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 platform),
232 remember not to count on the existence or the contents of
233 system-specific files or directories, like F</etc/passwd>,
234 F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
235 example, F</etc/passwd> may exist but it may not contain the encrypted
236 passwords because the system is using some form of enhanced security --
237 or it may not contain all the accounts because the system is using NIS.
238 If code does need to rely on such a file, include a description of the
239 file and its format in the code's documentation, and make it easy for
240 the user to override the default location of the file.
242 Don't assume a text file will end with a newline.
244 Do not have two files of the same name with different case, like
245 F<test.pl> and F<Test.pl>, as many platforms have case-insensitive
246 filenames. Also, try not to have non-word characters (except for C<.>)
247 in the names, and keep them to the 8.3 convention, for maximum
250 Likewise, if using C<AutoSplit>, try to keep the split functions to
251 8.3 naming and case-insensitive conventions; or, at the very least,
252 make it so the resulting files have a unique (case-insensitively)
255 Don't assume C<E<gt>> won't be the first character of a filename. Always
256 use C<E<lt>> explicitly to open a file for reading.
258 open(FILE, "<$existing_file") or die $!;
260 Actually, though, if filenames might use strange characters, it is
261 safest to open it with C<sysopen> instead of C<open>, which is magic.
264 =head2 System Interaction
266 Not all platforms provide for the notion of a command line, necessarily.
267 These are usually platforms that rely on a Graphical User Interface (GUI)
268 for user interaction. So a program requiring command lines might not work
269 everywhere. But this is probably for the user of the program to deal
272 Some platforms can't delete or rename files that are being held open by
273 the system. Remember to C<close> files when you are done with them.
274 Don't C<unlink> or C<rename> an open file. Don't C<tie> to or C<open> a
275 file that is already tied to or opened; C<untie> or C<close> first.
277 Don't open the same file more than once at a time for writing, as some
278 operating systems put mandatory locks on such files.
280 Don't count on a specific environment variable existing in C<%ENV>.
281 Don't count on C<%ENV> entries being case-sensitive, or even
284 Don't count on signals.
286 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
289 Don't count on per-program environment variables, or per-program current
292 Don't count on specific values of C<$!>.
295 =head2 Interprocess Communication (IPC)
297 In general, don't directly access the system in code that is meant to be
298 portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>, C<``>,
299 C<qx//>, C<open> with a C<|>, nor any of the other things that makes being
300 a Unix perl hacker worth being.
302 Commands that launch external processes are generally supported on
303 most platforms (though many of them do not support any type of forking),
304 but the problem with using them arises from what you invoke with them.
305 External tools are often named differently on different platforms, often
306 not available in the same location, often accept different arguments,
307 often behave differently, and often represent their results in a
308 platform-dependent way. Thus you should seldom depend on them to produce
311 One especially common bit of Perl code is opening a pipe to sendmail:
313 open(MAIL, '|/usr/lib/sendmail -t') or die $!;
315 This is fine for systems programming when sendmail is known to be
316 available. But it is not fine for many non-Unix systems, and even
317 some Unix systems that may not have sendmail installed. If a portable
318 solution is needed, see the C<Mail::Send> and C<Mail::Mailer> modules
319 in the C<MailTools> distribution. C<Mail::Mailer> provides several
320 mailing methods, including mail, sendmail, and direct SMTP
321 (via C<Net::SMTP>) if a mail transfer agent is not available.
323 The rule of thumb for portable code is: Do it all in portable Perl, or
324 use a module (that may internally implement it with platform-specific
325 code, but expose a common interface).
327 The UNIX System V IPC (C<msg*(), sem*(), shm*()>) is not available
328 even in all UNIX platforms.
331 =head2 External Subroutines (XS)
333 XS code, in general, can be made to work with any platform; but dependent
334 libraries, header files, etc., might not be readily available or
335 portable, or the XS code itself might be platform-specific, just as Perl
336 code might be. If the libraries and headers are portable, then it is
337 normally reasonable to make sure the XS code is portable, too.
339 There is a different kind of portability issue with writing XS
340 code: availability of a C compiler on the end-user's system. C brings
341 with it its own portability issues, and writing XS code will expose you to
342 some of those. Writing purely in perl is a comparatively easier way to
346 =head2 Standard Modules
348 In general, the standard modules work across platforms. Notable
349 exceptions are C<CPAN.pm> (which currently makes connections to external
350 programs that may not be available), platform-specific modules (like
351 C<ExtUtils::MM_VMS>), and DBM modules.
353 There is no one DBM module that is available on all platforms.
354 C<SDBM_File> and the others are generally available on all Unix and DOSish
355 ports, but not in MacPerl, where only C<NBDM_File> and C<DB_File> are
358 The good news is that at least some DBM module should be available, and
359 C<AnyDBM_File> will use whichever module it can find. Of course, then
360 the code needs to be fairly strict, dropping to the lowest common
361 denominator (e.g., not exceeding 1K for each record).
