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 (<IMG SRC="yellow_sign.gif" ALT="Under Construction">).
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 A common cause of unportable programs is the misuse of chop() to trim
107 You can get away with this on Unix and MacOS (they have a single
108 character end-of-line), but the same program will break under DOSish
109 perls because you're only chop()ing half the end-of-line. Instead,
110 chomp() should be used to trim newlines. The Dunce::Files module can
111 help audit your code for misuses of chop().
113 When dealing with binary files (or text files in binary mode) be sure
114 to explicitly set $/ to the appropriate value for your file format
115 before using chomp().
117 Because of the "text" mode translation, DOSish perls have limitations
118 in using C<seek> and C<tell> on a file accessed in "text" mode.
119 Stick to C<seek>-ing to locations you got from C<tell> (and no
120 others), and you are usually free to use C<seek> and C<tell> even
121 in "text" mode. Using C<seek> or C<tell> or other file operations
122 may be non-portable. If you use C<binmode> on a file, however, you
123 can usually C<seek> and C<tell> with arbitrary values in safety.
125 A common misconception in socket programming is that C<\n> eq C<\012>
126 everywhere. When using protocols such as common Internet protocols,
127 C<\012> and C<\015> are called for specifically, and the values of
128 the logical C<\n> and C<\r> (carriage return) are not reliable.
130 print SOCKET "Hi there, client!\r\n"; # WRONG
131 print SOCKET "Hi there, client!\015\012"; # RIGHT
133 However, using C<\015\012> (or C<\cM\cJ>, or C<\x0D\x0A>) can be tedious
134 and unsightly, as well as confusing to those maintaining the code. As
135 such, the Socket module supplies the Right Thing for those who want it.
137 use Socket qw(:DEFAULT :crlf);
138 print SOCKET "Hi there, client!$CRLF" # RIGHT
140 When reading from a socket, remember that the default input record
141 separator C<$/> is C<\n>, but robust socket code will recognize as
142 either C<\012> or C<\015\012> as end of line:
148 Because both CRLF and LF end in LF, the input record separator can
149 be set to LF and any CR stripped later. Better to write:
151 use Socket qw(:DEFAULT :crlf);
152 local($/) = LF; # not needed if $/ is already \012
155 s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
156 # s/\015?\012/\n/; # same thing
159 This example is preferred over the previous one--even for Unix
160 platforms--because now any C<\015>'s (C<\cM>'s) are stripped out
161 (and there was much rejoicing).
163 Similarly, functions that return text data--such as a function that
164 fetches a web page--should sometimes translate newlines before
165 returning the data, if they've not yet been translated to the local
166 newline representation. A single line of code will often suffice:
168 $data =~ s/\015?\012/\n/g;
171 Some of this may be confusing. Here's a handy reference to the ASCII CR
172 and LF characters. You can print it out and stick it in your wallet.
174 LF == \012 == \x0A == \cJ == ASCII 10
175 CR == \015 == \x0D == \cM == ASCII 13
178 ---------------------------
181 \n * | LF | CRLF | CR |
182 \r * | CR | CR | LF |
183 ---------------------------
186 The Unix column assumes that you are not accessing a serial line
187 (like a tty) in canonical mode. If you are, then CR on input becomes
188 "\n", and "\n" on output becomes CRLF.
190 These are just the most common definitions of C<\n> and C<\r> in Perl.
191 There may well be others.
193 =head2 Numbers endianness and Width
195 Different CPUs store integers and floating point numbers in different
196 orders (called I<endianness>) and widths (32-bit and 64-bit being the
197 most common today). This affects your programs when they attempt to transfer
198 numbers in binary format from one CPU architecture to another,
199 usually either "live" via network connection, or by storing the
200 numbers to secondary storage such as a disk file or tape.
202 Conflicting storage orders make utter mess out of the numbers. If a
203 little-endian host (Intel, VAX) stores 0x12345678 (305419896 in
204 decimal), a big-endian host (Motorola, Sparc, PA) reads it as
205 0x78563412 (2018915346 in decimal). Alpha and MIPS can be either:
206 Digital/Compaq used/uses them in little-endian mode; SGI/Cray uses
207 them in big-endian mode. To avoid this problem in network (socket)
208 connections use the C<pack> and C<unpack> formats C<n> and C<N>, the
209 "network" orders. These are guaranteed to be portable.
211 You can explore the endianness of your platform by unpacking a
212 data structure packed in native format such as:
214 print unpack("h*", pack("s2", 1, 2)), "\n";
215 # '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
216 # '00100020' on e.g. Motorola 68040
218 If you need to distinguish between endian architectures you could use
219 either of the variables set like so:
221 $is_big_endian = unpack("h*", pack("s", 1)) =~ /01/;
222 $is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;
224 Differing widths can cause truncation even between platforms of equal
225 endianness. The platform of shorter width loses the upper parts of the
226 number. There is no good solution for this problem except to avoid
227 transferring or storing raw binary numbers.
229 One can circumnavigate both these problems in two ways. Either
230 transfer and store numbers always in text format, instead of raw
231 binary, or else consider using modules like Data::Dumper (included in
232 the standard distribution as of Perl 5.005) and Storable (included as
233 of perl 5.8). Keeping all data as text significantly simplifies matters.
235 =head2 Files and Filesystems
237 Most platforms these days structure files in a hierarchical fashion.
238 So, it is reasonably safe to assume that all platforms support the
239 notion of a "path" to uniquely identify a file on the system. How
240 that path is really written, though, differs considerably.
242 Although similar, file path specifications differ between Unix,
243 Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS>, and probably others.
244 Unix, for example, is one of the few OSes that has the elegant idea
245 of a single root directory.
247 DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with C</>
248 as path separator, or in their own idiosyncratic ways (such as having
249 several root directories and various "unrooted" device files such NIL:
252 S<Mac OS> uses C<:> as a path separator instead of C</>.
254 The filesystem may support neither hard links (C<link>) nor
255 symbolic links (C<symlink>, C<readlink>, C<lstat>).
257 The filesystem may support neither access timestamp nor change
258 timestamp (meaning that about the only portable timestamp is the
259 modification timestamp), or one second granularity of any timestamps
260 (e.g. the FAT filesystem limits the time granularity to two seconds).
262 VOS perl can emulate Unix filenames with C</> as path separator. The
263 native pathname characters greater-than, less-than, number-sign, and
264 percent-sign are always accepted.
266 S<RISC OS> perl can emulate Unix filenames with C</> as path
267 separator, or go native and use C<.> for path separator and C<:> to
268 signal filesystems and disk names.
270 If all this is intimidating, have no (well, maybe only a little)
271 fear. There are modules that can help. The File::Spec modules
272 provide methods to do the Right Thing on whatever platform happens
273 to be running the program.
275 use File::Spec::Functions;
276 chdir(updir()); # go up one directory
277 $file = catfile(curdir(), 'temp', 'file.txt');
278 # on Unix and Win32, './temp/file.txt'
279 # on Mac OS, ':temp:file.txt'
280 # on VMS, '[.temp]file.txt'
282 File::Spec is available in the standard distribution as of version
283 5.004_05. File::Spec::Functions is only in File::Spec 0.7 and later,
284 and some versions of perl come with version 0.6. If File::Spec
285 is not updated to 0.7 or later, you must use the object-oriented
286 interface from File::Spec (or upgrade File::Spec).
288 In general, production code should not have file paths hardcoded.
289 Making them user-supplied or read from a configuration file is
290 better, keeping in mind that file path syntax varies on different
293 This is especially noticeable in scripts like Makefiles and test suites,
294 which often assume C</> as a path separator for subdirectories.
296 Also of use is File::Basename from the standard distribution, which
297 splits a pathname into pieces (base filename, full path to directory,
300 Even when on a single platform (if you can call Unix a single platform),
301 remember not to count on the existence or the contents of particular
302 system-specific files or directories, like F</etc/passwd>,
303 F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
304 example, F</etc/passwd> may exist but not contain the encrypted
305 passwords, because the system is using some form of enhanced security.
