeBSD freebsd freebsd-i386
545 Linux linux i386-linux
546 Linux linux i586-linux
547 Linux linux ppc-linux
548 HP-UX hpux PA-RISC1.1
550 openbsd openbsd i386-openbsd
551 OSF1 dec_osf alpha-dec_osf
552 reliantunix-n svr4 RM400-svr4
553 SCO_SV sco_sv i386-sco_sv
554 SINIX-N svr4 RM400-svr4
555 sn4609 unicos CRAY_C90-unicos
556 sn6521 unicosmk t3e-unicosmk
557 sn9617 unicos CRAY_J90-unicos
558 sn9716 unicos CRAY_J90-unicos
559 SunOS solaris sun4-solaris
560 SunOS solaris i86pc-solaris
561 SunOS4 sunos sun4-sunos
563 Note that because the C<$Config{'archname'}> may depend on the hardware
564 architecture it may vary quite a lot, much more than the C<$^O>.
567 =head2 DOS and Derivatives
569 Perl has long been ported to PC style microcomputers running under
570 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
571 bring yourself to mention (except for Windows CE, if you count that).
572 Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should
573 be aware that each of these file specifications may have subtle
576 $filespec0 = "c:/foo/bar/file.txt";
577 $filespec1 = "c:\\foo\\bar\\file.txt";
578 $filespec2 = 'c:\foo\bar\file.txt';
579 $filespec3 = 'c:\\foo\\bar\\file.txt';
581 System calls accept either C</> or C<\> as the path separator. However,
582 many command-line utilities of DOS vintage treat C</> as the option
583 prefix, so they may get confused by filenames containing C</>. Aside
584 from calling any external programs, C</> will work just fine, and
585 probably better, as it is more consistent with popular usage, and avoids
586 the problem of remembering what to backwhack and what not to.
588 The DOS FAT filesystem can only accommodate "8.3" style filenames. Under
589 the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT)
590 filesystems you may have to be careful about case returned with functions
591 like C<readdir> or used with functions like C<open> or C<opendir>.
593 DOS also treats several filenames as special, such as AUX, PRN, NUL, CON,
594 COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work
595 if you include an explicit directory prefix, in some cases. It is best
596 to avoid such filenames, if you want your code to be portable to DOS
599 Users of these operating systems may also wish to make use of
600 scripts such as F<pl2bat.bat> or F<pl2cmd> as appropriate to
601 put wrappers around your scripts.
603 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
604 and writing to files (see L<"Newlines">). C<binmode(FILEHANDLE)>
605 will keep C<\n> translated as C<\012> for that filehandle. Since it is a
606 no-op on other systems, C<binmode> should be used for cross-platform code
607 that deals with binary data.
609 The C<$^O> variable and the C<$Config{'archname'}> values for various
610 DOSish perls are as follows:
612 OS $^O $Config{'archname'}
613 --------------------------------------------
617 Windows 95 MSWin32 MSWin32-x86
618 Windows 98 MSWin32 MSWin32-x86
619 Windows NT MSWin32 MSWin32-x86
620 Windows NT MSWin32 MSWin32-ALPHA
621 Windows NT MSWin32 MSWin32-ppc
627 =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/>
629 =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>,
630 C<http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html> or
631 C<ftp://hobbes.nmsu.edu/pub/os2/dev/emx>
633 =item Build instructions for Win32, L<perlwin32>.
635 =item The ActiveState Pages, C<http://www.activestate.com/>
642 Any module requiring XS compilation is right out for most people, because
643 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
644 modules that can work with MacPerl are built and distributed in binary
647 Directories are specified as:
649 volume:folder:file for absolute pathnames
650 volume:folder: for absolute pathnames
651 :folder:file for relative pathnames
652 :folder: for relative pathnames
653 :file for relative pathnames
654 file for relative pathnames
656 Files in a directory are stored in alphabetical order. Filenames are
657 limited to 31 characters, and may include any character except for
658 null and C<:>, which is reserved as path separator.
660 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
661 Mac::Files module, or C<chmod(0444, ...)> and C<chmod(0666, ...)>.
663 In the MacPerl application, you can't run a program from the command line;
664 programs that expect C<@ARGV> to be populated can be edited with something
665 like the following, which brings up a dialog box asking for the command
669 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
672 A MacPerl script saved as a droplet will populate C<@ARGV> with the full
673 pathnames of the files dropped onto the script.
