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 B<a> particular type
17 of computer, and taking advantage of a full B<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:
37 =item Not all Perl programs have to be portable
39 There is no reason why you should not use Perl as a language to glue Unix
40 tools together, or to prototype a Macintosh application, or to manage the
41 Windows registry. If it makes no sense to aim for portability for one
42 reason or another in a given program, then don't bother.
44 =item The vast majority of Perl B<is> portable
46 Don't be fooled into thinking that it is hard to create portable Perl
47 code. It isn't. Perl tries its level-best to bridge the gaps between
48 what's available on different platforms, and all the means available to
49 use those features. Thus almost all Perl code runs on any machine
50 without modification. But there I<are> some significant issues in
51 writing portable code, and this document is entirely about those issues.
55 Here's the general rule: When you approach a task that is commonly done
56 using a whole range of platforms, think in terms of writing portable
57 code. That way, you don't sacrifice much by way of the implementation
58 choices you can avail yourself of, and at the same time you can give
59 your users lots of platform choices. On the other hand, when you have to
60 take advantage of some unique feature of a particular platform, as is
61 often the case with systems programming (whether for Unix, Windows,
62 S<Mac OS>, VMS, etc.), consider writing platform-specific code.
64 When the code will run on only two or three operating systems, then you
65 may only need to consider the differences of those particular systems.
66 The important thing is to decide where the code will run, and to be
67 deliberate in your decision.
69 The material below is separated into three main sections: main issues of
70 portability (L<"ISSUES">, platform-specific issues (L<"PLATFORMS">, and
71 builtin perl functions that behave differently on various ports
72 (L<"FUNCTION IMPLEMENTATIONS">.
74 This information should not be considered complete; it includes possibly
75 transient information about idiosyncrasies of some of the ports, almost
76 all of which are in a state of constant evolution. Thus this material
77 should be considered a perpetual work in progress
78 (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)
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 [NOTE: this does not necessarily apply to communications that are
117 filtered by another program or module before sending to the socket; the
118 the most popular EBCDIC webserver, for instance, accepts C<\r\n>,
119 which translates those characters, along with all other
120 characters in text streams, from EBCDIC to ASCII.]
122 However, using C<\015\012> (or C<\cM\cJ>, or C<\x0D\x0A>) can be tedious
123 and unsightly, as well as confusing to those maintaining the code. As
124 such, the C<Socket> module supplies the Right Thing for those who want it.
126 use Socket qw(:DEFAULT :crlf);
127 print SOCKET "Hi there, client!$CRLF" # RIGHT
129 When reading I<from> a socket, remember that the default input record
130 separator (C<$/>) is C<\n>, but code like this should recognize C<$/> as
131 C<\012> or C<\015\012>:
139 use Socket qw(:DEFAULT :crlf);
140 local($/) = LF; # not needed if $/ is already \012
143 s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
144 # s/\015?\012/\n/; # same thing
147 And this example is actually better than the previous one even for Unix
148 platforms, because now any C<\015>'s (C<\cM>'s) are stripped out
149 (and there was much rejoicing).
152 =head2 Numbers endianness and Width
154 Different CPUs store integers and floating point numbers in different
155 orders (called I<endianness>) and widths (32-bit and 64-bit being the
156 most common). This affects your programs if they attempt to transfer
157 numbers in binary format from a CPU architecture to another over some
158 channel: either 'live' via network connections or storing the numbers
159 to secondary storage such as a disk file.
161 Conflicting storage orders make utter mess out of the numbers: if a
162 little-endian host (Intel, Alpha) stores 0x12345678 (305419896 in
163 decimal), a big-endian host (Motorola, MIPS, Sparc, PA) reads it as
164 0x78563412 (2018915346 in decimal). To avoid this problem in network
165 (socket) connections use the C<pack()> and C<unpack()> formats C<"n">
166 and C<"N">, the "network" orders, they are guaranteed to be portable.
168 Different widths can cause truncation even between platforms of equal
169 endianness: the platform of shorter width loses the upper parts of the
170 number. There is no good solution for this problem except to avoid
171 transferring or storing raw binary numbers.
173 One can circumnavigate both these problems in two ways: either
174 transfer and store numbers always in text format, instead of raw
175 binary, or consider using modules like C<Data::Dumper> (included in
176 the standard distribution as of Perl 5.005) and C<Storable>.
180 Most platforms these days structure files in a hierarchical fashion.
181 So, it is reasonably safe to assume that any platform supports the
182 notion of a "path" to uniquely identify a file on the system. Just
183 how that path is actually written, differs.
185 While they are similar, file path specifications differ between Unix,
186 Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS> and probably others.
187 Unix, for example, is one of the few OSes that has the idea of a single
190 VMS, Windows, and OS/2 can work similarly to Unix with C</> as path
191 separator, or in their own idiosyncratic ways (such as having several
192 root directories and various "unrooted" device files such NIL: and
195 S<Mac OS> uses C<:> as a path separator instead of C</>.
197 VOS perl can emulate Unix filenames with C</> as path separator. The
198 native pathname characters greater-than, less-than, number-sign, and
199 percent-sign are always accepted.
201 C<RISC OS> perl can emulate Unix filenames with C</> as path
202 separator, or go native and use C<.> for path separator and C<:> to
203 signal filing systems and disc names.
205 As with the newline problem above, there are modules that can help. The
206 C<File::Spec> modules provide methods to do the Right Thing on whatever
207 platform happens to be running the program.