306 Or it may not contain all the accounts, because the system is using NIS.
307 If code does need to rely on such a file, include a description of the
308 file and its format in the code's documentation, then make it easy for
309 the user to override the default location of the file.
311 Don't assume a text file will end with a newline. They should,
314 Do not have two files of the same name with different case, like
315 F<test.pl> and F<Test.pl>, as many platforms have case-insensitive
316 filenames. Also, try not to have non-word characters (except for C<.>)
317 in the names, and keep them to the 8.3 convention, for maximum
318 portability, onerous a burden though this may appear.
320 Likewise, when using the AutoSplit module, try to keep your functions to
321 8.3 naming and case-insensitive conventions; or, at the least,
322 make it so the resulting files have a unique (case-insensitively)
325 Whitespace in filenames is tolerated on most systems, but not all.
326 Many systems (DOS, VMS) cannot have more than one C<.> in their filenames.
328 Don't assume C<< > >> won't be the first character of a filename.
329 Always use C<< < >> explicitly to open a file for reading,
330 unless you want the user to be able to specify a pipe open.
332 open(FILE, "< $existing_file") or die $!;
334 If filenames might use strange characters, it is safest to open it
335 with C<sysopen> instead of C<open>. C<open> is magic and can
336 translate characters like C<< > >>, C<< < >>, and C<|>, which may
337 be the wrong thing to do. (Sometimes, though, it's the right thing.)
339 =head2 System Interaction
341 Not all platforms provide a command line. These are usually platforms
342 that rely primarily on a Graphical User Interface (GUI) for user
343 interaction. A program requiring a command line interface might
344 not work everywhere. This is probably for the user of the program
345 to deal with, so don't stay up late worrying about it.
347 Some platforms can't delete or rename files held open by the system.
348 Remember to C<close> files when you are done with them. Don't
349 C<unlink> or C<rename> an open file. Don't C<tie> or C<open> a
350 file already tied or opened; C<untie> or C<close> it first.
352 Don't open the same file more than once at a time for writing, as some
353 operating systems put mandatory locks on such files.
355 Don't assume that write/modify permission on a directory gives the
356 right to add or delete files/directories in that directory. That is
357 filesystem specific: in some filesystems you need write/modify
358 permission also (or even just) in the file/directory itself. In some
359 filesystems (AFS, DFS) the permission to add/delete directory entries
360 is a completely separate permission.
362 Don't assume that a single C<unlink> completely gets rid of the file:
363 some filesystems (most notably the ones in VMS) have versioned
364 filesystems, and unlink() removes only the most recent one (it doesn't
365 remove all the versions because by default the native tools on those
366 platforms remove just the most recent version, too). The portable
367 idiom to remove all the versions of a file is
369 1 while unlink "file";
371 This will terminate if the file is undeleteable for some reason
372 (protected, not there, and so on).
374 Don't count on a specific environment variable existing in C<%ENV>.
375 Don't count on C<%ENV> entries being case-sensitive, or even
376 case-preserving. Don't try to clear %ENV by saying C<%ENV = ();>, or,
377 if you really have to, make it conditional on C<$^O ne 'VMS'> since in
378 VMS the C<%ENV> table is much more than a per-process key-value string
381 Don't count on signals or C<%SIG> for anything.
383 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
386 Don't count on per-program environment variables, or per-program current
389 Don't count on specific values of C<$!>.
391 =head2 Interprocess Communication (IPC)
393 In general, don't directly access the system in code meant to be
394 portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>,
395 C<``>, C<qx//>, C<open> with a C<|>, nor any of the other things
396 that makes being a perl hacker worth being.
398 Commands that launch external processes are generally supported on
399 most platforms (though many of them do not support any type of
400 forking). The problem with using them arises from what you invoke
401 them on. External tools are often named differently on different
402 platforms, may not be available in the same location, might accept
403 different arguments, can behave differently, and often present their
404 results in a platform-dependent way. Thus, you should seldom depend
405 on them to produce consistent results. (Then again, if you're calling
406 I<netstat -a>, you probably don't expect it to run on both Unix and CP/M.)
408 One especially common bit of Perl code is opening a pipe to B<sendmail>:
410 open(MAIL, '|/usr/lib/sendmail -t')
411 or die "cannot fork sendmail: $!";
413 This is fine for systems programming when sendmail is known to be
414 available. But it is not fine for many non-Unix systems, and even
415 some Unix systems that may not have sendmail installed. If a portable
416 solution is needed, see the various distributions on CPAN that deal
417 with it. Mail::Mailer and Mail::Send in the MailTools distribution are
418 commonly used, and provide several mailing methods, including mail,
419 sendmail, and direct SMTP (via Net::SMTP) if a mail transfer agent is
420 not available. Mail::Sendmail is a standalone module that provides
421 simple, platform-independent mailing.
423 The Unix System V IPC (C<msg*(), sem*(), shm*()>) is not available
424 even on all Unix platforms.
426 Do not use either the bare result of C<pack("N", 10, 20, 30, 40)>
427 or bare v-strings (such as C<v10.20.30.40>) or the to represent
428 IPv4 addresses: both forms just pack the four bytes into network order.
429 That this would be equal to the C language C<in_addr> struct (which is
430 what the socket code internally uses) is not guaranteed. To be
431 portable use the routines of the Socket extension, such as
432 C<inet_aton()>, C<inet_ntoa()>, and C<sockaddr_in()>.
434 The rule of thumb for portable code is: Do it all in portable Perl, or
435 use a module (that may internally implement it with platform-specific
436 code, but expose a common interface).
438 =head2 External Subroutines (XS)
440 XS code can usually be made to work with any platform, but dependent
441 libraries, header files, etc., might not be readily available or
442 portable, or the XS code itself might be platform-specific, just as Perl
443 code might be. If the libraries and headers are portable, then it is
444 normally reasonable to make sure the XS code is portable, too.
446 A different type of portability issue arises when writing XS code:
447 availability of a C compiler on the end-user's system. C brings
448 with it its own portability issues, and writing XS code will expose
449 you to some of those. Writing purely in Perl is an easier way to
452 =head2 Standard Modules
454 In general, the standard modules work across platforms. Notable
455 exceptions are the CPAN module (which currently makes connections to external
456 programs that may not be available), platform-specific modules (like
457 ExtUtils::MM_VMS), and DBM modules.
459 There is no one DBM module available on all platforms.
460 SDBM_File and the others are generally available on all Unix and DOSish
461 ports, but not in MacPerl, where only NBDM_File and DB_File are
464 The good news is that at least some DBM module should be available, and
465 AnyDBM_File will use whichever module it can find. Of course, then
466 the code needs to be fairly strict, dropping to the greatest common
467 factor (e.g., not exceeding 1K for each record), so that it will
468 work with any DBM module. See L<AnyDBM_File> for more details.
472 The system's notion of time of day and calendar date is controlled in
473 widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>,
474 and even if it is, don't assume that you can control the timezone through
477 Don't assume that the epoch starts at 00:00:00, January 1, 1970,
478 because that is OS- and implementation-specific. It is better to store a date
479 in an unambiguous representation. The ISO-8601 standard defines
480 "YYYY-MM-DD" as the date format. A text representation (like "1987-12-18")
481 can be easily converted into an OS-specific value using a module like
482 Date::Parse. An array of values, such as those returned by
483 C<localtime>, can be converted to an OS-specific representation using
486 When calculating specific times, such as for tests in time or date modules,
487 it may be appropriate to calculate an offset for the epoch.
490 $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
492 The value for C<$offset> in Unix will be C<0>, but in Mac OS will be
493 some large number. C<$offset> can then be added to a Unix time value
494 to get what should be the proper value on any system.