675 Mac users can use programs on a kind of command line under MPW (Macintosh
676 Programmer's Workshop, a free development environment from Apple).
677 MacPerl was first introduced as an MPW tool, and MPW can be used like a
680 perl myscript.plx some arguments
682 ToolServer is another app from Apple that provides access to MPW tools
683 from MPW and the MacPerl app, which allows MacPerl programs to use
684 C<system>, backticks, and piped C<open>.
686 "S<Mac OS>" is the proper name for the operating system, but the value
687 in C<$^O> is "MacOS". To determine architecture, version, or whether
688 the application or MPW tool version is running, check:
690 $is_app = $MacPerl::Version =~ /App/;
691 $is_tool = $MacPerl::Version =~ /MPW/;
692 ($version) = $MacPerl::Version =~ /^(\S+)/;
693 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
694 $is_68k = $MacPerl::Architecture eq 'Mac68K';
696 S<Mac OS X> and S<Mac OS X Server>, based on NeXT's OpenStep OS, will
697 (in theory) be able to run MacPerl natively, under the "Classic"
698 environment. The new "Cocoa" environment (formerly called the "Yellow Box")
699 may run a slightly modified version of MacPerl, using the Carbon interfaces.
701 S<Mac OS X Server> and its Open Source version, Darwin, both run Unix
702 perl natively (with a small number of patches). Full support for these
703 is slated for perl5.006.
710 =item The MacPerl Pages, C<http://www.macperl.com/>.
712 =item The MacPerl mailing lists, C<http://www.macperl.org/>.
714 =item MacPerl Module Porters, C<http://pudge.net/mmp/>.
721 Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
722 Note that perl on VMS can accept either VMS- or Unix-style file
723 specifications as in either of the following:
725 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
726 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
728 but not a mixture of both as in:
730 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
731 Can't open sys$login:/login.com: file specification syntax error
733 Interacting with Perl from the Digital Command Language (DCL) shell
734 often requires a different set of quotation marks than Unix shells do.
737 $ perl -e "print ""Hello, world.\n"""
740 There are a number of ways to wrap your perl scripts in DCL .COM files if
741 you are so inclined. For example:
743 $ write sys$output "Hello from DCL!"
745 $ then perl -x 'f$environment("PROCEDURE")
746 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
747 $ deck/dollars="__END__"
750 print "Hello from Perl!\n";
755 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
756 perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>.
758 Filenames are in the format "name.extension;version". The maximum
759 length for filenames is 39 characters, and the maximum length for
760 extensions is also 39 characters. Version is a number from 1 to
761 32767. Valid characters are C</[A-Z0-9$_-]/>.
763 VMS' RMS filesystem is case insensitive and does not preserve case.
764 C<readdir> returns lowercased filenames, but specifying a file for
765 opening remains case insensitive. Files without extensions have a
766 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
767 will return F<a.> (though that file could be opened with
770 RMS had an eight level limit on directory depths from any rooted logical
771 (allowing 16 levels overall) prior to VMS 7.2. Hence
772 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
773 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
774 have to take this into account, but at least they can refer to the former
775 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
777 The VMS::Filespec module, which gets installed as part of the build
778 process on VMS, is a pure Perl module that can easily be installed on
779 non-VMS platforms and can be helpful for conversions to and from RMS
782 What C<\n> represents depends on the type of file that is open. It could
783 be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file
784 translates newlines to C<\012>, unless C<binmode> was executed on that
785 handle, just like DOSish perls.
787 TCP/IP stacks are optional on VMS, so socket routines might not be
788 implemented. UDP sockets may not be supported.
790 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
791 that you are running on without resorting to loading all of C<%Config>
792 you can examine the content of the C<@INC> array like so:
794 if (grep(/VMS_AXP/, @INC)) {
795 print "I'm on Alpha!\n";
797 } elsif (grep(/VMS_VAX/, @INC)) {
798 print "I'm on VAX!\n";
801 print "I'm not so sure about where $^O is...\n";
804 On VMS perl determines the UTC offset from the C<SYS$TIMEZONE_DIFFERENTIAL>
805 logical name. Though the VMS epoch began at 17-NOV-1858 00:00:00.00,
806 calls to C<localtime> are adjusted to count offsets from
807 01-JAN-1970 00:00:00.00 just like Unix.
