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1 | =head1 NAME |
2 | |
3 | perlport - Writing portable Perl |
4 | |
5 | |
6 | =head1 DESCRIPTION |
7 | |
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 |
10 | features. |
11 | |
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. |
15 | |
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. |
27 | |
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. |
30 | |
31 | Be aware of two important points: |
32 | |
33 | =over 4 |
34 | |
35 | =item Not all Perl programs have to be portable |
36 | |
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. |
41 | |
42 | =item The vast majority of Perl B<is> portable |
43 | |
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. |
50 | |
51 | =back |
52 | |
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. |
61 | |
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 |
65 | in your decision. |
66 | |
67 | This information should not be considered complete; it includes possibly |
68 | transient information about idiosyncracies 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>). |
72 | |
73 | |
74 | =head1 ISSUES |
75 | |
76 | =head2 Newlines |
77 | |
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>. |
82 | |
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) |
87 | C<\015\012>. |
88 | |
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. |
98 | |
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. |
103 | |
104 | print SOCKET "Hi there, client!\r\n"; # WRONG |
105 | print SOCKET "Hi there, client!\015\012"; # RIGHT |
106 | |
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.] |
112 | |
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. |
116 | |
117 | use Socket qw(:DEFAULT :crlf); |
118 | print SOCKET "Hi there, client!$CRLF" # RIGHT |
119 | |
120 | When reading I<from> a socket, remember that the default input record |
121 | separator (C<$/>) is C<\n>, but code like this should recognize C<$/> as |
122 | C<\012> or C<\015\012>: |
123 | |
124 | while (<SOCKET>) { |
125 | # ... |
126 | } |
127 | |
128 | Better: |
129 | |
130 | use Socket qw(:DEFAULT :crlf); |
131 | local($/) = LF; # not needed if $/ is already \012 |
132 | |
133 | while (<SOCKET>) { |
134 | s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK |
135 | # s/\015?\012/\n/; # same thing |
136 | } |
137 | |
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). |
141 | |
142 | |
143 | =head2 File Paths |
144 | |
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. |
149 | |
150 | While they are similar, file path specifications differ between Unix, |
151 | Windows, S<Mac OS>, OS/2, VMS and probably others. Unix, for example, is |
152 | one of the few OSes that has the idea of a root directory. S<Mac OS> |
153 | uses C<:> as a path separator instead of C</>. VMS, Windows, and OS/2 |
154 | can work similarly to Unix with C</> as path separator, or in their own |
155 | idiosyncratic ways. |
156 | |
157 | As with the newline problem above, there are modules that can help. The |
158 | C<File::Spec> modules provide methods to do the Right Thing on whatever |
159 | platform happens to be running the program. |
160 | |
161 | use File::Spec; |
162 | chdir(File::Spec->updir()); # go up one directory |
163 | $file = File::Spec->catfile( |
164 | File::Spec->curdir(), 'temp', 'file.txt' |
165 | ); |
166 | # on Unix and Win32, './temp/file.txt' |
167 | # on Mac OS, ':temp:file.txt' |
168 | |
169 | File::Spec is available in the standard distribution, as of version |
170 | 5.004_05. |
171 | |
172 | In general, production code should not have file paths hardcoded; making |
173 | them user supplied or from a configuration file is better, keeping in mind |
174 | that file path syntax varies on different machines. |
175 | |
176 | This is especially noticeable in scripts like Makefiles and test suites, |
177 | which often assume C</> as a path separator for subdirectories. |
178 | |
179 | Also of use is C<File::Basename>, from the standard distribution, which |
180 | splits a pathname into pieces (base filename, full path to directory, |
181 | and file suffix). |
182 | |
183 | Remember not to count on the existence of system-specific files, like |
184 | F</etc/resolv.conf>. If code does need to rely on such a file, include a |
185 | description of the file and its format in the code's documentation, and |
186 | make it easy for the user to override the default location of the file. |
