3 perlport - Writing portable Perl
8 Perl runs on a variety of operating systems. While most of them share
9 a lot in common, they also have their own very particular and unique
12 This document is meant to help you to find out what constitutes portable
13 perl code, so that once you have made your decision to write portably,
14 you know where the lines are drawn, and you can stay within them.
16 There is a tradeoff between taking full advantage of B<a> particular type
17 of computer, and taking advantage of a full B<range> of them. Naturally,
18 as you make your range bigger (and thus more diverse), the common denominators
19 drop, and you are left with fewer areas of common ground in which
20 you can operate to accomplish a particular task. Thus, when you begin
21 attacking a problem, it is important to consider which part of the tradeoff
22 curve you want to operate under. Specifically, whether it is important to
23 you that the task that you are coding needs the full generality of being
24 portable, or if it is sufficient to just get the job done. This is the
25 hardest choice to be made. The rest is easy, because Perl provides lots
26 of choices, whichever way you want to approach your problem.
28 Looking at it another way, writing portable code is usually about willfully
29 limiting your available choices. Naturally, it takes discipline to do that.
31 Be aware of two important points:
35 =item Not all Perl programs have to be portable
37 There is no reason why you should not use Perl as a language to glue Unix
38 tools together, or to prototype a Macintosh application, or to manage the
39 Windows registry. If it makes no sense to aim for portability for one
40 reason or another in a given program, then don't bother.
42 =item The vast majority of Perl B<is> portable
44 Don't be fooled into thinking that it is hard to create portable Perl
45 code. It isn't. Perl tries its level-best to bridge the gaps between
46 what's available on different platforms, and all the means available to
47 use those features. Thus almost all Perl code runs on any machine
48 without modification. But there I<are> some significant issues in
49 writing portable code, and this document is entirely about those issues.
53 Here's the general rule: When you approach a task that is commonly done
54 using a whole range of platforms, think in terms of writing portable
55 code. That way, you don't sacrifice much by way of the implementation
56 choices you can avail yourself of, and at the same time you can give
57 your users lots of platform choices. On the other hand, when you have to
58 take advantage of some unique feature of a particular platform, as is
59 often the case with systems programming (whether for Unix, Windows,
60 S<Mac OS>, VMS, etc.), consider writing platform-specific code.
62 When the code will run on only two or three operating systems, then you may
63 only need to consider the differences of those particular systems. The
64 important thing is to decide where the code will run, and to be deliberate
67 This information should not be considered complete; it includes possibly
68 transient information about idiosyncrasies of some of the ports, almost
69 all of which are in a state of constant evolution. Thus this material
70 should be considered a perpetual work in progress
71 (E<lt>IMG SRC="yellow_sign.gif" ALT="Under Construction"E<gt>).
78 In most operating systems, lines in files are separated with newlines.
79 Just what is used as a newline may vary from OS to OS. Unix
80 traditionally uses C<\012>, one kind of Windows I/O uses C<\015\012>,
81 and S<Mac OS> uses C<\015>.
83 Perl uses C<\n> to represent the "logical" newline, where what
84 is logical may depend on the platform in use. In MacPerl, C<\n>
85 always means C<\015>. In DOSish perls, C<\n> usually means C<\012>, but
86 when accessing a file in "text" mode, STDIO translates it to (or from)
89 Due to the "text" mode translation, DOSish perls have limitations
90 of using C<seek> and C<tell> when a file is being accessed in "text"
91 mode. Specifically, if you stick to C<seek>-ing to locations you got
92 from C<tell> (and no others), you are usually free to use C<seek> and
93 C<tell> even in "text" mode. In general, using C<seek> or C<tell> or
94 other file operations that count bytes instead of characters, without
95 considering the length of C<\n>, may be non-portable. If you use
96 C<binmode> on a file, however, you can usually use C<seek> and C<tell>
97 with arbitrary values quite safely.
99 A common misconception in socket programming is that C<\n> eq C<\012>
100 everywhere. When using protocols, such as common Internet protocols,
101 C<\012> and C<\015> are called for specifically, and the values of
102 the logical C<\n> and C<\r> (carriage return) are not reliable.
104 print SOCKET "Hi there, client!\r\n"; # WRONG
105 print SOCKET "Hi there, client!\015\012"; # RIGHT
107 [NOTE: this does not necessarily apply to communications that are
108 filtered by another program or module before sending to the socket; the
109 the most popular EBCDIC webserver, for instance, accepts C<\r\n>,
110 which translates those characters, along with all other
111 characters in text streams, from EBCDIC to ASCII.]
113 However, C<\015\012> (or C<\cM\cJ>, or C<\x0D\x0A>) can be tedious and
114 unsightly, as well as confusing to those maintaining the code. As such,
115 the C<Socket> module supplies the Right Thing for those who want it.
117 use Socket qw(:DEFAULT :crlf);
118 print SOCKET "Hi there, client!$CRLF" # RIGHT
120 When reading I<from> a socket, remember that the default input record
121 separator (C<$/>) is C<\n>, but code like this should recognize C<$/> as
122 C<\012> or C<\015\012>:
130 use Socket qw(:DEFAULT :crlf);
131 local($/) = LF; # not needed if $/ is already \012
134 s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
135 # s/\015?\012/\n/; # same thing
138 And this example is actually better than the previous one even for Unix
139 platforms, because now any C<\015>'s (C<\cM>'s) are stripped out
140 (and there was much rejoicing).