815 =item vmsperl list, C<majordomo@perl.org>
817 Put the words C<subscribe vmsperl> in message body.
819 =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html>
826 Perl on VOS is discussed in F<README.vos> in the perl distribution.
827 Note that perl on VOS can accept either VOS- or Unix-style file
828 specifications as in either of the following:
830 $ perl -ne "print if /perl_setup/i" >system>notices
831 $ perl -ne "print if /perl_setup/i" /system/notices
833 or even a mixture of both as in:
835 $ perl -ne "print if /perl_setup/i" >system/notices
837 Note that even though VOS allows the slash character to appear in object
838 names, because the VOS port of Perl interprets it as a pathname
839 delimiting character, VOS files, directories, or links whose names
840 contain a slash character cannot be processed. Such files must be
841 renamed before they can be processed by Perl.
843 The following C functions are unimplemented on VOS, and any attempt by
844 Perl to use them will result in a fatal error message and an immediate
845 exit from Perl: dup, do_aspawn, do_spawn, fork, waitpid. Once these
846 functions become available in the VOS POSIX.1 implementation, you can
847 either recompile and rebind Perl, or you can download a newer port from
850 The value of C<$^O> on VOS is "VOS". To determine the architecture that
851 you are running on without resorting to loading all of C<%Config> you
852 can examine the content of the C<@INC> array like so:
854 if (grep(/VOS/, @INC)) {
855 print "I'm on a Stratus box!\n";
857 print "I'm not on a Stratus box!\n";
861 if (grep(/860/, @INC)) {
862 print "This box is a Stratus XA/R!\n";
864 } elsif (grep(/7100/, @INC)) {
865 print "This box is a Stratus HP 7100 or 8000!\n";
867 } elsif (grep(/8000/, @INC)) {
868 print "This box is a Stratus HP 8000!\n";
871 print "This box is a Stratus 68K...\n";
880 =item VOS mailing list
882 There is no specific mailing list for Perl on VOS. You can post
883 comments to the comp.sys.stratus newsgroup, or subscribe to the general
884 Stratus mailing list. Send a letter with "Subscribe Info-Stratus" in
885 the message body to majordomo@list.stratagy.com.
887 =item VOS Perl on the web at C<http://ftp.stratus.com/pub/vos/vos.html>
892 =head2 EBCDIC Platforms
894 Recent versions of Perl have been ported to platforms such as OS/400 on
895 AS/400 minicomputers as well as OS/390 & VM/ESA for IBM Mainframes. Such
896 computers use EBCDIC character sets internally (usually Character Code
897 Set ID 00819 for OS/400 and IBM-1047 for OS/390 & VM/ESA). Note that on
898 the mainframe perl currently works under the "Unix system services
899 for OS/390" (formerly known as OpenEdition) and VM/ESA OpenEdition.
901 As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
902 sub-systems do not support the C<#!> shebang trick for script invocation.
903 Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
904 similar to the following simple script:
907 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
909 #!/usr/local/bin/perl # just a comment really
911 print "Hello from perl!\n";
913 On the AS/400, assuming that PERL5 is in your library list, you may need
914 to wrap your perl scripts in a CL procedure to invoke them like so:
917 CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
920 This will invoke the perl script F<hello.pl> in the root of the
921 QOpenSys file system. On the AS/400 calls to C<system> or backticks
924 On these platforms, bear in mind that the EBCDIC character set may have
925 an effect on what happens with some perl functions (such as C<chr>,
926 C<pack>, C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>), as
927 well as bit-fiddling with ASCII constants using operators like C<^>, C<&>
928 and C<|>, not to mention dealing with socket interfaces to ASCII computers
931 Fortunately, most web servers for the mainframe will correctly translate
932 the C<\n> in the following statement to its ASCII equivalent (note that
933 C<\r> is the same under both Unix and OS/390 & VM/ESA):
935 print "Content-type: text/html\r\n\r\n";
937 The value of C<$^O> on OS/390 is "os390".
939 The value of C<$^O> on VM/ESA is "vmesa".
941 Some simple tricks for determining if you are running on an EBCDIC
942 platform could include any of the following (perhaps all):
944 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
946 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
948 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
950 Note that one thing you may not want to rely on is the EBCDIC encoding
951 of punctuation characters since these may differ from code page to code
952 page (and once your module or script is rumoured to work with EBCDIC,
953 folks will want it to work with all EBCDIC character sets).