210 chdir(File::Spec->updir()); # go up one directory
211 $file = File::Spec->catfile(
212 File::Spec->curdir(), 'temp', 'file.txt'
214 # on Unix and Win32, './temp/file.txt'
215 # on Mac OS, ':temp:file.txt'
217 File::Spec is available in the standard distribution, as of version
220 In general, production code should not have file paths hardcoded; making
221 them user supplied or from a configuration file is better, keeping in mind
222 that file path syntax varies on different machines.
224 This is especially noticeable in scripts like Makefiles and test suites,
225 which often assume C</> as a path separator for subdirectories.
227 Also of use is C<File::Basename>, from the standard distribution, which
228 splits a pathname into pieces (base filename, full path to directory,
231 Even when on a single platform (if you can call UNIX a single
232 platform), remember not to count on the existence or the contents of
233 system-specific files, like F</etc/passwd>, F</etc/sendmail.conf>, or
234 F</etc/resolv.conf>. For example the F</etc/passwd> may exist but it
235 may not contain the encrypted passwords because the system is using
236 some form of enhanced security-- or it may not contain all the
237 accounts because the system is using NIS. If code does need to rely
238 on such a file, include a description of the file and its format in
239 the code's documentation, and make it easy for the user to override
240 the default location of the file.
242 Do not have two files of the same name with different case, like
243 F<test.pl> and <Test.pl>, as many platforms have case-insensitive
244 filenames. Also, try not to have non-word characters (except for C<.>)
245 in the names, and keep them to the 8.3 convention, for maximum
248 Likewise, if using C<AutoSplit>, try to keep the split functions to
249 8.3 naming and case-insensitive conventions; or, at the very least,
250 make it so the resulting files have a unique (case-insensitively)
253 Don't assume C<E<lt>> won't be the first character of a filename. Always
254 use C<E<lt>> explicitly to open a file for reading:
256 open(FILE, "<$existing_file") or die $!;
259 =head2 System Interaction
261 Not all platforms provide for the notion of a command line, necessarily.
262 These are usually platforms that rely on a Graphical User Interface (GUI)
263 for user interaction. So a program requiring command lines might not work
264 everywhere. But this is probably for the user of the program to deal
267 Some platforms can't delete or rename files that are being held open by
268 the system. Remember to C<close> files when you are done with them.
269 Don't C<unlink> or C<rename> an open file. Don't C<tie> to or C<open> a
270 file that is already tied to or opened; C<untie> or C<close> first.
272 Don't open the same file more than once at a time for writing, as some
273 operating systems put mandatory locks on such files.
275 Don't count on a specific environment variable existing in C<%ENV>.
276 Don't count on C<%ENV> entries being case-sensitive, or even
279 Don't count on signals.
281 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
284 Don't count on per-program environment variables, or per-program current
288 =head2 Interprocess Communication (IPC)
290 In general, don't directly access the system in code that is meant to be
291 portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>, C<``>,
292 C<qx//>, C<open> with a C<|>, nor any of the other things that makes being
293 a Unix perl hacker worth being.
295 Commands that launch external processes are generally supported on
296 most platforms (though many of them do not support any type of forking),
297 but the problem with using them arises from what you invoke with them.
298 External tools are often named differently on different platforms, often
299 not available in the same location, often accept different arguments,
300 often behave differently, and often represent their results in a
301 platform-dependent way. Thus you should seldom depend on them to produce
304 One especially common bit of Perl code is opening a pipe to sendmail:
306 open(MAIL, '|/usr/lib/sendmail -t') or die $!;
308 This is fine for systems programming when sendmail is known to be
309 available. But it is not fine for many non-Unix systems, and even
310 some Unix systems that may not have sendmail installed. If a portable
311 solution is needed, see the C<Mail::Send> and C<Mail::Mailer> modules
312 in the C<MailTools> distribution. C<Mail::Mailer> provides several
313 mailing methods, including mail, sendmail, and direct SMTP
314 (via C<Net::SMTP>) if a mail transfer agent is not available.
316 The rule of thumb for portable code is: Do it all in portable Perl, or
317 use a module (that may internally implement it with platform-specific
318 code, but expose a common interface).
320 The UNIX System V IPC (C<msg*(), sem*(), shm*()>) is not available
321 even in all UNIX platforms.
323 =head2 External Subroutines (XS)
325 XS code, in general, can be made to work with any platform; but dependent
326 libraries, header files, etc., might not be readily available or
327 portable, or the XS code itself might be platform-specific, just as Perl
328 code might be. If the libraries and headers are portable, then it is
329 normally reasonable to make sure the XS code is portable, too.
331 There is a different kind of portability issue with writing XS
332 code: availability of a C compiler on the end-user's system. C brings
333 with it its own portability issues, and writing XS code will expose you to
334 some of those. Writing purely in perl is a comparatively easier way to
338 =head2 Standard Modules
340 In general, the standard modules work across platforms. Notable
341 exceptions are C<CPAN.pm> (which currently makes connections to external
342 programs that may not be available), platform-specific modules (like
343 C<ExtUtils::MM_VMS>), and DBM modules.
345 There is no one DBM module that is available on all platforms.
346 C<SDBM_File> and the others are generally available on all Unix and DOSish
347 ports, but not in MacPerl, where only C<NBDM_File> and C<DB_File> are
350 The good news is that at least some DBM module should be available, and
351 C<AnyDBM_File> will use whichever module it can find. Of course, then
352 the code needs to be fairly strict, dropping to the lowest common
353 denominator (e.g., not exceeding 1K for each record).
