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).
151 An important thing to remember is that functions that return data
152 should translate newlines when appropriate. Often one line of code
155 $data =~ s/\015?\012/\n/g;
159 =head2 Numbers endianness and Width
161 Different CPUs store integers and floating point numbers in different
162 orders (called I<endianness>) and widths (32-bit and 64-bit being the
163 most common). This affects your programs if they attempt to transfer
164 numbers in binary format from a CPU architecture to another over some
165 channel: either 'live' via network connections or storing the numbers
166 to secondary storage such as a disk file.
168 Conflicting storage orders make utter mess out of the numbers: if a
169 little-endian host (Intel, Alpha) stores 0x12345678 (305419896 in
170 decimal), a big-endian host (Motorola, MIPS, Sparc, PA) reads it as
171 0x78563412 (2018915346 in decimal). To avoid this problem in network
172 (socket) connections use the C<pack()> and C<unpack()> formats C<"n">
173 and C<"N">, the "network" orders, they are guaranteed to be portable.
175 Different widths can cause truncation even between platforms of equal
176 endianness: the platform of shorter width loses the upper parts of the
177 number. There is no good solution for this problem except to avoid
178 transferring or storing raw binary numbers.
180 One can circumnavigate both these problems in two ways: either
181 transfer and store numbers always in text format, instead of raw
182 binary, or consider using modules like C<Data::Dumper> (included in
183 the standard distribution as of Perl 5.005) and C<Storable>.
185 =head2 Files and Filesystems
187 Most platforms these days structure files in a hierarchical fashion.
188 So, it is reasonably safe to assume that any platform supports the
189 notion of a "path" to uniquely identify a file on the system. Just
190 how that path is actually written, differs.
192 While they are similar, file path specifications differ between Unix,
193 Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS> and probably others.
194 Unix, for example, is one of the few OSes that has the idea of a single
197 VMS, Windows, and OS/2 can work similarly to Unix with C</> as path
198 separator, or in their own idiosyncratic ways (such as having several
199 root directories and various "unrooted" device files such NIL: and
202 S<Mac OS> uses C<:> as a path separator instead of C</>.
204 The filesystem may support neither hard links (C<link()>) nor
205 symbolic links (C<symlink()>, C<readlink()>, C<lstat()>).
207 The filesystem may not support neither access timestamp nor change
208 timestamp (meaning that about the only portable timestamp is the
209 modification timestamp), or one second granularity of any timestamps
210 (e.g. the FAT filesystem limits the time granularity to two seconds).
212 VOS perl can emulate Unix filenames with C</> as path separator. The
213 native pathname characters greater-than, less-than, number-sign, and
214 percent-sign are always accepted.
216 C<RISC OS> perl can emulate Unix filenames with C</> as path
217 separator, or go native and use C<.> for path separator and C<:> to
218 signal filing systems and disc names.
220 As with the newline problem above, there are modules that can help. The
221 C<File::Spec> modules provide methods to do the Right Thing on whatever
222 platform happens to be running the program.
225 chdir(File::Spec->updir()); # go up one directory
226 $file = File::Spec->catfile(
227 File::Spec->curdir(), 'temp', 'file.txt'
229 # on Unix and Win32, './temp/file.txt'
230 # on Mac OS, ':temp:file.txt'
232 File::Spec is available in the standard distribution, as of version
235 In general, production code should not have file paths hardcoded; making
236 them user supplied or from a configuration file is better, keeping in mind
237 that file path syntax varies on different machines.
239 This is especially noticeable in scripts like Makefiles and test suites,
240 which often assume C</> as a path separator for subdirectories.
242 Also of use is C<File::Basename>, from the standard distribution, which
243 splits a pathname into pieces (base filename, full path to directory,
246 Even when on a single platform (if you can call UNIX a single platform),
247 remember not to count on the existence or the contents of
248 system-specific files or directories, like F</etc/passwd>,
249 F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
250 example, F</etc/passwd> may exist but it may not contain the encrypted
251 passwords because the system is using some form of enhanced security --
252 or it may not contain all the accounts because the system is using NIS.
253 If code does need to rely on such a file, include a description of the
254 file and its format in the code's documentation, and make it easy for
255 the user to override the default location of the file.
257 Don't assume a text file will end with a newline.
259 Do not have two files of the same name with different case, like
260 F<test.pl> and F<Test.pl>, as many platforms have case-insensitive
261 filenames. Also, try not to have non-word characters (except for C<.>)
262 in the names, and keep them to the 8.3 convention, for maximum
265 Likewise, if using C<AutoSplit>, try to keep the split functions to
266 8.3 naming and case-insensitive conventions; or, at the very least,
267 make it so the resulting files have a unique (case-insensitively)
270 There certainly can be whitespace in filenames. Many systems (DOS,
271 VMS) cannot have more than one C<"."> in their filenames.
273 Don't assume C<E<gt>> won't be the first character of a filename.
274 Always use C<E<lt>> explicitly to open a file for reading.
276 open(FILE, "<$existing_file") or die $!;
278 Actually, though, if filenames might use strange characters, it is
279 safest to open it with C<sysopen> instead of C<open>, which is magic.
282 =head2 System Interaction
284 Not all platforms provide for the notion of a command line, necessarily.
285 These are usually platforms that rely on a Graphical User Interface (GUI)
286 for user interaction. So a program requiring command lines might not work
287 everywhere. But this is probably for the user of the program to deal
290 Some platforms can't delete or rename files that are being held open by
291 the system. Remember to C<close> files when you are done with them.
292 Don't C<unlink> or C<rename> an open file. Don't C<tie> to or C<open> a
293 file that is already tied to or opened; C<untie> or C<close> first.