187 | |
188 | |
189 | =head2 System Interaction |
190 | |
191 | Not all platforms provide for the notion of a command line, necessarily. |
192 | These are usually platforms that rely on a Graphical User Interface (GUI) |
193 | for user interaction. So a program requiring command lines might not work |
194 | everywhere. But this is probably for the user of the program to deal |
195 | with. |
196 | |
197 | Some platforms can't delete or rename files that are being held open by |
198 | the system. Remember to C<close> files when you are done with them. |
199 | Don't C<unlink> or C<rename> an open file. Don't C<tie> to or C<open> a |
200 | file that is already tied to or opened; C<untie> or C<close> first. |
201 | |
202 | Don't count on a specific environment variable existing in C<%ENV>. |
203 | Don't even count on C<%ENV> entries being case-sensitive, or even |
204 | case-preserving. |
205 | |
206 | Don't count on signals in portable programs. |
207 | |
208 | Don't count on filename globbing. Use C<opendir>, C<readdir>, and |
209 | C<closedir> instead. |
210 | |
211 | |
212 | =head2 Interprocess Communication (IPC) |
213 | |
214 | In general, don't directly access the system in code that is meant to be |
215 | portable. That means, no: C<system>, C<exec>, C<fork>, C<pipe>, C<``>, |
216 | C<qx//>, C<open> with a C<|>, or any of the other things that makes being |
217 | a Unix perl hacker worth being. |
218 | |
219 | Commands that launch external processes are generally supported on |
220 | most platforms (though many of them do not support any type of forking), |
221 | but the problem with using them arises from what you invoke with them. |
222 | External tools are often named differently on different platforms, often |
223 | not available in the same location, often accept different arguments, |
224 | often behave differently, and often represent their results in a |
225 | platform-dependent way. Thus you should seldom depend on them to produce |
226 | consistent results. |
227 | |
228 | One especially common bit of Perl code is opening a pipe to sendmail: |
229 | |
230 | open(MAIL, '|/usr/lib/sendmail -t') or die $!; |
231 | |
232 | This is fine for systems programming when sendmail is known to be |
233 | available. But it is not fine for many non-Unix systems, and even |
234 | some Unix systems that may not have sendmail installed. If a portable |
235 | solution is needed, see the C<Mail::Send> and C<Mail::Mailer> modules |
236 | in the C<MailTools> distribution. C<Mail::Mailer> provides several |
237 | mailing methods, including mail, sendmail, and direct SMTP |
238 | (via C<Net::SMTP>) if a mail transfer agent is not available. |
239 | |
240 | The rule of thumb for portable code is: Do it all in portable Perl, or |
241 | use a module that may internally implement it with platform-specific code, |
242 | but expose a common interface. By portable Perl, we mean code that |
243 | avoids the constructs described in this document as being non-portable. |
244 | |
245 | |
246 | =head2 External Subroutines (XS) |
247 | |
248 | XS code, in general, can be made to work with any platform; but dependent |
249 | libraries, header files, etc., might not be readily available or |
250 | portable, or the XS code itself might be platform-specific, just as Perl |
251 | code might be. If the libraries and headers are portable, then it is |
252 | normally reasonable to make sure the XS code is portable, too. |
253 | |
254 | There is a different kind of portability issue with writing XS |
255 | code: availability of a C compiler on the end-user's system. C brings with |
256 | it its own portability issues, and writing XS code will expose you to |
257 | some of those. Writing purely in perl is a comparatively easier way to |
258 | achieve portability. |
259 | |
260 | |
261 | =head2 Standard Modules |
262 | |
263 | In general, the standard modules work across platforms. Notable |
264 | exceptions are C<CPAN.pm> (which currently makes connections to external |
265 | programs that may not be available), platform-specific modules (like |
266 | C<ExtUtils::MM_VMS>), and DBM modules. |
267 | |
268 | There is no one DBM module that is available on all platforms. |
269 | C<SDBM_File> and the others are generally available on all Unix and DOSish |
270 | ports, but not in MacPerl, where C<NBDM_File> and C<DB_File> are available. |
271 | |
272 | The good news is that at least some DBM module should be available, and |