145 Most platforms these days structure files in a hierarchical fashion.
146 So, it is reasonably safe to assume that any platform supports the
147 notion of a "path" to uniquely identify a file on the system. Just
148 how that path is actually written, differs.
150 While they are similar, file path specifications differ between Unix,
151 Windows, S<Mac OS>, OS/2, VMS, S<RISC OS> and probably others. Unix,
152 for example, is one of the few OSes that has the idea of a root directory.
153 S<Mac OS> uses C<:> as a path separator instead of C</>. VMS, Windows, and
154 OS/2 can work similarly to Unix with C</> as path separator, or in their own
155 idiosyncratic ways. C<RISC OS> perl can emulate Unix filenames with C</>
156 as path separator, or go native and use C<.> for path separator and C<:>
157 to signal filing systems and disc names.
159 As with the newline problem above, there are modules that can help. The
160 C<File::Spec> modules provide methods to do the Right Thing on whatever
161 platform happens to be running the program.
164 chdir(File::Spec->updir()); # go up one directory
165 $file = File::Spec->catfile(
166 File::Spec->curdir(), 'temp', 'file.txt'
168 # on Unix and Win32, './temp/file.txt'
169 # on Mac OS, ':temp:file.txt'
171 File::Spec is available in the standard distribution, as of version
174 In general, production code should not have file paths hardcoded; making
175 them user supplied or from a configuration file is better, keeping in mind
176 that file path syntax varies on different machines.
178 This is especially noticeable in scripts like Makefiles and test suites,
179 which often assume C</> as a path separator for subdirectories.
181 Also of use is C<File::Basename>, from the standard distribution, which
182 splits a pathname into pieces (base filename, full path to directory,
185 Remember not to count on the existence of system-specific files, like
186 F</etc/resolv.conf>. If code does need to rely on such a file, include a
187 description of the file and its format in the code's documentation, and
188 make it easy for the user to override the default location of the file.
190 Don't assume that a you can open a full pathname for input with
191 C<open (FILE, $name)>, as some platforms can use characters such as C<E<lt>>
192 which will perl C<open> will interpret and eat.
195 =head2 System Interaction
197 Not all platforms provide for the notion of a command line, necessarily.
198 These are usually platforms that rely on a Graphical User Interface (GUI)
199 for user interaction. So a program requiring command lines might not work
200 everywhere. But this is probably for the user of the program to deal
203 Some platforms can't delete or rename files that are being held open by
204 the system. Remember to C<close> files when you are done with them.
205 Don't C<unlink> or C<rename> an open file. Don't C<tie> to or C<open> a
206 file that is already tied to or opened; C<untie> or C<close> first.
208 Don't count on a specific environment variable existing in C<%ENV>.
209 Don't even count on C<%ENV> entries being case-sensitive, or even
212 Don't count on signals in portable programs.
214 Don't count on filename globbing. Use C<opendir>, C<readdir>, and
217 Don't count on per-program environment variables, or per-program current
221 =head2 Interprocess Communication (IPC)
223 In general, don't directly access the system in code that is meant to be
224 portable. That means, no: C<system>, C<exec>, C<fork>, C<pipe>, C<``>,
225 C<qx//>, C<open> with a C<|>, or any of the other things that makes being
226 a Unix perl hacker worth being.
228 Commands that launch external processes are generally supported on
229 most platforms (though many of them do not support any type of forking),
230 but the problem with using them arises from what you invoke with them.
231 External tools are often named differently on different platforms, often
232 not available in the same location, often accept different arguments,
233 often behave differently, and often represent their results in a
234 platform-dependent way. Thus you should seldom depend on them to produce
237 One especially common bit of Perl code is opening a pipe to sendmail:
239 open(MAIL, '|/usr/lib/sendmail -t') or die $!;
241 This is fine for systems programming when sendmail is known to be
242 available. But it is not fine for many non-Unix systems, and even
243 some Unix systems that may not have sendmail installed. If a portable
244 solution is needed, see the C<Mail::Send> and C<Mail::Mailer> modules
245 in the C<MailTools> distribution. C<Mail::Mailer> provides several
246 mailing methods, including mail, sendmail, and direct SMTP
247 (via C<Net::SMTP>) if a mail transfer agent is not available.
249 The rule of thumb for portable code is: Do it all in portable Perl, or
250 use a module that may internally implement it with platform-specific code,
251 but expose a common interface. By portable Perl, we mean code that
252 avoids the constructs described in this document as being non-portable.
255 =head2 External Subroutines (XS)
257 XS code, in general, can be made to work with any platform; but dependent
258 libraries, header files, etc., might not be readily available or
259 portable, or the XS code itself might be platform-specific, just as Perl
260 code might be. If the libraries and headers are portable, then it is
261 normally reasonable to make sure the XS code is portable, too.
263 There is a different kind of portability issue with writing XS
264 code: availability of a C compiler on the end-user's system. C brings with
265 it its own portability issues, and writing XS code will expose you to
266 some of those. Writing purely in perl is a comparatively easier way to
270 =head2 Standard Modules
272 In general, the standard modules work across platforms. Notable
273 exceptions are C<CPAN.pm> (which currently makes connections to external
274 programs that may not be available), platform-specific modules (like
275 C<ExtUtils::MM_VMS>), and DBM modules.
277 There is no one DBM module that is available on all platforms.
278 C<SDBM_File> and the others are generally available on all Unix and DOSish
279 ports, but not in MacPerl, where C<NBDM_File> and C<DB_File> are available.