366 The system's notion of time of day and calendar date is controlled in
367 widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>,
368 and even if it is, don't assume that you can control the timezone through
371 Don't assume that the epoch starts at 00:00:00, January 1, 1970,
372 because that is OS-specific. Better to store a date in an unambiguous
373 representation. The ISO 8601 standard defines YYYY-MM-DD as the date
374 format. A text representation (like C<1 Jan 1970>) can be easily
375 converted into an OS-specific value using a module like
376 C<Date::Parse>. An array of values, such as those returned by
377 C<localtime>, can be converted to an OS-specific representation using
381 =head2 Character sets and character encoding
383 Assume very little about character sets. Do not assume anything about
384 the numerical values (C<ord()>, C<chr()>) of characters. Do not
385 assume that the alphabetic characters are encoded contiguously (in
386 numerical sense). Do not assume anything about the ordering of the
387 characters. The lowercase letters may come before or after the
388 uppercase letters, the lowercase and uppercase may be interlaced so
389 that both 'a' and 'A' come before the 'b', the accented and other
390 international characters may be interlaced so that E<auml> comes
394 =head2 Internationalisation
396 If you may assume POSIX (a rather large assumption, that in practice
397 means UNIX), you may read more about the POSIX locale system from
398 L<perllocale>. The locale system at least attempts to make things a
399 little bit more portable, or at least more convenient and
400 native-friendly for non-English users. The system affects character
401 sets and encoding, and date and time formatting, among other things.
404 =head2 System Resources
406 If your code is destined for systems with severely constrained (or
407 missing!) virtual memory systems then you want to be I<especially> mindful
408 of avoiding wasteful constructs such as:
410 # NOTE: this is no longer "bad" in perl5.005
411 for (0..10000000) {} # bad
412 for (my $x = 0; $x <= 10000000; ++$x) {} # good
414 @lines = <VERY_LARGE_FILE>; # bad
416 while (<FILE>) {$file .= $_} # sometimes bad
417 $file = join('', <FILE>); # better
419 The last two may appear unintuitive to most people. The first of those
420 two constructs repeatedly grows a string, while the second allocates a
421 large chunk of memory in one go. On some systems, the latter is more
422 efficient that the former.
427 Most multi-user platforms provide basic levels of security that is usually
428 felt at the file-system level. Other platforms usually don't
429 (unfortunately). Thus the notion of user id, or "home" directory, or even
430 the state of being logged-in, may be unrecognizable on many platforms. If
431 you write programs that are security conscious, it is usually best to know
432 what type of system you will be operating under, and write code explicitly
433 for that platform (or class of platforms).
438 For those times when it is necessary to have platform-specific code,
439 consider keeping the platform-specific code in one place, making porting
440 to other platforms easier. Use the C<Config> module and the special
441 variable C<$^O> to differentiate platforms, as described in
447 Modules uploaded to CPAN are tested by a variety of volunteers on
448 different platforms. These CPAN testers are notified by mail of each
449 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
450 this platform), or UNKNOWN (unknown), along with any relevant notations.
452 The purpose of the testing is twofold: one, to help developers fix any
453 problems in their code that crop up because of lack of testing on other
454 platforms; two, to provide users with information about whether or not
455 a given module works on a given platform.
459 =item Mailing list: cpan-testers@perl.org
461 =item Testing results: C<http://www.connect.net/gbarr/cpan-test/>
468 As of version 5.002, Perl is built with a C<$^O> variable that
469 indicates the operating system it was built on. This was implemented
470 to help speed up code that would otherwise have to C<use Config;> and
471 use the value of C<$Config{'osname'}>. Of course, to get
472 detailed information about the system, looking into C<%Config> is
473 certainly recommended.
477 Perl works on a bewildering variety of Unix and Unix-like platforms (see
478 e.g. most of the files in the F<hints/> directory in the source code kit).
479 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
480 too) is determined by lowercasing and stripping punctuation from the first
481 field of the string returned by typing C<uname -a> (or a similar command)
482 at the shell prompt. Here, for example, are a few of the more popular
485 uname $^O $Config{'archname'}
486 -------------------------------------------
488 FreeBSD freebsd freebsd-i386
489 Linux linux i386-linux
490 HP-UX hpux PA-RISC1.1
492 OSF1 dec_osf alpha-dec_osf
493 SunOS solaris sun4-solaris
494 SunOS solaris i86pc-solaris
495 SunOS4 sunos sun4-sunos
497 Note that because the C<$Config{'archname'}> may depend on the hardware
498 architecture it may vary quite a lot, much more than the C<$^O>.
500 =head2 DOS and Derivatives
502 Perl has long been ported to PC style microcomputers running under
503 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
504 bring yourself to mention (except for Windows CE, if you count that).
505 Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should
506 be aware that each of these file specifications may have subtle
509 $filespec0 = "c:/foo/bar/file.txt";
510 $filespec1 = "c:\\foo\\bar\\file.txt";
511 $filespec2 = 'c:\foo\bar\file.txt';
512 $filespec3 = 'c:\\foo\\bar\\file.txt';
514 System calls accept either C</> or C<\> as the path separator. However,
515 many command-line utilities of DOS vintage treat C</> as the option
516 prefix, so they may get confused by filenames containing C</>. Aside
517 from calling any external programs, C</> will work just fine, and
518 probably better, as it is more consistent with popular usage, and avoids
519 the problem of remembering what to backwhack and what not to.