273 | C<AnyDBM_File> will use whichever module it can find. Of course, then |
274 | the code needs to be fairly strict, dropping to the lowest common |
275 | denominator (e.g., not exceeding 1K for each record). |
276 | |
277 | |
278 | =head2 Time and Date |
279 | |
280 | The system's notion of time of day and calendar date is controlled in widely |
281 | different ways. Don't assume the timezone is stored in C<$ENV{TZ}>, and even |
282 | if it is, don't assume that you can control the timezone through that |
283 | variable. |
284 | |
285 | Don't assume that the epoch starts at January 1, 1970, because that is |
286 | OS-specific. Better to store a date in an unambiguous representation. |
287 | A text representation (like C<1 Jan 1970>) can be easily converted into an |
288 | OS-specific value using a module like C<Date::Parse>. An array of values, |
289 | such as those returned by C<localtime>, can be converted to an OS-specific |
290 | representation using C<Time::Local>. |
291 | |
292 | |
293 | =head2 System Resources |
294 | |
295 | If your code is destined for systems with severely constrained (or missing!) |
296 | virtual memory systems then you want to be especially mindful of avoiding |
297 | wasteful constructs such as: |
298 | |
299 | # NOTE: this is no longer "bad" in perl5.005 |
300 | for (0..10000000) {} # bad |
301 | for (my $x = 0; $x <= 10000000; ++$x) {} # good |
302 | |
303 | @lines = <VERY_LARGE_FILE>; # bad |
304 | |
305 | while (<FILE>) {$file .= $_} # sometimes bad |
306 | $file = join '', <FILE>; # better |
307 | |
308 | The last two may appear unintuitive to most people. The first of those |
309 | two constructs repeatedly grows a string, while the second allocates a |
310 | large chunk of memory in one go. On some systems, the latter is more |
311 | efficient that the former. |
312 | |
313 | =head2 Security |
314 | |
315 | Most Unix platforms provide basic levels of security that is usually felt |
316 | at the file-system level. Other platforms usually don't (unfortunately). |
317 | Thus the notion of User-ID, or "home" directory, or even the state of |
318 | being logged-in may be unrecognizable on may platforms. If you write |
319 | programs that are security conscious, it is usually best to know what |
320 | type of system you will be operating under, and write code explicitly |
321 | for that platform (or class of platforms). |
322 | |
323 | =head2 Style |
324 | |
325 | For those times when it is necessary to have platform-specific code, |
326 | consider keeping the platform-specific code in one place, making porting |
327 | to other platforms easier. Use the C<Config> module and the special |
328 | variable C<$^O> to differentiate platforms, as described in L<"PLATFORMS">. |
329 | |
330 | |
331 | =head1 CPAN TESTERS |
332 | |
333 | Module uploaded to CPAN are tested by a variety of volunteers on |
334 | different platforms. These CPAN testers are notified by e-mail of each |
335 | new upload, and reply to the list with PASS, FAIL, NA (not applicable to |
336 | this platform), or ???? (unknown), along with any relevant notations. |
337 | |
338 | The purpose of the testing is twofold: one, to help developers fix any |
339 | problems in their code; two, to provide users with information about |
340 | whether or not a given module works on a given platform. |
341 | |
342 | =over 4 |
343 | |
344 | =item Mailing list: cpan-testers@perl.org |
345 | |
346 | =item Testing results: C<http://www.connect.net/gbarr/cpan-test/> |
347 | |
348 | =back |
349 | |
350 | |
351 | =head1 PLATFORMS |
352 | |
353 | As of version 5.002, Perl is built with a C<$^O> variable that |
354 | indicates the operating system it was built on. This was implemented |
355 | to help speed up code that would otherwise have to C<use Config;> and |
356 | use the value of C<$Config{'osname'}>. Of course, to get |
357 | detailed information about the system, looking into C<%Config> is |
358 | certainly recommended. |
359 | |
360 | =head2 Unix |
361 | |
362 | Perl works on a bewildering variety of Unix and Unix-like platforms (see |
363 | e.g. most of the files in the F<hints/> directory in the source code kit). |
364 | On most of these systems, the value of C<$^O> (hence C<$Config{'osname'}>, |
365 | too) is determined by lowercasing and stripping punctuation from the first |
366 | field of the string returned by typing |
367 | |
368 | % uname -a |