496 =head2 Character sets and character encoding
498 Assume little about character sets. Assume nothing about
499 numerical values (C<ord>, C<chr>) of characters. Do not
500 assume that the alphabetic characters are encoded contiguously (in
501 the numeric sense). Do not assume anything about the ordering of the
502 characters. The lowercase letters may come before or after the
503 uppercase letters; the lowercase and uppercase may be interlaced so
504 that both `a' and `A' come before `b'; the accented and other
505 international characters may be interlaced so that E<auml> comes
508 =head2 Internationalisation
510 If you may assume POSIX (a rather large assumption), you may read
511 more about the POSIX locale system from L<perllocale>. The locale
512 system at least attempts to make things a little bit more portable,
513 or at least more convenient and native-friendly for non-English
514 users. The system affects character sets and encoding, and date
515 and time formatting--amongst other things.
517 =head2 System Resources
519 If your code is destined for systems with severely constrained (or
520 missing!) virtual memory systems then you want to be I<especially> mindful
521 of avoiding wasteful constructs such as:
523 # NOTE: this is no longer "bad" in perl5.005
524 for (0..10000000) {} # bad
525 for (my $x = 0; $x <= 10000000; ++$x) {} # good
527 @lines = <VERY_LARGE_FILE>; # bad
529 while (<FILE>) {$file .= $_} # sometimes bad
530 $file = join('', <FILE>); # better
532 The last two constructs may appear unintuitive to most people. The
533 first repeatedly grows a string, whereas the second allocates a
534 large chunk of memory in one go. On some systems, the second is
535 more efficient that the first.
539 Most multi-user platforms provide basic levels of security, usually
540 implemented at the filesystem level. Some, however, do
541 not--unfortunately. Thus the notion of user id, or "home" directory,
542 or even the state of being logged-in, may be unrecognizable on many
543 platforms. If you write programs that are security-conscious, it
544 is usually best to know what type of system you will be running
545 under so that you can write code explicitly for that platform (or
550 For those times when it is necessary to have platform-specific code,
551 consider keeping the platform-specific code in one place, making porting
552 to other platforms easier. Use the Config module and the special
553 variable C<$^O> to differentiate platforms, as described in
556 Be careful in the tests you supply with your module or programs.
557 Module code may be fully portable, but its tests might not be. This
558 often happens when tests spawn off other processes or call external
559 programs to aid in the testing, or when (as noted above) the tests
560 assume certain things about the filesystem and paths. Be careful
561 not to depend on a specific output style for errors, such as when
562 checking C<$!> after an system call. Some platforms expect a certain
563 output format, and perl on those platforms may have been adjusted
564 accordingly. Most specifically, don't anchor a regex when testing
569 Modules uploaded to CPAN are tested by a variety of volunteers on
570 different platforms. These CPAN testers are notified by mail of each
571 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
572 this platform), or UNKNOWN (unknown), along with any relevant notations.
574 The purpose of the testing is twofold: one, to help developers fix any
575 problems in their code that crop up because of lack of testing on other
576 platforms; two, to provide users with information about whether
577 a given module works on a given platform.
581 =item Mailing list: cpan-testers@perl.org
583 =item Testing results: http://testers.cpan.org/
589 As of version 5.002, Perl is built with a C<$^O> variable that
590 indicates the operating system it was built on. This was implemented
591 to help speed up code that would otherwise have to C<use Config>
592 and use the value of C<$Config{osname}>. Of course, to get more
593 detailed information about the system, looking into C<%Config> is
594 certainly recommended.
596 C<%Config> cannot always be trusted, however, because it was built
597 at compile time. If perl was built in one place, then transferred
598 elsewhere, some values may be wrong. The values may even have been
599 edited after the fact.
603 Perl works on a bewildering variety of Unix and Unix-like platforms (see
604 e.g. most of the files in the F<hints/> directory in the source code kit).
605 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
606 too) is determined either by lowercasing and stripping punctuation from the
607 first field of the string returned by typing C<uname -a> (or a similar command)
608 at the shell prompt or by testing the file system for the presence of
609 uniquely named files such as a kernel or header file. Here, for example,
610 are a few of the more popular Unix flavors:
612 uname $^O $Config{'archname'}
613 --------------------------------------------
615 BSD/OS bsdos i386-bsdos
616 dgux dgux AViiON-dgux
617 DYNIX/ptx dynixptx i386-dynixptx
618 FreeBSD freebsd freebsd-i386
619 Linux linux arm-linux
620 Linux linux i386-linux
621 Linux linux i586-linux
622 Linux linux ppc-linux
623 HP-UX hpux PA-RISC1.1
625 Mac OS X darwin darwin
626 MachTen PPC machten powerpc-machten
628 NeXT 4 next OPENSTEP-Mach
629 openbsd openbsd i386-openbsd
630 OSF1 dec_osf alpha-dec_osf
631 reliantunix-n svr4 RM400-svr4
632 SCO_SV sco_sv i386-sco_sv
633 SINIX-N svr4 RM400-svr4
634 sn4609 unicos CRAY_C90-unicos
635 sn6521 unicosmk t3e-unicosmk
636 sn9617 unicos CRAY_J90-unicos
637 SunOS solaris sun4-solaris
638 SunOS solaris i86pc-solaris
639 SunOS4 sunos sun4-sunos
641 Because the value of C<$Config{archname}> may depend on the
642 hardware architecture, it can vary more than the value of C<$^O>.
644 =head2 DOS and Derivatives
646 Perl has long been ported to Intel-style microcomputers running under
647 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
648 bring yourself to mention (except for Windows CE, if you count that).
649 Users familiar with I<COMMAND.COM> or I<CMD.EXE> style shells should
650 be aware that each of these file specifications may have subtle
653 $filespec0 = "c:/foo/bar/file.txt";
654 $filespec1 = "c:\\foo\\bar\\file.txt";
655 $filespec2 = 'c:\foo\bar\file.txt';
656 $filespec3 = 'c:\\foo\\bar\\file.txt';
658 System calls accept either C</> or C<\> as the path separator.
659 However, many command-line utilities of DOS vintage treat C</> as
660 the option prefix, so may get confused by filenames containing C</>.
661 Aside from calling any external programs, C</> will work just fine,
662 and probably better, as it is more consistent with popular usage,
663 and avoids the problem of remembering what to backwhack and what
666 The DOS FAT filesystem can accommodate only "8.3" style filenames. Under
667 the "case-insensitive, but case-preserving" HPFS (OS/2) and NTFS (NT)
668 filesystems you may have to be careful about case returned with functions
669 like C<readdir> or used with functions like C<open> or C<opendir>.
671 DOS also treats several filenames as special, such as AUX, PRN,
672 NUL, CON, COM1, LPT1, LPT2, etc. Unfortunately, sometimes these
673 filenames won't even work if you include an explicit directory
674 prefix. It is best to avoid such filenames, if you want your code
675 to be portable to DOS and its derivatives. It's hard to know what
676 these all are, unfortunately.
678 Users of these operating systems may also wish to make use of
679 scripts such as I<pl2bat.bat> or I<pl2cmd> to
680 put wrappers around your scripts.
682 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
683 and writing to files (see L<"Newlines">). C<binmode(FILEHANDLE)>
684 will keep C<\n> translated as C<\012> for that filehandle. Since it is a
685 no-op on other systems, C<binmode> should be used for cross-platform code
686 that deals with binary data. That's assuming you realize in advance
687 that your data is in binary. General-purpose programs should
688 often assume nothing about their data.
690 The C<$^O> variable and the C<$Config{archname}> values for various
691 DOSish perls are as follows:
693 OS $^O $Config{'archname'}
694 --------------------------------------------
698 Windows 95 MSWin32 MSWin32-x86
699 Windows 98 MSWin32 MSWin32-x86
700 Windows NT MSWin32 MSWin32-x86
701 Windows NT MSWin32 MSWin32-ALPHA
702 Windows NT MSWin32 MSWin32-ppc
705 The various MSWin32 Perl's can distinguish the OS they are running on
706 via the value of the fifth element of the list returned from
707 Win32::GetOSVersion(). For example:
709 if ($^O eq 'MSWin32') {
710 my @os_version_info = Win32::GetOSVersion();
711 print +('3.1','95','NT')[$os_version_info[4]],"\n";
720 The djgpp environment for DOS, http://www.delorie.com/djgpp/
725 The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
726 http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or
727 ftp://hobbes.nmsu.edu/pub/os2/dev/emx. Also L<perlos2>.