295 Don't open the same file more than once at a time for writing, as some
296 operating systems put mandatory locks on such files.
298 Don't count on a specific environment variable existing in C<%ENV>.
299 Don't count on C<%ENV> entries being case-sensitive, or even
302 Don't count on signals.
304 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
307 Don't count on per-program environment variables, or per-program current
310 Don't count on specific values of C<$!>.
313 =head2 Interprocess Communication (IPC)
315 In general, don't directly access the system in code that is meant to be
316 portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>, C<``>,
317 C<qx//>, C<open> with a C<|>, nor any of the other things that makes being
318 a Unix perl hacker worth being.
320 Commands that launch external processes are generally supported on
321 most platforms (though many of them do not support any type of forking),
322 but the problem with using them arises from what you invoke with them.
323 External tools are often named differently on different platforms, often
324 not available in the same location, often accept different arguments,
325 often behave differently, and often represent their results in a
326 platform-dependent way. Thus you should seldom depend on them to produce
329 One especially common bit of Perl code is opening a pipe to sendmail:
331 open(MAIL, '|/usr/lib/sendmail -t') or die $!;
333 This is fine for systems programming when sendmail is known to be
334 available. But it is not fine for many non-Unix systems, and even
335 some Unix systems that may not have sendmail installed. If a portable
336 solution is needed, see the C<Mail::Send> and C<Mail::Mailer> modules
337 in the C<MailTools> distribution. C<Mail::Mailer> provides several
338 mailing methods, including mail, sendmail, and direct SMTP
339 (via C<Net::SMTP>) if a mail transfer agent is not available.
341 The rule of thumb for portable code is: Do it all in portable Perl, or
342 use a module (that may internally implement it with platform-specific
343 code, but expose a common interface).
345 The UNIX System V IPC (C<msg*(), sem*(), shm*()>) is not available
346 even in all UNIX platforms.
349 =head2 External Subroutines (XS)
351 XS code, in general, can be made to work with any platform; but dependent
352 libraries, header files, etc., might not be readily available or
353 portable, or the XS code itself might be platform-specific, just as Perl
354 code might be. If the libraries and headers are portable, then it is
355 normally reasonable to make sure the XS code is portable, too.
357 There is a different kind of portability issue with writing XS
358 code: availability of a C compiler on the end-user's system. C brings
359 with it its own portability issues, and writing XS code will expose you to
360 some of those. Writing purely in perl is a comparatively easier way to
364 =head2 Standard Modules
366 In general, the standard modules work across platforms. Notable
367 exceptions are C<CPAN.pm> (which currently makes connections to external
368 programs that may not be available), platform-specific modules (like
369 C<ExtUtils::MM_VMS>), and DBM modules.
371 There is no one DBM module that is available on all platforms.
372 C<SDBM_File> and the others are generally available on all Unix and DOSish
373 ports, but not in MacPerl, where only C<NBDM_File> and C<DB_File> are
376 The good news is that at least some DBM module should be available, and
377 C<AnyDBM_File> will use whichever module it can find. Of course, then
378 the code needs to be fairly strict, dropping to the lowest common
379 denominator (e.g., not exceeding 1K for each record).
384 The system's notion of time of day and calendar date is controlled in
385 widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>,
386 and even if it is, don't assume that you can control the timezone through
389 Don't assume that the epoch starts at 00:00:00, January 1, 1970,
390 because that is OS-specific. Better to store a date in an unambiguous
391 representation. The ISO 8601 standard defines YYYY-MM-DD as the date
392 format. A text representation (like C<1 Jan 1970>) can be easily
393 converted into an OS-specific value using a module like
394 C<Date::Parse>. An array of values, such as those returned by
395 C<localtime>, can be converted to an OS-specific representation using
399 =head2 Character sets and character encoding
401 Assume very little about character sets. Do not assume anything about
402 the numerical values (C<ord()>, C<chr()>) of characters. Do not
403 assume that the alphabetic characters are encoded contiguously (in
404 numerical sense). Do not assume anything about the ordering of the
405 characters. The lowercase letters may come before or after the
406 uppercase letters, the lowercase and uppercase may be interlaced so
407 that both 'a' and 'A' come before the 'b', the accented and other
408 international characters may be interlaced so that E<auml> comes
412 =head2 Internationalisation
414 If you may assume POSIX (a rather large assumption, that in practice
415 means UNIX), you may read more about the POSIX locale system from
416 L<perllocale>. The locale system at least attempts to make things a
417 little bit more portable, or at least more convenient and
418 native-friendly for non-English users. The system affects character
419 sets and encoding, and date and time formatting, among other things.
422 =head2 System Resources
424 If your code is destined for systems with severely constrained (or
425 missing!) virtual memory systems then you want to be I<especially> mindful
426 of avoiding wasteful constructs such as:
428 # NOTE: this is no longer "bad" in perl5.005
429 for (0..10000000) {} # bad
430 for (my $x = 0; $x <= 10000000; ++$x) {} # good
432 @lines = <VERY_LARGE_FILE>; # bad
434 while (<FILE>) {$file .= $_} # sometimes bad
435 $file = join('', <FILE>); # better
437 The last two may appear unintuitive to most people. The first of those
438 two constructs repeatedly grows a string, while the second allocates a
439 large chunk of memory in one go. On some systems, the latter is more
440 efficient that the former.
445 Most multi-user platforms provide basic levels of security that is usually
446 felt at the file-system level. Other platforms usually don't
447 (unfortunately). Thus the notion of user id, or "home" directory, or even
448 the state of being logged-in, may be unrecognizable on many platforms. If
449 you write programs that are security conscious, it is usually best to know
450 what type of system you will be operating under, and write code explicitly
451 for that platform (or class of platforms).