369 | |
370 | (or a similar command) at the shell prompt. Here, for example, are a few |
371 | of the more popular Unix flavors: |
372 | |
373 | uname $^O |
374 | -------------------- |
375 | AIX aix |
376 | FreeBSD freebsd |
377 | Linux linux |
378 | HP-UX hpux |
379 | OSF1 dec_osf |
380 | SunOS solaris |
381 | SunOS4 sunos |
382 | |
383 | |
384 | =head2 DOS and Derivatives |
385 | |
386 | Perl has long been ported to PC style microcomputers running under |
387 | systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can |
388 | bring yourself to mention (except for Windows CE, if you count that). |
389 | Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should |
390 | be aware that each of these file specifications may have subtle |
391 | differences: |
392 | |
393 | $filespec0 = "c:/foo/bar/file.txt"; |
394 | $filespec1 = "c:\\foo\\bar\\file.txt"; |
395 | $filespec2 = 'c:\foo\bar\file.txt'; |
396 | $filespec3 = 'c:\\foo\\bar\\file.txt'; |
397 | |
398 | System calls accept either C</> or C<\> as the path separator. However, |
399 | many command-line utilities of DOS vintage treat C</> as the option |
400 | prefix, so they may get confused by filenames containing C</>. Aside |
401 | from calling any external programs, C</> will work just fine, and |
402 | probably better, as it is more consistent with popular usage, and avoids |
403 | the problem of remembering what to backwhack and what not to. |
404 | |
405 | The DOS FAT file system can only accomodate "8.3" style filenames. Under |
406 | the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT) |
407 | file systems you may have to be careful about case returned with functions |
408 | like C<readdir> or used with functions like C<open> or C<opendir>. |
409 | |
410 | DOS also treats several filenames as special, such as AUX, PRN, NUL, CON, |
411 | COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work |
412 | if you include an explicit directory prefix, in some cases. It is best |
413 | to avoid such filenames, if you want your code to be portable to DOS |
414 | and its derivatives. |
415 | |
416 | Users of these operating systems may also wish to make use of |
417 | scripts such as I<pl2bat.bat> or I<pl2cmd> as appropriate to |
418 | put wrappers around your scripts. |
419 | |
420 | Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from |
421 | and writing to files. C<binmode(FILEHANDLE)> will keep C<\n> translated |
422 | as C<\012> for that filehandle. Since it is a noop on other systems, |
423 | C<binmode> should be used for cross-platform code that deals with binary |
424 | data. |
425 | |
426 | The C<$^O> variable and the C<$Config{'archname'}> values for various |
427 | DOSish perls are as follows: |
428 | |
429 | OS $^O $Config{'archname'} |
430 | -------------------------------------------- |
431 | MS-DOS dos |
432 | PC-DOS dos |
433 | OS/2 os2 |
434 | Windows 95 MSWin32 MSWin32-x86 |
435 | Windows NT MSWin32 MSWin32-x86 |
436 | Windows NT MSWin32 MSWin32-alpha |
437 | Windows NT MSWin32 MSWin32-ppc |
438 | |
439 | Also see: |
440 | |
441 | =over 4 |
442 | |
443 | =item The djgpp environment for DOS, C<http://www.delorie.com/djgpp/> |
444 | |
445 | =item The EMX environment for DOS, OS/2, etc. C<emx@iaehv.nl>, |
446 | C<http://www.juge.com/bbs/Hobb.19.html> |
447 | |
448 | =item Build instructions for Win32, L<perlwin32>. |
449 | |
450 | =item The ActiveState Pages, C<http://www.activestate.com/> |
451 | |
452 | =back |
453 | |
454 | |
455 | =head2 MacPerl |
456 | |
457 | Any module requiring XS compilation is right out for most people, because |
458 | MacPerl is built using non-free (and non-cheap!) compilers. Some XS |
459 | modules that can work with MacPerl are built and distributed in binary |
460 | form on CPAN. See I<MacPerl: Power and Ease> for more details. |
461 | |
462 | Directories are specified as: |
463 | |
464 | volume:folder:file for absolute pathnames |
465 | volume:folder: for absolute pathnames |
466 | :folder:file for relative pathnames |
467 | :folder: for relative pathnames |
468 | :file for relative pathnames |
469 | file for relative pathnames |
470 | |
471 | Files in a directory are stored in alphabetical order. Filenames are |
472 | limited to 31 characters, and may include any character except C<:>, |
473 | which is reserved as a path separator. |
474 | |
475 | Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in |
476 | C<Mac::Files>. |
477 | |