358 The system's notion of time of day and calendar date is controlled in
359 widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>,
360 and even if it is, don't assume that you can control the timezone through
363 Don't assume that the epoch starts at 00:00:00, January 1, 1970,
364 because that is OS-specific. Better to store a date in an unambiguous
365 representation. The ISO 8601 standard defines YYYY-MM-DD as the date
366 format. A text representation (like C<1 Jan 1970>) can be easily
367 converted into an OS-specific value using a module like
368 C<Date::Parse>. An array of values, such as those returned by
369 C<localtime>, can be converted to an OS-specific representation using
373 =head2 Character sets and character encoding
375 Assume very little about character sets. Do not assume anything about
376 the numerical values (C<ord()>, C<chr()>) of characters. Do not
377 assume that the alphabetic characters are encoded contiguously (in
378 numerical sense). Do no assume anything about the ordering of the
379 characters. The lowercase letters may come before or after the
380 uppercase letters, the lowercase and uppercase may be interlaced so
381 that both 'a' and 'A' come before the 'b', the accented and other
382 international characters may be interlaced so that E<auml> comes
386 =head2 Internationalisation
388 If you may assume POSIX (a rather large assumption, that: in practise
389 that means UNIX) you may read more about the POSIX locale system from
390 L<perllocale>. The locale system at least attempts to make things a
391 little bit more portable or at least more convenient and
392 native-friendly for non-English users. The system affects character
393 sets and encoding, and date and time formatting, among other things.
396 =head2 System Resources
398 If your code is destined for systems with severely constrained (or
399 missing!) virtual memory systems then you want to be I<especially> mindful
400 of avoiding wasteful constructs such as:
402 # NOTE: this is no longer "bad" in perl5.005
403 for (0..10000000) {} # bad
404 for (my $x = 0; $x <= 10000000; ++$x) {} # good
406 @lines = <VERY_LARGE_FILE>; # bad
408 while (<FILE>) {$file .= $_} # sometimes bad
409 $file = join('', <FILE>); # better
411 The last two may appear unintuitive to most people. The first of those
412 two constructs repeatedly grows a string, while the second allocates a
413 large chunk of memory in one go. On some systems, the latter is more
414 efficient that the former.
419 Most multi-user platforms provide basic levels of security that is usually
420 felt at the file-system level. Other platforms usually don't
421 (unfortunately). Thus the notion of user id, or "home" directory, or even
422 the state of being logged-in, may be unrecognizable on many platforms. If
423 you write programs that are security conscious, it is usually best to know
424 what type of system you will be operating under, and write code explicitly
425 for that platform (or class of platforms).
430 For those times when it is necessary to have platform-specific code,
431 consider keeping the platform-specific code in one place, making porting
432 to other platforms easier. Use the C<Config> module and the special
433 variable C<$^O> to differentiate platforms, as described in
439 Modules uploaded to CPAN are tested by a variety of volunteers on
440 different platforms. These CPAN testers are notified by mail of each
441 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
442 this platform), or UNKNOWN (unknown), along with any relevant notations.
444 The purpose of the testing is twofold: one, to help developers fix any
445 problems in their code that crop up because of lack of testing on other
446 platforms; two, to provide users with information about whether or not
447 a given module works on a given platform.
451 =item Mailing list: cpan-testers@perl.org
453 =item Testing results: C<http://www.connect.net/gbarr/cpan-test/>
460 As of version 5.002, Perl is built with a C<$^O> variable that
461 indicates the operating system it was built on. This was implemented
462 to help speed up code that would otherwise have to C<use Config;> and
463 use the value of C<$Config{'osname'}>. Of course, to get
464 detailed information about the system, looking into C<%Config> is
465 certainly recommended.
469 Perl works on a bewildering variety of Unix and Unix-like platforms (see
470 e.g. most of the files in the F<hints/> directory in the source code kit).
471 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
472 too) is determined by lowercasing and stripping punctuation from the first
473 field of the string returned by typing C<uname -a> (or a similar command)
474 at the shell prompt. Here, for example, are a few of the more popular
477 uname $^O $Config{'archname'}
478 -------------------------------------------
480 FreeBSD freebsd freebsd-i386
481 Linux linux i386-linux
482 HP-UX hpux PA-RISC1.1
484 OSF1 dec_osf alpha-dec_osf
485 SunOS solaris sun4-solaris
486 SunOS solaris i86pc-solaris
487 SunOS4 sunos sun4-sunos
489 Note that because the C<$Config{'archname'}> may depend on the hardware
490 architecture it may vary quite a lot, much more than the C<$^O>.
492 =head2 DOS and Derivatives
494 Perl has long been ported to PC style microcomputers running under
495 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
496 bring yourself to mention (except for Windows CE, if you count that).
497 Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should
498 be aware that each of these file specifications may have subtle
501 $filespec0 = "c:/foo/bar/file.txt";
502 $filespec1 = "c:\\foo\\bar\\file.txt";
503 $filespec2 = 'c:\foo\bar\file.txt';
504 $filespec3 = 'c:\\foo\\bar\\file.txt';
506 System calls accept either C</> or C<\> as the path separator. However,
507 many command-line utilities of DOS vintage treat C</> as the option
508 prefix, so they may get confused by filenames containing C</>. Aside
509 from calling any external programs, C</> will work just fine, and
510 probably better, as it is more consistent with popular usage, and avoids
511 the problem of remembering what to backwhack and what not to.
513 The DOS FAT filesystem can only accommodate "8.3" style filenames. Under
514 the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT)
515 filesystems you may have to be careful about case returned with functions
516 like C<readdir> or used with functions like C<open> or C<opendir>.
518 DOS also treats several filenames as special, such as AUX, PRN, NUL, CON,
519 COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work
520 if you include an explicit directory prefix, in some cases. It is best
521 to avoid such filenames, if you want your code to be portable to DOS
524 Users of these operating systems may also wish to make use of
525 scripts such as I<pl2bat.bat> or I<pl2cmd> as appropriate to
526 put wrappers around your scripts.