456 For those times when it is necessary to have platform-specific code,
457 consider keeping the platform-specific code in one place, making porting
458 to other platforms easier. Use the C<Config> module and the special
459 variable C<$^O> to differentiate platforms, as described in
465 Modules uploaded to CPAN are tested by a variety of volunteers on
466 different platforms. These CPAN testers are notified by mail of each
467 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
468 this platform), or UNKNOWN (unknown), along with any relevant notations.
470 The purpose of the testing is twofold: one, to help developers fix any
471 problems in their code that crop up because of lack of testing on other
472 platforms; two, to provide users with information about whether or not
473 a given module works on a given platform.
477 =item Mailing list: cpan-testers@perl.org
479 =item Testing results: C<http://www.connect.net/gbarr/cpan-test/>
486 As of version 5.002, Perl is built with a C<$^O> variable that
487 indicates the operating system it was built on. This was implemented
488 to help speed up code that would otherwise have to C<use Config;> and
489 use the value of C<$Config{'osname'}>. Of course, to get
490 detailed information about the system, looking into C<%Config> is
491 certainly recommended.
495 Perl works on a bewildering variety of Unix and Unix-like platforms (see
496 e.g. most of the files in the F<hints/> directory in the source code kit).
497 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
498 too) is determined by lowercasing and stripping punctuation from the first
499 field of the string returned by typing C<uname -a> (or a similar command)
500 at the shell prompt. Here, for example, are a few of the more popular
503 uname $^O $Config{'archname'}
504 -------------------------------------------
506 FreeBSD freebsd freebsd-i386
507 Linux linux i386-linux
508 HP-UX hpux PA-RISC1.1
510 OSF1 dec_osf alpha-dec_osf
511 SunOS solaris sun4-solaris
512 SunOS solaris i86pc-solaris
513 SunOS4 sunos sun4-sunos
515 Note that because the C<$Config{'archname'}> may depend on the hardware
516 architecture it may vary quite a lot, much more than the C<$^O>.
518 =head2 DOS and Derivatives
520 Perl has long been ported to PC style microcomputers running under
521 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
522 bring yourself to mention (except for Windows CE, if you count that).
523 Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should
524 be aware that each of these file specifications may have subtle
527 $filespec0 = "c:/foo/bar/file.txt";
528 $filespec1 = "c:\\foo\\bar\\file.txt";
529 $filespec2 = 'c:\foo\bar\file.txt';
530 $filespec3 = 'c:\\foo\\bar\\file.txt';
532 System calls accept either C</> or C<\> as the path separator. However,
533 many command-line utilities of DOS vintage treat C</> as the option
534 prefix, so they may get confused by filenames containing C</>. Aside
535 from calling any external programs, C</> will work just fine, and
536 probably better, as it is more consistent with popular usage, and avoids
537 the problem of remembering what to backwhack and what not to.
539 The DOS FAT filesystem can only accommodate "8.3" style filenames. Under
540 the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT)
541 filesystems you may have to be careful about case returned with functions
542 like C<readdir> or used with functions like C<open> or C<opendir>.
544 DOS also treats several filenames as special, such as AUX, PRN, NUL, CON,
545 COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work
546 if you include an explicit directory prefix, in some cases. It is best
547 to avoid such filenames, if you want your code to be portable to DOS
550 Users of these operating systems may also wish to make use of
551 scripts such as I<pl2bat.bat> or I<pl2cmd> as appropriate to
552 put wrappers around your scripts.
554 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
555 and writing to files. C<binmode(FILEHANDLE)> will keep C<\n> translated
556 as C<\012> for that filehandle. Since it is a noop on other systems,
557 C<binmode> should be used for cross-platform code that deals with binary
560 The C<$^O> variable and the C<$Config{'archname'}> values for various
561 DOSish perls are as follows:
563 OS $^O $Config{'archname'}
564 --------------------------------------------
568 Windows 95 MSWin32 MSWin32-x86
569 Windows NT MSWin32 MSWin32-x86
570 Windows NT MSWin32 MSWin32-alpha
571 Windows NT MSWin32 MSWin32-ppc
577 =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/>
579 =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>,
580 C<http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html> or
581 C<ftp://hobbes.nmsu.edu/pub/os2/dev/emx>
583 =item Build instructions for Win32, L<perlwin32>.
585 =item The ActiveState Pages, C<http://www.activestate.com/>
592 Any module requiring XS compilation is right out for most people, because
593 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
594 modules that can work with MacPerl are built and distributed in binary
595 form on CPAN. See I<MacPerl: Power and Ease> and L<"CPAN Testers">
598 Directories are specified as:
600 volume:folder:file for absolute pathnames
601 volume:folder: for absolute pathnames
602 :folder:file for relative pathnames
603 :folder: for relative pathnames
604 :file for relative pathnames
605 file for relative pathnames
607 Files in a directory are stored in alphabetical order. Filenames are
608 limited to 31 characters, and may include any character except C<:>,
609 which is reserved as a path separator.
611 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
612 C<Mac::Files> module, or C<chmod(0444, ...)> and C<chmod(0666, ...)>.
614 In the MacPerl application, you can't run a program from the command line;
615 programs that expect C<@ARGV> to be populated can be edited with something
616 like the following, which brings up a dialog box asking for the command
620 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
623 A MacPerl script saved as a droplet will populate C<@ARGV> with the full
624 pathnames of the files dropped onto the script.