731 Build instructions for Win32 in L<perlwin32>, or under the Cygnus environment
736 The C<Win32::*> modules in L<Win32>.
740 The ActiveState Pages, http://www.activestate.com/
744 The Cygwin environment for Win32; F<README.cygwin> (installed
745 as L<perlcygwin>), http://www.cygwin.com/
749 The U/WIN environment for Win32,
750 http://www.research.att.com/sw/tools/uwin/
754 Build instructions for OS/2, L<perlos2>
760 Any module requiring XS compilation is right out for most people, because
761 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
762 modules that can work with MacPerl are built and distributed in binary
765 Directories are specified as:
767 volume:folder:file for absolute pathnames
768 volume:folder: for absolute pathnames
769 :folder:file for relative pathnames
770 :folder: for relative pathnames
771 :file for relative pathnames
772 file for relative pathnames
774 Files are stored in the directory in alphabetical order. Filenames are
775 limited to 31 characters, and may include any character except for
776 null and C<:>, which is reserved as the path separator.
778 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
779 Mac::Files module, or C<chmod(0444, ...)> and C<chmod(0666, ...)>.
781 In the MacPerl application, you can't run a program from the command line;
782 programs that expect C<@ARGV> to be populated can be edited with something
783 like the following, which brings up a dialog box asking for the command
787 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
790 A MacPerl script saved as a "droplet" will populate C<@ARGV> with the full
791 pathnames of the files dropped onto the script.
793 Mac users can run programs under a type of command line interface
794 under MPW (Macintosh Programmer's Workshop, a free development
795 environment from Apple). MacPerl was first introduced as an MPW
796 tool, and MPW can be used like a shell:
798 perl myscript.plx some arguments
800 ToolServer is another app from Apple that provides access to MPW tools
801 from MPW and the MacPerl app, which allows MacPerl programs to use
802 C<system>, backticks, and piped C<open>.
804 "S<Mac OS>" is the proper name for the operating system, but the value
805 in C<$^O> is "MacOS". To determine architecture, version, or whether
806 the application or MPW tool version is running, check:
808 $is_app = $MacPerl::Version =~ /App/;
809 $is_tool = $MacPerl::Version =~ /MPW/;
810 ($version) = $MacPerl::Version =~ /^(\S+)/;
811 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
812 $is_68k = $MacPerl::Architecture eq 'Mac68K';
814 S<Mac OS X>, based on NeXT's OpenStep OS, runs MacPerl natively, under the
815 "Classic" environment. There is no "Carbon" version of MacPerl to run
816 under the primary Mac OS X environment. S<Mac OS X> and its Open Source
817 version, Darwin, both run Unix perl natively.
825 MacPerl Development, http://dev.macperl.org/ .
829 The MacPerl Pages, http://www.macperl.com/ .
833 The MacPerl mailing lists, http://lists.perl.org/ .
839 Perl on VMS is discussed in L<perlvms> in the perl distribution.
840 Perl on VMS can accept either VMS- or Unix-style file
841 specifications as in either of the following:
843 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
844 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
846 but not a mixture of both as in:
848 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
849 Can't open sys$login:/login.com: file specification syntax error
851 Interacting with Perl from the Digital Command Language (DCL) shell
852 often requires a different set of quotation marks than Unix shells do.
855 $ perl -e "print ""Hello, world.\n"""
858 There are several ways to wrap your perl scripts in DCL F<.COM> files, if
859 you are so inclined. For example:
861 $ write sys$output "Hello from DCL!"
863 $ then perl -x 'f$environment("PROCEDURE")
864 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
865 $ deck/dollars="__END__"
868 print "Hello from Perl!\n";
873 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
874 perl-in-DCL script expects to do things like C<< $read = <STDIN>; >>.
876 Filenames are in the format "name.extension;version". The maximum
877 length for filenames is 39 characters, and the maximum length for
878 extensions is also 39 characters. Version is a number from 1 to
879 32767. Valid characters are C</[A-Z0-9$_-]/>.
881 VMS's RMS filesystem is case-insensitive and does not preserve case.
882 C<readdir> returns lowercased filenames, but specifying a file for
883 opening remains case-insensitive. Files without extensions have a
884 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
885 will return F<a.> (though that file could be opened with
888 RMS had an eight level limit on directory depths from any rooted logical
889 (allowing 16 levels overall) prior to VMS 7.2. Hence
890 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
891 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
892 have to take this into account, but at least they can refer to the former
893 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
895 The VMS::Filespec module, which gets installed as part of the build
896 process on VMS, is a pure Perl module that can easily be installed on
897 non-VMS platforms and can be helpful for conversions to and from RMS
900 What C<\n> represents depends on the type of file opened. It usually
901 represents C<\012> but it could also be C<\015>, C<\012>, C<\015\012>,
902 C<\000>, C<\040>, or nothing depending on the file organiztion and
903 record format. The VMS::Stdio module provides access to the
904 special fopen() requirements of files with unusual attributes on VMS.
906 TCP/IP stacks are optional on VMS, so socket routines might not be
907 implemented. UDP sockets may not be supported.
909 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
910 that you are running on without resorting to loading all of C<%Config>
911 you can examine the content of the C<@INC> array like so:
913 if (grep(/VMS_AXP/, @INC)) {
914 print "I'm on Alpha!\n";
916 } elsif (grep(/VMS_VAX/, @INC)) {
917 print "I'm on VAX!\n";
920 print "I'm not so sure about where $^O is...\n";
923 On VMS, perl determines the UTC offset from the C<SYS$TIMEZONE_DIFFERENTIAL>
924 logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00,
925 calls to C<localtime> are adjusted to count offsets from
926 01-JAN-1970 00:00:00.00, just like Unix.
934 F<README.vms> (installed as L<README_vms>), L<perlvms>
938 vmsperl list, majordomo@perl.org
940 (Put the words C<subscribe vmsperl> in message body.)
944 vmsperl on the web, http://www.sidhe.org/vmsperl/index.html
950 Perl on VOS is discussed in F<README.vos> in the perl distribution
951 (installed as L<perlvos>). Perl on VOS can accept either VOS- or
952 Unix-style file specifications as in either of the following:
954 $ perl -ne "print if /perl_setup/i" >system>notices
955 $ perl -ne "print if /perl_setup/i" /system/notices
957 or even a mixture of both as in:
959 $ perl -ne "print if /perl_setup/i" >system/notices
961 Even though VOS allows the slash character to appear in object
962 names, because the VOS port of Perl interprets it as a pathname
963 delimiting character, VOS files, directories, or links whose names
964 contain a slash character cannot be processed. Such files must be
965 renamed before they can be processed by Perl. Note that VOS limits
966 file names to 32 or fewer characters.
968 See F<README.vos> for restrictions that apply when Perl is built
969 with the alpha version of VOS POSIX.1 support.
971 Perl on VOS is built without any extensions and does not support
974 The value of C<$^O> on VOS is "VOS". To determine the architecture that
975 you are running on without resorting to loading all of C<%Config> you
976 can examine the content of the @INC array like so:
979 print "I'm on a Stratus box!\n";
981 print "I'm not on a Stratus box!\n";
985 if (grep(/860/, @INC)) {
986 print "This box is a Stratus XA/R!\n";
988 } elsif (grep(/7100/, @INC)) {
989 print "This box is a Stratus HP 7100 or 8xxx!\n";
991 } elsif (grep(/8000/, @INC)) {
992 print "This box is a Stratus HP 8xxx!\n";
995 print "This box is a Stratus 68K!\n";
1008 The VOS mailing list.
1010 There is no specific mailing list for Perl on VOS. You can post
1011 comments to the comp.sys.stratus newsgroup, or subscribe to the general
1012 Stratus mailing list. Send a letter with "Subscribe Info-Stratus" in
1013 the message body to majordomo@list.stratagy.com.