281 The good news is that at least some DBM module should be available, and
282 C<AnyDBM_File> will use whichever module it can find. Of course, then
283 the code needs to be fairly strict, dropping to the lowest common
284 denominator (e.g., not exceeding 1K for each record).
289 The system's notion of time of day and calendar date is controlled in widely
290 different ways. Don't assume the timezone is stored in C<$ENV{TZ}>, and even
291 if it is, don't assume that you can control the timezone through that
294 Don't assume that the epoch starts at January 1, 1970, because that is
295 OS-specific. Better to store a date in an unambiguous representation.
296 A text representation (like C<1 Jan 1970>) can be easily converted into an
297 OS-specific value using a module like C<Date::Parse>. An array of values,
298 such as those returned by C<localtime>, can be converted to an OS-specific
299 representation using C<Time::Local>.
302 =head2 System Resources
304 If your code is destined for systems with severely constrained (or missing!)
305 virtual memory systems then you want to be especially mindful of avoiding
306 wasteful constructs such as:
308 # NOTE: this is no longer "bad" in perl5.005
309 for (0..10000000) {} # bad
310 for (my $x = 0; $x <= 10000000; ++$x) {} # good
312 @lines = <VERY_LARGE_FILE>; # bad
314 while (<FILE>) {$file .= $_} # sometimes bad
315 $file = join '', <FILE>; # better
317 The last two may appear unintuitive to most people. The first of those
318 two constructs repeatedly grows a string, while the second allocates a
319 large chunk of memory in one go. On some systems, the latter is more
320 efficient that the former.
324 Most multi-user platforms provide basic levels of security that is usually felt
325 at the file-system level. Other platforms usually don't (unfortunately).
326 Thus the notion of User-ID, or "home" directory, or even the state of
327 being logged-in may be unrecognizable on many platforms. If you write
328 programs that are security conscious, it is usually best to know what
329 type of system you will be operating under, and write code explicitly
330 for that platform (or class of platforms).
334 For those times when it is necessary to have platform-specific code,
335 consider keeping the platform-specific code in one place, making porting
336 to other platforms easier. Use the C<Config> module and the special
337 variable C<$^O> to differentiate platforms, as described in L<"PLATFORMS">.
342 Module uploaded to CPAN are tested by a variety of volunteers on
343 different platforms. These CPAN testers are notified by e-mail of each
344 new upload, and reply to the list with PASS, FAIL, NA (not applicable to
345 this platform), or ???? (unknown), along with any relevant notations.
347 The purpose of the testing is twofold: one, to help developers fix any
348 problems in their code; two, to provide users with information about
349 whether or not a given module works on a given platform.
353 =item Mailing list: cpan-testers@perl.org
355 =item Testing results: C<http://www.connect.net/gbarr/cpan-test/>
362 As of version 5.002, Perl is built with a C<$^O> variable that
363 indicates the operating system it was built on. This was implemented
364 to help speed up code that would otherwise have to C<use Config;> and
365 use the value of C<$Config{'osname'}>. Of course, to get
366 detailed information about the system, looking into C<%Config> is
367 certainly recommended.
371 Perl works on a bewildering variety of Unix and Unix-like platforms (see
372 e.g. most of the files in the F<hints/> directory in the source code kit).
373 On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>,
374 too) is determined by lowercasing and stripping punctuation from the first
375 field of the string returned by typing
379 (or a similar command) at the shell prompt. Here, for example, are a few
380 of the more popular Unix flavors:
382 uname $^O $Config{'archname'}
383 -------------------------------------------
389 SunOS solaris sun4-solaris
390 SunOS solaris i86pc-solaris
394 =head2 DOS and Derivatives
396 Perl has long been ported to PC style microcomputers running under
397 systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
398 bring yourself to mention (except for Windows CE, if you count that).
399 Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should
400 be aware that each of these file specifications may have subtle
403 $filespec0 = "c:/foo/bar/file.txt";
404 $filespec1 = "c:\\foo\\bar\\file.txt";
405 $filespec2 = 'c:\foo\bar\file.txt';
406 $filespec3 = 'c:\\foo\\bar\\file.txt';
408 System calls accept either C</> or C<\> as the path separator. However,
409 many command-line utilities of DOS vintage treat C</> as the option
410 prefix, so they may get confused by filenames containing C</>. Aside
411 from calling any external programs, C</> will work just fine, and
412 probably better, as it is more consistent with popular usage, and avoids
413 the problem of remembering what to backwhack and what not to.
415 The DOS FAT file system can only accommodate "8.3" style filenames. Under
416 the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT)
417 file systems you may have to be careful about case returned with functions
418 like C<readdir> or used with functions like C<open> or C<opendir>.
420 DOS also treats several filenames as special, such as AUX, PRN, NUL, CON,
421 COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work
422 if you include an explicit directory prefix, in some cases. It is best
423 to avoid such filenames, if you want your code to be portable to DOS
426 Users of these operating systems may also wish to make use of
427 scripts such as I<pl2bat.bat> or I<pl2cmd> as appropriate to
428 put wrappers around your scripts.