521 The DOS FAT filesystem can only accommodate "8.3" style filenames. Under
522 the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT)
523 filesystems you may have to be careful about case returned with functions
524 like C<readdir> or used with functions like C<open> or C<opendir>.
526 DOS also treats several filenames as special, such as AUX, PRN, NUL, CON,
527 COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work
528 if you include an explicit directory prefix, in some cases. It is best
529 to avoid such filenames, if you want your code to be portable to DOS
532 Users of these operating systems may also wish to make use of
533 scripts such as I<pl2bat.bat> or I<pl2cmd> as appropriate to
534 put wrappers around your scripts.
536 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
537 and writing to files. C<binmode(FILEHANDLE)> will keep C<\n> translated
538 as C<\012> for that filehandle. Since it is a noop on other systems,
539 C<binmode> should be used for cross-platform code that deals with binary
542 The C<$^O> variable and the C<$Config{'archname'}> values for various
543 DOSish perls are as follows:
545 OS $^O $Config{'archname'}
546 --------------------------------------------
550 Windows 95 MSWin32 MSWin32-x86
551 Windows NT MSWin32 MSWin32-x86
552 Windows NT MSWin32 MSWin32-alpha
553 Windows NT MSWin32 MSWin32-ppc
559 =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/>
561 =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>,
562 C<http://www.juge.com/bbs/Hobb.19.html>
564 =item Build instructions for Win32, L<perlwin32>.
566 =item The ActiveState Pages, C<http://www.activestate.com/>
573 Any module requiring XS compilation is right out for most people, because
574 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
575 modules that can work with MacPerl are built and distributed in binary
576 form on CPAN. See I<MacPerl: Power and Ease> and L<"CPAN Testers">
579 Directories are specified as:
581 volume:folder:file for absolute pathnames
582 volume:folder: for absolute pathnames
583 :folder:file for relative pathnames
584 :folder: for relative pathnames
585 :file for relative pathnames
586 file for relative pathnames
588 Files in a directory are stored in alphabetical order. Filenames are
589 limited to 31 characters, and may include any character except C<:>,
590 which is reserved as a path separator.
592 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
593 C<Mac::Files> module, or C<chmod(0444, ...)> and C<chmod(0666, ...)>.
595 In the MacPerl application, you can't run a program from the command line;
596 programs that expect C<@ARGV> to be populated can be edited with something
597 like the following, which brings up a dialog box asking for the command
601 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
604 A MacPerl script saved as a droplet will populate C<@ARGV> with the full
605 pathnames of the files dropped onto the script.
607 Mac users can use programs on a kind of command line under MPW (Macintosh
608 Programmer's Workshop, a free development environment from Apple).
609 MacPerl was first introduced as an MPW tool, and MPW can be used like a
612 perl myscript.plx some arguments
614 ToolServer is another app from Apple that provides access to MPW tools
615 from MPW and the MacPerl app, which allows MacPerl programs to use
616 C<system>, backticks, and piped C<open>.
618 "S<Mac OS>" is the proper name for the operating system, but the value
619 in C<$^O> is "MacOS". To determine architecture, version, or whether
620 the application or MPW tool version is running, check:
622 $is_app = $MacPerl::Version =~ /App/;
623 $is_tool = $MacPerl::Version =~ /MPW/;
624 ($version) = $MacPerl::Version =~ /^(\S+)/;
625 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
626 $is_68k = $MacPerl::Architecture eq 'Mac68K';
628 S<Mac OS X>, to be based on NeXT's OpenStep OS, will (in theory) be able
629 to run MacPerl natively, but Unix perl will also run natively under the
630 built-in Unix environment.
636 =item The MacPerl Pages, C<http://www.ptf.com/macperl/>.
638 =item The MacPerl mailing list, C<mac-perl-request@iis.ee.ethz.ch>.
645 Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
646 Note that perl on VMS can accept either VMS- or Unix-style file
647 specifications as in either of the following:
649 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
650 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
652 but not a mixture of both as in:
654 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
655 Can't open sys$login:/login.com: file specification syntax error
657 Interacting with Perl from the Digital Command Language (DCL) shell
658 often requires a different set of quotation marks than Unix shells do.
661 $ perl -e "print ""Hello, world.\n"""
664 There are a number of ways to wrap your perl scripts in DCL .COM files if
665 you are so inclined. For example:
667 $ write sys$output "Hello from DCL!"
669 $ then perl -x 'f$environment("PROCEDURE")
670 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
671 $ deck/dollars="__END__"
674 print "Hello from Perl!\n";
679 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
680 perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>.
682 Filenames are in the format "name.extension;version". The maximum
683 length for filenames is 39 characters, and the maximum length for
684 extensions is also 39 characters. Version is a number from 1 to
685 32767. Valid characters are C</[A-Z0-9$_-]/>.