961 The perl-mvs@perl.org list is for discussion of porting issues as well as
962 general usage issues for all EBCDIC Perls. Send a message body of
963 "subscribe perl-mvs" to majordomo@perl.org.
965 =item AS/400 Perl information at C<http://as400.rochester.ibm.com/>
972 As Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
973 Unix and Unix filename emulation is turned on by default, it is quite
974 likely that most simple scripts will work "out of the box". The native
975 filesystem is modular, and individual filesystems are free to be
976 case-sensitive or insensitive, and are usually case-preserving. Some
977 native filesystems have name length limits which file and directory
978 names are silently truncated to fit. Scripts should be aware that the
979 standard filesystem currently has a name length limit of B<10>
980 characters, with up to 77 items in a directory, but other filesystems
981 may not impose such limitations.
983 Native filenames are of the form
985 Filesystem#Special_Field::DiskName.$.Directory.Directory.File
989 Special_Field is not usually present, but may contain . and $ .
990 Filesystem =~ m|[A-Za-z0-9_]|
991 DsicName =~ m|[A-Za-z0-9_/]|
992 $ represents the root directory
993 . is the path separator
994 @ is the current directory (per filesystem but machine global)
995 ^ is the parent directory
996 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
998 The default filename translation is roughly C<tr|/.|./|;>
1000 Note that C<"ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'> and that
1001 the second stage of C<$> interpolation in regular expressions will fall
1002 foul of the C<$.> if scripts are not careful.
1004 Logical paths specified by system variables containing comma-separated
1005 search lists are also allowed, hence C<System:Modules> is a valid
1006 filename, and the filesystem will prefix C<Modules> with each section of
1007 C<System$Path> until a name is made that points to an object on disk.
1008 Writing to a new file C<System:Modules> would only be allowed if
1009 C<System$Path> contains a single item list. The filesystem will also
1010 expand system variables in filenames if enclosed in angle brackets, so
1011 C<E<lt>System$DirE<gt>.Modules> would look for the file
1012 S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious implication of this is
1013 that B<fully qualified filenames can start with C<E<lt>E<gt>>> and should
1014 be protected when C<open> is used for input.
1016 Because C<.> was in use as a directory separator and filenames could not
1017 be assumed to be unique after 10 characters, Acorn implemented the C
1018 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
1019 filenames specified in source code and store the respective files in
1020 subdirectories named after the suffix. Hence files are translated:
1023 C:foo.h C:h.foo (logical path variable)
1024 sys/os.h sys.h.os (C compiler groks Unix-speak)
1025 10charname.c c.10charname
1026 10charname.o o.10charname
1027 11charname_.c c.11charname (assuming filesystem truncates at 10)
