3 perlport - Writing portable Perl
7 Perl runs on numerous operating systems. While most of them share
8 much in common, they also have their own unique features.
10 This document is meant to help you to find out what constitutes portable
11 Perl code. That way once you make a decision to write portably,
12 you know where the lines are drawn, and you can stay within them.
14 There is a tradeoff between taking full advantage of one particular
15 type of computer and taking advantage of a full range of them.
16 Naturally, as you broaden your range and become more diverse, the
17 common factors drop, and you are left with an increasingly smaller
18 area of common ground in which you can operate to accomplish a
19 particular task. Thus, when you begin attacking a problem, it is
20 important to consider under which part of the tradeoff curve you
21 want to operate. Specifically, you must decide whether it is
22 important that the task that you are coding have the full generality
23 of being portable, or whether to just get the job done right now.
24 This is the hardest choice to be made. The rest is easy, because
25 Perl provides many choices, whichever way you want to approach your
28 Looking at it another way, writing portable code is usually about
29 willfully limiting your available choices. Naturally, it takes
30 discipline and sacrifice to do that. The product of portability
31 and convenience may be a constant. You have been warned.
33 Be aware of two important points:
37 =item Not all Perl programs have to be portable
39 There is no reason 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 Nearly all of Perl already I<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 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 commonly done
56 using a whole range of platforms, think about 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, you
65 may need to consider only 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 built-in 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>).
84 In most operating systems, lines in files are terminated by newlines.
85 Just what is used as a newline may vary from OS to OS. Unix
86 traditionally uses C<\012>, one type of DOSish I/O uses C<\015\012>,
87 and S<Mac OS> uses C<\015>.
89 Perl uses C<\n> to represent the "logical" newline, where what is
90 logical may depend on the platform in use. In MacPerl, C<\n> always
91 means C<\015>. In DOSish perls, C<\n> usually means C<\012>, but
92 when accessing a file in "text" mode, STDIO translates it to (or
93 from) C<\015\012>, depending on whether you're reading or writing.
94 Unix does the same thing on ttys in canonical mode. C<\015\012>
95 is commonly referred to as CRLF.
97 Because of the "text" mode translation, DOSish perls have limitations
98 in using C<seek> and C<tell> on a file accessed in "text" mode.
99 Stick to C<seek>-ing to locations you got from C<tell> (and no
100 others), and you are usually free to use C<seek> and C<tell> even
101 in "text" mode. Using C<seek> or C<tell> or other file operations
102 may be non-portable. If you use C<binmode> on a file, however, you
103 can usually C<seek> and C<tell> with arbitrary values in safety.
105 A common misconception in socket programming is that C<\n> eq C<\012>
106 everywhere. When using protocols such as common Internet protocols,
107 C<\012> and C<\015> are called for specifically, and the values of
108 the logical C<\n> and C<\r> (carriage return) are not reliable.
110 print SOCKET "Hi there, client!\r\n"; # WRONG
111 print SOCKET "Hi there, client!\015\012"; # RIGHT
113 However, using C<\015\012> (or C<\cM\cJ>, or C<\x0D\x0A>) can be tedious
114 and unsightly, as well as confusing to those maintaining the code. As
115 such, the Socket module supplies the Right Thing for those who want it.
117 use Socket qw(:DEFAULT :crlf);
118 print SOCKET "Hi there, client!$CRLF" # RIGHT
120 When reading from a socket, remember that the default input record
121 separator C<$/> is C<\n>, but robust socket code will recognize as
122 either C<\012> or C<\015\012> as end of line:
128 Because both CRLF and LF end in LF, the input record separator can
129 be set to LF and any CR stripped later. Better to write:
131 use Socket qw(:DEFAULT :crlf);
132 local($/) = LF; # not needed if $/ is already \012
135 s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
136 # s/\015?\012/\n/; # same thing
139 This example is preferred over the previous one--even for Unix
140 platforms--because now any C<\015>'s (C<\cM>'s) are stripped out
141 (and there was much rejoicing).
143 Similarly, functions that return text data--such as a function that
144 fetches a web page--should sometimes translate newlines before
145 returning the data, if they've not yet been translated to the local
146 newline representation. A single line of code will often suffice:
148 $data =~ s/\015?\012/\n/g;
151 Some of this may be confusing. Here's a handy reference to the ASCII CR
152 and LF characters. You can print it out and stick it in your wallet.
154 LF == \012 == \x0A == \cJ == ASCII 10
155 CR == \015 == \x0D == \cM == ASCII 13
158 ---------------------------
161 \n * | LF | CRLF | CR |
162 \r * | CR | CR | LF |
163 ---------------------------
166 The Unix column assumes that you are not accessing a serial line
167 (like a tty) in canonical mode. If you are, then CR on input becomes
168 "\n", and "\n" on output becomes CRLF.
170 These are just the most common definitions of C<\n> and C<\r> in Perl.
171 There may well be others.
173 =head2 Numbers endianness and Width
175 Different CPUs store integers and floating point numbers in different
176 orders (called I<endianness>) and widths (32-bit and 64-bit being the
177 most common today). This affects your programs when they attempt to transfer
178 numbers in binary format from one CPU architecture to another,
179 usually either "live" via network connection, or by storing the
180 numbers to secondary storage such as a disk file or tape.
182 Conflicting storage orders make utter mess out of the numbers. If a
183 little-endian host (Intel, VAX) stores 0x12345678 (305419896 in
184 decimal), a big-endian host (Motorola, MIPS, Sparc, PA) reads it as
185 0x78563412 (2018915346 in decimal). To avoid this problem in network
186 (socket) connections use the C<pack> and C<unpack> formats C<n>
187 and C<N>, the "network" orders. These are guaranteed to be portable.
189 You can explore the endianness of your platform by unpacking a
190 data structure packed in native format such as:
192 print unpack("h*", pack("s2", 1, 2)), "\n";
193 # '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
194 # '00100020' on e.g. Motorola 68040
196 If you need to distinguish between endian architectures you could use
197 either of the variables set like so:
199 $is_big_endian = unpack("h*", pack("s", 1)) =~ /01/;
200 $is_litte_endian = unpack("h*", pack("s", 1)) =~ /^1/;
202 Differing widths can cause truncation even between platforms of equal
203 endianness. The platform of shorter width loses the upper parts of the
204 number. There is no good solution for this problem except to avoid
205 transferring or storing raw binary numbers.
207 One can circumnavigate both these problems in two ways. Either
208 transfer and store numbers always in text format, instead of raw
209 binary, or else consider using modules like Data::Dumper (included in
210 the standard distribution as of Perl 5.005) and Storable. Keeping
211 all data as text significantly simplifies matters.
213 =head2 Files and Filesystems
215 Most platforms these days structure files in a hierarchical fashion.
216 So, it is reasonably safe to assume that all platforms support the
217 notion of a "path" to uniquely identify a file on the system. How
218 that path is really written, though, differs considerably.
220 Atlhough similar, file path specifications differ between Unix,
221 Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS>, and probably others.
222 Unix, for example, is one of the few OSes that has the elegant idea
223 of a single root directory.