1017 VOS Perl on the web at http://ftp.stratus.com/pub/vos/vos.html
1021 =head2 EBCDIC Platforms
1023 Recent versions of Perl have been ported to platforms such as OS/400 on
1024 AS/400 minicomputers as well as OS/390, VM/ESA, and BS2000 for S/390
1025 Mainframes. Such computers use EBCDIC character sets internally (usually
1026 Character Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC for S/390
1027 systems). On the mainframe perl currently works under the "Unix system
1028 services for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or
1029 the BS200 POSIX-BC system (BS2000 is supported in perl 5.6 and greater).
1030 See L<perlos390> for details.
1032 As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
1033 sub-systems do not support the C<#!> shebang trick for script invocation.
1034 Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
1035 similar to the following simple script:
1038 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
1040 #!/usr/local/bin/perl # just a comment really
1042 print "Hello from perl!\n";
1044 OS/390 will support the C<#!> shebang trick in release 2.8 and beyond.
1045 Calls to C<system> and backticks can use POSIX shell syntax on all
1048 On the AS/400, if PERL5 is in your library list, you may need
1049 to wrap your perl scripts in a CL procedure to invoke them like so:
1052 CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
1055 This will invoke the perl script F<hello.pl> in the root of the
1056 QOpenSys file system. On the AS/400 calls to C<system> or backticks
1059 On these platforms, bear in mind that the EBCDIC character set may have
1060 an effect on what happens with some perl functions (such as C<chr>,
1061 C<pack>, C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>), as
1062 well as bit-fiddling with ASCII constants using operators like C<^>, C<&>
1063 and C<|>, not to mention dealing with socket interfaces to ASCII computers
1064 (see L<"Newlines">).
1066 Fortunately, most web servers for the mainframe will correctly
1067 translate the C<\n> in the following statement to its ASCII equivalent
1068 (C<\r> is the same under both Unix and OS/390 & VM/ESA):
1070 print "Content-type: text/html\r\n\r\n";
1072 The values of C<$^O> on some of these platforms includes:
1074 uname $^O $Config{'archname'}
1075 --------------------------------------------
1078 POSIX-BC posix-bc BS2000-posix-bc
1081 Some simple tricks for determining if you are running on an EBCDIC
1082 platform could include any of the following (perhaps all):
1084 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
1086 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
1088 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
1090 One thing you may not want to rely on is the EBCDIC encoding
1091 of punctuation characters since these may differ from code page to code
1092 page (and once your module or script is rumoured to work with EBCDIC,
1093 folks will want it to work with all EBCDIC character sets).
1103 L<perlos390>, F<README.os390>, F<perlbs2000>, F<README.vmesa>,
1108 The perl-mvs@perl.org list is for discussion of porting issues as well as
1109 general usage issues for all EBCDIC Perls. Send a message body of
1110 "subscribe perl-mvs" to majordomo@perl.org.
1114 AS/400 Perl information at
1115 http://as400.rochester.ibm.com/
1116 as well as on CPAN in the F<ports/> directory.
1120 =head2 Acorn RISC OS
1122 Because Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
1123 Unix, and because Unix filename emulation is turned on by default,
1124 most simple scripts will probably work "out of the box". The native
1125 filesystem is modular, and individual filesystems are free to be
1126 case-sensitive or insensitive, and are usually case-preserving. Some
1127 native filesystems have name length limits, which file and directory
1128 names are silently truncated to fit. Scripts should be aware that the
1129 standard filesystem currently has a name length limit of B<10>
1130 characters, with up to 77 items in a directory, but other filesystems
1131 may not impose such limitations.
1133 Native filenames are of the form
1135 Filesystem#Special_Field::DiskName.$.Directory.Directory.File
1139 Special_Field is not usually present, but may contain . and $ .
1140 Filesystem =~ m|[A-Za-z0-9_]|
1141 DsicName =~ m|[A-Za-z0-9_/]|
1142 $ represents the root directory
1143 . is the path separator
1144 @ is the current directory (per filesystem but machine global)
1145 ^ is the parent directory
1146 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
1148 The default filename translation is roughly C<tr|/.|./|;>
1150 Note that C<"ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'> and that
1151 the second stage of C<$> interpolation in regular expressions will fall
1152 foul of the C<$.> if scripts are not careful.
1154 Logical paths specified by system variables containing comma-separated
1155 search lists are also allowed; hence C<System:Modules> is a valid
1156 filename, and the filesystem will prefix C<Modules> with each section of
1157 C<System$Path> until a name is made that points to an object on disk.
1158 Writing to a new file C<System:Modules> would be allowed only if
1159 C<System$Path> contains a single item list. The filesystem will also
1160 expand system variables in filenames if enclosed in angle brackets, so
1161 C<< <System$Dir>.Modules >> would look for the file
1162 S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious implication of this is
1163 that B<fully qualified filenames can start with C<< <> >>> and should
1164 be protected when C<open> is used for input.
1166 Because C<.> was in use as a directory separator and filenames could not
1167 be assumed to be unique after 10 characters, Acorn implemented the C
1168 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
1169 filenames specified in source code and store the respective files in
1170 subdirectories named after the suffix. Hence files are translated:
1173 C:foo.h C:h.foo (logical path variable)
1174 sys/os.h sys.h.os (C compiler groks Unix-speak)
1175 10charname.c c.10charname
1176 10charname.o o.10charname
1177 11charname_.c c.11charname (assuming filesystem truncates at 10)
1179 The Unix emulation library's translation of filenames to native assumes
1180 that this sort of translation is required, and it allows a user-defined list
1181 of known suffixes that it will transpose in this fashion. This may
1182 seem transparent, but consider that with these rules C<foo/bar/baz.h>
1183 and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
1184 C<glob> cannot and do not attempt to emulate the reverse mapping. Other
1185 C<.>'s in filenames are translated to C</>.
1187 As implied above, the environment accessed through C<%ENV> is global, and
1188 the convention is that program specific environment variables are of the
1189 form C<Program$Name>. Each filesystem maintains a current directory,
1190 and the current filesystem's current directory is the B<global> current
1191 directory. Consequently, sociable programs don't change the current
1192 directory but rely on full pathnames, and programs (and Makefiles) cannot
1193 assume that they can spawn a child process which can change the current
1194 directory without affecting its parent (and everyone else for that
1197 Because native operating system filehandles are global and are currently
1198 allocated down from 255, with 0 being a reserved value, the Unix emulation
1199 library emulates Unix filehandles. Consequently, you can't rely on
1200 passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
1202 The desire of users to express filenames of the form
1203 C<< <Foo$Dir>.Bar >> on the command line unquoted causes problems,
1204 too: C<``> command output capture has to perform a guessing game. It
1205 assumes that a string C<< <[^<>]+\$[^<>]> >> is a
1206 reference to an environment variable, whereas anything else involving
1207 C<< < >> or C<< > >> is redirection, and generally manages to be 99%
1208 right. Of course, the problem remains that scripts cannot rely on any
1209 Unix tools being available, or that any tools found have Unix-like command
1212 Extensions and XS are, in theory, buildable by anyone using free
1213 tools. In practice, many don't, as users of the Acorn platform are
1214 used to binary distributions. MakeMaker does run, but no available
1215 make currently copes with MakeMaker's makefiles; even if and when
1216 this should be fixed, the lack of a Unix-like shell will cause
1217 problems with makefile rules, especially lines of the form C<cd
1218 sdbm && make all>, and anything using quoting.
1220 "S<RISC OS>" is the proper name for the operating system, but the value
1221 in C<$^O> is "riscos" (because we don't like shouting).