626 Mac users can use programs on a kind of command line under MPW (Macintosh
627 Programmer's Workshop, a free development environment from Apple).
628 MacPerl was first introduced as an MPW tool, and MPW can be used like a
631 perl myscript.plx some arguments
633 ToolServer is another app from Apple that provides access to MPW tools
634 from MPW and the MacPerl app, which allows MacPerl programs to use
635 C<system>, backticks, and piped C<open>.
637 "S<Mac OS>" is the proper name for the operating system, but the value
638 in C<$^O> is "MacOS". To determine architecture, version, or whether
639 the application or MPW tool version is running, check:
641 $is_app = $MacPerl::Version =~ /App/;
642 $is_tool = $MacPerl::Version =~ /MPW/;
643 ($version) = $MacPerl::Version =~ /^(\S+)/;
644 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
645 $is_68k = $MacPerl::Architecture eq 'Mac68K';
647 S<Mac OS X>, to be based on NeXT's OpenStep OS, will (in theory) be able
648 to run MacPerl natively, but Unix perl will also run natively under the
649 built-in Unix environment.
655 =item The MacPerl Pages, C<http://www.ptf.com/macperl/>.
657 =item The MacPerl mailing list, C<mac-perl-request@iis.ee.ethz.ch>.
664 Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
665 Note that perl on VMS can accept either VMS- or Unix-style file
666 specifications as in either of the following:
668 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
669 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
671 but not a mixture of both as in:
673 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
674 Can't open sys$login:/login.com: file specification syntax error
676 Interacting with Perl from the Digital Command Language (DCL) shell
677 often requires a different set of quotation marks than Unix shells do.
680 $ perl -e "print ""Hello, world.\n"""
683 There are a number of ways to wrap your perl scripts in DCL .COM files if
684 you are so inclined. For example:
686 $ write sys$output "Hello from DCL!"
688 $ then perl -x 'f$environment("PROCEDURE")
689 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
690 $ deck/dollars="__END__"
693 print "Hello from Perl!\n";
698 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
699 perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>.
701 Filenames are in the format "name.extension;version". The maximum
702 length for filenames is 39 characters, and the maximum length for
703 extensions is also 39 characters. Version is a number from 1 to
704 32767. Valid characters are C</[A-Z0-9$_-]/>.
706 VMS' RMS filesystem is case insensitive and does not preserve case.
707 C<readdir> returns lowercased filenames, but specifying a file for
708 opening remains case insensitive. Files without extensions have a
709 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
710 will return F<a.> (though that file could be opened with
713 RMS had an eight level limit on directory depths from any rooted logical
714 (allowing 16 levels overall) prior to VMS 7.2. Hence
715 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
716 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
717 have to take this into account, but at least they can refer to the former
718 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
720 The C<VMS::Filespec> module, which gets installed as part of the build
721 process on VMS, is a pure Perl module that can easily be installed on
722 non-VMS platforms and can be helpful for conversions to and from RMS
725 What C<\n> represents depends on the type of file that is open. It could
726 be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file
727 translates newlines to C<\012>, unless C<binmode> was executed on that
728 handle, just like DOSish perls.
730 TCP/IP stacks are optional on VMS, so socket routines might not be
731 implemented. UDP sockets may not be supported.
733 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
734 that you are running on without resorting to loading all of C<%Config>
735 you can examine the content of the C<@INC> array like so:
737 if (grep(/VMS_AXP/, @INC)) {
738 print "I'm on Alpha!\n";
739 } elsif (grep(/VMS_VAX/, @INC)) {
740 print "I'm on VAX!\n";
742 print "I'm not so sure about where $^O is...\n";
751 =item vmsperl list, C<vmsperl-request@newman.upenn.edu>
753 Put words C<SUBSCRIBE VMSPERL> in message body.
755 =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html>
762 Perl on VOS is discussed in F<README.vos> in the perl distribution.
763 Note that perl on VOS can accept either VOS- or Unix-style file
764 specifications as in either of the following:
766 $ perl -ne "print if /perl_setup/i" >system>notices
767 $ perl -ne "print if /perl_setup/i" /system/notices
769 or even a mixture of both as in:
771 $ perl -ne "print if /perl_setup/i" >system/notices
773 Note that even though VOS allows the slash character to appear in object
774 names, because the VOS port of Perl interprets it as a pathname
775 delimiting character, VOS files, directories, or links whose names
776 contain a slash character cannot be processed. Such files must be
777 renamed before they can be processed by Perl.
779 The following C functions are unimplemented on VOS, and any attempt by
780 Perl to use them will result in a fatal error message and an immediate
781 exit from Perl: dup, do_aspawn, do_spawn, fork, waitpid. Once these
782 functions become available in the VOS POSIX.1 implementation, you can
783 either recompile and rebind Perl, or you can download a newer port from
786 The value of C<$^O> on VOS is "VOS". To determine the architecture that
787 you are running on without resorting to loading all of C<%Config> you
788 can examine the content of the C<@INC> array like so:
790 if (grep(/VOS/, @INC)) {
791 print "I'm on a Stratus box!\n";
793 print "I'm not on a Stratus box!\n";
797 if (grep(/860/, @INC)) {
798 print "This box is a Stratus XA/R!\n";
799 } elsif (grep(/7100/, @INC)) {
800 print "This box is a Stratus HP 7100 or 8000!\n";
801 } elsif (grep(/8000/, @INC)) {
802 print "This box is a Stratus HP 8000!\n";
804 print "This box is a Stratus 68K...\n";
813 =item VOS mailing list
815 There is no specific mailing list for Perl on VOS. You can post
816 comments to the comp.sys.stratus newsgroup, or subscribe to the general
817 Stratus mailing list. Send a letter with "Subscribe Info-Stratus" in
818 the message body to majordomo@list.stratagy.com.