225 DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with C</>
226 as path separator, or in their own idiosyncratic ways (such as having
227 several root directories and various "unrooted" device files such NIL:
230 S<Mac OS> uses C<:> as a path separator instead of C</>.
232 The filesystem may support neither hard links (C<link>) nor
233 symbolic links (C<symlink>, C<readlink>, C<lstat>).
235 The filesystem may support neither access timestamp nor change
236 timestamp (meaning that about the only portable timestamp is the
237 modification timestamp), or one second granularity of any timestamps
238 (e.g. the FAT filesystem limits the time granularity to two seconds).
240 VOS perl can emulate Unix filenames with C</> as path separator. The
241 native pathname characters greater-than, less-than, number-sign, and
242 percent-sign are always accepted.
244 S<RISC OS> perl can emulate Unix filenames with C</> as path
245 separator, or go native and use C<.> for path separator and C<:> to
246 signal filesystems and disk names.
248 If all this is intimidating, have no (well, maybe only a little)
249 fear. There are modules that can help. The File::Spec modules
250 provide methods to do the Right Thing on whatever platform happens
251 to be running the program.
253 use File::Spec::Functions;
254 chdir(updir()); # go up one directory
255 $file = catfile(curdir(), 'temp', 'file.txt');
256 # on Unix and Win32, './temp/file.txt'
257 # on Mac OS, ':temp:file.txt'
258 # on VMS, '[.temp]file.txt'
260 File::Spec is available in the standard distribution as of version
261 5.004_05. File::Spec::Functions is only in File::Spec 0.7 and later,
262 and some versions of perl come with version 0.6. If File::Spec
263 is not updated to 0.7 or later, you must use the object-oriented
264 interface from File::Spec (or upgrade File::Spec).
266 In general, production code should not have file paths hardcoded.
267 Making them user-supplied or read from a configuration file is
268 better, keeping in mind that file path syntax varies on different
271 This is especially noticeable in scripts like Makefiles and test suites,
272 which often assume C</> as a path separator for subdirectories.
274 Also of use is File::Basename from the standard distribution, which
275 splits a pathname into pieces (base filename, full path to directory,
278 Even when on a single platform (if you can call Unix a single platform),
279 remember not to count on the existence or the contents of particular
280 system-specific files or directories, like F</etc/passwd>,
281 F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
282 example, F</etc/passwd> may exist but not contain the encrypted
283 passwords, because the system is using some form of enhanced security.
284 Or it may not contain all the accounts, because the system is using NIS.
285 If code does need to rely on such a file, include a description of the
286 file and its format in the code's documentation, then make it easy for
287 the user to override the default location of the file.
289 Don't assume a text file will end with a newline. They should,
292 Do not have two files of the same name with different case, like
293 F<test.pl> and F<Test.pl>, as many platforms have case-insensitive
294 filenames. Also, try not to have non-word characters (except for C<.>)
295 in the names, and keep them to the 8.3 convention, for maximum
296 portability, onerous a burden though this may appear.
298 Likewise, when using the AutoSplit module, try to keep your functions to
299 8.3 naming and case-insensitive conventions; or, at the least,
300 make it so the resulting files have a unique (case-insensitively)
303 Whitespace in filenames is tolerated on most systems, but not all.
304 Many systems (DOS, VMS) cannot have more than one C<.> in their filenames.
306 Don't assume C<E<gt>> won't be the first character of a filename.
307 Always use C<E<lt>> explicitly to open a file for reading,
308 unless you want the user to be able to specify a pipe open.
310 open(FILE, "< $existing_file") or die $!;
312 If filenames might use strange characters, it is safest to open it
313 with C<sysopen> instead of C<open>. C<open> is magic and can
314 translate characters like C<E<gt>>, C<E<lt>>, and C<|>, which may
315 be the wrong thing to do. (Sometimes, though, it's the right thing.)
317 =head2 System Interaction
319 Not all platforms provide a command line. These are usually platforms
320 that rely primarily on a Graphical User Interface (GUI) for user
321 interaction. A program requiring a command line interface might
322 not work everywhere. This is probably for the user of the program
323 to deal with, so don't stay up late worrying about it.
325 Some platforms can't delete or rename files held open by the system.
326 Remember to C<close> files when you are done with them. Don't
327 C<unlink> or C<rename> an open file. Don't C<tie> or C<open> a
328 file already tied or opened; C<untie> or C<close> it first.
330 Don't open the same file more than once at a time for writing, as some
331 operating systems put mandatory locks on such files.
333 Don't count on a specific environment variable existing in C<%ENV>.
334 Don't count on C<%ENV> entries being case-sensitive, or even
337 Don't count on signals or C<%SIG> for anything.
339 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
342 Don't count on per-program environment variables, or per-program current
345 Don't count on specific values of C<$!>.
347 =head2 Interprocess Communication (IPC)
349 In general, don't directly access the system in code meant to be
350 portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>,
351 C<``>, C<qx//>, C<open> with a C<|>, nor any of the other things
352 that makes being a perl hacker worth being.
354 Commands that launch external processes are generally supported on
355 most platforms (though many of them do not support any type of
356 forking). The problem with using them arises from what you invoke
357 them on. External tools are often named differently on different
358 platforms, may not be available in the same location, migth accept
359 different arguments, can behave differently, and often present their
360 results in a platform-dependent way. Thus, you should seldom depend
361 on them to produce consistent results. (Then again, if you're calling
362 I<netstat -a>, you probably don't expect it to run on both Unix and CP/M.)
364 One especially common bit of Perl code is opening a pipe to B<sendmail>:
366 open(MAIL, '|/usr/lib/sendmail -t')
367 or die "cannot fork sendmail: $!";
369 This is fine for systems programming when sendmail is known to be
370 available. But it is not fine for many non-Unix systems, and even
371 some Unix systems that may not have sendmail installed. If a portable
372 solution is needed, see the various distributions on CPAN that deal
373 with it. Mail::Mailer and Mail::Send in the MailTools distribution are
374 commonly used, and provide several mailing methods, including mail,
375 sendmail, and direct SMTP (via Net::SMTP) if a mail transfer agent is
376 not available. Mail::Sendmail is a standalone module that provides
377 simple, platform-independent mailing.
379 The Unix System V IPC (C<msg*(), sem*(), shm*()>) is not available
380 even on all Unix platforms.
382 The rule of thumb for portable code is: Do it all in portable Perl, or
383 use a module (that may internally implement it with platform-specific
384 code, but expose a common interface).
386 =head2 External Subroutines (XS)
388 XS code can usually be made to work with any platform, but dependent
389 libraries, header files, etc., might not be readily available or
390 portable, or the XS code itself might be platform-specific, just as Perl
391 code might be. If the libraries and headers are portable, then it is
392 normally reasonable to make sure the XS code is portable, too.