1029 The Unix emulation library's translation of filenames to native assumes
1030 that this sort of translation is required, and allows a user defined list
1031 of known suffixes which it will transpose in this fashion. This may
1032 appear transparent, but consider that with these rules C<foo/bar/baz.h>
1033 and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
1034 C<glob> cannot and do not attempt to emulate the reverse mapping. Other
1035 C<.>'s in filenames are translated to C</>.
1037 As implied above the environment accessed through C<%ENV> is global, and
1038 the convention is that program specific environment variables are of the
1039 form C<Program$Name>. Each filesystem maintains a current directory,
1040 and the current filesystem's current directory is the B<global> current
1041 directory. Consequently, sociable scripts don't change the current
1042 directory but rely on full pathnames, and scripts (and Makefiles) cannot
1043 assume that they can spawn a child process which can change the current
1044 directory without affecting its parent (and everyone else for that
1047 As native operating system filehandles are global and currently are
1048 allocated down from 255, with 0 being a reserved value the Unix emulation
1049 library emulates Unix filehandles. Consequently, you can't rely on
1050 passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
1052 The desire of users to express filenames of the form
1053 C<E<lt>Foo$DirE<gt>.Bar> on the command line unquoted causes problems,
1054 too: C<``> command output capture has to perform a guessing game. It
1055 assumes that a string C<E<lt>[^E<lt>E<gt>]+\$[^E<lt>E<gt>]E<gt>> is a
1056 reference to an environment variable, whereas anything else involving
1057 C<E<lt>> or C<E<gt>> is redirection, and generally manages to be 99%
1058 right. Of course, the problem remains that scripts cannot rely on any
1059 Unix tools being available, or that any tools found have Unix-like command
1062 Extensions and XS are, in theory, buildable by anyone using free tools.
1063 In practice, many don't, as users of the Acorn platform are used to binary
1064 distribution. MakeMaker does run, but no available make currently copes
1065 with MakeMaker's makefiles; even if/when this is fixed, the lack of a
1066 Unix-like shell can cause problems with makefile rules, especially lines
1067 of the form C<cd sdbm && make all>, and anything using quoting.
1069 "S<RISC OS>" is the proper name for the operating system, but the value
1070 in C<$^O> is "riscos" (because we don't like shouting).
1075 Perl has been ported to a variety of platforms that do not fit into any of
1076 the above categories. Some, such as AmigaOS, Atari MiNT, BeOS, HP MPE/iX,
1077 QNX, Plan 9, and VOS, have been well-integrated into the standard Perl source
1078 code kit. You may need to see the F<ports/> directory on CPAN for
1079 information, and possibly binaries, for the likes of: aos, Atari ST, lynxos,
1080 riscos, Novell Netware, Tandem Guardian, I<etc.> (yes we know that some of
1081 these OSes may fall under the Unix category, but we are not a standards body.)
1087 =item Atari, Guido Flohr's page C<http://stud.uni-sb.de/~gufl0000/>
1089 =item HP 300 MPE/iX C<http://www.cccd.edu/~markb/perlix.html>
1091 =item Novell Netware
1093 A free perl5-based PERL.NLM for Novell Netware is available in
1094 precompiled binary and source code form from C<http://www.novell.com/>
1095 as well as from CPAN.
1100 =head1 FUNCTION IMPLEMENTATIONS
1102 Listed below are functions unimplemented or implemented differently on
1103 various platforms. Following each description will be, in parentheses, a
1104 list of platforms that the description applies to.
1106 The list may very well be incomplete, or wrong in some places. When in
1107 doubt, consult the platform-specific README files in the Perl source
1108 distribution, and other documentation resources for a given port.
1110 Be aware, moreover, that even among Unix-ish systems there are variations.
1112 For many functions, you can also query C<%Config>, exported by default
1113 from the Config module. For example, to check if the platform has the C<lstat>
1114 call, check C<$Config{'d_lstat'}>. See L<Config> for a full
1115 description of available variables.
1118 =head2 Alphabetical Listing of Perl Functions
1128 C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories
1129 and applications are executable, and there are no uid/gid
1130 considerations. C<-o> is not supported. (S<Mac OS>)
1132 C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible,
1133 which may not reflect UIC-based file protections. (VMS)
1135 C<-s> returns the size of the data fork, not the total size of data fork
1136 plus resource fork. (S<Mac OS>).
1138 C<-s> by name on an open file will return the space reserved on disk,
1139 rather than the current extent. C<-s> on an open filehandle returns the
1140 current size. (S<RISC OS>)
1142 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
1143 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1145 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
1148 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
1149 (Win32, VMS, S<RISC OS>)
1151 C<-d> is true if passed a device spec without an explicit directory.
1154 C<-T> and C<-B> are implemented, but might misclassify Mac text files
1155 with foreign characters; this is the case will all platforms, but may
1156 affect S<Mac OS> often. (S<Mac OS>)
1158 C<-x> (or C<-X>) determine if a file ends in one of the executable
1159 suffixes. C<-S> is meaningless. (Win32)
1161 C<-x> (or C<-X>) determine if a file has an executable file type.
1164 =item binmode FILEHANDLE
1166 Meaningless. (S<Mac OS>, S<RISC OS>)
1168 Reopens file and restores pointer; if function fails, underlying
1169 filehandle may be closed, or pointer may be in a different position.