820 =item VOS Perl on the web at C<http://ftp.stratus.com/pub/vos/vos.html>
825 =head2 EBCDIC Platforms
827 Recent versions of Perl have been ported to platforms such as OS/400 on
828 AS/400 minicomputers as well as OS/390 & VM/ESA for IBM Mainframes. Such
829 computers use EBCDIC character sets internally (usually Character Code
830 Set ID 00819 for OS/400 and IBM-1047 for OS/390 & VM/ESA). Note that on
831 the mainframe perl currently works under the "Unix system services
832 for OS/390" (formerly known as OpenEdition) and VM/ESA OpenEdition.
834 As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
835 sub-systems do not support the C<#!> shebang trick for script invocation.
836 Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
837 similar to the following simple script:
840 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
842 #!/usr/local/bin/perl # just a comment really
844 print "Hello from perl!\n";
846 On these platforms, bear in mind that the EBCDIC character set may have
847 an effect on what happens with some perl functions (such as C<chr>,
848 C<pack>, C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>), as
849 well as bit-fiddling with ASCII constants using operators like C<^>, C<&>
850 and C<|>, not to mention dealing with socket interfaces to ASCII computers
853 Fortunately, most web servers for the mainframe will correctly translate
854 the C<\n> in the following statement to its ASCII equivalent (note that
855 C<\r> is the same under both Unix and OS/390 & VM/ESA):
857 print "Content-type: text/html\r\n\r\n";
859 The value of C<$^O> on OS/390 is "os390".
861 The value of C<$^O> on VM/ESA is "vmesa".
863 Some simple tricks for determining if you are running on an EBCDIC
864 platform could include any of the following (perhaps all):
866 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
868 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
870 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
872 Note that one thing you may not want to rely on is the EBCDIC encoding
873 of punctuation characters since these may differ from code page to code
874 page (and once your module or script is rumoured to work with EBCDIC,
875 folks will want it to work with all EBCDIC character sets).
883 The perl-mvs@perl.org list is for discussion of porting issues as well as
884 general usage issues for all EBCDIC Perls. Send a message body of
885 "subscribe perl-mvs" to majordomo@perl.org.
887 =item AS/400 Perl information at C<http://as400.rochester.ibm.com/>
894 As Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
895 Unix and Unix filename emulation is turned on by default, it is quite
896 likely that most simple scripts will work "out of the box". The native
897 filing system is modular, and individual filing systems are free to be
898 case-sensitive or insensitive, and are usually case-preserving. Some
899 native filing systems have name length limits which file and directory
900 names are silently truncated to fit - scripts should be aware that the
901 standard disc filing system currently has a name length limit of B<10>
902 characters, with up to 77 items in a directory, but other filing systems
903 may not impose such limitations.
905 Native filenames are of the form
907 Filesystem#Special_Field::DiscName.$.Directory.Directory.File
911 Special_Field is not usually present, but may contain . and $ .
912 Filesystem =~ m|[A-Za-z0-9_]|
913 DsicName =~ m|[A-Za-z0-9_/]|
914 $ represents the root directory
915 . is the path separator
916 @ is the current directory (per filesystem but machine global)
917 ^ is the parent directory
918 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
920 The default filename translation is roughly C<tr|/.|./|;>
922 Note that C<"ADFS::HardDisc.$.File" ne 'ADFS::HardDisc.$.File'> and that
923 the second stage of C<$> interpolation in regular expressions will fall
924 foul of the C<$.> if scripts are not careful.
926 Logical paths specified by system variables containing comma-separated
927 search lists are also allowed, hence C<System:Modules> is a valid
928 filename, and the filesystem will prefix C<Modules> with each section of
929 C<System$Path> until a name is made that points to an object on disc.
930 Writing to a new file C<System:Modules> would only be allowed if
931 C<System$Path> contains a single item list. The filesystem will also
932 expand system variables in filenames if enclosed in angle brackets, so
933 C<E<lt>System$DirE<gt>.Modules> would look for the file
934 S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious implication of this is
935 that B<fully qualified filenames can start with C<E<lt>E<gt>>> and should
936 be protected when C<open> is used for input.
938 Because C<.> was in use as a directory separator and filenames could not
939 be assumed to be unique after 10 characters, Acorn implemented the C
940 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
941 filenames specified in source code and store the respective files in
942 subdirectories named after the suffix. Hence files are translated:
945 C:foo.h C:h.foo (logical path variable)
946 sys/os.h sys.h.os (C compiler groks Unix-speak)
947 10charname.c c.10charname
948 10charname.o o.10charname
949 11charname_.c c.11charname (assuming filesystem truncates at 10)