394 A different type of portability issue arises when writing XS code:
395 availability of a C compiler on the end-user's system. C brings
396 with it its own portability issues, and writing XS code will expose
397 you to some of those. Writing purely in Perl is an easier way to
400 =head2 Standard Modules
402 In general, the standard modules work across platforms. Notable
403 exceptions are the CPAN module (which currently makes connections to external
404 programs that may not be available), platform-specific modules (like
405 ExtUtils::MM_VMS), and DBM modules.
407 There is no one DBM module available on all platforms.
408 SDBM_File and the others are generally available on all Unix and DOSish
409 ports, but not in MacPerl, where only NBDM_File and DB_File are
412 The good news is that at least some DBM module should be available, and
413 AnyDBM_File will use whichever module it can find. Of course, then
414 the code needs to be fairly strict, dropping to the greatest common
415 factor (e.g., not exceeding 1K for each record), so that it will
416 work with any DBM module. See L<AnyDBM_File> for more details.
420 The system's notion of time of day and calendar date is controlled in
421 widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>,
422 and even if it is, don't assume that you can control the timezone through
425 Don't assume that the epoch starts at 00:00:00, January 1, 1970,
426 because that is OS- and implementation-specific. It is better to store a date
427 in an unambiguous representation. The ISO-8601 standard defines
428 "YYYY-MM-DD" as the date format. A text representation (like "1987-12-18")
429 can be easily converted into an OS-specific value using a module like
430 Date::Parse. An array of values, such as those returned by
431 C<localtime>, can be converted to an OS-specific representation using
434 When calculating specific times, such as for tests in time or date modules,
435 it may be appropriate to calculate an offset for the epoch.
438 $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
440 The value for C<$offset> in Unix will be C<0>, but in Mac OS will be
441 some large number. C<$offset> can then be added to a Unix time value
442 to get what should be the proper value on any system.
444 =head2 Character sets and character encoding
446 Assume little about character sets. Assume nothing about
447 numerical values (C<ord>, C<chr>) of characters. Do not
448 assume that the alphabetic characters are encoded contiguously (in
449 the numeric sense). Do not assume anything about the ordering of the
450 characters. The lowercase letters may come before or after the
451 uppercase letters; the lowercase and uppercase may be interlaced so
452 that both `a' and `A' come before `b'; the accented and other
453 international characters may be interlaced so that E<auml> comes
456 =head2 Internationalisation
458 If you may assume POSIX (a rather large assumption), you may read
459 more about the POSIX locale system from L<perllocale>. The locale
460 system at least attempts to make things a little bit more portable,
461 or at least more convenient and native-friendly for non-English
462 users. The system affects character sets and encoding, and date
463 and time formatting--amongst other things.
465 =head2 System Resources
467 If your code is destined for systems with severely constrained (or
468 missing!) virtual memory systems then you want to be I<especially> mindful
469 of avoiding wasteful constructs such as:
471 # NOTE: this is no longer "bad" in perl5.005
472 for (0..10000000) {} # bad
473 for (my $x = 0; $x <= 10000000; ++$x) {} # good
475 @lines = <VERY_LARGE_FILE>; # bad
477 while (<FILE>) {$file .= $_} # sometimes bad
478 $file = join('', <FILE>); # better
480 The last two constructs may appear unintuitive to most people. The
481 first repeatedly grows a string, whereas the second allocates a
482 large chunk of memory in one go. On some systems, the second is
483 more efficient that the first.
487 Most multi-user platforms provide basic levels of security, usually
488 implemented at the filesystem level. Some, however, do
489 not--unfortunately. Thus the notion of user id, or "home" directory,
490 or even the state of being logged-in, may be unrecognizable on many
491 platforms. If you write programs that are security-conscious, it
492 is usually best to know what type of system you will be running
493 under so that you can write code explicitly for that platform (or
498 For those times when it is necessary to have platform-specific code,
499 consider keeping the platform-specific code in one place, making porting
500 to other platforms easier. Use the Config module and the special
501 variable C<$^O> to differentiate platforms, as described in
504 Be careful in the tests you supply with your module or programs.
505 Module code may be fully portable, but its tests might not be. This
506 often happens when tests spawn off other processes or call external
507 programs to aid in the testing, or when (as noted above) the tests
508 assume certain things about the filesystem and paths. Be careful
509 not to depend on a specific output style for errors, such as when
510 checking C<$!> after an system call. Some platforms expect a certain
511 output format, and perl on those platforms may have been adjusted
512 accordingly. Most specifically, don't anchor a regex when testing
517 Modules uploaded to CPAN are tested by a variety of volunteers on
518 different platforms. These CPAN testers are notified by mail of each
519 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
520 this platform), or UNKNOWN (unknown), along with any relevant notations.
522 The purpose of the testing is twofold: one, to help developers fix any
523 problems in their code that crop up because of lack of testing on other
524 platforms; two, to provide users with information about whether
525 a given module works on a given platform.
529 =item Mailing list: cpan-testers@perl.org
531 =item Testing results: C<http://www.perl.org/cpan-testers/>
537 As of version 5.002, Perl is built with a C<$^O> variable that
538 indicates the operating system it was built on. This was implemented
539 to help speed up code that would otherwise have to C<use Config>
540 and use the value of C<$Config{osname}>. Of course, to get more
541 detailed information about the system, looking into C<%Config> is
542 certainly recommended.
544 C<%Config> cannot always be trusted, however, because it was built
545 at compile time. If perl was built in one place, then transferred
546 elsewhere, some values may be wrong. The values may even have been
547 edited after the fact.
551 Perl works on a bewildering variety of Unix and Unix-like platforms (see
552 e.g. most of the files in the F<hints/> directory in the source code kit).
553 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
554 too) is determined either by lowercasing and stripping punctuation from the
555 first field of the string returned by typing C<uname -a> (or a similar command)
556 at the shell prompt or by testing the file system for the presence of
557 uniquely named files such as a kernel or header file. Here, for example,
558 are a few of the more popular Unix flavors:
560 uname $^O $Config{'archname'}
561 --------------------------------------------
563 BSD/OS bsdos i386-bsdos
564 dgux dgux AViiON-dgux
565 DYNIX/ptx dynixptx i386-dynixptx
566 FreeBSD freebsd freebsd-i386
567 Linux linux arm-linux
568 Linux linux i386-linux
569 Linux linux i586-linux
570 Linux linux ppc-linux
571 HP-UX hpux PA-RISC1.1
573 Mac OS X rhapsody rhapsody
574 MachTen PPC machten powerpc-machten
576 NeXT 4 next OPENSTEP-Mach
577 openbsd openbsd i386-openbsd
578 OSF1 dec_osf alpha-dec_osf
579 reliantunix-n svr4 RM400-svr4
580 SCO_SV sco_sv i386-sco_sv
581 SINIX-N svr4 RM400-svr4
582 sn4609 unicos CRAY_C90-unicos
583 sn6521 unicosmk t3e-unicosmk
584 sn9617 unicos CRAY_J90-unicos
585 SunOS solaris sun4-solaris
586 SunOS solaris i86pc-solaris
587 SunOS4 sunos sun4-sunos
589 Because the value of C<$Config{archname}> may depend on the
590 hardware architecture, it can vary more than the value of C<$^O>.
592 =head2 DOS and Derivatives
594 Perl has long been ported to Intel-style microcomputers running under
595 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
596 bring yourself to mention (except for Windows CE, if you count that).