1225 Perl has been ported to many platforms that do not fit into any of
1226 the categories listed above. Some, such as AmigaOS, Atari MiNT,
1227 BeOS, HP MPE/iX, QNX, Plan 9, and VOS, have been well-integrated
1228 into the standard Perl source code kit. You may need to see the
1229 F<ports/> directory on CPAN for information, and possibly binaries,
1230 for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware,
1231 Tandem Guardian, I<etc.> (Yes, we know that some of these OSes may
1232 fall under the Unix category, but we are not a standards body.)
1234 Some approximate operating system names and their C<$^O> values
1235 in the "OTHER" category include:
1237 OS $^O $Config{'archname'}
1238 ------------------------------------------
1239 Amiga DOS amigaos m68k-amigos
1240 MPE/iX mpeix PA-RISC1.1
1248 Amiga, F<README.amiga> (installed as L<perlamiga>).
1252 Atari, F<README.mint> and Guido Flohr's web page
1253 http://stud.uni-sb.de/~gufl0000/
1257 Be OS, F<README.beos>
1261 HP 300 MPE/iX, F<README.mpeix> and Mark Bixby's web page
1262 http://www.bixby.org/mark/perlix.html
1266 A free perl5-based PERL.NLM for Novell Netware is available in
1267 precompiled binary and source code form from http://www.novell.com/
1268 as well as from CPAN.
1272 Plan 9, F<README.plan9>
1276 =head1 FUNCTION IMPLEMENTATIONS
1278 Listed below are functions that are either completely unimplemented
1279 or else have been implemented differently on various platforms.
1280 Following each description will be, in parentheses, a list of
1281 platforms that the description applies to.
1283 The list may well be incomplete, or even wrong in some places. When
1284 in doubt, consult the platform-specific README files in the Perl
1285 source distribution, and any other documentation resources accompanying
1288 Be aware, moreover, that even among Unix-ish systems there are variations.
1290 For many functions, you can also query C<%Config>, exported by
1291 default from the Config module. For example, to check whether the
1292 platform has the C<lstat> call, check C<$Config{d_lstat}>. See
1293 L<Config> for a full description of available variables.
1295 =head2 Alphabetical Listing of Perl Functions
1305 C<-r>, C<-w>, and C<-x> have a limited meaning only; directories
1306 and applications are executable, and there are no uid/gid
1307 considerations. C<-o> is not supported. (S<Mac OS>)
1309 C<-r>, C<-w>, C<-x>, and C<-o> tell whether the file is accessible,
1310 which may not reflect UIC-based file protections. (VMS)
1312 C<-s> returns the size of the data fork, not the total size of data fork
1313 plus resource fork. (S<Mac OS>).
1315 C<-s> by name on an open file will return the space reserved on disk,
1316 rather than the current extent. C<-s> on an open filehandle returns the
1317 current size. (S<RISC OS>)
1319 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
1320 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1322 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
1325 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
1326 (Win32, VMS, S<RISC OS>)
1328 C<-d> is true if passed a device spec without an explicit directory.
1331 C<-T> and C<-B> are implemented, but might misclassify Mac text files
1332 with foreign characters; this is the case will all platforms, but may
1333 affect S<Mac OS> often. (S<Mac OS>)
1335 C<-x> (or C<-X>) determine if a file ends in one of the executable
1336 suffixes. C<-S> is meaningless. (Win32)
1338 C<-x> (or C<-X>) determine if a file has an executable file type.
1345 Not implemented. (Win32)
1347 =item binmode FILEHANDLE
1349 Meaningless. (S<Mac OS>, S<RISC OS>)
1351 Reopens file and restores pointer; if function fails, underlying
1352 filehandle may be closed, or pointer may be in a different position.
1355 The value returned by C<tell> may be affected after the call, and
1356 the filehandle may be flushed. (Win32)
1360 Only limited meaning. Disabling/enabling write permission is mapped to
1361 locking/unlocking the file. (S<Mac OS>)
1363 Only good for changing "owner" read-write access, "group", and "other"
1364 bits are meaningless. (Win32)
1366 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
1368 Access permissions are mapped onto VOS access-control list changes. (VOS)
1372 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
1374 Does nothing, but won't fail. (Win32)
1376 =item chroot FILENAME
1380 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS, VM/ESA)
1382 =item crypt PLAINTEXT,SALT
1384 May not be available if library or source was not provided when building
1387 Not implemented. (VOS)
1391 Not implemented. (VMS, Plan9, VOS)
1393 =item dbmopen HASH,DBNAME,MODE
1395 Not implemented. (VMS, Plan9, VOS)
1399 Not useful. (S<Mac OS>, S<RISC OS>)
1401 Not implemented. (Win32)
1403 Invokes VMS debugger. (VMS)
1407 Not implemented. (S<Mac OS>)
1409 Implemented via Spawn. (VM/ESA)
1411 Does not automatically flush output handles on some platforms.
1412 (SunOS, Solaris, HP-UX)
1414 =item fcntl FILEHANDLE,FUNCTION,SCALAR
1416 Not implemented. (Win32, VMS)
1418 =item flock FILEHANDLE,OPERATION
1420 Not implemented (S<Mac OS>, VMS, S<RISC OS>, VOS).
1422 Available only on Windows NT (not on Windows 95). (Win32)
1426 Not implemented. (S<Mac OS>, AmigaOS, S<RISC OS>, VOS, VM/ESA)
1428 Emulated using multiple interpreters. See L<perlfork>. (Win32)
1430 Does not automatically flush output handles on some platforms.
1431 (SunOS, Solaris, HP-UX)
1435 Not implemented. (S<Mac OS>, S<RISC OS>)
1439 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1443 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1445 =item getpriority WHICH,WHO
1447 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1451 Not implemented. (S<Mac OS>, Win32)
1453 Not useful. (S<RISC OS>)
1457 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1459 =item getnetbyname NAME
1461 Not implemented. (S<Mac OS>, Win32, Plan9)
1465 Not implemented. (S<Mac OS>, Win32)
1467 Not useful. (S<RISC OS>)
1471 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1473 =item getnetbyaddr ADDR,ADDRTYPE
1475 Not implemented. (S<Mac OS>, Win32, Plan9)
1477 =item getprotobynumber NUMBER
1479 Not implemented. (S<Mac OS>)
1481 =item getservbyport PORT,PROTO
1483 Not implemented. (S<Mac OS>)
1487 Not implemented. (S<Mac OS>, Win32, VM/ESA)
1491 Not implemented. (S<Mac OS>, Win32, VMS, VM/ESA)
1495 Not implemented. (S<Mac OS>, Win32)
1499 Not implemented. (S<Mac OS>, Win32, Plan9)
1503 Not implemented. (S<Mac OS>, Win32, Plan9)
1507 Not implemented. (Win32, Plan9)
1511 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1515 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1517 =item sethostent STAYOPEN
1519 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1521 =item setnetent STAYOPEN
1523 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1525 =item setprotoent STAYOPEN
1527 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1529 =item setservent STAYOPEN
1531 Not implemented. (Plan9, Win32, S<RISC OS>)
1535 Not implemented. (S<Mac OS>, MPE/iX, VM/ESA, Win32)
1539 Not implemented. (S<Mac OS>, MPE/iX, S<RISC OS>, VM/ESA, VMS, Win32)
1543 Not implemented. (S<Mac OS>, Win32)
1547 Not implemented. (S<Mac OS>, Win32, Plan9)
1551 Not implemented. (S<Mac OS>, Win32, Plan9)
1555 Not implemented. (Plan9, Win32)
1561 Emulates UNIX exit() (which considers C<exit 1> to indicate an error) by
1562 mapping the C<1> to SS$_ABORT (C<44>). This behavior may be overridden
1563 with the pragma C<use vmsish 'exit'>. As with the CRTL's exit()
1564 function, C<exit 0> is also mapped to an exit status of SS$_NORMAL
1565 (C<1>); this mapping cannot be overridden. Any other argument to exit()
1566 is used directly as Perl's exit status. (VMS)
1568 =item getsockopt SOCKET,LEVEL,OPTNAME
1570 Not implemented. (S<Mac OS>, Plan9)
1576 This operator is implemented via the File::Glob extension on most
1577 platforms. See L<File::Glob> for portability information.