951 The Unix emulation library's translation of filenames to native assumes
952 that this sort of translation is required, and allows a user defined list
953 of known suffixes which it will transpose in this fashion. This may
954 appear transparent, but consider that with these rules C<foo/bar/baz.h>
955 and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
956 C<glob> cannot and do not attempt to emulate the reverse mapping. Other
957 C<.>s in filenames are translated to C</>.
959 As implied above the environment accessed through C<%ENV> is global, and
960 the convention is that program specific environment variables are of the
961 form C<Program$Name>. Each filing system maintains a current directory,
962 and the current filing system's current directory is the B<global> current
963 directory. Consequently, sociable scripts don't change the current
964 directory but rely on full pathnames, and scripts (and Makefiles) cannot
965 assume that they can spawn a child process which can change the current
966 directory without affecting its parent (and everyone else for that
969 As native operating system filehandles are global and currently are
970 allocated down from 255, with 0 being a reserved value the Unix emulation
971 library emulates Unix filehandles. Consequently, you can't rely on
972 passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
974 The desire of users to express filenames of the form
975 C<E<lt>Foo$DirE<gt>.Bar> on the command line unquoted causes problems,
976 too: C<``> command output capture has to perform a guessing game. It
977 assumes that a string C<E<lt>[^E<lt>E<gt>]+\$[^E<lt>E<gt>]E<gt>> is a
978 reference to an environment variable, whereas anything else involving
979 C<E<lt>> or C<E<gt>> is redirection, and generally manages to be 99%
980 right. Of course, the problem remains that scripts cannot rely on any
981 Unix tools being available, or that any tools found have Unix-like command
984 Extensions and XS are, in theory, buildable by anyone using free tools.
985 In practice, many don't, as users of the Acorn platform are used to binary
986 distribution. MakeMaker does run, but no available make currently copes
987 with MakeMaker's makefiles; even if/when this is fixed, the lack of a
988 Unix-like shell can cause problems with makefile rules, especially lines
989 of the form C<cd sdbm && make all>, and anything using quoting.
991 "S<RISC OS>" is the proper name for the operating system, but the value
992 in C<$^O> is "riscos" (because we don't like shouting).
1005 Perl has been ported to a variety of platforms that do not fit into any of
1006 the above categories. Some, such as AmigaOS, BeOS, QNX, and Plan 9, have
1007 been well-integrated into the standard Perl source code kit. You may need
1008 to see the F<ports/> directory on CPAN for information, and possibly
1009 binaries, for the likes of: aos, atari, lynxos, riscos, Tandem Guardian,
1010 vos, I<etc.> (yes we know that some of these OSes may fall under the Unix
1011 category, but we are not a standards body.)
1017 =item Atari, Guido Flohr's page C<http://stud.uni-sb.de/~gufl0000/>
1019 =item HP 300 MPE/iX C<http://www.cccd.edu/~markb/perlix.html>
1021 =item Novell Netware
1023 A free perl5-based PERL.NLM for Novell Netware is available from
1024 C<http://www.novell.com/>
1029 =head1 FUNCTION IMPLEMENTATIONS
1031 Listed below are functions unimplemented or implemented differently on
1032 various platforms. Following each description will be, in parentheses, a
1033 list of platforms that the description applies to.
1035 The list may very well be incomplete, or wrong in some places. When in
1036 doubt, consult the platform-specific README files in the Perl source
1037 distribution, and other documentation resources for a given port.
1039 Be aware, moreover, that even among Unix-ish systems there are variations.
1041 For many functions, you can also query C<%Config>, exported by default
1042 from C<Config.pm>. For example, to check if the platform has the C<lstat>
1043 call, check C<$Config{'d_lstat'}>. See L<Config.pm> for a full
1044 description of available variables.
1047 =head2 Alphabetical Listing of Perl Functions
1057 C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories
1058 and applications are executable, and there are no uid/gid
1059 considerations. C<-o> is not supported. (S<Mac OS>)
1061 C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible,
1062 which may not reflect UIC-based file protections. (VMS)
1064 C<-s> returns the size of the data fork, not the total size of data fork
1065 plus resource fork. (S<Mac OS>).
1067 C<-s> by name on an open file will return the space reserved on disk,
1068 rather than the current extent. C<-s> on an open filehandle returns the
1069 current size. (S<RISC OS>)
1071 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
1072 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1074 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
1077 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
1078 (Win32, VMS, S<RISC OS>)
1080 C<-d> is true if passed a device spec without an explicit directory.
1083 C<-T> and C<-B> are implemented, but might misclassify Mac text files
1084 with foreign characters; this is the case will all platforms, but may
1085 affect S<Mac OS> often. (S<Mac OS>)
1087 C<-x> (or C<-X>) determine if a file ends in one of the executable
1088 suffixes. C<-S> is meaningless. (Win32)
1090 C<-x> (or C<-X>) determine if a file has an executable file type.
1093 =item binmode FILEHANDLE
1095 Meaningless. (S<Mac OS>, S<RISC OS>)
1097 Reopens file and restores pointer; if function fails, underlying
1098 filehandle may be closed, or pointer may be in a different position.
1101 The value returned by C<tell> may be affected after the call, and
1102 the filehandle may be flushed. (Win32)
1106 Only limited meaning. Disabling/enabling write permission is mapped to
1107 locking/unlocking the file. (S<Mac OS>)
1109 Only good for changing "owner" read-write access, "group", and "other"
1110 bits are meaningless. (Win32)
1112 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
1114 Access permissions are mapped onto VOS access-control list changes. (VOS)
1118 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
1120 Does nothing, but won't fail. (Win32)
1122 =item chroot FILENAME
1126 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS, VM/ESA)