430 Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
431 and writing to files. C<binmode(FILEHANDLE)> will keep C<\n> translated
432 as C<\012> for that filehandle. Since it is a noop on other systems,
433 C<binmode> should be used for cross-platform code that deals with binary
436 The C<$^O> variable and the C<$Config{'archname'}> values for various
437 DOSish perls are as follows:
439 OS $^O $Config{'archname'}
440 --------------------------------------------
444 Windows 95 MSWin32 MSWin32-x86
445 Windows NT MSWin32 MSWin32-x86
446 Windows NT MSWin32 MSWin32-alpha
447 Windows NT MSWin32 MSWin32-ppc
453 =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/>
455 =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>,
456 C<http://www.juge.com/bbs/Hobb.19.html>
458 =item Build instructions for Win32, L<perlwin32>.
460 =item The ActiveState Pages, C<http://www.activestate.com/>
467 Any module requiring XS compilation is right out for most people, because
468 MacPerl is built using non-free (and non-cheap!) compilers. Some XS
469 modules that can work with MacPerl are built and distributed in binary
470 form on CPAN. See I<MacPerl: Power and Ease> for more details.
472 Directories are specified as:
474 volume:folder:file for absolute pathnames
475 volume:folder: for absolute pathnames
476 :folder:file for relative pathnames
477 :folder: for relative pathnames
478 :file for relative pathnames
479 file for relative pathnames
481 Files in a directory are stored in alphabetical order. Filenames are
482 limited to 31 characters, and may include any character except C<:>,
483 which is reserved as a path separator.
485 Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in
488 In the MacPerl application, you can't run a program from the command line;
489 programs that expect C<@ARGV> to be populated can be edited with something
490 like the following, which brings up a dialog box asking for the command
494 @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
497 A MacPerl script saved as a droplet will populate C<@ARGV> with the full
498 pathnames of the files dropped onto the script.
500 Mac users can use programs on a kind of command line under MPW (Macintosh
501 Programmer's Workshop, a free development environment from Apple).
502 MacPerl was first introduced as an MPW tool, and MPW can be used like a
505 perl myscript.plx some arguments
507 ToolServer is another app from Apple that provides access to MPW tools
508 from MPW and the MacPerl app, which allows MacPerl program to use
509 C<system>, backticks, and piped C<open>.
511 "S<Mac OS>" is the proper name for the operating system, but the value
512 in C<$^O> is "MacOS". To determine architecture, version, or whether
513 the application or MPW tool version is running, check:
515 $is_app = $MacPerl::Version =~ /App/;
516 $is_tool = $MacPerl::Version =~ /MPW/;
517 ($version) = $MacPerl::Version =~ /^(\S+)/;
518 $is_ppc = $MacPerl::Architecture eq 'MacPPC';
519 $is_68k = $MacPerl::Architecture eq 'Mac68K';
526 =item The MacPerl Pages, C<http://www.ptf.com/macperl/>.
528 =item The MacPerl mailing list, C<mac-perl-request@iis.ee.ethz.ch>.
535 Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
536 Note that perl on VMS can accept either VMS or Unix style file
537 specifications as in either of the following:
539 $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
540 $ perl -ne "print if /perl_setup/i" /sys$login/login.com
542 but not a mixture of both as in:
544 $ perl -ne "print if /perl_setup/i" sys$login:/login.com
545 Can't open sys$login:/login.com: file specification syntax error
547 Interacting with Perl from the Digital Command Language (DCL) shell
548 often requires a different set of quotation marks than Unix shells do.
551 $ perl -e "print ""Hello, world.\n"""
554 There are a number of ways to wrap your perl scripts in DCL .COM files if
555 you are so inclined. For example:
557 $ write sys$output "Hello from DCL!"
559 $ then perl -x 'f$environment("PROCEDURE")
560 $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
561 $ deck/dollars="__END__"
564 print "Hello from Perl!\n";
569 Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your
570 perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>.
572 Filenames are in the format "name.extension;version". The maximum
573 length for filenames is 39 characters, and the maximum length for
574 extensions is also 39 characters. Version is a number from 1 to
575 32767. Valid characters are C</[A-Z0-9$_-]/>.
577 VMS' RMS filesystem is case insensitive and does not preserve case.
578 C<readdir> returns lowercased filenames, but specifying a file for
579 opening remains case insensitive. Files without extensions have a
580 trailing period on them, so doing a C<readdir> with a file named F<A.;5>
581 will return F<a.> (though that file could be opened with C<open(FH, 'A')>.
583 RMS had an eight level limit on directory depths from any rooted logical
584 (allowing 16 levels overall) prior to VMS 7.2. Hence
585 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> is a valid directory specification but
586 C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> is not. F<Makefile.PL> authors might
587 have to take this into account, but at least they can refer to the former
588 as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>.
590 The C<VMS::Filespec> module, which gets installed as part
591 of the build process on VMS, is a pure Perl module that can easily be
592 installed on non-VMS platforms and can be helpful for conversions to
593 and from RMS native formats.
595 What C<\n> represents depends on the type of file that is open. It could
596 be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file
597 translates newlines to C<\012>, unless C<binmode> was executed on that
598 handle, just like DOSish perls.
600 TCP/IP stacks are optional on VMS, so socket routines might not be
601 implemented. UDP sockets may not be supported.