1579 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1581 Not implemented. (VMS)
1583 Available only for socket handles, and it does what the ioctlsocket() call
1584 in the Winsock API does. (Win32)
1586 Available only for socket handles. (S<RISC OS>)
1588 =item kill SIGNAL, LIST
1590 C<kill(0, LIST)> is implemented for the sake of taint checking;
1591 use with other signals is unimplemented. (S<Mac OS>)
1593 Not implemented, hence not useful for taint checking. (S<RISC OS>)
1595 C<kill()> doesn't have the semantics of C<raise()>, i.e. it doesn't send
1596 a signal to the identified process like it does on Unix platforms.
1597 Instead C<kill($sig, $pid)> terminates the process identified by $pid,
1598 and makes it exit immediately with exit status $sig. As in Unix, if
1599 $sig is 0 and the specified process exists, it returns true without
1600 actually terminating it. (Win32)
1602 =item link OLDFILE,NEWFILE
1604 Not implemented. (S<Mac OS>, MPE/iX, VMS, S<RISC OS>)
1606 Link count not updated because hard links are not quite that hard
1607 (They are sort of half-way between hard and soft links). (AmigaOS)
1609 Hard links are implemented on Win32 (Windows NT and Windows 2000)
1612 =item lstat FILEHANDLE
1618 Not implemented. (VMS, S<RISC OS>)
1620 Return values (especially for device and inode) may be bogus. (Win32)
1622 =item msgctl ID,CMD,ARG
1624 =item msgget KEY,FLAGS
1626 =item msgsnd ID,MSG,FLAGS
1628 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1630 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>, VOS)
1632 =item open FILEHANDLE,EXPR
1634 =item open FILEHANDLE
1636 The C<|> variants are supported only if ToolServer is installed.
1639 open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1641 Opening a process does not automatically flush output handles on some
1642 platforms. (SunOS, Solaris, HP-UX)
1644 =item pipe READHANDLE,WRITEHANDLE
1646 Very limited functionality. (MiNT)
1652 Not implemented. (Win32, VMS, S<RISC OS>)
1654 =item select RBITS,WBITS,EBITS,TIMEOUT
1656 Only implemented on sockets. (Win32)
1658 Only reliable on sockets. (S<RISC OS>)
1660 Note that the C<socket FILEHANDLE> form is generally portable.
1662 =item semctl ID,SEMNUM,CMD,ARG
1664 =item semget KEY,NSEMS,FLAGS
1666 =item semop KEY,OPSTRING
1668 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1672 Not implemented. (MPE/iX, Win32)
1674 =item setpgrp PID,PGRP
1676 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1678 =item setpriority WHICH,WHO,PRIORITY
1680 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1684 Not implemented. (MPE/iX, Win32)
1686 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1688 Not implemented. (S<Mac OS>, Plan9)
1690 =item shmctl ID,CMD,ARG
1692 =item shmget KEY,SIZE,FLAGS
1694 =item shmread ID,VAR,POS,SIZE
1696 =item shmwrite ID,STRING,POS,SIZE
1698 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS)
1700 =item sockatmark SOCKET
1702 A relatively recent addition to socket functions, may not
1703 be implemented even in UNIX platforms.
1705 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1707 Not implemented. (Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1709 =item stat FILEHANDLE
1715 Platforms that do not have rdev, blksize, or blocks will return these
1716 as '', so numeric comparison or manipulation of these fields may cause
1717 'not numeric' warnings.
1719 mtime and atime are the same thing, and ctime is creation time instead of
1720 inode change time. (S<Mac OS>)
1722 device and inode are not meaningful. (Win32)
1724 device and inode are not necessarily reliable. (VMS)
1726 mtime, atime and ctime all return the last modification time. Device and
1727 inode are not necessarily reliable. (S<RISC OS>)
1729 dev, rdev, blksize, and blocks are not available. inode is not
1730 meaningful and will differ between stat calls on the same file. (os2)
1732 some versions of cygwin when doing a stat("foo") and if not finding it
1733 may then attempt to stat("foo.exe") (Cygwin)
1735 =item symlink OLDFILE,NEWFILE
1737 Not implemented. (Win32, VMS, S<RISC OS>)
1741 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>, VOS, VM/ESA)
1743 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1745 The traditional "0", "1", and "2" MODEs are implemented with different
1746 numeric values on some systems. The flags exported by C<Fcntl>
1747 (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (S<Mac
1748 OS>, OS/390, VM/ESA)
1752 Only implemented if ToolServer is installed. (S<Mac OS>)
1754 As an optimization, may not call the command shell specified in
1755 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1756 process and immediately returns its process designator, without
1757 waiting for it to terminate. Return value may be used subsequently
1758 in C<wait> or C<waitpid>. Failure to spawn() a subprocess is indicated
1759 by setting $? to "255 << 8". C<$?> is set in a way compatible with
1760 Unix (i.e. the exitstatus of the subprocess is obtained by "$? >> 8",
1761 as described in the documentation). (Win32)
1763 There is no shell to process metacharacters, and the native standard is
1764 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1765 program. Redirection such as C<< > foo >> is performed (if at all) by
1766 the run time library of the spawned program. C<system> I<list> will call
1767 the Unix emulation library's C<exec> emulation, which attempts to provide
1768 emulation of the stdin, stdout, stderr in force in the parent, providing
1769 the child program uses a compatible version of the emulation library.
1770 I<scalar> will call the native command line direct and no such emulation
1771 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1773 Far from being POSIX compliant. Because there may be no underlying
1774 /bin/sh tries to work around the problem by forking and execing the
1775 first token in its argument string. Handles basic redirection
1776 ("<" or ">") on its own behalf. (MiNT)
1778 Does not automatically flush output handles on some platforms.
1779 (SunOS, Solaris, HP-UX)
1781 The return value is POSIX-like (shifted up by 8 bits), which only allows
1782 room for a made-up value derived from the severity bits of the native
1783 32-bit condition code (unless overridden by C<use vmsish 'status'>).
1784 For more details see L<perlvms/$?>. (VMS)
1788 Only the first entry returned is nonzero. (S<Mac OS>)
1790 "cumulative" times will be bogus. On anything other than Windows NT
1791 or Windows 2000, "system" time will be bogus, and "user" time is
1792 actually the time returned by the clock() function in the C runtime
1795 Not useful. (S<RISC OS>)
1797 =item truncate FILEHANDLE,LENGTH
1799 =item truncate EXPR,LENGTH
1801 Not implemented. (Older versions of VMS)
1803 Truncation to zero-length only. (VOS)
1805 If a FILEHANDLE is supplied, it must be writable and opened in append
1806 mode (i.e., use C<<< open(FH, '>>filename') >>>
1807 or C<sysopen(FH,...,O_APPEND|O_RDWR)>. If a filename is supplied, it
1808 should not be held open elsewhere. (Win32)
1814 Returns undef where unavailable, as of version 5.005.
1816 C<umask> works but the correct permissions are set only when the file
1817 is finally closed. (AmigaOS)
1821 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1823 May not behave as expected. Behavior depends on the C runtime
1824 library's implementation of utime(), and the filesystem being
1825 used. The FAT filesystem typically does not support an "access
1826 time" field, and it may limit timestamps to a granularity of
1827 two seconds. (Win32)
1831 =item waitpid PID,FLAGS
1833 Not implemented. (S<Mac OS>, VOS)
1835 Can only be applied to process handles returned for processes spawned
1836 using C<system(1, ...)> or pseudo processes created with C<fork()>. (Win32)
1838 Not useful. (S<RISC OS>)
1846 =item v1.48, 02 February 2001
1848 Various updates from perl5-porters over the past year, supported
1849 platforms update from Jarkko Hietaniemi.