528 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
529 and writing to files. C<binmode(FILEHANDLE)> will keep C<\n> translated
530 as C<\012> for that filehandle. Since it is a noop on other systems,
531 C<binmode> should be used for cross-platform code that deals with binary
534 The C<$^O> variable and the C<$Config{'archname'}> values for various
535 DOSish perls are as follows:
537 OS $^O $Config{'archname'}
538 --------------------------------------------
542 Windows 95 MSWin32 MSWin32-x86
543 Windows NT MSWin32 MSWin32-x86
544 Windows NT MSWin32 MSWin32-alpha
545 Windows NT MSWin32 MSWin32-ppc
551 =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/>
553 =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>,
554 C<http://www.juge.com/bbs/Hobb.19.html>
556 =item Build instructions for Win32, L<perlwin32>.
558 =item The ActiveState Pages, C<http://www.activestate.com/>
565 Any module requiring XS compilation is right out for most people, because
566 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
567 modules that can work with MacPerl are built and distributed in binary
568 form on CPAN. See I<MacPerl: Power and Ease> and L<"CPAN Testers">
571 Directories are specified as:
573 volume:folder:file for absolute pathnames
574 volume:folder: for absolute pathnames
575 :folder:file for relative pathnames
576 :folder: for relative pathnames
577 :file for relative pathnames
578 file for relative pathnames
580 Files in a directory are stored in alphabetical order. Filenames are
581 limited to 31 characters, and may include any character except C<:>,
582 which is reserved as a path separator.
584 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
585 C<Mac::Files> module.
587 In the MacPerl application, you can't run a program from the command line;
588 programs that expect C<@ARGV> to be populated can be edited with something
589 like the following, which brings up a dialog box asking for the command
593 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
596 A MacPerl script saved as a droplet will populate C<@ARGV> with the full
597 pathnames of the files dropped onto the script.
599 Mac users can use programs on a kind of command line under MPW (Macintosh
600 Programmer's Workshop, a free development environment from Apple).
601 MacPerl was first introduced as an MPW tool, and MPW can be used like a
604 perl myscript.plx some arguments
606 ToolServer is another app from Apple that provides access to MPW tools
607 from MPW and the MacPerl app, which allows MacPerl programs to use
608 C<system>, backticks, and piped C<open>.
610 "S<Mac OS>" is the proper name for the operating system, but the value
611 in C<$^O> is "MacOS". To determine architecture, version, or whether
612 the application or MPW tool version is running, check:
614 $is_app = $MacPerl::Version =~ /App/;
615 $is_tool = $MacPerl::Version =~ /MPW/;
616 ($version) = $MacPerl::Version =~ /^(\S+)/;
617 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
618 $is_68k = $MacPerl::Architecture eq 'Mac68K';
620 S<Mac OS X>, to be based on NeXT's OpenStep OS, will be able to run
621 MacPerl natively (in the Blue Box, and even in the Yellow Box, once some
622 changes to the toolbox calls are made), but Unix perl will also run
629 =item The MacPerl Pages, C<http://www.ptf.com/macperl/>.
631 =item The MacPerl mailing list, C<mac-perl-request@iis.ee.ethz.ch>.
638 Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
639 Note that perl on VMS can accept either VMS- or Unix-style file
640 specifications as in either of the following:
642 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
643 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
645 but not a mixture of both as in:
647 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
648 Can't open sys$login:/login.com: file specification syntax error
650 Interacting with Perl from the Digital Command Language (DCL) shell
651 often requires a different set of quotation marks than Unix shells do.
654 $ perl -e "print ""Hello, world.\n"""
657 There are a number of ways to wrap your perl scripts in DCL .COM files if
658 you are so inclined. For example:
660 $ write sys$output "Hello from DCL!"
662 $ then perl -x 'f$environment("PROCEDURE")
663 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
664 $ deck/dollars="__END__"
667 print "Hello from Perl!\n";
672 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
673 perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>.
675 Filenames are in the format "name.extension;version". The maximum
676 length for filenames is 39 characters, and the maximum length for
677 extensions is also 39 characters. Version is a number from 1 to
678 32767. Valid characters are C</[A-Z0-9$_-]/>.
680 VMS' RMS filesystem is case insensitive and does not preserve case.
681 C<readdir> returns lowercased filenames, but specifying a file for
682 opening remains case insensitive. Files without extensions have a
683 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
684 will return F<a.> (though that file could be opened with
687 RMS had an eight level limit on directory depths from any rooted logical
688 (allowing 16 levels overall) prior to VMS 7.2. Hence
689 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
690 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
691 have to take this into account, but at least they can refer to the former
692 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
694 The C<VMS::Filespec> module, which gets installed as part of the build
695 process on VMS, is a pure Perl module that can easily be installed on
696 non-VMS platforms and can be helpful for conversions to and from RMS
699 What C<\n> represents depends on the type of file that is open. It could
700 be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file
701 translates newlines to C<\012>, unless C<binmode> was executed on that
702 handle, just like DOSish perls.
704 TCP/IP stacks are optional on VMS, so socket routines might not be
705 implemented. UDP sockets may not be supported.