478 | In the MacPerl application, you can't run a program from the command line; |
479 | programs that expect C<@ARGV> to be populated can be edited with something |
480 | like the following, which brings up a dialog box asking for the command |
481 | line arguments. |
482 | |
483 | if (!@ARGV) { |
484 | @ARGV = split /\s+/, MacPerl::Ask('Arguments?'); |
485 | } |
486 | |
487 | A MacPerl script saved as a droplet will populate C<@ARGV> with the full |
488 | pathnames of the files dropped onto the script. |
489 | |
490 | Mac users can use programs on a kind of command line under MPW (Macintosh |
491 | Programmer's Workshop, a free development environment from Apple). |
492 | MacPerl was first introduced as an MPW tool, and MPW can be used like a |
493 | shell: |
494 | |
495 | perl myscript.plx some arguments |
496 | |
497 | ToolServer is another app from Apple that provides access to MPW tools |
498 | from MPW and the MacPerl app, which allows MacPerl program to use |
499 | C<system>, backticks, and piped C<open>. |
500 | |
501 | "S<Mac OS>" is the proper name for the operating system, but the value |
502 | in C<$^O> is "MacOS". To determine architecture, version, or whether |
503 | the application or MPW tool version is running, check: |
504 | |
505 | $is_app = $MacPerl::Version =~ /App/; |
506 | $is_tool = $MacPerl::Version =~ /MPW/; |
507 | ($version) = $MacPerl::Version =~ /^(\S+)/; |
508 | $is_ppc = $MacPerl::Architecture eq 'MacPPC'; |
509 | $is_68k = $MacPerl::Architecture eq 'Mac68K'; |
510 | |
511 | |
512 | Also see: |
513 | |
514 | =over 4 |
515 | |
516 | =item The MacPerl Pages, C<http://www.ptf.com/macperl/>. |
517 | |
518 | =item The MacPerl mailing list, C<mac-perl-request@iis.ee.ethz.ch>. |
519 | |
520 | =back |
521 | |
522 | |
523 | =head2 VMS |
524 | |
525 | Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution. |
526 | Note that perl on VMS can accept either VMS or Unix style file |
527 | specifications as in either of the following: |
528 | |
529 | $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM |
530 | $ perl -ne "print if /perl_setup/i" /sys$login/login.com |
531 | |
532 | but not a mixture of both as in: |
533 | |
534 | $ perl -ne "print if /perl_setup/i" sys$login:/login.com |
535 | Can't open sys$login:/login.com: file specification syntax error |
536 | |
537 | Interacting with Perl from the Digital Command Language (DCL) shell |
538 | often requires a different set of quotation marks than Unix shells do. |
539 | For example: |
540 | |
541 | $ perl -e "print ""Hello, world.\n""" |
542 | Hello, world. |
543 | |
544 | There are a number of ways to wrap your perl scripts in DCL .COM files if |
545 | you are so inclined. For example: |
546 | |
547 | $ write sys$output "Hello from DCL!" |
548 | $ if p1 .eqs. "" |
549 | $ then perl -x 'f$environment("PROCEDURE") |
550 | $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8 |
551 | $ deck/dollars="__END__" |
552 | #!/usr/bin/perl |
553 | |
554 | print "Hello from Perl!\n"; |
555 | |
556 | __END__ |
557 | $ endif |
558 | |
559 | Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your |
560 | perl-in-DCL script expects to do things like C<$read = E<lt>STDINE<gt>;>. |
561 | |
562 | Filenames are in the format "name.extension;version". The maximum |
563 | length for filenames is 39 characters, and the maximum length for |
564 | extensions is also 39 characters. Version is a number from 1 to |
565 | 32767. Valid characters are C</[A-Z0-9$_-]/>. |
566 | |
567 | VMS' RMS filesystem is case insensitive and does not preserve case. |
568 | C<readdir> returns lowercased filenames, but specifying a file for |
569 | opening remains case insensitive. Files without extensions have a |
570 | trailing period on them, so doing a C<readdir> with a file named F<A.;5> |
571 | will return F<a.> (though that file could be opened with C<open(FH, 'A')>. |
572 | |
573 | RMS has an eight level limit on directory depths from any rooted logical |
574 | (allowing 16 levels overall). Hence C<PERL_ROOT:[LIB.2.3.4.5.6.7.8]> |
575 | is a valid directory specification but C<PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]> |
576 | is not. F<Makefile.PL> authors might have to take this into account, but |
577 | at least they can refer to the former as C</PERL_ROOT/lib/2/3/4/5/6/7/8/>. |
578 | |
579 | The C<VMS::Filespec> module, which gets installed as part |
580 | of the build process on VMS, is a pure Perl module that can easily be |