597 Users familiar with I<COMMAND.COM> or I<CMD.EXE> style shells should
598 be aware that each of these file specifications may have subtle
601 $filespec0 = "c:/foo/bar/file.txt";
602 $filespec1 = "c:\\foo\\bar\\file.txt";
603 $filespec2 = 'c:\foo\bar\file.txt';
604 $filespec3 = 'c:\\foo\\bar\\file.txt';
606 System calls accept either C</> or C<\> as the path separator.
607 However, many command-line utilities of DOS vintage treat C</> as
608 the option prefix, so may get confused by filenames containing C</>.
609 Aside from calling any external programs, C</> will work just fine,
610 and probably better, as it is more consistent with popular usage,
611 and avoids the problem of remembering what to backwhack and what
614 The DOS FAT filesystem can accommodate only "8.3" style filenames. Under
615 the "case-insensitive, but case-preserving" HPFS (OS/2) and NTFS (NT)
616 filesystems you may have to be careful about case returned with functions
617 like C<readdir> or used with functions like C<open> or C<opendir>.
619 DOS also treats several filenames as special, such as AUX, PRN,
620 NUL, CON, COM1, LPT1, LPT2, etc. Unfortunately, sometimes these
621 filenames won't even work if you include an explicit directory
622 prefix. It is best to avoid such filenames, if you want your code
623 to be portable to DOS and its derivatives. It's hard to know what
624 these all are, unfortunately.
626 Users of these operating systems may also wish to make use of
627 scripts such as I<pl2bat.bat> or I<pl2cmd> to
628 put wrappers around your scripts.
630 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
631 and writing to files (see L<"Newlines">). C<binmode(FILEHANDLE)>
632 will keep C<\n> translated as C<\012> for that filehandle. Since it is a
633 no-op on other systems, C<binmode> should be used for cross-platform code
634 that deals with binary data. That's assuming you realize in advance
635 that your data is in binary. General-purpose programs should
636 often assume nothing about their data.
638 The C<$^O> variable and the C<$Config{archname}> values for various
639 DOSish perls are as follows:
641 OS $^O $Config{'archname'}
642 --------------------------------------------
646 Windows 95 MSWin32 MSWin32-x86
647 Windows 98 MSWin32 MSWin32-x86
648 Windows NT MSWin32 MSWin32-x86
649 Windows NT MSWin32 MSWin32-ALPHA
650 Windows NT MSWin32 MSWin32-ppc
656 =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/>
658 =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>,
659 C<http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html> or
660 C<ftp://hobbes.nmsu.edu/pub/os2/dev/emx>
662 =item Build instructions for Win32, L<perlwin32>.
664 =item The ActiveState Pages, C<http://www.activestate.com/>
666 =item The Cygwin environment for Win32; L<README.cygwin>,
667 C<http://sourceware.cygnus.com/cygwin/>
669 =item The U/WIN environment for Win32,
670 C<http://www.research.att.com/sw/tools/uwin/>
677 Any module requiring XS compilation is right out for most people, because
678 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
679 modules that can work with MacPerl are built and distributed in binary
682 Directories are specified as:
684 volume:folder:file for absolute pathnames
685 volume:folder: for absolute pathnames
686 :folder:file for relative pathnames
687 :folder: for relative pathnames
688 :file for relative pathnames
689 file for relative pathnames
691 Files are stored in the directory in alphabetical order. Filenames are
692 limited to 31 characters, and may include any character except for
693 null and C<:>, which is reserved as the path separator.
695 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
696 Mac::Files module, or C<chmod(0444, ...)> and C<chmod(0666, ...)>.
698 In the MacPerl application, you can't run a program from the command line;
699 programs that expect C<@ARGV> to be populated can be edited with something
700 like the following, which brings up a dialog box asking for the command
704 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
707 A MacPerl script saved as a "droplet" will populate C<@ARGV> with the full
708 pathnames of the files dropped onto the script.
710 Mac users can run programs under a type of command line interface
711 under MPW (Macintosh Programmer's Workshop, a free development
712 environment from Apple). MacPerl was first introduced as an MPW
713 tool, and MPW can be used like a shell:
715 perl myscript.plx some arguments
717 ToolServer is another app from Apple that provides access to MPW tools
718 from MPW and the MacPerl app, which allows MacPerl programs to use
719 C<system>, backticks, and piped C<open>.
721 "S<Mac OS>" is the proper name for the operating system, but the value
722 in C<$^O> is "MacOS". To determine architecture, version, or whether
723 the application or MPW tool version is running, check:
725 $is_app = $MacPerl::Version =~ /App/;
726 $is_tool = $MacPerl::Version =~ /MPW/;
727 ($version) = $MacPerl::Version =~ /^(\S+)/;
728 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
729 $is_68k = $MacPerl::Architecture eq 'Mac68K';
731 S<Mac OS X> and S<Mac OS X Server>, based on NeXT's OpenStep OS, will
732 (in theory) be able to run MacPerl natively, under the "Classic"
733 environment. The new "Cocoa" environment (formerly called the "Yellow Box")
734 may run a slightly modified version of MacPerl, using the Carbon interfaces.
736 S<Mac OS X Server> and its Open Source version, Darwin, both run Unix
737 perl natively (with a few patches). Full support for these
738 is slated for perl 5.6.
744 =item The MacPerl Pages, C<http://www.macperl.com/>.
746 =item The MacPerl mailing lists, C<http://www.macperl.org/>.
748 =item MacPerl Module Porters, C<http://pudge.net/mmp/>.
754 Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
755 Perl on VMS can accept either VMS- or Unix-style file
756 specifications as in either of the following:
758 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
759 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
761 but not a mixture of both as in:
763 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
764 Can't open sys$login:/login.com: file specification syntax error
766 Interacting with Perl from the Digital Command Language (DCL) shell
767 often requires a different set of quotation marks than Unix shells do.
770 $ perl -e "print ""Hello, world.\n"""
773 There are several ways to wrap your perl scripts in DCL F<.COM> files, if
774 you are so inclined. For example:
776 $ write sys$output "Hello from DCL!"
778 $ then perl -x 'f$environment("PROCEDURE")
779 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
780 $ deck/dollars="__END__"
783 print "Hello from Perl!\n";
788 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
789 perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>.
791 Filenames are in the format "name.extension;version". The maximum
792 length for filenames is 39 characters, and the maximum length for
793 extensions is also 39 characters. Version is a number from 1 to
794 32767. Valid characters are C</[A-Z0-9$_-]/>.
796 VMS's RMS filesystem is case-insensitive and does not preserve case.
797 C<readdir> returns lowercased filenames, but specifying a file for
798 opening remains case-insensitive. Files without extensions have a
799 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
800 will return F<a.> (though that file could be opened with
803 RMS had an eight level limit on directory depths from any rooted logical
804 (allowing 16 levels overall) prior to VMS 7.2. Hence
805 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
806 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
807 have to take this into account, but at least they can refer to the former
808 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
810 The VMS::Filespec module, which gets installed as part of the build
811 process on VMS, is a pure Perl module that can easily be installed on
812 non-VMS platforms and can be helpful for conversions to and from RMS
815 What C<\n> represents depends on the type of file opened. It could
816 be C<\015>, C<\012>, C<\015\012>, or nothing. The VMS::Stdio module
817 provides access to the special fopen() requirements of files with unusual
820 TCP/IP stacks are optional on VMS, so socket routines might not be
821 implemented. UDP sockets may not be supported.