707 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
708 that you are running on without resorting to loading all of C<%Config>
709 you can examine the content of the C<@INC> array like so:
711 if (grep(/VMS_AXP/, @INC)) {
712 print "I'm on Alpha!\n";
713 } elsif (grep(/VMS_VAX/, @INC)) {
714 print "I'm on VAX!\n";
716 print "I'm not so sure about where $^O is...\n";
725 =item vmsperl list, C<vmsperl-request@newman.upenn.edu>
727 Put words C<SUBSCRIBE VMSPERL> in message body.
729 =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html>
736 Perl on VOS is discussed in F<README.vos> in the perl distribution.
737 Note that perl on VOS can accept either VOS- or Unix-style file
738 specifications as in either of the following:
740 $ perl -ne "print if /perl_setup/i" >system>notices
741 $ perl -ne "print if /perl_setup/i" /system/notices
743 or even a mixture of both as in:
745 $ perl -ne "print if /perl_setup/i" >system/notices
747 Note that even though VOS allows the slash character to appear in object
748 names, because the VOS port of Perl interprets it as a pathname
749 delimiting character, VOS files, directories, or links whose names
750 contain a slash character cannot be processed. Such files must be
751 renamed before they can be processed by Perl.
753 The following C functions are unimplemented on VOS, any any attempt by
754 Perl to use them will result in a fatal error message and an immediate
755 exit from Perl: dup, do_aspawn, do_spawn, execlp, execl, execvp, fork,
756 waitpid. Once these functions become available in the VOS POSIX.1
757 implementation, you can either recompile and rebind Perl, or you can
758 download a newer port from ftp.stratus.com.
760 The value of C<$^O> on VOS is "VOS". To determine the architecture that
761 you are running on without resorting to loading all of C<%Config> you
762 can examine the content of the C<@INC> array like so:
764 if (grep(/VOS/, @INC)) {
765 print "I'm on a Stratus box!\n";
767 print "I'm not on a Stratus box!\n";
771 if (grep(/860/, @INC)) {
772 print "This box is a Stratus XA/R!\n";
773 } elsif (grep(/7100/, @INC)) {
774 print "This box is a Stratus HP 7100 or 8000!\n";
775 } elsif (grep(/8000/, @INC)) {
776 print "This box is a Stratus HP 8000!\n";
778 print "This box is a Stratus 68K...\n";
787 =item VOS mailing list
789 There is no specific mailing list for Perl on VOS. You can post
790 comments to the comp.sys.stratus newsgroup, or subscribe to the general
791 Stratus mailing list. Send a letter with "Subscribe Info-Stratus" in
792 the message body to majordomo@list.stratagy.com.
794 =item VOS Perl on the web at C<http://ftp.stratus.com/pub/vos/vos.html>
799 =head2 EBCDIC Platforms
801 Recent versions of Perl have been ported to platforms such as OS/400 on
802 AS/400 minicomputers as well as OS/390 for IBM Mainframes. Such computers
803 use EBCDIC character sets internally (usually Character Code Set ID 00819
804 for OS/400 and IBM-1047 for OS/390). Note that on the mainframe perl
805 currently works under the "Unix system services for OS/390" (formerly
806 known as OpenEdition).
808 As of R2.5 of USS for OS/390 that Unix sub-system did not support the
809 C<#!> shebang trick for script invocation. Hence, on OS/390 perl scripts
810 can executed with a header similar to the following simple script:
813 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
815 #!/usr/local/bin/perl # just a comment really
817 print "Hello from perl!\n";
819 On these platforms, bear in mind that the EBCDIC character set may have
820 an effect on what happens with some perl functions (such as C<chr>,
821 C<pack>, C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>), as
822 well as bit-fiddling with ASCII constants using operators like C<^>, C<&>
823 and C<|>, not to mention dealing with socket interfaces to ASCII computers
826 Fortunately, most web servers for the mainframe will correctly translate
827 the C<\n> in the following statement to its ASCII equivalent (note that
828 C<\r> is the same under both Unix and OS/390):
830 print "Content-type: text/html\r\n\r\n";
832 The value of C<$^O> on OS/390 is "os390".
834 Some simple tricks for determining if you are running on an EBCDIC
835 platform could include any of the following (perhaps all):
837 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
839 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
841 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
843 Note that one thing you may not want to rely on is the EBCDIC encoding
844 of punctuation characters since these may differ from code page to code
845 page (and once your module or script is rumoured to work with EBCDIC,
846 folks will want it to work with all EBCDIC character sets).
854 The perl-mvs@perl.org list is for discussion of porting issues as well as
855 general usage issues for all EBCDIC Perls. Send a message body of
856 "subscribe perl-mvs" to majordomo@perl.org.
858 =item AS/400 Perl information at C<http://as400.rochester.ibm.com/>
865 As Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
866 Unix and Unix filename emulation is turned on by default, it is quite
867 likely that most simple scripts will work "out of the box". The native
868 filing system is modular, and individual filing systems are free to be
869 case-sensitive or insensitive, and are usually case-preserving. Some
870 native filing systems have name length limits which file and directory
871 names are silently truncated to fit - scripts should be aware that the
872 standard disc filing system currently has a name length limit of B<10>
873 characters, with up to 77 items in a directory, but other filing systems
874 may not impose such limitations.
876 Native filenames are of the form
878 Filesystem#Special_Field::DiscName.$.Directory.Directory.File
882 Special_Field is not usually present, but may contain . and $ .
883 Filesystem =~ m|[A-Za-z0-9_]|
884 DsicName =~ m|[A-Za-z0-9_/]|
885 $ represents the root directory
886 . is the path separator
887 @ is the current directory (per filesystem but machine global)
888 ^ is the parent directory
889 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
891 The default filename translation is roughly C<tr|/.|./|;>
893 Note that C<"ADFS::HardDisc.$.File" ne 'ADFS::HardDisc.$.File'> and that
894 the second stage of C<$> interpolation in regular expressions will fall
895 foul of the C<$.> if scripts are not careful.