1172 The value returned by C<tell> may be affected after the call, and
1173 the filehandle may be flushed. (Win32)
1177 Only limited meaning. Disabling/enabling write permission is mapped to
1178 locking/unlocking the file. (S<Mac OS>)
1180 Only good for changing "owner" read-write access, "group", and "other"
1181 bits are meaningless. (Win32)
1183 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
1185 Access permissions are mapped onto VOS access-control list changes. (VOS)
1189 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
1191 Does nothing, but won't fail. (Win32)
1193 =item chroot FILENAME
1197 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS, VM/ESA)
1199 =item crypt PLAINTEXT,SALT
1201 May not be available if library or source was not provided when building
1204 Not implemented. (VOS)
1208 Not implemented. (VMS, Plan9, VOS)
1210 =item dbmopen HASH,DBNAME,MODE
1212 Not implemented. (VMS, Plan9, VOS)
1216 Not useful. (S<Mac OS>, S<RISC OS>)
1218 Not implemented. (Win32)
1220 Invokes VMS debugger. (VMS)
1224 Not implemented. (S<Mac OS>)
1226 Implemented via Spawn. (VM/ESA)
1228 =item fcntl FILEHANDLE,FUNCTION,SCALAR
1230 Not implemented. (Win32, VMS)
1232 =item flock FILEHANDLE,OPERATION
1234 Not implemented (S<Mac OS>, VMS, S<RISC OS>, VOS).
1236 Available only on Windows NT (not on Windows 95). (Win32)
1240 Not implemented. (S<Mac OS>, Win32, AmigaOS, S<RISC OS>, VOS, VM/ESA)
1244 Not implemented. (S<Mac OS>, S<RISC OS>)
1248 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1252 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1254 =item getpriority WHICH,WHO
1256 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1260 Not implemented. (S<Mac OS>, Win32)
1262 Not useful. (S<RISC OS>)
1266 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1268 =item getnetbyname NAME
1270 Not implemented. (S<Mac OS>, Win32, Plan9)
1274 Not implemented. (S<Mac OS>, Win32)
1276 Not useful. (S<RISC OS>)
1280 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1282 =item getnetbyaddr ADDR,ADDRTYPE
1284 Not implemented. (S<Mac OS>, Win32, Plan9)
1286 =item getprotobynumber NUMBER
1288 Not implemented. (S<Mac OS>)
1290 =item getservbyport PORT,PROTO
1292 Not implemented. (S<Mac OS>)
1296 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1300 Not implemented. (S<Mac OS>, Win32, VMS, VM/ESA)
1304 Not implemented. (S<Mac OS>, Win32)
1308 Not implemented. (S<Mac OS>, Win32, Plan9)
1312 Not implemented. (S<Mac OS>, Win32, Plan9)
1316 Not implemented. (Win32, Plan9)
1320 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1324 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1326 =item sethostent STAYOPEN
1328 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1330 =item setnetent STAYOPEN
1332 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1334 =item setprotoent STAYOPEN
1336 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1338 =item setservent STAYOPEN
1340 Not implemented. (Plan9, Win32, S<RISC OS>)
1344 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1348 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VM/ESA)
1352 Not implemented. (S<Mac OS>, Win32)
1356 Not implemented. (S<Mac OS>, Win32, Plan9)
1360 Not implemented. (S<Mac OS>, Win32, Plan9)
1364 Not implemented. (Plan9, Win32)
1366 =item getsockopt SOCKET,LEVEL,OPTNAME
1368 Not implemented. (S<Mac OS>, Plan9)
1374 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1377 Features depend on external perlglob.exe or perlglob.bat. May be
1378 overridden with something like File::DosGlob, which is recommended.
1381 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1382 Globbing relies on operating system calls, which may return filenames
1383 in any order. As most filesystems are case-insensitive, even "sorted"
1384 filenames will not be in case-sensitive order. (S<RISC OS>)
1386 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1388 Not implemented. (VMS)
1390 Available only for socket handles, and it does what the ioctlsocket() call
1391 in the Winsock API does. (Win32)
1393 Available only for socket handles. (S<RISC OS>)
1397 Not implemented, hence not useful for taint checking. (S<Mac OS>,
1400 Available only for process handles returned by the C<system(1, ...)>
1401 method of spawning a process. (Win32)
1403 =item link OLDFILE,NEWFILE
1405 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1407 Link count not updated because hard links are not quite that hard
1408 (They are sort of half-way between hard and soft links). (AmigaOS)
1410 =item lstat FILEHANDLE
1416 Not implemented. (VMS, S<RISC OS>)
1418 Return values may be bogus. (Win32)
1420 =item msgctl ID,CMD,ARG
1422 =item msgget KEY,FLAGS
1424 =item msgsnd ID,MSG,FLAGS
1426 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1428 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1430 =item open FILEHANDLE,EXPR