823 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
824 that you are running on without resorting to loading all of C<%Config>
825 you can examine the content of the C<@INC> array like so:
827 if (grep(/VMS_AXP/, @INC)) {
828 print "I'm on Alpha!\n";
830 } elsif (grep(/VMS_VAX/, @INC)) {
831 print "I'm on VAX!\n";
834 print "I'm not so sure about where $^O is...\n";
837 On VMS, perl determines the UTC offset from the C<SYS$TIMEZONE_DIFFERENTIAL>
838 logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00,
839 calls to C<localtime> are adjusted to count offsets from
840 01-JAN-1970 00:00:00.00, just like Unix.
846 =item L<README.vms>, L<perlvms.pod>
848 =item vmsperl list, C<majordomo@perl.org>
850 Put the words C<subscribe vmsperl> in message body.
852 =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html>
858 Perl on VOS is discussed in F<README.vos> in the perl distribution.
859 Perl on VOS can accept either VOS- or Unix-style file
860 specifications as in either of the following:
862 $ perl -ne "print if /perl_setup/i" >system>notices
863 $ perl -ne "print if /perl_setup/i" /system/notices
865 or even a mixture of both as in:
867 $ perl -ne "print if /perl_setup/i" >system/notices
869 Even though VOS allows the slash character to appear in object
870 names, because the VOS port of Perl interprets it as a pathname
871 delimiting character, VOS files, directories, or links whose names
872 contain a slash character cannot be processed. Such files must be
873 renamed before they can be processed by Perl. Note that VOS limits
874 file names to 32 or fewer characters.
876 The following C functions are unimplemented on VOS, and any attempt by
877 Perl to use them will result in a fatal error message and an immediate
878 exit from Perl: dup, do_aspawn, do_spawn, fork, waitpid. Once these
879 functions become available in the VOS POSIX.1 implementation, you can
880 either recompile and rebind Perl, or you can download a newer port from
883 The value of C<$^O> on VOS is "VOS". To determine the architecture that
884 you are running on without resorting to loading all of C<%Config> you
885 can examine the content of the C<@INC> array like so:
888 print "I'm on a Stratus box!\n";
890 print "I'm not on a Stratus box!\n";
894 if (grep(/860/, @INC)) {
895 print "This box is a Stratus XA/R!\n";
897 } elsif (grep(/7100/, @INC)) {
898 print "This box is a Stratus HP 7100 or 8xxx!\n";
900 } elsif (grep(/8000/, @INC)) {
901 print "This box is a Stratus HP 8xxx!\n";
904 print "This box is a Stratus 68K!\n";
913 =item VOS mailing list
915 There is no specific mailing list for Perl on VOS. You can post
916 comments to the comp.sys.stratus newsgroup, or subscribe to the general
917 Stratus mailing list. Send a letter with "Subscribe Info-Stratus" in
918 the message body to majordomo@list.stratagy.com.
920 =item VOS Perl on the web at C<http://ftp.stratus.com/pub/vos/vos.html>
924 =head2 EBCDIC Platforms
926 Recent versions of Perl have been ported to platforms such as OS/400 on
927 AS/400 minicomputers as well as OS/390, VM/ESA, and BS2000 for S/390
928 Mainframes. Such computers use EBCDIC character sets internally (usually
929 Character Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC for S/390
930 systems). On the mainframe perl currently works under the "Unix system
931 services for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or
932 the BS200 POSIX-BC system (BS2000 is supported in perl 5.6 and greater).
934 As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
935 sub-systems do not support the C<#!> shebang trick for script invocation.
936 Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
937 similar to the following simple script:
940 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
942 #!/usr/local/bin/perl # just a comment really
944 print "Hello from perl!\n";
946 OS/390 will support the C<#!> shebang trick in release 2.8 and beyond.
947 Calls to C<system> and backticks can use POSIX shell syntax on all
950 On the AS/400, if PERL5 is in your library list, you may need
951 to wrap your perl scripts in a CL procedure to invoke them like so:
954 CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
957 This will invoke the perl script F<hello.pl> in the root of the
958 QOpenSys file system. On the AS/400 calls to C<system> or backticks
961 On these platforms, bear in mind that the EBCDIC character set may have
962 an effect on what happens with some perl functions (such as C<chr>,
963 C<pack>, C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>), as
964 well as bit-fiddling with ASCII constants using operators like C<^>, C<&>
965 and C<|>, not to mention dealing with socket interfaces to ASCII computers
968 Fortunately, most web servers for the mainframe will correctly
969 translate the C<\n> in the following statement to its ASCII equivalent
970 (C<\r> is the same under both Unix and OS/390 & VM/ESA):
972 print "Content-type: text/html\r\n\r\n";
974 The values of C<$^O> on some of these platforms includes:
976 uname $^O $Config{'archname'}
977 --------------------------------------------
980 POSIX-BC posix-bc BS2000-posix-bc
983 Some simple tricks for determining if you are running on an EBCDIC
984 platform could include any of the following (perhaps all):
986 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
988 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
990 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
992 One thing you may not want to rely on is the EBCDIC encoding
993 of punctuation characters since these may differ from code page to code
994 page (and once your module or script is rumoured to work with EBCDIC,
995 folks will want it to work with all EBCDIC character sets).
1001 =item L<README.os390>, L<README.posix-bc>, L<README.vmesa>
1005 The perl-mvs@perl.org list is for discussion of porting issues as well as
1006 general usage issues for all EBCDIC Perls. Send a message body of
1007 "subscribe perl-mvs" to majordomo@perl.org.
1009 =item AS/400 Perl information at C<http://as400.rochester.ibm.com/>
1010 as well as on CPAN in the F<ports/> directory.
1014 =head2 Acorn RISC OS
1016 Because Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
1017 Unix, and because Unix filename emulation is turned on by default,
1018 most simple scripts will probably work "out of the box". The native
1019 filesystem is modular, and individual filesystems are free to be
1020 case-sensitive or insensitive, and are usually case-preserving. Some
1021 native filesystems have name length limits, which file and directory
1022 names are silently truncated to fit. Scripts should be aware that the
1023 standard filesystem currently has a name length limit of B<10>
1024 characters, with up to 77 items in a directory, but other filesystems
1025 may not impose such limitations.
1027 Native filenames are of the form
1029 Filesystem#Special_Field::DiskName.$.Directory.Directory.File
1033 Special_Field is not usually present, but may contain . and $ .
1034 Filesystem =~ m|[A-Za-z0-9_]|
1035 DsicName =~ m|[A-Za-z0-9_/]|
1036 $ represents the root directory
1037 . is the path separator
1038 @ is the current directory (per filesystem but machine global)
1039 ^ is the parent directory
1040 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
1042 The default filename translation is roughly C<tr|/.|./|;>
1044 Note that C<"ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'> and that
1045 the second stage of C<$> interpolation in regular expressions will fall
1046 foul of the C<$.> if scripts are not careful.