603 The value of C<$^O> on OpenVMS is "VMS". To determine the architecture
604 that you are running on without resorting to loading all of C<%Config>
605 you can examine the content of the C<@INC> array like so:
607 if (grep(/VMS_AXP/, @INC)) {
608 print "I'm on Alpha!\n";
609 } elsif (grep(/VMS_VAX/, @INC)) {
610 print "I'm on VAX!\n";
612 print "I'm not so sure about where $^O is...\n";
621 =item vmsperl list, C<vmsperl-request@newman.upenn.edu>
623 Put words C<SUBSCRIBE VMSPERL> in message body.
625 =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html>
630 =head2 EBCDIC Platforms
632 Recent versions of Perl have been ported to platforms such as OS/400 on
633 AS/400 minicomputers as well as OS/390 for IBM Mainframes. Such computers
634 use EBCDIC character sets internally (usually Character Code Set ID 00819
635 for OS/400 and IBM-1047 for OS/390). Note that on the mainframe perl
636 currently works under the "Unix system services for OS/390" (formerly
637 known as OpenEdition).
639 As of R2.5 of USS for OS/390 that Unix sub-system did not support the
640 C<#!> shebang trick for script invocation. Hence, on OS/390 perl scripts
641 can executed with a header similar to the following simple script:
644 eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
646 #!/usr/local/bin/perl # just a comment really
648 print "Hello from perl!\n";
650 On these platforms, bear in mind that the EBCDIC character set may have
651 an effect on what happens with perl functions such as C<chr>, C<pack>,
652 C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>; as well as
653 bit-fiddling with ASCII constants using operators like C<^>, C<&> and
654 C<|>; not to mention dealing with socket interfaces to ASCII computers
657 Fortunately, most web servers for the mainframe will correctly translate
658 the C<\n> in the following statement to its ASCII equivalent (note that
659 C<\r> is the same under both ASCII and EBCDIC):
661 print "Content-type: text/html\r\n\r\n";
663 The value of C<$^O> on OS/390 is "os390".
665 Some simple tricks for determining if you are running on an EBCDIC
666 platform could include any of the following (perhaps all):
668 if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
670 if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
672 if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
674 Note that one thing you may not want to rely on is the EBCDIC encoding
675 of punctuation characters since these may differ from code page to code page
676 (and once your module or script is rumoured to work with EBCDIC, folks will
677 want it to work with all EBCDIC character sets).
685 The perl-mvs@perl.org list is for discussion of porting issues as well as
686 general usage issues for all EBCDIC Perls. Send a message body of
687 "subscribe perl-mvs" to majordomo@perl.org.
689 =item AS/400 Perl information at C<http://as400.rochester.ibm.com>
696 As Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like Unix
697 and Unix filename emulation is turned on by default, it is quite likely that
698 most simple scripts will work "out of the box". The native filing system is
699 modular, and individual filing systems are free to be case sensitive or
700 insensitive, usually case preserving. Some native filing systems have name
701 length limits which file and directory names are silently truncated to fit -
702 scripts should be aware that the standard disc filing system currently has
703 a name length limit of B<10> characters, with up to 77 items in a directory,
704 but other filing systems may not impose such limitations.
706 Native filenames are of the form
708 Filesystem#Special_Field::DiscName.$.Directory.Directory.File
712 Special_Field is not usually present, but may contain . and $ .
713 Filesystem =~ m|[A-Za-z0-9_]|
714 DsicName =~ m|[A-Za-z0-9_/]|
715 $ represents the root directory
716 . is the path separator
717 @ is the current directory (per filesystem but machine global)
718 ^ is the parent directory
719 Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
721 The default filename translation is roughly C<tr|/.|./|;>
723 Note that C<"ADFS::HardDisc.$.File" ne 'ADFS::HardDisc.$.File'> and that
724 the second stage of $ interpolation in regular expressions will fall foul
725 of the C<$.> if scripts are not careful.
727 Logical paths specified by system variables containing comma separated
728 search lists are also allowed, hence C<System:Modules> is a valid filename,
729 and the filesystem will prefix C<Modules> with each section of C<System$Path>
730 until a name is made that points to an object on disc. Writing to a new
731 file C<System:Modules> would only be allowed if C<System$Path> contains a
732 single item list. The filesystem will also expand system variables in
733 filenames if enclosed in angle brackets, so C<E<lt>System$DirE<gt>.Modules>
734 would look for the file S<C<$ENV{'System$Dir'} . 'Modules'>>. The obvious
735 implication of this is that B<fully qualified filenames can start with C<E<lt>E<gt>>>
736 and should be protected when C<open> is used for input.
738 Because C<.> was in use as a directory separator and filenames could not
739 be assumed to be unique after 10 characters, Acorn implemented the C
740 compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
741 filenames specified in source code and store the respective files in
742 subdirectories named after the suffix. Hence files are translated:
745 C:foo.h C:h.foo (logical path variable)
746 sys/os.h sys.h.os (C compiler groks Unix-speak)
747 10charname.c c.10charname
748 10charname.o o.10charname
749 11charname_.c c.11charname (assuming filesystem truncates at 10)
751 The Unix emulation library's translation of filenames to native assumes
752 that this sort of translation is required, and allows a user defined list of
753 known suffixes which it will transpose in this fashion. This may appear
754 transparent, but consider that with these rules C<foo/bar/baz.h> and
755 C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
756 C<glob> cannot and do not attempt to emulate the reverse mapping. Other '.'s
757 in filenames are translated to '/'.