897 Logical paths specified by system variables containing comma-separated
898 search lists are also allowed, hence C<System:Modules> is a valid
899 filename, and the filesystem will prefix C<Modules> with each section of
900 C<System$Path> until a name is made that points to an object on disc.
901 Writing to a new file C<System:Modules> would only be allowed if
902 C<System$Path> contains a single item list. The filesystem will also
903 expand system variables in filenames if enclosed in angle brackets, so
904 C<E<lt>System$DirE<gt>.Modules> would look for the file
905 S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious implication of this is
906 that B<fully qualified filenames can start with C<E<lt>E<gt>> and should
907 be protected when C<open> is used for input.
909 Because C<.> was in use as a directory separator and filenames could not
910 be assumed to be unique after 10 characters, Acorn implemented the C
911 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
912 filenames specified in source code and store the respective files in
913 subdirectories named after the suffix. Hence files are translated:
916 C:foo.h C:h.foo (logical path variable)
917 sys/os.h sys.h.os (C compiler groks Unix-speak)
918 10charname.c c.10charname
919 10charname.o o.10charname
920 11charname_.c c.11charname (assuming filesystem truncates at 10)
922 The Unix emulation library's translation of filenames to native assumes
923 that this sort of translation is required, and allows a user defined list
924 of known suffixes which it will transpose in this fashion. This may
925 appear transparent, but consider that with these rules C<foo/bar/baz.h>
926 and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
927 C<glob> cannot and do not attempt to emulate the reverse mapping. Other
928 C<.>s in filenames are translated to C</>.
930 As implied above the environment accessed through C<%ENV> is global, and
931 the convention is that program specific environment variables are of the
932 form C<Program$Name>. Each filing system maintains a current directory,
933 and the current filing system's current directory is the B<global> current
934 directory. Consequently, sociable scripts don't change the current
935 directory but rely on full pathnames, and scripts (and Makefiles) cannot
936 assume that they can spawn a child process which can change the current
937 directory without affecting its parent (and everyone else for that
940 As native operating system filehandles are global and currently are
941 allocated down from 255, with 0 being a reserved value the Unix emulation
942 library emulates Unix filehandles. Consequently, you can't rely on
943 passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
945 The desire of users to express filenames of the form
946 C<E<lt>Foo$DirE<gt>.Bar> on the command line unquoted causes problems,
947 too: C<``> command output capture has to perform a guessing game. It
948 assumes that a string C<E<lt>[^E<lt>E<gt>]+\$[^E<lt>E<gt>]E<gt>> is a
949 reference to an environment variable, whereas anything else involving
950 C<E<lt>> or C<E<gt>> is redirection, and generally manages to be 99%
951 right. Of course, the problem remains that scripts cannot rely on any
952 Unix tools being available, or that any tools found have Unix-like command
955 Extensions and XS are, in theory, buildable by anyone using free tools.
956 In practice, many don't, as users of the Acorn platform are used to binary
957 distribution. MakeMaker does run, but no available make currently copes
958 with MakeMaker's makefiles; even if/when this is fixed, the lack of a
959 Unix-like shell can cause problems with makefile rules, especially lines
960 of the form C<cd sdbm && make all>, and anything using quoting.
962 "S<RISC OS>" is the proper name for the operating system, but the value
963 in C<$^O> is "riscos" (because we don't like shouting).
976 Perl has been ported to a variety of platforms that do not fit into any of
977 the above categories. Some, such as AmigaOS, BeOS, QNX, and Plan 9, have
978 been well-integrated into the standard Perl source code kit. You may need
979 to see the F<ports/> directory on CPAN for information, and possibly
980 binaries, for the likes of: aos, atari, lynxos, riscos, Tandem Guardian,
981 vos, I<etc.> (yes we know that some of these OSes may fall under the Unix
982 category, but we are not a standards body.)
988 =item Atari, Guido Flohr's page C<http://stud.uni-sb.de/~gufl0000/>
990 =item HP 300 MPE/iX C<http://www.cccd.edu/~markb/perlix.html>
994 A free perl5-based PERL.NLM for Novell Netware is available from
995 C<http://www.novell.com/>
1000 =head1 FUNCTION IMPLEMENTATIONS
1002 Listed below are functions unimplemented or implemented differently on
1003 various platforms. Following each description will be, in parentheses, a
1004 list of platforms that the description applies to.
1006 The list may very well be incomplete, or wrong in some places. When in
1007 doubt, consult the platform-specific README files in the Perl source
1008 distribution, and other documentation resources for a given port.
1010 Be aware, moreover, that even among Unix-ish systems there are variations.
1012 For many functions, you can also query C<%Config>, exported by default
1013 from C<Config.pm>. For example, to check if the platform has the C<lstat>
1014 call, check C<$Config{'d_lstat'}>. See L<Config.pm> for a full
1015 description of available variables.
1018 =head2 Alphabetical Listing of Perl Functions
1028 C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories
1029 and applications are executable, and there are no uid/gid
1030 considerations. C<-o> is not supported. (S<Mac OS>)
1032 C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible,
1033 which may not reflect UIC-based file protections. (VMS)
1035 C<-s> returns the size of the data fork, not the total size of data fork
1036 plus resource fork. (S<Mac OS>).