1048 Logical paths specified by system variables containing comma-separated
1049 search lists are also allowed; hence C<System:Modules> is a valid
1050 filename, and the filesystem will prefix C<Modules> with each section of
1051 C<System$Path> until a name is made that points to an object on disk.
1052 Writing to a new file C<System:Modules> would be allowed only if
1053 C<System$Path> contains a single item list. The filesystem will also
1054 expand system variables in filenames if enclosed in angle brackets, so
1055 C<E<lt>System$DirE<gt>.Modules> would look for the file
1056 S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious implication of this is
1057 that B<fully qualified filenames can start with C<E<lt>E<gt>>> and should
1058 be protected when C<open> is used for input.
1060 Because C<.> was in use as a directory separator and filenames could not
1061 be assumed to be unique after 10 characters, Acorn implemented the C
1062 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
1063 filenames specified in source code and store the respective files in
1064 subdirectories named after the suffix. Hence files are translated:
1067 C:foo.h C:h.foo (logical path variable)
1068 sys/os.h sys.h.os (C compiler groks Unix-speak)
1069 10charname.c c.10charname
1070 10charname.o o.10charname
1071 11charname_.c c.11charname (assuming filesystem truncates at 10)
1073 The Unix emulation library's translation of filenames to native assumes
1074 that this sort of translation is required, and it allows a user-defined list
1075 of known suffixes that it will transpose in this fashion. This may
1076 seem transparent, but consider that with these rules C<foo/bar/baz.h>
1077 and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
1078 C<glob> cannot and do not attempt to emulate the reverse mapping. Other
1079 C<.>'s in filenames are translated to C</>.
1081 As implied above, the environment accessed through C<%ENV> is global, and
1082 the convention is that program specific environment variables are of the
1083 form C<Program$Name>. Each filesystem maintains a current directory,
1084 and the current filesystem's current directory is the B<global> current
1085 directory. Consequently, sociable programs don't change the current
1086 directory but rely on full pathnames, and programs (and Makefiles) cannot
1087 assume that they can spawn a child process which can change the current
1088 directory without affecting its parent (and everyone else for that
1091 Because native operating system filehandles are global and are currently
1092 allocated down from 255, with 0 being a reserved value, the Unix emulation
1093 library emulates Unix filehandles. Consequently, you can't rely on
1094 passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
1096 The desire of users to express filenames of the form
1097 C<E<lt>Foo$DirE<gt>.Bar> on the command line unquoted causes problems,
1098 too: C<``> command output capture has to perform a guessing game. It
1099 assumes that a string C<E<lt>[^E<lt>E<gt>]+\$[^E<lt>E<gt>]E<gt>> is a
1100 reference to an environment variable, whereas anything else involving
1101 C<E<lt>> or C<E<gt>> is redirection, and generally manages to be 99%
1102 right. Of course, the problem remains that scripts cannot rely on any
1103 Unix tools being available, or that any tools found have Unix-like command
1106 Extensions and XS are, in theory, buildable by anyone using free
1107 tools. In practice, many don't, as users of the Acorn platform are
1108 used to binary distributions. MakeMaker does run, but no available
1109 make currently copes with MakeMaker's makefiles; even if and when
1110 this should be fixed, the lack of a Unix-like shell will cause
1111 problems with makefile rules, especially lines of the form C<cd
1112 sdbm && make all>, and anything using quoting.
1114 "S<RISC OS>" is the proper name for the operating system, but the value
1115 in C<$^O> is "riscos" (because we don't like shouting).
1119 Perl has been ported to many platforms that do not fit into any of
1120 the categories listed above. Some, such as AmigaOS, Atari MiNT,
1121 BeOS, HP MPE/iX, QNX, Plan 9, and VOS, have been well-integrated
1122 into the standard Perl source code kit. You may need to see the
1123 F<ports/> directory on CPAN for information, and possibly binaries,
1124 for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware,
1125 Tandem Guardian, I<etc.> (Yes, we know that some of these OSes may
1126 fall under the Unix category, but we are not a standards body.)
1128 Some approximate operating system names and their C<$^O> values
1129 in the "OTHER" category include:
1131 OS $^O $Config{'archname'}
1132 ------------------------------------------
1133 Amiga DOS amigaos m68k-amigos
1134 MPE/iX mpeix PA-RISC1.1
1140 =item Amiga, L<README.amiga>
1142 =item Atari, L<README.mint> and Guido Flohr's web page
1143 C<http://stud.uni-sb.de/~gufl0000/>
1145 =item Be OS, L<README.beos>
1147 =item HP 300 MPE/iX, L<README.mpeix> and Mark Bixby's web page
1148 C<http://www.cccd.edu/~markb/perlix.html>
1150 =item Novell Netware
1152 A free perl5-based PERL.NLM for Novell Netware is available in
1153 precompiled binary and source code form from C<http://www.novell.com/>
1154 as well as from CPAN.
1156 =item Plan 9, L<README.plan9>
1160 =head1 FUNCTION IMPLEMENTATIONS
1162 Listed below are functions that are either completely unimplemented
1163 or else have been implemented differently on various platforms.
1164 Following each description will be, in parentheses, a list of
1165 platforms that the description applies to.
1167 The list may well be incomplete, or even wrong in some places. When
1168 in doubt, consult the platform-specific README files in the Perl
1169 source distribution, and any other documentation resources accompanying
1172 Be aware, moreover, that even among Unix-ish systems there are variations.
1174 For many functions, you can also query C<%Config>, exported by
1175 default from the Config module. For example, to check whether the
1176 platform has the C<lstat> call, check C<$Config{d_lstat}>. See
1177 L<Config> for a full description of available variables.
1179 =head2 Alphabetical Listing of Perl Functions
1189 C<-r>, C<-w>, and C<-x> have a limited meaning only; directories
1190 and applications are executable, and there are no uid/gid
1191 considerations. C<-o> is not supported. (S<Mac OS>)
1193 C<-r>, C<-w>, C<-x>, and C<-o> tell whether the file is accessible,
1194 which may not reflect UIC-based file protections. (VMS)
1196 C<-s> returns the size of the data fork, not the total size of data fork
1197 plus resource fork. (S<Mac OS>).
1199 C<-s> by name on an open file will return the space reserved on disk,
1200 rather than the current extent. C<-s> on an open filehandle returns the
1201 current size. (S<RISC OS>)
1203 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
1204 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1206 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
1209 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
1210 (Win32, VMS, S<RISC OS>)
1212 C<-d> is true if passed a device spec without an explicit directory.
1215 C<-T> and C<-B> are implemented, but might misclassify Mac text files
1216 with foreign characters; this is the case will all platforms, but may
1217 affect S<Mac OS> often. (S<Mac OS>)
1219 C<-x> (or C<-X>) determine if a file ends in one of the executable
1220 suffixes. C<-S> is meaningless. (Win32)
1222 C<-x> (or C<-X>) determine if a file has an executable file type.
1225 =item binmode FILEHANDLE
1227 Meaningless. (S<Mac OS>, S<RISC OS>)
1229 Reopens file and restores pointer; if function fails, underlying
1230 filehandle may be closed, or pointer may be in a different position.