1432 =item open FILEHANDLE
1434 The C<|> variants are only supported if ToolServer is installed.
1437 open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1439 =item pipe READHANDLE,WRITEHANDLE
1441 Not implemented. (S<Mac OS>)
1443 Very limited functionality. (MiNT)
1449 Not implemented. (Win32, VMS, S<RISC OS>)
1451 =item select RBITS,WBITS,EBITS,TIMEOUT
1453 Only implemented on sockets. (Win32)
1455 Only reliable on sockets. (S<RISC OS>)
1457 =item semctl ID,SEMNUM,CMD,ARG
1459 =item semget KEY,NSEMS,FLAGS
1461 =item semop KEY,OPSTRING
1463 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1465 =item setpgrp PID,PGRP
1467 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1469 =item setpriority WHICH,WHO,PRIORITY
1471 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1473 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1475 Not implemented. (S<Mac OS>, Plan9)
1477 =item shmctl ID,CMD,ARG
1479 =item shmget KEY,SIZE,FLAGS
1481 =item shmread ID,VAR,POS,SIZE
1483 =item shmwrite ID,STRING,POS,SIZE
1485 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1487 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1489 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1491 =item stat FILEHANDLE
1497 mtime and atime are the same thing, and ctime is creation time instead of
1498 inode change time. (S<Mac OS>)
1500 device and inode are not meaningful. (Win32)
1502 device and inode are not necessarily reliable. (VMS)
1504 mtime, atime and ctime all return the last modification time. Device and
1505 inode are not necessarily reliable. (S<RISC OS>)
1507 =item symlink OLDFILE,NEWFILE
1509 Not implemented. (Win32, VMS, S<RISC OS>)
1513 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1515 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1517 The traditional "0", "1", and "2" MODEs are implemented with different
1518 numeric values on some systems. The flags exported by C<Fcntl>
1519 (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (S<Mac
1520 OS>, OS/390, VM/ESA)
1524 Only implemented if ToolServer is installed. (S<Mac OS>)
1526 As an optimization, may not call the command shell specified in
1527 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1528 process and immediately returns its process designator, without
1529 waiting for it to terminate. Return value may be used subsequently
1530 in C<wait> or C<waitpid>. (Win32)
1532 There is no shell to process metacharacters, and the native standard is
1533 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1534 program. Redirection such as C<E<gt> foo> is performed (if at all) by
1535 the run time library of the spawned program. C<system> I<list> will call
1536 the Unix emulation library's C<exec> emulation, which attempts to provide
1537 emulation of the stdin, stdout, stderr in force in the parent, providing
1538 the child program uses a compatible version of the emulation library.
1539 I<scalar> will call the native command line direct and no such emulation
1540 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1542 Far from being POSIX compliant. Because there may be no underlying
1543 /bin/sh tries to work around the problem by forking and execing the
1544 first token in its argument string. Handles basic redirection
1545 ("E<lt>" or "E<gt>") on its own behalf. (MiNT)
1549 Only the first entry returned is nonzero. (S<Mac OS>)
1551 "cumulative" times will be bogus. On anything other than Windows NT,
1552 "system" time will be bogus, and "user" time is actually the time
1553 returned by the clock() function in the C runtime library. (Win32)
1555 Not useful. (S<RISC OS>)
1557 =item truncate FILEHANDLE,LENGTH
1559 =item truncate EXPR,LENGTH
1561 Not implemented. (VMS)
1563 Truncation to zero-length only. (VOS)
1565 If a FILEHANDLE is supplied, it must be writable and opened in append
1566 mode (i.e., use C<open(FH, '>>filename')>
1567 or C<sysopen(FH,...,O_APPEND|O_RDWR)>. If a filename is supplied, it
1568 should not be held open elsewhere. (Win32)