1128 =item crypt PLAINTEXT,SALT
1130 May not be available if library or source was not provided when building
1133 Not implemented. (VOS)
1137 Not implemented. (VMS, Plan9, VOS)
1139 =item dbmopen HASH,DBNAME,MODE
1141 Not implemented. (VMS, Plan9, VOS)
1145 Not useful. (S<Mac OS>, S<RISC OS>)
1147 Not implemented. (Win32)
1149 Invokes VMS debugger. (VMS)
1153 Not implemented. (S<Mac OS>)
1155 Implemented via Spawn. (VM/ESA)
1157 =item fcntl FILEHANDLE,FUNCTION,SCALAR
1159 Not implemented. (Win32, VMS)
1161 =item flock FILEHANDLE,OPERATION
1163 Not implemented (S<Mac OS>, VMS, S<RISC OS>, VOS).
1165 Available only on Windows NT (not on Windows 95). (Win32)
1169 Not implemented. (S<Mac OS>, Win32, AmigaOS, S<RISC OS>, VOS, VM/ESA)
1173 Not implemented. (S<Mac OS>, S<RISC OS>)
1177 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1181 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1183 =item getpriority WHICH,WHO
1185 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1189 Not implemented. (S<Mac OS>, Win32)
1191 Not useful. (S<RISC OS>)
1195 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1197 =item getnetbyname NAME
1199 Not implemented. (S<Mac OS>, Win32, Plan9)
1203 Not implemented. (S<Mac OS>, Win32)
1205 Not useful. (S<RISC OS>)
1209 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1211 =item getnetbyaddr ADDR,ADDRTYPE
1213 Not implemented. (S<Mac OS>, Win32, Plan9)
1215 =item getprotobynumber NUMBER
1217 Not implemented. (S<Mac OS>)
1219 =item getservbyport PORT,PROTO
1221 Not implemented. (S<Mac OS>)
1225 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1229 Not implemented. (S<Mac OS>, Win32, VMS, VM/ESA)
1233 Not implemented. (S<Mac OS>, Win32)
1237 Not implemented. (S<Mac OS>, Win32, Plan9)
1241 Not implemented. (S<Mac OS>, Win32, Plan9)
1245 Not implemented. (Win32, Plan9)
1249 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1253 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1255 =item sethostent STAYOPEN
1257 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1259 =item setnetent STAYOPEN
1261 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1263 =item setprotoent STAYOPEN
1265 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1267 =item setservent STAYOPEN
1269 Not implemented. (Plan9, Win32, S<RISC OS>)
1273 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1277 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VM/ESA)
1281 Not implemented. (S<Mac OS>, Win32)
1285 Not implemented. (S<Mac OS>, Win32, Plan9)
1289 Not implemented. (S<Mac OS>, Win32, Plan9)
1293 Not implemented. (Plan9, Win32)
1295 =item getsockopt SOCKET,LEVEL,OPTNAME
1297 Not implemented. (S<Mac OS>, Plan9)
1303 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1306 Features depend on external perlglob.exe or perlglob.bat. May be
1307 overridden with something like File::DosGlob, which is recommended.
1310 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1311 Globbing relies on operating system calls, which may return filenames
1312 in any order. As most filesystems are case-insensitive, even "sorted"
1313 filenames will not be in case-sensitive order. (S<RISC OS>)
1315 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1317 Not implemented. (VMS)
1319 Available only for socket handles, and it does what the ioctlsocket() call
1320 in the Winsock API does. (Win32)
1322 Available only for socket handles. (S<RISC OS>)
1326 Not implemented, hence not useful for taint checking. (S<Mac OS>,
1329 Available only for process handles returned by the C<system(1, ...)>
1330 method of spawning a process. (Win32)
1332 =item link OLDFILE,NEWFILE
1334 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1336 Link count not updated because hard links are not quite that hard
1337 (They are sort of half-way between hard and soft links). (AmigaOS)
1339 =item lstat FILEHANDLE
1345 Not implemented. (VMS, S<RISC OS>)
1347 Return values may be bogus. (Win32)
1349 =item msgctl ID,CMD,ARG
1351 =item msgget KEY,FLAGS
1353 =item msgsnd ID,MSG,FLAGS
1355 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1357 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1359 =item open FILEHANDLE,EXPR
1361 =item open FILEHANDLE
1363 The C<|> variants are only supported if ToolServer is installed.
1366 open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1368 =item pipe READHANDLE,WRITEHANDLE
1370 Not implemented. (S<Mac OS>)
1372 Very limited functionality. (MiNT)
1378 Not implemented. (Win32, VMS, S<RISC OS>)
1380 =item select RBITS,WBITS,EBITS,TIMEOUT
1382 Only implemented on sockets. (Win32)
1384 Only reliable on sockets. (S<RISC OS>)
1386 =item semctl ID,SEMNUM,CMD,ARG
1388 =item semget KEY,NSEMS,FLAGS
1390 =item semop KEY,OPSTRING
1392 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1394 =item setpgrp PID,PGRP
1396 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1398 =item setpriority WHICH,WHO,PRIORITY
1400 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1402 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1404 Not implemented. (S<Mac OS>, Plan9)
1406 =item shmctl ID,CMD,ARG
1408 =item shmget KEY,SIZE,FLAGS
1410 =item shmread ID,VAR,POS,SIZE
1412 =item shmwrite ID,STRING,POS,SIZE
1414 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1416 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1418 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1420 =item stat FILEHANDLE
1426 mtime and atime are the same thing, and ctime is creation time instead of
1427 inode change time. (S<Mac OS>)
1429 device and inode are not meaningful. (Win32)
1431 device and inode are not necessarily reliable. (VMS)
1433 mtime, atime and ctime all return the last modification time. Device and
1434 inode are not necessarily reliable. (S<RISC OS>)
1436 =item symlink OLDFILE,NEWFILE
1438 Not implemented. (Win32, VMS, S<RISC OS>)
1442 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1444 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1446 The traditional "0", "1", and "2" MODEs are implemented with different
1447 numeric values on some systems. The flags exported by C<Fcntl>
1448 (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (S<Mac
1449 OS>, OS/390, VM/ESA)
1453 Only implemented if ToolServer is installed. (S<Mac OS>)
1455 As an optimization, may not call the command shell specified in
1456 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1457 process and immediately returns its process designator, without
1458 waiting for it to terminate. Return value may be used subsequently
1459 in C<wait> or C<waitpid>. (Win32)
1461 There is no shell to process metacharacters, and the native standard is
1462 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1463 program. Redirection such as C<E<gt> foo> is performed (if at all) by
1464 the run time library of the spawned program. C<system> I<list> will call
1465 the Unix emulation library's C<exec> emulation, which attempts to provide
1466 emulation of the stdin, stdout, stderr in force in the parent, providing
1467 the child program uses a compatible version of the emulation library.