687 VMS' RMS filesystem is case insensitive and does not preserve case.
688 C<readdir> returns lowercased filenames, but specifying a file for
689 opening remains case insensitive. Files without extensions have a
690 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
691 will return F<a.> (though that file could be opened with
694 RMS had an eight level limit on directory depths from any rooted logical
695 (allowing 16 levels overall) prior to VMS 7.2. Hence
696 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
697 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
698 have to take this into account, but at least they can refer to the former
699 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
701 The C<VMS::Filespec> module, which gets installed as part of the build
702 process on VMS, is a pure Perl module that can easily be installed on
703 non-VMS platforms and can be helpful for conversions to and from RMS
706 What C<\n> represents depends on the type of file that is open. It could
707 be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file
708 translates newlines to C<\012>, unless C<binmode> was executed on that
709 handle, just like DOSish perls.
711 TCP/IP stacks are optional on VMS, so socket routines might not be
712 implemented. UDP sockets may not be supported.
714 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
715 that you are running on without resorting to loading all of C<%Config>
716 you can examine the content of the C<@INC> array like so:
718 if (grep(/VMS_AXP/, @INC)) {
719 print "I'm on Alpha!\n";
720 } elsif (grep(/VMS_VAX/, @INC)) {
721 print "I'm on VAX!\n";
723 print "I'm not so sure about where $^O is...\n";
732 =item vmsperl list, C<vmsperl-request@newman.upenn.edu>
734 Put words C<SUBSCRIBE VMSPERL> in message body.
736 =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html>
743 Perl on VOS is discussed in F<README.vos> in the perl distribution.
744 Note that perl on VOS can accept either VOS- or Unix-style file
745 specifications as in either of the following:
747 $ perl -ne "print if /perl_setup/i" >system>notices
748 $ perl -ne "print if /perl_setup/i" /system/notices
750 or even a mixture of both as in:
752 $ perl -ne "print if /perl_setup/i" >system/notices
754 Note that even though VOS allows the slash character to appear in object
755 names, because the VOS port of Perl interprets it as a pathname
756 delimiting character, VOS files, directories, or links whose names
757 contain a slash character cannot be processed. Such files must be
758 renamed before they can be processed by Perl.
760 The following C functions are unimplemented on VOS, any any attempt by
761 Perl to use them will result in a fatal error message and an immediate
762 exit from Perl: dup, do_aspawn, do_spawn, execlp, execl, execvp, fork,
763 waitpid. Once these functions become available in the VOS POSIX.1
764 implementation, you can either recompile and rebind Perl, or you can
765 download a newer port from ftp.stratus.com.
767 The value of C<$^O> on VOS is "VOS". To determine the architecture that
768 you are running on without resorting to loading all of C<%Config> you
769 can examine the content of the C<@INC> array like so:
771 if (grep(/VOS/, @INC)) {
772 print "I'm on a Stratus box!\n";
774 print "I'm not on a Stratus box!\n";
778 if (grep(/860/, @INC)) {
779 print "This box is a Stratus XA/R!\n";
780 } elsif (grep(/7100/, @INC)) {
781 print "This box is a Stratus HP 7100 or 8000!\n";
782 } elsif (grep(/8000/, @INC)) {
783 print "This box is a Stratus HP 8000!\n";
785 print "This box is a Stratus 68K...\n";
794 =item VOS mailing list
796 There is no specific mailing list for Perl on VOS. You can post
797 comments to the comp.sys.stratus newsgroup, or subscribe to the general
798 Stratus mailing list. Send a letter with "Subscribe Info-Stratus" in
799 the message body to majordomo@list.stratagy.com.
801 =item VOS Perl on the web at C<http://ftp.stratus.com/pub/vos/vos.html>
806 =head2 EBCDIC Platforms
808 Recent versions of Perl have been ported to platforms such as OS/400 on
809 AS/400 minicomputers as well as OS/390 & VM/ESA for IBM Mainframes. Such
810 computers use EBCDIC character sets internally (usually Character Code
811 Set ID 00819 for OS/400 and IBM-1047 for OS/390 & VM/ESA). Note that on
812 the mainframe perl currently works under the "Unix system services
813 for OS/390" (formerly known as OpenEdition) and VM/ESA OpenEdition.
815 As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
816 sub-systems do not support the C<#!> shebang trick for script invocation.
817 Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
818 similar to the following simple script:
821 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
823 #!/usr/local/bin/perl # just a comment really
825 print "Hello from perl!\n";
827 On these platforms, bear in mind that the EBCDIC character set may have
828 an effect on what happens with some perl functions (such as C<chr>,
829 C<pack>, C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>), as
830 well as bit-fiddling with ASCII constants using operators like C<^>, C<&>
831 and C<|>, not to mention dealing with socket interfaces to ASCII computers
834 Fortunately, most web servers for the mainframe will correctly translate
835 the C<\n> in the following statement to its ASCII equivalent (note that
836 C<\r> is the same under both Unix and OS/390 & VM/ESA):
838 print "Content-type: text/html\r\n\r\n";
840 The value of C<$^O> on OS/390 is "os390".
842 The value of C<$^O> on VM/ESA is "vmesa".
844 Some simple tricks for determining if you are running on an EBCDIC
845 platform could include any of the following (perhaps all):
847 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
849 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
851 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
853 Note that one thing you may not want to rely on is the EBCDIC encoding
854 of punctuation characters since these may differ from code page to code
855 page (and once your module or script is rumoured to work with EBCDIC,
856 folks will want it to work with all EBCDIC character sets).