759 S<RISC OS> has "image files", files that behave as directories. For
760 example with suitable software this allows the contents of a zip file to
761 be treated as a directory at command line (and therefore script) level,
762 with full read-write random access. At present the perl port treats images
763 as directories: C<-d> returns true, C<-f> false, and C<unlink> checks to
764 ensure that recognised images are empty before deleting them. In theory
765 images should never trouble a script, but in practice they may do so if
766 the software to deal with an image file is loaded and registered while the
767 script is running, as suddenly "files" that it had cached information on
768 metamorphose into directories.
770 As implied above the environment accessed through C<%ENV> is global, and the
771 convention is that program specific environment variables are of the form
772 C<Program$Name>. Each filing system maintains a current directory, and
773 the current filing system's current directory is the B<global> current
774 directory. Consequently sociable scripts don't change the current directory
775 but rely on full pathnames, and scripts (and Makefiles) cannot assume that
776 they can spawn a child process which can change the current directory
777 without affecting its parent (and everyone else for that matter).
779 As native operating system filehandles are global and currently are allocated
780 down from 255, with 0 being a reserved value the Unix emulation library
781 emulates Unix filehandles. Consequently you can't rely on passing C<STDIN>
782 C<STDOUT> or C<STDERR> to your children. Run time libraries perform
783 command line processing to emulate Unix shell style C<>> redirection, but
784 the core operating system is written in assembler and has its own private,
785 obscure and somewhat broken convention. All this is further complicated by
786 the desire of users to express filenames of the form C<E<lt>Foo$DirE<gt>.Bar> on
787 the command line unquoted. (Oh yes, it's run time libraries interpreting the
788 quoting convention.) Hence C<``> command output capture has to perform
789 a guessing game as to how the command is going to interpret the command line
790 so that it can bodge it correctly to capture output. It assumes that a
791 string C<E<lt>[^E<lt>E<gt>]+\$[^E<lt>E<gt>]E<gt>> is a reference to an environment
792 variable, whereas anything else involving C<E<lt>> or C<E<gt>> is redirection,
793 and generally manages to be 99% right. Despite all this the problem remains
794 that scripts cannot rely on any Unix tools being available, or that any tools
795 found have Unix-like command line arguments.
797 Extensions and XS are in theory buildable by anyone using free tools. In
798 practice many don't as the Acorn platform is used to binary distribution.
799 MakeMaker does itself run, but no make currently copes with MakeMaker's
800 makefiles! Even if (when) this is fixed os that the lack of a Unix-like
801 shell can cause problems with makefile rules, especially lines of the form
802 C<cd sdbm && make all> and anything using quoting.
804 "S<RISC OS>" is the proper name for the operating system, but the value
805 in C<$^O> is "riscos" (because we don't like shouting).
818 Perl has been ported to a variety of platforms that do not fit into any of
819 the above categories. Some, such as AmigaOS, BeOS, QNX, and Plan 9, have
820 been well integrated into the standard Perl source code kit. You may need
821 to see the F<ports/> directory on CPAN for information, and possibly
822 binaries, for the likes of: aos, atari, lynxos, HP-MPE/iX, riscos,
823 Tandem Guardian, vos, I<etc.> (yes we know that some of these OSes may fall
824 under the Unix category but we are not a standards body.)
830 =item Atari, Guido Flohr's page C<http://stud.uni-sb.de/~gufl0000/>
832 =item HP 300 MPE/iX C<http://www.cccd.edu/~markb/perlix.html>
836 A free Perl 5 based PERL.NLM for Novell Netware is available from
837 C<http://www.novell.com/>
842 =head1 FUNCTION IMPLEMENTATIONS
844 Listed below are functions unimplemented or implemented differently on
845 various platforms. Following each description will be, in parentheses, a
846 list of platforms that the description applies to.
848 The list may very well be incomplete, or wrong in some places. When in
849 doubt, consult the platform-specific README files in the Perl source
850 distribution, and other documentation resources for a given port.
852 Be aware, moreover, that even among Unix-ish systems there are variations,
853 and not all functions listed here are necessarily available, though
856 For many functions, you can also query C<%Config>, exported by default
857 from C<Config.pm>. For example, to check if the platform has the C<lstat>
858 call, check C<$Config{'d_lstat'}>. See L<Config> for a full description
859 of available variables.
862 =head2 Alphabetical Listing of Perl Functions
872 C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories
873 and applications are executable, and there are no uid/gid
874 considerations. C<-o> is not supported. (S<Mac OS>)
876 C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible,
877 which may not reflect UIC-based file protections. (VMS)
879 C<-s> returns the size of the data fork, not the total size of data fork
880 plus resource fork. (S<Mac OS>).
882 C<-s> by name on an open file will return the space reserved on disk,
883 rather than the current extent. C<-s> on an open filehandle returns the
884 current size. (S<RISC OS>)
886 C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
887 C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
889 C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
892 C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
893 (Win32, VMS, S<RISC OS>)
895 C<-d> is true if passed a device spec without an explicit directory.
898 C<-T> and C<-B> are implemented, but might misclassify Mac text files
899 with foreign characters; this is the case will all platforms, but
900 affects S<Mac OS> a lot. (S<Mac OS>)
902 C<-x> (or C<-X>) determine if a file ends in one of the executable
903 suffixes. C<-S> is meaningless. (Win32)
905 C<-x> (or C<-X>) determine if a file has an executable file type.
908 =item binmode FILEHANDLE
910 Meaningless. (S<Mac OS>, S<RISC OS>)
912 Reopens file and restores pointer; if function fails, underlying
913 filehandle may be closed, or pointer may be in a different position.