1233 The value returned by C<tell> may be affected after the call, and
1234 the filehandle may be flushed. (Win32)
1238 Only limited meaning. Disabling/enabling write permission is mapped to
1239 locking/unlocking the file. (S<Mac OS>)
1241 Only good for changing "owner" read-write access, "group", and "other"
1242 bits are meaningless. (Win32)
1244 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
1246 Access permissions are mapped onto VOS access-control list changes. (VOS)
1250 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
1252 Does nothing, but won't fail. (Win32)
1254 =item chroot FILENAME
1258 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS, VM/ESA)
1260 =item crypt PLAINTEXT,SALT
1262 May not be available if library or source was not provided when building
1265 Not implemented. (VOS)
1269 Not implemented. (VMS, Plan9, VOS)
1271 =item dbmopen HASH,DBNAME,MODE
1273 Not implemented. (VMS, Plan9, VOS)
1277 Not useful. (S<Mac OS>, S<RISC OS>)
1279 Not implemented. (Win32)
1281 Invokes VMS debugger. (VMS)
1285 Not implemented. (S<Mac OS>)
1287 Implemented via Spawn. (VM/ESA)
1289 =item fcntl FILEHANDLE,FUNCTION,SCALAR
1291 Not implemented. (Win32, VMS)
1293 =item flock FILEHANDLE,OPERATION
1295 Not implemented (S<Mac OS>, VMS, S<RISC OS>, VOS).
1297 Available only on Windows NT (not on Windows 95). (Win32)
1301 Not implemented. (S<Mac OS>, Win32, AmigaOS, S<RISC OS>, VOS, VM/ESA)
1305 Not implemented. (S<Mac OS>, S<RISC OS>)
1309 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1313 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1315 =item getpriority WHICH,WHO
1317 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1321 Not implemented. (S<Mac OS>, Win32)
1323 Not useful. (S<RISC OS>)
1327 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1329 =item getnetbyname NAME
1331 Not implemented. (S<Mac OS>, Win32, Plan9)
1335 Not implemented. (S<Mac OS>, Win32)
1337 Not useful. (S<RISC OS>)
1341 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1343 =item getnetbyaddr ADDR,ADDRTYPE
1345 Not implemented. (S<Mac OS>, Win32, Plan9)
1347 =item getprotobynumber NUMBER
1349 Not implemented. (S<Mac OS>)
1351 =item getservbyport PORT,PROTO
1353 Not implemented. (S<Mac OS>)
1357 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1361 Not implemented. (S<Mac OS>, Win32, VMS, VM/ESA)
1365 Not implemented. (S<Mac OS>, Win32)
1369 Not implemented. (S<Mac OS>, Win32, Plan9)
1373 Not implemented. (S<Mac OS>, Win32, Plan9)
1377 Not implemented. (Win32, Plan9)
1381 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1385 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1387 =item sethostent STAYOPEN
1389 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1391 =item setnetent STAYOPEN
1393 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1395 =item setprotoent STAYOPEN
1397 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1399 =item setservent STAYOPEN
1401 Not implemented. (Plan9, Win32, S<RISC OS>)
1405 Not implemented. (S<Mac OS>, MPE/iX, VM/ESA, Win32)
1409 Not implemented. (S<Mac OS>, MPE/iX, S<RISC OS>, VM/ESA, VMS, Win32)
1413 Not implemented. (S<Mac OS>, Win32)
1417 Not implemented. (S<Mac OS>, Win32, Plan9)
1421 Not implemented. (S<Mac OS>, Win32, Plan9)
1425 Not implemented. (Plan9, Win32)
1427 =item getsockopt SOCKET,LEVEL,OPTNAME
1429 Not implemented. (S<Mac OS>, Plan9)
1435 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1438 Features depend on external perlglob.exe or perlglob.bat. May be
1439 overridden with something like File::DosGlob, which is recommended.
1442 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1443 Globbing relies on operating system calls, which may return filenames
1444 in any order. As most filesystems are case-insensitive, even "sorted"
1445 filenames will not be in case-sensitive order. (S<RISC OS>)
1447 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1449 Not implemented. (VMS)
1451 Available only for socket handles, and it does what the ioctlsocket() call
1452 in the Winsock API does. (Win32)
1454 Available only for socket handles. (S<RISC OS>)
1456 =item kill SIGNAL, LIST
1458 Not implemented, hence not useful for taint checking. (S<Mac OS>,
1461 Unlike Unix platforms, C<kill(0, $pid)> will actually terminate
1462 the process. (Win32)
1464 =item link OLDFILE,NEWFILE
1466 Not implemented. (S<Mac OS>, MPE/iX, VMS, S<RISC OS>)
1468 Link count not updated because hard links are not quite that hard
1469 (They are sort of half-way between hard and soft links). (AmigaOS)
1471 Hard links are implemented on Win32 (Windows NT and Windows 2000)
1474 =item lstat FILEHANDLE
1480 Not implemented. (VMS, S<RISC OS>)
1482 Return values may be bogus. (Win32)
1484 =item msgctl ID,CMD,ARG
1486 =item msgget KEY,FLAGS
1488 =item msgsnd ID,MSG,FLAGS
1490 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1492 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1494 =item open FILEHANDLE,EXPR
1496 =item open FILEHANDLE
1498 The C<|> variants are supported only if ToolServer is installed.
1501 open to C<|E<45>> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1503 =item pipe READHANDLE,WRITEHANDLE
1505 Not implemented. (S<Mac OS>)
1507 Very limited functionality. (MiNT)
1513 Not implemented. (Win32, VMS, S<RISC OS>)
1515 =item select RBITS,WBITS,EBITS,TIMEOUT
1517 Only implemented on sockets. (Win32)
1519 Only reliable on sockets. (S<RISC OS>)
1521 =item semctl ID,SEMNUM,CMD,ARG
1523 =item semget KEY,NSEMS,FLAGS
1525 =item semop KEY,OPSTRING
1527 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1531 Not implemented. (MPE/iX, Win32)
1533 =item setpgrp PID,PGRP
1535 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1537 =item setpriority WHICH,WHO,PRIORITY
1539 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1543 Not implemented. (MPE/iX, Win32)
1545 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1547 Not implemented. (S<Mac OS>, Plan9)
1549 =item shmctl ID,CMD,ARG
1551 =item shmget KEY,SIZE,FLAGS
1553 =item shmread ID,VAR,POS,SIZE
1555 =item shmwrite ID,STRING,POS,SIZE
1557 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1559 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1561 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1563 =item stat FILEHANDLE
1569 mtime and atime are the same thing, and ctime is creation time instead of
1570 inode change time. (S<Mac OS>)
1572 device and inode are not meaningful. (Win32)
1574 device and inode are not necessarily reliable. (VMS)
1576 mtime, atime and ctime all return the last modification time. Device and
1577 inode are not necessarily reliable. (S<RISC OS>)
1579 =item symlink OLDFILE,NEWFILE
1581 Not implemented. (Win32, VMS, S<RISC OS>)
1585 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1587 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1589 The traditional "0", "1", and "2" MODEs are implemented with different
1590 numeric values on some systems. The flags exported by C<Fcntl>
1591 (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (S<Mac
1592 OS>, OS/390, VM/ESA)
1596 Only implemented if ToolServer is installed. (S<Mac OS>)
1598 As an optimization, may not call the command shell specified in
1599 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1600 process and immediately returns its process designator, without
1601 waiting for it to terminate. Return value may be used subsequently
1602 in C<wait> or C<waitpid>. (Win32)
1604 There is no shell to process metacharacters, and the native standard is
1605 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1606 program. Redirection such as C<E<gt> foo> is performed (if at all) by
1607 the run time library of the spawned program. C<system> I<list> will call
1608 the Unix emulation library's C<exec> emulation, which attempts to provide
1609 emulation of the stdin, stdout, stderr in force in the parent, providing
1610 the child program uses a compatible version of the emulation library.