1851 =item v1.47, 22 March 2000
1853 Various cleanups from Tom Christiansen, including migration of
1854 long platform listings from L<perl>.
1856 =item v1.46, 12 February 2000
1858 Updates for VOS and MPE/iX. (Peter Prymmer) Other small changes.
1860 =item v1.45, 20 December 1999
1862 Small changes from 5.005_63 distribution, more changes to EBCDIC info.
1864 =item v1.44, 19 July 1999
1866 A bunch of updates from Peter Prymmer for C<$^O> values,
1867 endianness, File::Spec, VMS, BS2000, OS/400.
1869 =item v1.43, 24 May 1999
1871 Added a lot of cleaning up from Tom Christiansen.
1873 =item v1.42, 22 May 1999
1875 Added notes about tests, sprintf/printf, and epoch offsets.
1877 =item v1.41, 19 May 1999
1879 Lots more little changes to formatting and content.
1881 Added a bunch of C<$^O> and related values
1882 for various platforms; fixed mail and web addresses, and added
1883 and changed miscellaneous notes. (Peter Prymmer)
1885 =item v1.40, 11 April 1999
1887 Miscellaneous changes.
1889 =item v1.39, 11 February 1999
1891 Changes from Jarkko and EMX URL fixes Michael Schwern. Additional
1892 note about newlines added.
1894 =item v1.38, 31 December 1998
1896 More changes from Jarkko.
1898 =item v1.37, 19 December 1998
1900 More minor changes. Merge two separate version 1.35 documents.
1902 =item v1.36, 9 September 1998
1904 Updated for Stratus VOS. Also known as version 1.35.
1906 =item v1.35, 13 August 1998
1908 Integrate more minor changes, plus addition of new sections under
1909 L<"ISSUES">: L<"Numbers endianness and Width">,
1910 L<"Character sets and character encoding">,
1911 L<"Internationalisation">.
1913 =item v1.33, 06 August 1998
1915 Integrate more minor changes.
1917 =item v1.32, 05 August 1998
1919 Integrate more minor changes.
1921 =item v1.30, 03 August 1998
1923 Major update for RISC OS, other minor changes.
1925 =item v1.23, 10 July 1998
1927 First public release with perl5.005.
1931 =head1 Supported Platforms
1933 As of early 2001 (the Perl releases 5.6.1 and 5.7.1), the following
1934 platforms are able to build Perl from the standard source code
1935 distribution available at http://www.perl.com/CPAN/src/index.html
1958 Tru64 UNIX (DEC OSF/1, Digital UNIX)
1964 1) in DOS mode either the DOS or OS/2 ports can be used
1965 2) Mac OS Classic (pre-X) is almost 5.6.1-ready; building from
1966 the source does work with 5.6.1, but additional MacOS specific
1967 source code is needed for a complete build. See the web
1968 site http://dev.macperl.org/ for more information.
1969 3) compilers: Borland, Cygwin, Mingw32 EGCS/GCC, VC++
1971 The following platforms worked for the previous releases (5.6.0 and 5.7.0),
1972 but we did not manage to test these in time for the 5.7.1 release.
1973 There is a very good chance that these will work fine with the 5.7.1.
1991 The following platform worked for the 5.005_03 major release but not
1992 for 5.6.0. Standardization on UTF-8 as the internal string
1993 representation in 5.6.0 and 5.6.1 introduced incompatibilities in this
1994 EBCDIC platform. While Perl 5.7.1 will build on this platform some
1995 regression tests may fail and the C<use utf8;> pragma typically
1996 introduces text handling errors.
2000 1) previously known as MVS, about to become z/OS.
2002 Strongly related to the OS/390 platform by also being EBCDIC-based
2003 mainframe platforms are the following platforms:
2008 These are also expected to work, albeit with no UTF-8 support, under 5.6.1
2009 for the same reasons as OS/390. Contact the mailing list perl-mvs@perl.org
2012 The following platforms have been known to build Perl from source in
2013 the past (5.005_03 and earlier), but we haven't been able to verify
2014 their status for the current release, either because the
2015 hardware/software platforms are rare or because we don't have an
2016 active champion on these platforms--or both. They used to work,
2017 though, so go ahead and try compiling them, and let perlbug@perl.org
2056 Support for the following platform is planned for a future Perl release:
2060 The following platforms have their own source code distributions and
2061 binaries available via http://www.perl.com/CPAN/ports/index.html:
2067 Tandem Guardian 5.004
2069 The following platforms have only binaries available via
2070 http://www.perl.com/CPAN/ports/index.html :
2074 Acorn RISCOS 5.005_02
2078 Although we do suggest that you always build your own Perl from
2079 the source code, both for maximal configurability and for security,
2080 in case you are in a hurry you can check
2081 http://www.perl.com/CPAN/ports/index.html for binary distributions.
2085 L<perlaix>, L<perlapollo>, L<perlamiga>, L<perlbeos>, L<perlbs200>,
2086 L<perlce>, L<perlcygwin>, L<perldgux>, L<perldos>, L<perlepoc>, L<perlebcdic>,
2087 L<perlhurd>, L<perlhpux>, L<perlmachten>, L<perlmacos>, L<perlmint>,
2088 L<perlmpeix>, L<perlnetware>, L<perlos2>, L<perlos390>, L<perlplan9>,
2089 L<perlqnx>, L<perlsolaris>, L<perltru64>, L<perlunicode>,
2090 L<perlvmesa>, L<perlvms>, L<perlvos>, L<perlwin32>, and L<Win32>.
2092 =head1 AUTHORS / CONTRIBUTORS
2094 Abigail <abigail@foad.org>,
2095 Charles Bailey <bailey@newman.upenn.edu>,
2096 Graham Barr <gbarr@pobox.com>,
2097 Tom Christiansen <tchrist@perl.com>,
2098 Nicholas Clark <nick@ccl4.org>,
2099 Thomas Dorner <Thomas.Dorner@start.de>,
2100 Andy Dougherty <doughera@lafayette.edu>,
2101 Dominic Dunlop <domo@computer.org>,
2102 Neale Ferguson <neale@vma.tabnsw.com.au>,
2103 David J. Fiander <davidf@mks.com>,
2104 Paul Green <Paul_Green@stratus.com>,
2105 M.J.T. Guy <mjtg@cam.ac.uk>,
2106 Jarkko Hietaniemi <jhi@iki.fi>,
2107 Luther Huffman <lutherh@stratcom.com>,
2108 Nick Ing-Simmons <nick@ing-simmons.net>,
2109 Andreas J. KE<ouml>nig <a.koenig@mind.de>,
2110 Markus Laker <mlaker@contax.co.uk>,
2111 Andrew M. Langmead <aml@world.std.com>,
2112 Larry Moore <ljmoore@freespace.net>,
2113 Paul Moore <Paul.Moore@uk.origin-it.com>,
2114 Chris Nandor <pudge@pobox.com>,
2115 Matthias Neeracher <neeri@iis.ee.ethz.ch>,
2116 Philip Newton <pne@cpan.org>,
2117 Gary Ng <71564.1743@CompuServe.COM>,
2118 Tom Phoenix <rootbeer@teleport.com>,
2119 AndrE<eacute> Pirard <A.Pirard@ulg.ac.be>,
2120 Peter Prymmer <pvhp@forte.com>,
2121 Hugo van der Sanden <hv@crypt0.demon.co.uk>,
2122 Gurusamy Sarathy <gsar@activestate.com>,
2123 Paul J. Schinder <schinder@pobox.com>,
2124 Michael G Schwern <schwern@pobox.com>,
2125 Dan Sugalski <dan@sidhe.org>,
2126 Nathan Torkington <gnat@frii.com>.
2130 Version 1.50, last modified 10 Jul 2001