916 The value returned by C<tell> may be affected after the call, and
917 the filehandle may be flushed. (Win32)
921 Only limited meaning. Disabling/enabling write permission is mapped to
922 locking/unlocking the file. (S<Mac OS>)
924 Only good for changing "owner" read-write access, "group", and "other"
925 bits are meaningless. (Win32)
927 Only good for changing "owner" and "other" read-write access. (S<RISC OS>)
931 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
933 Does nothing, but won't fail. (Win32)
935 =item chroot FILENAME
939 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>)
941 =item crypt PLAINTEXT,SALT
943 May not be available if library or source was not provided when building
948 Not implemented. (VMS, Plan9)
950 =item dbmopen HASH,DBNAME,MODE
952 Not implemented. (VMS, Plan9)
956 Not useful. (S<Mac OS>, S<RISC OS>)
958 Not implemented. (Win32)
960 Invokes VMS debugger. (VMS)
964 Not implemented. (S<Mac OS>)
966 =item fcntl FILEHANDLE,FUNCTION,SCALAR
968 Not implemented. (Win32, VMS)
970 =item flock FILEHANDLE,OPERATION
972 Not implemented (S<Mac OS>, VMS, S<RISC OS>).
974 Available only on Windows NT (not on Windows 95). (Win32)
978 Not implemented. (S<Mac OS>, Win32, AmigaOS, S<RISC OS>)
982 Not implemented. (S<Mac OS>, S<RISC OS>)
986 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
990 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
992 =item getpriority WHICH,WHO
994 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
998 Not implemented. (S<Mac OS>, Win32)
1000 Not useful. (S<RISC OS>)
1004 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1006 =item getnetbyname NAME
1008 Not implemented. (S<Mac OS>, Win32, Plan9)
1012 Not implemented. (S<Mac OS>, Win32)
1014 Not useful. (S<RISC OS>)
1018 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1020 =item getnetbyaddr ADDR,ADDRTYPE
1022 Not implemented. (S<Mac OS>, Win32, Plan9)
1024 =item getprotobynumber NUMBER
1026 Not implemented. (S<Mac OS>)
1028 =item getservbyport PORT,PROTO
1030 Not implemented. (S<Mac OS>)
1034 Not implemented. (S<Mac OS>, Win32)
1038 Not implemented. (S<Mac OS>, Win32, VMS)
1042 Not implemented. (S<Mac OS>, Win32)
1046 Not implemented. (S<Mac OS>, Win32, Plan9)
1050 Not implemented. (S<Mac OS>, Win32, Plan9)
1054 Not implemented. (Win32, Plan9)
1058 Not implemented. (S<Mac OS>, Win32, S<RISC OS>)
1062 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1064 =item sethostent STAYOPEN
1066 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1068 =item setnetent STAYOPEN
1070 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1072 =item setprotoent STAYOPEN
1074 Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>)
1076 =item setservent STAYOPEN
1078 Not implemented. (Plan9, Win32, S<RISC OS>)
1082 Not implemented. (S<Mac OS>, Win32)
1086 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1090 Not implemented. (S<Mac OS>, Win32)
1094 Not implemented. (S<Mac OS>, Win32, Plan9)
1098 Not implemented. (S<Mac OS>, Win32, Plan9)
1102 Not implemented. (Plan9, Win32)
1104 =item getsockopt SOCKET,LEVEL,OPTNAME
1106 Not implemented. (S<Mac OS>, Plan9)
1112 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1115 Features depend on external perlglob.exe or perlglob.bat. May be overridden
1116 with something like File::DosGlob, which is recommended. (Win32)
1118 Globbing built-in, but only C<*> and C<?> metacharacters are supported.
1119 Globbing relies on operating system calls, which may return filenames in
1120 any order. As most filesystems are case insensitive even "sorted"
1121 filenames will not be in case sensitive order. (S<RISC OS>)
1123 =item ioctl FILEHANDLE,FUNCTION,SCALAR
1125 Not implemented. (VMS)
1127 Available only for socket handles, and it does what the ioctlsocket() call
1128 in the Winsock API does. (Win32)
1130 Available only for socket handles. (S<RISC OS>)
1134 Not implemented, hence not useful for taint checking. (S<Mac OS>, S<RISC OS>)
1136 Available only for process handles returned by the C<system(1, ...)> method of
1137 spawning a process. (Win32)
1139 =item link OLDFILE,NEWFILE
1141 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1143 =item lstat FILEHANDLE