1038 C<-s> by name on an open file will return the space reserved on disk,
1039 rather than the current extent. C<-s> on an open filehandle returns the
1040 current size. (S<RISC OS>)
1042 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
1043 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1045 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
1048 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
1049 (Win32, VMS, S<RISC OS>)
1051 C<-d> is true if passed a device spec without an explicit directory.
1054 C<-T> and C<-B> are implemented, but might misclassify Mac text files
1055 with foreign characters; this is the case will all platforms, but may
1056 affect S<Mac OS> often. (S<Mac OS>)
1058 C<-x> (or C<-X>) determine if a file ends in one of the executable
1059 suffixes. C<-S> is meaningless. (Win32)
1061 C<-x> (or C<-X>) determine if a file has an executable file type.
1064 =item binmode FILEHANDLE
1066 Meaningless. (S<Mac OS>, S<RISC OS>)
1068 Reopens file and restores pointer; if function fails, underlying
1069 filehandle may be closed, or pointer may be in a different position.
1072 The value returned by C<tell> may be affected after the call, and
1073 the filehandle may be flushed. (Win32)
1077 Only limited meaning. Disabling/enabling write permission is mapped to
1078 locking/unlocking the file. (S<Mac OS>)
1080 Only good for changing "owner" read-write access, "group", and "other"
1081 bits are meaningless. (Win32)
1083 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
1085 Access permissions are mapped onto VOS access-control list changes. (VOS)
1089 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
1091 Does nothing, but won't fail. (Win32)
1093 =item chroot FILENAME
1097 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1099 =item crypt PLAINTEXT,SALT
1101 May not be available if library or source was not provided when building
1104 Not implemented. (VOS)
1108 Not implemented. (VMS, Plan9, VOS)
1110 =item dbmopen HASH,DBNAME,MODE
1112 Not implemented. (VMS, Plan9, VOS)
1116 Not useful. (S<Mac OS>, S<RISC OS>)
1118 Not implemented. (Win32)
1120 Invokes VMS debugger. (VMS)
1124 Not implemented. (S<Mac OS>)
1126 =item fcntl FILEHANDLE,FUNCTION,SCALAR
1128 Not implemented. (Win32, VMS)
1130 =item flock FILEHANDLE,OPERATION
1132 Not implemented (S<Mac OS>, VMS, S<RISC OS>, VOS).
1134 Available only on Windows NT (not on Windows 95). (Win32)
1138 Not implemented. (S<Mac OS>, Win32, AmigaOS, S<RISC OS>, VOS)
1142 Not implemented. (S<Mac OS>, S<RISC OS>)
1146 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1150 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1152 =item getpriority WHICH,WHO
1154 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1158 Not implemented. (S<Mac OS>, Win32)
1160 Not useful. (S<RISC OS>)
1164 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1166 =item getnetbyname NAME
1168 Not implemented. (S<Mac OS>, Win32, Plan9)
1172 Not implemented. (S<Mac OS>, Win32)
1174 Not useful. (S<RISC OS>)
1178 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1180 =item getnetbyaddr ADDR,ADDRTYPE
1182 Not implemented. (S<Mac OS>, Win32, Plan9)
1184 =item getprotobynumber NUMBER
1186 Not implemented. (S<Mac OS>)
1188 =item getservbyport PORT,PROTO
1190 Not implemented. (S<Mac OS>)
1194 Not implemented. (S<Mac OS>, Win32)
1198 Not implemented. (S<Mac OS>, Win32, VMS)
1202 Not implemented. (S<Mac OS>, Win32)
1206 Not implemented. (S<Mac OS>, Win32, Plan9)
1210 Not implemented. (S<Mac OS>, Win32, Plan9)
1214 Not implemented. (Win32, Plan9)
1218 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1222 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1224 =item sethostent STAYOPEN
1226 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1228 =item setnetent STAYOPEN
1230 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1232 =item setprotoent STAYOPEN
1234 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1236 =item setservent STAYOPEN
1238 Not implemented. (Plan9, Win32, S<RISC OS>)
1242 Not implemented. (S<Mac OS>, Win32)
1246 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1250 Not implemented. (S<Mac OS>, Win32)
1254 Not implemented. (S<Mac OS>, Win32, Plan9)
1258 Not implemented. (S<Mac OS>, Win32, Plan9)
1262 Not implemented. (Plan9, Win32)
1264 =item getsockopt SOCKET,LEVEL,OPTNAME
1266 Not implemented. (S<Mac OS>, Plan9)
1272 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1275 Features depend on external perlglob.exe or perlglob.bat. May be
1276 overridden with something like File::DosGlob, which is recommended.
1279 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1280 Globbing relies on operating system calls, which may return filenames
1281 in any order. As most filesystems are case-insensitive, even "sorted"
1282 filenames will not be in case-sensitive order. (S<RISC OS>)
1284 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1286 Not implemented. (VMS)
1288 Available only for socket handles, and it does what the ioctlsocket() call
1289 in the Winsock API does. (Win32)
1291 Available only for socket handles. (S<RISC OS>)
1295 Not implemented, hence not useful for taint checking. (S<Mac OS>,
1298 Available only for process handles returned by the C<system(1, ...)>
1299 method of spawning a process. (Win32)
1301 =item link OLDFILE,NEWFILE
1303 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1305 =item lstat FILEHANDLE
1311 Not implemented. (VMS, S<RISC OS>)
1313 Return values may be bogus. (Win32)
1315 =item msgctl ID,CMD,ARG
1317 =item msgget KEY,FLAGS
1319 =item msgsnd ID,MSG,FLAGS
1321 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1323 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1325 =item open FILEHANDLE,EXPR