1611 I<scalar> will call the native command line direct and no such emulation
1612 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1614 Far from being POSIX compliant. Because there may be no underlying
1615 /bin/sh tries to work around the problem by forking and execing the
1616 first token in its argument string. Handles basic redirection
1617 ("E<lt>" or "E<gt>") on its own behalf. (MiNT)
1621 Only the first entry returned is nonzero. (S<Mac OS>)
1623 "cumulative" times will be bogus. On anything other than Windows NT,
1624 "system" time will be bogus, and "user" time is actually the time
1625 returned by the clock() function in the C runtime library. (Win32)
1627 Not useful. (S<RISC OS>)
1629 =item truncate FILEHANDLE,LENGTH
1631 =item truncate EXPR,LENGTH
1633 Not implemented. (VMS)
1635 Truncation to zero-length only. (VOS)
1637 If a FILEHANDLE is supplied, it must be writable and opened in append
1638 mode (i.e., use C<open(FH, '>>filename')>
1639 or C<sysopen(FH,...,O_APPEND|O_RDWR)>. If a filename is supplied, it
1640 should not be held open elsewhere. (Win32)
1646 Returns undef where unavailable, as of version 5.005.
1648 C<umask> works but the correct permissions are set only when the file
1649 is finally closed. (AmigaOS)
1653 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1655 May not behave as expected. Behavior depends on the C runtime
1656 library's implementation of utime(), and the filesystem being
1657 used. The FAT filesystem typically does not support an "access
1658 time" field, and it may limit timestamps to a granularity of
1659 two seconds. (Win32)
1663 =item waitpid PID,FLAGS
1665 Not implemented. (S<Mac OS>, VOS)
1667 Can only be applied to process handles returned for processes spawned
1668 using C<system(1, ...)>. (Win32)
1670 Not useful. (S<RISC OS>)
1678 =item v1.46, 12 February 2000
1680 Updates for VOS and MPE/iX. (Peter Prymmer) Other small changes.
1682 =item v1.45, 20 December 1999
1684 Small changes from 5.005_63 distribution, more changes to EBCDIC info.
1686 =item v1.44, 19 July 1999
1688 A bunch of updates from Peter Prymmer for C<$^O> values,
1689 endianness, File::Spec, VMS, BS2000, OS/400.
1691 =item v1.43, 24 May 1999
1693 Added a lot of cleaning up from Tom Christiansen.
1695 =item v1.42, 22 May 1999
1697 Added notes about tests, sprintf/printf, and epoch offsets.
1699 =item v1.41, 19 May 1999
1701 Lots more little changes to formatting and content.
1703 Added a bunch of C<$^O> and related values
1704 for various platforms; fixed mail and web addresses, and added
1705 and changed miscellaneous notes. (Peter Prymmer)
1707 =item v1.40, 11 April 1999
1709 Miscellaneous changes.
1711 =item v1.39, 11 February 1999
1713 Changes from Jarkko and EMX URL fixes Michael Schwern. Additional
1714 note about newlines added.
1716 =item v1.38, 31 December 1998
1718 More changes from Jarkko.
1720 =item v1.37, 19 December 1998
1722 More minor changes. Merge two separate version 1.35 documents.
1724 =item v1.36, 9 September 1998
1726 Updated for Stratus VOS. Also known as version 1.35.
1728 =item v1.35, 13 August 1998
1730 Integrate more minor changes, plus addition of new sections under
1731 L<"ISSUES">: L<"Numbers endianness and Width">,
1732 L<"Character sets and character encoding">,
1733 L<"Internationalisation">.
1735 =item v1.33, 06 August 1998
1737 Integrate more minor changes.
1739 =item v1.32, 05 August 1998
1741 Integrate more minor changes.
1743 =item v1.30, 03 August 1998
1745 Major update for RISC OS, other minor changes.
1747 =item v1.23, 10 July 1998
1749 First public release with perl5.005.
1753 =head1 AUTHORS / CONTRIBUTORS
1755 Abigail E<lt>abigail@fnx.comE<gt>,
1756 Charles Bailey E<lt>bailey@newman.upenn.eduE<gt>,
1757 Graham Barr E<lt>gbarr@pobox.comE<gt>,
1758 Tom Christiansen E<lt>tchrist@perl.comE<gt>,
1759 Nicholas Clark E<lt>Nicholas.Clark@liverpool.ac.ukE<gt>,
1760 Thomas Dorner E<lt>Thomas.Dorner@start.deE<gt>,
1761 Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>,
1762 Dominic Dunlop E<lt>domo@vo.luE<gt>,
1763 Neale Ferguson E<lt>neale@mailbox.tabnsw.com.auE<gt>,
1764 David J. Fiander E<lt>davidf@mks.comE<gt>,
1765 Paul Green E<lt>Paul_Green@stratus.comE<gt>,
1766 M.J.T. Guy E<lt>mjtg@cus.cam.ac.ukE<gt>,
1767 Jarkko Hietaniemi E<lt>jhi@iki.fi<gt>,
1768 Luther Huffman E<lt>lutherh@stratcom.comE<gt>,
1769 Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>,
1770 Andreas J. KE<ouml>nig E<lt>koenig@kulturbox.deE<gt>,
1771 Markus Laker E<lt>mlaker@contax.co.ukE<gt>,
1772 Andrew M. Langmead E<lt>aml@world.std.comE<gt>,
1773 Larry Moore E<lt>ljmoore@freespace.netE<gt>,
1774 Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>,
1775 Chris Nandor E<lt>pudge@pobox.comE<gt>,
1776 Matthias Neeracher E<lt>neeri@iis.ee.ethz.chE<gt>,
1777 Gary Ng E<lt>71564.1743@CompuServe.COME<gt>,
1778 Tom Phoenix E<lt>rootbeer@teleport.comE<gt>,
1779 AndrE<eacute> Pirard E<lt>A.Pirard@ulg.ac.beE<gt>,
1780 Peter Prymmer E<lt>pvhp@forte.comE<gt>,
1781 Hugo van der Sanden E<lt>hv@crypt0.demon.co.ukE<gt>,
1782 Gurusamy Sarathy E<lt>gsar@activestate.comE<gt>,
1783 Paul J. Schinder E<lt>schinder@pobox.comE<gt>,
1784 Michael G Schwern E<lt>schwern@pobox.comE<gt>,
1785 Dan Sugalski E<lt>sugalskd@ous.eduE<gt>,
1786 Nathan Torkington E<lt>gnat@frii.comE<gt>.
1788 This document is maintained by Chris Nandor
1789 E<lt>pudge@pobox.comE<gt>.
1793 Version 1.46, last modified 12 February 2000