864 The perl-mvs@perl.org list is for discussion of porting issues as well as
865 general usage issues for all EBCDIC Perls. Send a message body of
866 "subscribe perl-mvs" to majordomo@perl.org.
868 =item AS/400 Perl information at C<http://as400.rochester.ibm.com/>
875 As Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
876 Unix and Unix filename emulation is turned on by default, it is quite
877 likely that most simple scripts will work "out of the box". The native
878 filing system is modular, and individual filing systems are free to be
879 case-sensitive or insensitive, and are usually case-preserving. Some
880 native filing systems have name length limits which file and directory
881 names are silently truncated to fit - scripts should be aware that the
882 standard disc filing system currently has a name length limit of B<10>
883 characters, with up to 77 items in a directory, but other filing systems
884 may not impose such limitations.
886 Native filenames are of the form
888 Filesystem#Special_Field::DiscName.$.Directory.Directory.File
892 Special_Field is not usually present, but may contain . and $ .
893 Filesystem =~ m|[A-Za-z0-9_]|
894 DsicName =~ m|[A-Za-z0-9_/]|
895 $ represents the root directory
896 . is the path separator
897 @ is the current directory (per filesystem but machine global)
898 ^ is the parent directory
899 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
901 The default filename translation is roughly C<tr|/.|./|;>
903 Note that C<"ADFS::HardDisc.$.File" ne 'ADFS::HardDisc.$.File'> and that
904 the second stage of C<$> interpolation in regular expressions will fall
905 foul of the C<$.> if scripts are not careful.
907 Logical paths specified by system variables containing comma-separated
908 search lists are also allowed, hence C<System:Modules> is a valid
909 filename, and the filesystem will prefix C<Modules> with each section of
910 C<System$Path> until a name is made that points to an object on disc.
911 Writing to a new file C<System:Modules> would only be allowed if
912 C<System$Path> contains a single item list. The filesystem will also
913 expand system variables in filenames if enclosed in angle brackets, so
914 C<E<lt>System$DirE<gt>.Modules> would look for the file
915 S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious implication of this is
916 that B<fully qualified filenames can start with C<E<lt>E<gt>>> and should
917 be protected when C<open> is used for input.
919 Because C<.> was in use as a directory separator and filenames could not
920 be assumed to be unique after 10 characters, Acorn implemented the C
921 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
922 filenames specified in source code and store the respective files in
923 subdirectories named after the suffix. Hence files are translated:
926 C:foo.h C:h.foo (logical path variable)
927 sys/os.h sys.h.os (C compiler groks Unix-speak)
928 10charname.c c.10charname
929 10charname.o o.10charname
930 11charname_.c c.11charname (assuming filesystem truncates at 10)
932 The Unix emulation library's translation of filenames to native assumes
933 that this sort of translation is required, and allows a user defined list
934 of known suffixes which it will transpose in this fashion. This may
935 appear transparent, but consider that with these rules C<foo/bar/baz.h>
936 and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
937 C<glob> cannot and do not attempt to emulate the reverse mapping. Other
938 C<.>s in filenames are translated to C</>.
940 As implied above the environment accessed through C<%ENV> is global, and
941 the convention is that program specific environment variables are of the
942 form C<Program$Name>. Each filing system maintains a current directory,
943 and the current filing system's current directory is the B<global> current
944 directory. Consequently, sociable scripts don't change the current
945 directory but rely on full pathnames, and scripts (and Makefiles) cannot
946 assume that they can spawn a child process which can change the current
947 directory without affecting its parent (and everyone else for that
950 As native operating system filehandles are global and currently are
951 allocated down from 255, with 0 being a reserved value the Unix emulation
952 library emulates Unix filehandles. Consequently, you can't rely on
953 passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
955 The desire of users to express filenames of the form
956 C<E<lt>Foo$DirE<gt>.Bar> on the command line unquoted causes problems,
957 too: C<``> command output capture has to perform a guessing game. It
958 assumes that a string C<E<lt>[^E<lt>E<gt>]+\$[^E<lt>E<gt>]E<gt>> is a
959 reference to an environment variable, whereas anything else involving
960 C<E<lt>> or C<E<gt>> is redirection, and generally manages to be 99%
961 right. Of course, the problem remains that scripts cannot rely on any
962 Unix tools being available, or that any tools found have Unix-like command
965 Extensions and XS are, in theory, buildable by anyone using free tools.
966 In practice, many don't, as users of the Acorn platform are used to binary
967 distribution. MakeMaker does run, but no available make currently copes
968 with MakeMaker's makefiles; even if/when this is fixed, the lack of a
969 Unix-like shell can cause problems with makefile rules, especially lines
970 of the form C<cd sdbm && make all>, and anything using quoting.