1149 Not implemented. (VMS, S<RISC OS>)
1151 Return values may be bogus. (Win32)
1153 =item msgctl ID,CMD,ARG
1155 =item msgget KEY,FLAGS
1157 =item msgsnd ID,MSG,FLAGS
1159 =item msgrcv ID,VAR,SIZE,TYPE,FLAGS
1161 Not implemented. (S<Mac OS>, Win32, VMS, Plan9, S<RISC OS>)
1163 =item open FILEHANDLE,EXPR
1165 =item open FILEHANDLE
1167 The C<|> variants are only supported if ToolServer is installed.
1170 open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
1172 =item pipe READHANDLE,WRITEHANDLE
1174 Not implemented. (S<Mac OS>)
1180 Not implemented. (Win32, VMS, S<RISC OS>)
1182 =item select RBITS,WBITS,EBITS,TIMEOUT
1184 Only implemented on sockets. (Win32)
1186 Only reliable on sockets. (S<RISC OS>)
1188 =item semctl ID,SEMNUM,CMD,ARG
1190 =item semget KEY,NSEMS,FLAGS
1192 =item semop KEY,OPSTRING
1194 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1196 =item setpgrp PID,PGRP
1198 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1200 =item setpriority WHICH,WHO,PRIORITY
1202 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1204 =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
1206 Not implemented. (S<Mac OS>, Plan9)
1208 =item shmctl ID,CMD,ARG
1210 =item shmget KEY,SIZE,FLAGS
1212 =item shmread ID,VAR,POS,SIZE
1214 =item shmwrite ID,STRING,POS,SIZE
1216 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1218 =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
1220 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1222 =item stat FILEHANDLE
1228 mtime and atime are the same thing, and ctime is creation time instead of
1229 inode change time. (S<Mac OS>)
1231 device and inode are not meaningful. (Win32)
1233 device and inode are not necessarily reliable. (VMS)
1235 mtime, atime and ctime all return the last modification time. Device and
1236 inode are not necessarily reliable. (S<RISC OS>)
1238 =item symlink OLDFILE,NEWFILE
1240 Not implemented. (Win32, VMS, S<RISC OS>)
1244 Not implemented. (S<Mac OS>, Win32, VMS, S<RISC OS>)
1246 =item sysopen FILEHANDLE,FILENAME,MODE,PERMS
1248 The traditional "0", "1", and "2" MODEs are implemented with different
1249 numeric values on some systems. The flags exported by C<Fcntl> should work
1250 everywhere though. (S<Mac OS>, OS/390)
1254 Only implemented if ToolServer is installed. (S<Mac OS>)
1256 As an optimization, may not call the command shell specified in
1257 C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
1258 process and immediately returns its process designator, without
1259 waiting for it to terminate. Return value may be used subsequently
1260 in C<wait> or C<waitpid>. (Win32)
1262 There is no shell to process metacharacters, and the native standard is
1263 to pass a command line terminated by "\n" "\r" or "\0" to the spawned
1264 program. Redirection such as C<E<gt> foo> is performed (if at all) by
1265 the run time library of the spawned program. C<system> I<list> will call
1266 the Unix emulation library's C<exec> emulation, which attempts to provide
1267 emulation of the stdin, stdout, stderr in force in the parent, providing
1268 the child program uses a compatible version of the emulation library.
1269 I<scalar> will call the native command line direct and no such emulation
1270 of a child Unix program will exists. Mileage B<will> vary. (S<RISC OS>)
1274 Only the first entry returned is nonzero. (S<Mac OS>)
1276 "cumulative" times will be bogus. On anything other than Windows NT,
1277 "system" time will be bogus, and "user" time is actually the time
1278 returned by the clock() function in the C runtime library. (Win32)
1280 Not useful. (S<RISC OS>)
1282 =item truncate FILEHANDLE,LENGTH
1284 =item truncate EXPR,LENGTH
1286 Not implemented. (VMS)
1292 Returns undef where unavailable, as of version 5.005.
1296 Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
1298 May not behave as expected. (Win32)
1302 =item waitpid PID,FLAGS
1304 Not implemented. (S<Mac OS>)
1306 Can only be applied to process handles returned for processes spawned
1307 using C<system(1, ...)>. (Win32)
1309 Not useful. (S<RISC OS>)
1317 =item 1.30, 03 August 1998
1319 Major update for RISC OS, other minor changes.
1321 =item 1.23, 10 July 1998
1323 First public release with perl5.005.
1327 =head1 AUTHORS / CONTRIBUTORS
1329 Chris Nandor E<lt>pudge@pobox.comE<gt>,
1330 Gurusamy Sarathy E<lt>gsar@umich.eduE<gt>,
1331 Peter Prymmer E<lt>pvhp@forte.comE<gt>,
1332 Tom Christiansen E<lt>tchrist@perl.comE<gt>,
1333 Nathan Torkington E<lt>gnat@frii.comE<gt>,
1334 Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>,
1335 Matthias Neercher E<lt>neeri@iis.ee.ethz.chE<gt>,
1336 Charles Bailey E<lt>bailey@genetics.upenn.eduE<gt>,
1337 Luther Huffman E<lt>lutherh@stratcom.comE<gt>,
1338 Gary Ng E<lt>71564.1743@CompuServe.COME<gt>,
1339 Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>,
1340 Paul J. Schinder E<lt>schinder@pobox.comE<gt>,
1341 Tom Phoenix E<lt>rootbeer@teleport.comE<gt>,
1342 Hugo van der Sanden E<lt>h.sanden@elsevier.nlE<gt>,
1343 Dominic Dunlop E<lt>domo@vo.luE<gt>,
1344 Dan Sugalski E<lt>sugalskd@ous.eduE<gt>,
1345 Andreas J. Koenig E<lt>koenig@kulturbox.deE<gt>,
1346 Andrew M. Langmead E<lt>aml@world.std.comE<gt>,
1347 Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>,
1348 Abigail E<lt>abigail@fnx.comE<gt>,
1349 Nicholas Clark E<lt>Nicholas.Clark@liverpool.ac.ukE<gt>.
1351 This document is maintained by Chris Nandor.
1355 Version 1.30, last modified 03 August 1998.