1468 I<scalar> will call the native command line direct and no such emulation
1469 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1471 Far from being POSIX compliant. Because there may be no underlying
1472 /bin/sh tries to work around the problem by forking and execing the
1473 first token in its argument string. Handles basic redirection
1474 ("E<lt>" or "E<gt>") on its own behalf. (MiNT)
1478 Only the first entry returned is nonzero. (S<Mac OS>)
1480 "cumulative" times will be bogus. On anything other than Windows NT,
1481 "system" time will be bogus, and "user" time is actually the time
1482 returned by the clock() function in the C runtime library. (Win32)
1484 Not useful. (S<RISC OS>)
1486 =item truncate FILEHANDLE,LENGTH
1488 =item truncate EXPR,LENGTH
1490 Not implemented. (VMS)
1492 Truncation to zero-length only. (VOS)
1494 If a FILEHANDLE is supplied, it must be writable and opened in append
1495 mode (i.e., use C<open(FH, '>>filename')>
1496 or C<sysopen(FH,...,O_APPEND|O_RDWR)>. If a filename is supplied, it
1497 should not be held open elsewhere. (Win32)
1503 Returns undef where unavailable, as of version 5.005.
1505 C<umask()> works but the correct permissions are only set when the file
1506 is finally close()d. (AmigaOS)
1510 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1512 May not behave as expected. Behavior depends on the C runtime
1513 library's implementation of utime(), and the filesystem being
1514 used. The FAT filesystem typically does not support an "access
1515 time" field, and it may limit timestamps to a granularity of
1516 two seconds. (Win32)
1520 =item waitpid PID,FLAGS
1522 Not implemented. (S<Mac OS>, VOS)
1524 Can only be applied to process handles returned for processes spawned
1525 using C<system(1, ...)>. (Win32)
1527 Not useful. (S<RISC OS>)
1535 =item v1.39, 11 February, 1999
1537 Changes from Jarkko and EMX URL fixes Michael Schwern. Additional
1538 note about newlines added.
1540 =item v1.38, 31 December 1998
1542 More changes from Jarkko.
1544 =item v1.37, 19 December 1998
1546 More minor changes. Merge two separate version 1.35 documents.
1548 =item v1.36, 9 September 1998
1550 Updated for Stratus VOS. Also known as version 1.35.
1552 =item v1.35, 13 August 1998
1554 Integrate more minor changes, plus addition of new sections under
1555 L<"ISSUES">: L<"Numbers endianness and Width">,
1556 L<"Character sets and character encoding">,
1557 L<"Internationalisation">.
1559 =item v1.33, 06 August 1998
1561 Integrate more minor changes.
1563 =item v1.32, 05 August 1998
1565 Integrate more minor changes.
1567 =item v1.30, 03 August 1998
1569 Major update for RISC OS, other minor changes.
1571 =item v1.23, 10 July 1998
1573 First public release with perl5.005.
1577 =head1 AUTHORS / CONTRIBUTORS
1579 Abigail E<lt>abigail@fnx.comE<gt>,
1580 Charles Bailey E<lt>bailey@newman.upenn.eduE<gt>,
1581 Graham Barr E<lt>gbarr@pobox.comE<gt>,
1582 Tom Christiansen E<lt>tchrist@perl.comE<gt>,
1583 Nicholas Clark E<lt>Nicholas.Clark@liverpool.ac.ukE<gt>,
1584 Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>,
1585 Dominic Dunlop E<lt>domo@vo.luE<gt>,
1586 Neale Ferguson E<lt>neale@mailbox.tabnsw.com.auE<gt>
1587 Paul Green E<lt>Paul_Green@stratus.comE<gt>,
1588 M.J.T. Guy E<lt>mjtg@cus.cam.ac.ukE<gt>,
1589 Jarkko Hietaniemi E<lt>jhi@iki.fi<gt>,
1590 Luther Huffman E<lt>lutherh@stratcom.comE<gt>,
1591 Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>,
1592 Andreas J. KE<ouml>nig E<lt>koenig@kulturbox.deE<gt>,
1593 Markus Laker E<lt>mlaker@contax.co.ukE<gt>,
1594 Andrew M. Langmead E<lt>aml@world.std.comE<gt>,
1595 Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>,
1596 Chris Nandor E<lt>pudge@pobox.comE<gt>,
1597 Matthias Neeracher E<lt>neeri@iis.ee.ethz.chE<gt>,
1598 Gary Ng E<lt>71564.1743@CompuServe.COME<gt>,
1599 Tom Phoenix E<lt>rootbeer@teleport.comE<gt>,
1600 Peter Prymmer E<lt>pvhp@forte.comE<gt>,
1601 Hugo van der Sanden E<lt>hv@crypt0.demon.co.ukE<gt>,
1602 Gurusamy Sarathy E<lt>gsar@umich.eduE<gt>,
1603 Paul J. Schinder E<lt>schinder@pobox.comE<gt>,
1604 Michael G Schwern E<lt>schwern@pobox.comE<gt>,
1605 Dan Sugalski E<lt>sugalskd@ous.eduE<gt>,
1606 Nathan Torkington E<lt>gnat@frii.comE<gt>.
1608 This document is maintained by Chris Nandor
1609 E<lt>pudge@pobox.comE<gt>.
1613 Version 1.39, last modified 11 February 1999