972 "S<RISC OS>" is the proper name for the operating system, but the value
973 in C<$^O> is "riscos" (because we don't like shouting).
986 Perl has been ported to a variety of platforms that do not fit into any of
987 the above categories. Some, such as AmigaOS, BeOS, QNX, and Plan 9, have
988 been well-integrated into the standard Perl source code kit. You may need
989 to see the F<ports/> directory on CPAN for information, and possibly
990 binaries, for the likes of: aos, atari, lynxos, riscos, Tandem Guardian,
991 vos, I<etc.> (yes we know that some of these OSes may fall under the Unix
992 category, but we are not a standards body.)
998 =item Atari, Guido Flohr's page C<http://stud.uni-sb.de/~gufl0000/>
1000 =item HP 300 MPE/iX C<http://www.cccd.edu/~markb/perlix.html>
1002 =item Novell Netware
1004 A free perl5-based PERL.NLM for Novell Netware is available from
1005 C<http://www.novell.com/>
1010 =head1 FUNCTION IMPLEMENTATIONS
1012 Listed below are functions unimplemented or implemented differently on
1013 various platforms. Following each description will be, in parentheses, a
1014 list of platforms that the description applies to.
1016 The list may very well be incomplete, or wrong in some places. When in
1017 doubt, consult the platform-specific README files in the Perl source
1018 distribution, and other documentation resources for a given port.
1020 Be aware, moreover, that even among Unix-ish systems there are variations.
1022 For many functions, you can also query C<%Config>, exported by default
1023 from C<Config.pm>. For example, to check if the platform has the C<lstat>
1024 call, check C<$Config{'d_lstat'}>. See L<Config.pm> for a full
1025 description of available variables.
1028 =head2 Alphabetical Listing of Perl Functions
1038 C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories
1039 and applications are executable, and there are no uid/gid
1040 considerations. C<-o> is not supported. (S<Mac OS>)
1042 C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible,
1043 which may not reflect UIC-based file protections. (VMS)
1045 C<-s> returns the size of the data fork, not the total size of data fork
1046 plus resource fork. (S<Mac OS>).
1048 C<-s> by name on an open file will return the space reserved on disk,
1049 rather than the current extent. C<-s> on an open filehandle returns the
1050 current size. (S<RISC OS>)
1052 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
1053 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1055 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
1058 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
1059 (Win32, VMS, S<RISC OS>)
1061 C<-d> is true if passed a device spec without an explicit directory.
1064 C<-T> and C<-B> are implemented, but might misclassify Mac text files
1065 with foreign characters; this is the case will all platforms, but may
1066 affect S<Mac OS> often. (S<Mac OS>)
1068 C<-x> (or C<-X>) determine if a file ends in one of the executable
1069 suffixes. C<-S> is meaningless. (Win32)
1071 C<-x> (or C<-X>) determine if a file has an executable file type.
1074 =item binmode FILEHANDLE
1076 Meaningless. (S<Mac OS>, S<RISC OS>)
1078 Reopens file and restores pointer; if function fails, underlying
1079 filehandle may be closed, or pointer may be in a different position.
1082 The value returned by C<tell> may be affected after the call, and
1083 the filehandle may be flushed. (Win32)
1087 Only limited meaning. Disabling/enabling write permission is mapped to
1088 locking/unlocking the file. (S<Mac OS>)
1090 Only good for changing "owner" read-write access, "group", and "other"
1091 bits are meaningless. (Win32)
1093 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
1095 Access permissions are mapped onto VOS access-control list changes. (VOS)
1099 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
1101 Does nothing, but won't fail. (Win32)
1103 =item chroot FILENAME
1107 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS, VM/ESA)