1574 Returns undef where unavailable, as of version 5.005.
1576 C<umask()> works but the correct permissions are only set when the file
1577 is finally close()d. (AmigaOS)
1581 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1583 May not behave as expected. Behavior depends on the C runtime
1584 library's implementation of utime(), and the filesystem being
1585 used. The FAT filesystem typically does not support an "access
1586 time" field, and it may limit timestamps to a granularity of
1587 two seconds. (Win32)
1591 =item waitpid PID,FLAGS
1593 Not implemented. (S<Mac OS>, VOS)
1595 Can only be applied to process handles returned for processes spawned
1596 using C<system(1, ...)>. (Win32)
1598 Not useful. (S<RISC OS>)
1606 =item v1.41, 19 May 1999
1608 Lots more little changes to formatting and content.
1610 Added a bunch of <$^O> and related values
1611 for various platforms; fixed mail and web addresses, and added
1612 and changed miscellaneous notes. (Peter Prymmer)
1614 =item v1.40, 11 April 1999
1616 Miscellaneous changes.
1618 =item v1.39, 11 February 1999
1620 Changes from Jarkko and EMX URL fixes Michael Schwern. Additional
1621 note about newlines added.
1623 =item v1.38, 31 December 1998
1625 More changes from Jarkko.
1627 =item v1.37, 19 December 1998
1629 More minor changes. Merge two separate version 1.35 documents.
1631 =item v1.36, 9 September 1998
1633 Updated for Stratus VOS. Also known as version 1.35.
1635 =item v1.35, 13 August 1998
1637 Integrate more minor changes, plus addition of new sections under
1638 L<"ISSUES">: L<"Numbers endianness and Width">,
1639 L<"Character sets and character encoding">,
1640 L<"Internationalisation">.
1642 =item v1.33, 06 August 1998
1644 Integrate more minor changes.
1646 =item v1.32, 05 August 1998
1648 Integrate more minor changes.
1650 =item v1.30, 03 August 1998
1652 Major update for RISC OS, other minor changes.
1654 =item v1.23, 10 July 1998
1656 First public release with perl5.005.
1660 =head1 AUTHORS / CONTRIBUTORS
1662 Abigail E<lt>abigail@fnx.comE<gt>,
1663 Charles Bailey E<lt>bailey@newman.upenn.eduE<gt>,
1664 Graham Barr E<lt>gbarr@pobox.comE<gt>,
1665 Tom Christiansen E<lt>tchrist@perl.comE<gt>,
1666 Nicholas Clark E<lt>Nicholas.Clark@liverpool.ac.ukE<gt>,
1667 Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>,
1668 Dominic Dunlop E<lt>domo@vo.luE<gt>,
1669 Neale Ferguson E<lt>neale@mailbox.tabnsw.com.auE<gt>
1670 Paul Green E<lt>Paul_Green@stratus.comE<gt>,
1671 M.J.T. Guy E<lt>mjtg@cus.cam.ac.ukE<gt>,
1672 Jarkko Hietaniemi E<lt>jhi@iki.fi<gt>,
1673 Luther Huffman E<lt>lutherh@stratcom.comE<gt>,
1674 Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>,
1675 Andreas J. KE<ouml>nig E<lt>koenig@kulturbox.deE<gt>,
1676 Markus Laker E<lt>mlaker@contax.co.ukE<gt>,
1677 Andrew M. Langmead E<lt>aml@world.std.comE<gt>,
1678 Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>,
1679 Chris Nandor E<lt>pudge@pobox.comE<gt>,
1680 Matthias Neeracher E<lt>neeri@iis.ee.ethz.chE<gt>,
1681 Gary Ng E<lt>71564.1743@CompuServe.COME<gt>,
1682 Tom Phoenix E<lt>rootbeer@teleport.comE<gt>,
1683 Peter Prymmer E<lt>pvhp@forte.comE<gt>,
1684 Hugo van der Sanden E<lt>hv@crypt0.demon.co.ukE<gt>,
1685 Gurusamy Sarathy E<lt>gsar@umich.eduE<gt>,
1686 Paul J. Schinder E<lt>schinder@pobox.comE<gt>,
1687 Michael G Schwern E<lt>schwern@pobox.comE<gt>,
1688 Dan Sugalski E<lt>sugalskd@ous.eduE<gt>,
1689 Nathan Torkington E<lt>gnat@frii.comE<gt>.
1691 This document is maintained by Chris Nandor
1692 E<lt>pudge@pobox.comE<gt>.
1696 Version 1.41, last modified 19 May 1999