1327 =item open FILEHANDLE
1329 The C<|> variants are only supported if ToolServer is installed.
1332 open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1334 =item pipe READHANDLE,WRITEHANDLE
1336 Not implemented. (S<Mac OS>)
1342 Not implemented. (Win32, VMS, S<RISC OS>)
1344 =item select RBITS,WBITS,EBITS,TIMEOUT
1346 Only implemented on sockets. (Win32)
1348 Only reliable on sockets. (S<RISC OS>)
1350 =item semctl ID,SEMNUM,CMD,ARG
1352 =item semget KEY,NSEMS,FLAGS
1354 =item semop KEY,OPSTRING
1356 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1358 =item setpgrp PID,PGRP
1360 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1362 =item setpriority WHICH,WHO,PRIORITY
1364 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1366 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1368 Not implemented. (S<Mac OS>, Plan9)
1370 =item shmctl ID,CMD,ARG
1372 =item shmget KEY,SIZE,FLAGS
1374 =item shmread ID,VAR,POS,SIZE
1376 =item shmwrite ID,STRING,POS,SIZE
1378 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1380 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1382 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1384 =item stat FILEHANDLE
1390 mtime and atime are the same thing, and ctime is creation time instead of
1391 inode change time. (S<Mac OS>)
1393 device and inode are not meaningful. (Win32)
1395 device and inode are not necessarily reliable. (VMS)
1397 mtime, atime and ctime all return the last modification time. Device and
1398 inode are not necessarily reliable. (S<RISC OS>)
1400 =item symlink OLDFILE,NEWFILE
1402 Not implemented. (Win32, VMS, S<RISC OS>)
1406 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1408 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1410 The traditional "0", "1", and "2" MODEs are implemented with different
1411 numeric values on some systems. The flags exported by C<Fcntl>
1412 (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (S<Mac
1417 Only implemented if ToolServer is installed. (S<Mac OS>)
1419 As an optimization, may not call the command shell specified in
1420 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1421 process and immediately returns its process designator, without
1422 waiting for it to terminate. Return value may be used subsequently
1423 in C<wait> or C<waitpid>. (Win32)
1425 There is no shell to process metacharacters, and the native standard is
1426 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1427 program. Redirection such as C<E<gt> foo> is performed (if at all) by
1428 the run time library of the spawned program. C<system> I<list> will call
1429 the Unix emulation library's C<exec> emulation, which attempts to provide
1430 emulation of the stdin, stdout, stderr in force in the parent, providing
1431 the child program uses a compatible version of the emulation library.
1432 I<scalar> will call the native command line direct and no such emulation
1433 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1437 Only the first entry returned is nonzero. (S<Mac OS>)
1439 "cumulative" times will be bogus. On anything other than Windows NT,
1440 "system" time will be bogus, and "user" time is actually the time
1441 returned by the clock() function in the C runtime library. (Win32)
1443 Not useful. (S<RISC OS>)
1445 =item truncate FILEHANDLE,LENGTH
1447 =item truncate EXPR,LENGTH
1449 Not implemented. (VMS)
1451 Truncation to zero-length only. (VOS)
1457 Returns undef where unavailable, as of version 5.005.
1461 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1463 May not behave as expected. Behavior depends on the C runtime
1464 library's implementation of utime(), and the filesystem being
1465 used. The FAT filesystem typically does not support an "access
1466 time" field, and it may limit timestamps to a granularity of
1467 two seconds. (Win32)
1471 =item waitpid PID,FLAGS
1473 Not implemented. (S<Mac OS>, VOS)
1475 Can only be applied to process handles returned for processes spawned
1476 using C<system(1, ...)>. (Win32)
1478 Not useful. (S<RISC OS>)
1486 =item 1.35, 9 September 1998
1488 Updated for Stratus VOS.
1490 =item 1.33, 06 August 1998
1492 Integrate more minor changes.
1494 =item 1.32, 05 August 1998
1496 Integrate more minor changes.
1498 =item 1.30, 03 August 1998
1500 Major update for RISC OS, other minor changes.
1502 =item 1.23, 10 July 1998
1504 First public release with perl5.005.
1508 =head1 AUTHORS / CONTRIBUTORS
1510 Abigail E<lt>abigail@fnx.comE<gt>,
1511 Charles Bailey E<lt>bailey@newman.upenn.eduE<gt>,
1512 Graham Barr E<lt>gbarr@pobox.comE<gt>,
1513 Tom Christiansen E<lt>tchrist@perl.comE<gt>,
1514 Nicholas Clark E<lt>Nicholas.Clark@liverpool.ac.ukE<gt>,
1515 Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>,
1516 Dominic Dunlop E<lt>domo@vo.luE<gt>,
1517 Paul Green E<lt>Paul_Green@stratus.comE<gt>,
1518 M.J.T. Guy E<lt>mjtg@cus.cam.ac.ukE<gt>,
1519 Luther Huffman E<lt>lutherh@stratcom.comE<gt>,
1520 Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>,
1521 Andreas J. KE<ouml>nig E<lt>koenig@kulturbox.deE<gt>,
1522 Andrew M. Langmead E<lt>aml@world.std.comE<gt>,
1523 Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>,
1524 Chris Nandor E<lt>pudge@pobox.comE<gt>,
1525 Matthias Neeracher E<lt>neeri@iis.ee.ethz.chE<gt>,
1526 Gary Ng E<lt>71564.1743@CompuServe.COME<gt>,
1527 Tom Phoenix E<lt>rootbeer@teleport.comE<gt>,
1528 Peter Prymmer E<lt>pvhp@forte.comE<gt>,
1529 Hugo van der Sanden E<lt>hv@crypt0.demon.co.ukE<gt>,
1530 Gurusamy Sarathy E<lt>gsar@umich.eduE<gt>,
1531 Paul J. Schinder E<lt>schinder@pobox.comE<gt>,
1532 Dan Sugalski E<lt>sugalskd@ous.eduE<gt>,
1533 Nathan Torkington E<lt>gnat@frii.comE<gt>.
1535 This document is maintained by Chris Nandor.
1539 Version 1.35, last modified 09 September 1998.