1109 =item crypt PLAINTEXT,SALT
1111 May not be available if library or source was not provided when building
1114 Not implemented. (VOS)
1118 Not implemented. (VMS, Plan9, VOS)
1120 =item dbmopen HASH,DBNAME,MODE
1122 Not implemented. (VMS, Plan9, VOS)
1126 Not useful. (S<Mac OS>, S<RISC OS>)
1128 Not implemented. (Win32)
1130 Invokes VMS debugger. (VMS)
1134 Not implemented. (S<Mac OS>)
1136 Implemented via Spawn. (VM/ESA)
1138 =item fcntl FILEHANDLE,FUNCTION,SCALAR
1140 Not implemented. (Win32, VMS)
1142 =item flock FILEHANDLE,OPERATION
1144 Not implemented (S<Mac OS>, VMS, S<RISC OS>, VOS).
1146 Available only on Windows NT (not on Windows 95). (Win32)
1150 Not implemented. (S<Mac OS>, Win32, AmigaOS, S<RISC OS>, VOS, VM/ESA)
1154 Not implemented. (S<Mac OS>, S<RISC OS>)
1158 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1162 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1164 =item getpriority WHICH,WHO
1166 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1170 Not implemented. (S<Mac OS>, Win32)
1172 Not useful. (S<RISC OS>)
1176 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1178 =item getnetbyname NAME
1180 Not implemented. (S<Mac OS>, Win32, Plan9)
1184 Not implemented. (S<Mac OS>, Win32)
1186 Not useful. (S<RISC OS>)
1190 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1192 =item getnetbyaddr ADDR,ADDRTYPE
1194 Not implemented. (S<Mac OS>, Win32, Plan9)
1196 =item getprotobynumber NUMBER
1198 Not implemented. (S<Mac OS>)
1200 =item getservbyport PORT,PROTO
1202 Not implemented. (S<Mac OS>)
1206 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1210 Not implemented. (S<Mac OS>, Win32, VMS, VM/ESA)
1214 Not implemented. (S<Mac OS>, Win32)
1218 Not implemented. (S<Mac OS>, Win32, Plan9)
1222 Not implemented. (S<Mac OS>, Win32, Plan9)
1226 Not implemented. (Win32, Plan9)
1230 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1234 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1236 =item sethostent STAYOPEN
1238 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1240 =item setnetent STAYOPEN
1242 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1244 =item setprotoent STAYOPEN
1246 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1248 =item setservent STAYOPEN
1250 Not implemented. (Plan9, Win32, S<RISC OS>)
1254 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1258 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VM/ESA)
1262 Not implemented. (S<Mac OS>, Win32)
1266 Not implemented. (S<Mac OS>, Win32, Plan9)
1270 Not implemented. (S<Mac OS>, Win32, Plan9)
1274 Not implemented. (Plan9, Win32)
1276 =item getsockopt SOCKET,LEVEL,OPTNAME
1278 Not implemented. (S<Mac OS>, Plan9)
1284 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1287 Features depend on external perlglob.exe or perlglob.bat. May be
1288 overridden with something like File::DosGlob, which is recommended.
1291 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1292 Globbing relies on operating system calls, which may return filenames
1293 in any order. As most filesystems are case-insensitive, even "sorted"
1294 filenames will not be in case-sensitive order. (S<RISC OS>)
1296 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1298 Not implemented. (VMS)
1300 Available only for socket handles, and it does what the ioctlsocket() call
1301 in the Winsock API does. (Win32)
1303 Available only for socket handles. (S<RISC OS>)
1307 Not implemented, hence not useful for taint checking. (S<Mac OS>,
1310 Available only for process handles returned by the C<system(1, ...)>
1311 method of spawning a process. (Win32)
1313 =item link OLDFILE,NEWFILE
1315 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1317 =item lstat FILEHANDLE
1323 Not implemented. (VMS, S<RISC OS>)
1325 Return values may be bogus. (Win32)
1327 =item msgctl ID,CMD,ARG
1329 =item msgget KEY,FLAGS
1331 =item msgsnd ID,MSG,FLAGS
1333 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1335 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1337 =item open FILEHANDLE,EXPR
1339 =item open FILEHANDLE
1341 The C<|> variants are only supported if ToolServer is installed.
1344 open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1346 =item pipe READHANDLE,WRITEHANDLE
1348 Not implemented. (S<Mac OS>)
1354 Not implemented. (Win32, VMS, S<RISC OS>)
1356 =item select RBITS,WBITS,EBITS,TIMEOUT
1358 Only implemented on sockets. (Win32)
1360 Only reliable on sockets. (S<RISC OS>)
1362 =item semctl ID,SEMNUM,CMD,ARG
1364 =item semget KEY,NSEMS,FLAGS
1366 =item semop KEY,OPSTRING
1368 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1370 =item setpgrp PID,PGRP
1372 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1374 =item setpriority WHICH,WHO,PRIORITY
1376 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1378 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1380 Not implemented. (S<Mac OS>, Plan9)
1382 =item shmctl ID,CMD,ARG
1384 =item shmget KEY,SIZE,FLAGS
1386 =item shmread ID,VAR,POS,SIZE
1388 =item shmwrite ID,STRING,POS,SIZE
1390 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1392 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1394 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1396 =item stat FILEHANDLE
1402 mtime and atime are the same thing, and ctime is creation time instead of
1403 inode change time. (S<Mac OS>)
1405 device and inode are not meaningful. (Win32)
1407 device and inode are not necessarily reliable. (VMS)
1409 mtime, atime and ctime all return the last modification time. Device and
1410 inode are not necessarily reliable. (S<RISC OS>)
1412 =item symlink OLDFILE,NEWFILE
1414 Not implemented. (Win32, VMS, S<RISC OS>)
1418 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1420 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1422 The traditional "0", "1", and "2" MODEs are implemented with different
1423 numeric values on some systems. The flags exported by C<Fcntl>
1424 (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (S<Mac
1425 OS>, OS/390, VM/ESA)
1429 Only implemented if ToolServer is installed. (S<Mac OS>)
1431 As an optimization, may not call the command shell specified in
1432 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1433 process and immediately returns its process designator, without
1434 waiting for it to terminate. Return value may be used subsequently
1435 in C<wait> or C<waitpid>. (Win32)
1437 There is no shell to process metacharacters, and the native standard is
1438 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1439 program. Redirection such as C<E<gt> foo> is performed (if at all) by
1440 the run time library of the spawned program. C<system> I<list> will call
1441 the Unix emulation library's C<exec> emulation, which attempts to provide
1442 emulation of the stdin, stdout, stderr in force in the parent, providing
1443 the child program uses a compatible version of the emulation library.
1444 I<scalar> will call the native command line direct and no such emulation
1445 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1449 Only the first entry returned is nonzero. (S<Mac OS>)
1451 "cumulative" times will be bogus. On anything other than Windows NT,
1452 "system" time will be bogus, and "user" time is actually the time
1453 returned by the clock() function in the C runtime library. (Win32)
1455 Not useful. (S<RISC OS>)
1457 =item truncate FILEHANDLE,LENGTH
1459 =item truncate EXPR,LENGTH
1461 Not implemented. (VMS)
1463 Truncation to zero-length only. (VOS)
1465 If a FILEHANDLE is supplied, it must be writable and opened in append
1466 mode (i.e., use C<open(FH, '>>filename')>
1467 or C<sysopen(FH,...,O_APPEND|O_RDWR)>. If a filename is supplied, it
1468 should not be held open elsewhere. (Win32)
1474 Returns undef where unavailable, as of version 5.005.
1478 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1480 May not behave as expected. Behavior depends on the C runtime
1481 library's implementation of utime(), and the filesystem being
1482 used. The FAT filesystem typically does not support an "access
1483 time" field, and it may limit timestamps to a granularity of
1484 two seconds. (Win32)
1488 =item waitpid PID,FLAGS
1490 Not implemented. (S<Mac OS>, VOS)
1492 Can only be applied to process handles returned for processes spawned
1493 using C<system(1, ...)>. (Win32)
1495 Not useful. (S<RISC OS>)
1503 =item v1.37, 19 December 1998
1505 More minor changes. Merge two separate version 1.35 documents.
1507 =item v1.36, 9 September 1998
1509 Updated for Stratus VOS. Also known as version 1.35.
1511 =item v1.35, 13 August 1998
1513 Integrate more minor changes, plus addition of new sections under
1514 L<"ISSUES">: L<"Numbers endianness and Width">,
1515 L<"Character sets and character encoding">,
1516 L<"Internationalisation">.
1518 =item v1.33, 06 August 1998
1520 Integrate more minor changes.
1522 =item v1.32, 05 August 1998
1524 Integrate more minor changes.
1526 =item v1.30, 03 August 1998
1528 Major update for RISC OS, other minor changes.
1530 =item v1.23, 10 July 1998
1532 First public release with perl5.005.
1536 =head1 AUTHORS / CONTRIBUTORS
1538 Abigail E<lt>abigail@fnx.comE<gt>,
1539 Charles Bailey E<lt>bailey@newman.upenn.eduE<gt>,
1540 Graham Barr E<lt>gbarr@pobox.comE<gt>,
1541 Tom Christiansen E<lt>tchrist@perl.comE<gt>,
1542 Nicholas Clark E<lt>Nicholas.Clark@liverpool.ac.ukE<gt>,
1543 Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>,
1544 Dominic Dunlop E<lt>domo@vo.luE<gt>,
1545 Neale Ferguson E<lt>neale@mailbox.tabnsw.com.auE<gt>
1546 Paul Green E<lt>Paul_Green@stratus.comE<gt>,
1547 M.J.T. Guy E<lt>mjtg@cus.cam.ac.ukE<gt>,
1548 Jarkko Hietaniemi E<lt>jhi@iki.fi<gt>,
1549 Luther Huffman E<lt>lutherh@stratcom.comE<gt>,
1550 Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>,
1551 Andreas J. KE<ouml>nig E<lt>koenig@kulturbox.deE<gt>,
1552 Markus Laker E<lt>mlaker@contax.co.ukE<gt>,
1553 Andrew M. Langmead E<lt>aml@world.std.comE<gt>,
1554 Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>,
1555 Chris Nandor E<lt>pudge@pobox.comE<gt>,
1556 Matthias Neeracher E<lt>neeri@iis.ee.ethz.chE<gt>,
1557 Gary Ng E<lt>71564.1743@CompuServe.COME<gt>,
1558 Tom Phoenix E<lt>rootbeer@teleport.comE<gt>,
1559 Peter Prymmer E<lt>pvhp@forte.comE<gt>,
1560 Hugo van der Sanden E<lt>hv@crypt0.demon.co.ukE<gt>,
1561 Gurusamy Sarathy E<lt>gsar@umich.eduE<gt>,
1562 Paul J. Schinder E<lt>schinder@pobox.comE<gt>,
1563 Dan Sugalski E<lt>sugalskd@ous.eduE<gt>,
1564 Nathan Torkington E<lt>gnat@frii.comE<gt>.
1566 This document is maintained by Chris Nandor
1567 E<lt>pudge@pobox.comE<gt>.
1571 Version 1.37, last modified 19 December 1998