581 | installed on non-VMS platforms and can be helpful for conversions to |
582 | and from RMS native formats. |
583 | |
584 | What C<\n> represents depends on the type of file that is open. It could |
585 | be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file |
586 | translates newlines to C<\012>, unless C<binmode> was executed on that |
587 | handle, just like DOSish perls. |
588 | |
589 | TCP/IP stacks are optional on VMS, so socket routines might not be |
590 | implemented. UDP sockets may not be supported. |
591 | |
592 | The value of C<$^O> on OpenVMS is "VMS". To determine the architecture |
593 | that you are running on without resorting to loading all of C<%Config> |
594 | you can examine the content of the C<@INC> array like so: |
595 | |
596 | if (grep(/VMS_AXP/, @INC)) { |
597 | print "I'm on Alpha!\n"; |
598 | } elsif (grep(/VMS_VAX/, @INC)) { |
599 | print "I'm on VAX!\n"; |
600 | } else { |
601 | print "I'm not so sure about where $^O is...\n"; |
602 | } |
603 | |
604 | Also see: |
605 | |
606 | =over 4 |
607 | |
608 | =item L<perlvms.pod> |
609 | |
610 | =item vmsperl list, C<vmsperl-request@newman.upenn.edu> |
611 | |
612 | Put words C<SUBSCRIBE VMSPERL> in message body. |
613 | |
614 | =item vmsperl on the web, C<http://www.sidhe.org/vmsperl/index.html> |
615 | |
616 | =back |
617 | |
618 | |
619 | =head2 EBCDIC Platforms |
620 | |
621 | Recent versions of Perl have been ported to platforms such as OS/400 on |
622 | AS/400 minicomputers as well as OS/390 for IBM Mainframes. Such computers |
623 | use EBCDIC character sets internally (usually Character Code Set ID 00819 |
624 | for OS/400 and IBM-1047 for OS/390). Note that on the mainframe perl |
625 | currently works under the "Unix system services for OS/390" (formerly |
626 | known as OpenEdition). |
627 | |
628 | As of R2.5 of USS for OS/390 that Unix sub-system did not support the |
629 | C<#!> shebang trick for script invocation. Hence, on OS/390 perl scripts |
630 | can executed with a header similar to the following simple script: |
631 | |
632 | : # use perl |
633 | eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}' |
634 | if 0; |
635 | #!/usr/local/bin/perl # just a comment really |
636 | |
637 | print "Hello from perl!\n"; |
638 | |
639 | On these platforms, bear in mind that the EBCDIC character set may have |
640 | an effect on what happens with perl functions such as C<chr>, C<pack>, |
641 | C<print>, C<printf>, C<ord>, C<sort>, C<sprintf>, C<unpack>; as well as |
642 | bit-fiddling with ASCII constants using operators like C<^>, C<&> and |
643 | C<|>; not to mention dealing with socket interfaces to ASCII computers |
644 | (see L<"NEWLINES">). |
645 | |
646 | Fortunately, most web servers for the mainframe will correctly translate |
647 | the C<\n> in the following statement to its ASCII equivalent (note that |
648 | C<\r> is the same under both ASCII and EBCDIC): |
649 | |
650 | print "Content-type: text/html\r\n\r\n"; |
651 | |
652 | The value of C<$^O> on OS/390 is "os390". |
653 | |
654 | Some simple tricks for determining if you are running on an EBCDIC |
655 | platform could include any of the following (perhaps all): |
656 | |
657 | if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; } |
658 | |
659 | if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; } |
660 | |
661 | if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; } |
662 | |
663 | Note that one thing you may not want to rely on is the EBCDIC encoding |
664 | of punctuation characters since these may differ from code page to code page |
665 | (and once your module or script is rumoured to work with EBCDIC, folks will |
666 | want it to work with all EBCDIC character sets). |
667 | |
668 | Also see: |
669 | |
670 | =over 4 |
671 | |
672 | =item perl-mvs list |
673 | |
674 | The perl-mvs@perl.org list is for discussion of porting issues as well as |
675 | general usage issues for all EBCDIC Perls. Send a message body of |
676 | "subscribe perl-mvs" to majordomo@perl.org. |
677 | |
678 | =item AS/400 Perl information at C<http://as400.rochester.ibm.com> |
679 | |
680 | =back |
681 | |
682 | =head2 Other perls |
683 | |
684 | Perl has been ported to a variety of platforms that do not fit into any of |
685 | the above categories. Some, such as AmigaOS, BeOS, QNX, and Plan 9, have |
686 | been well integrated into the standard Perl source code kit. You may need |
687 | to see the F<ports/> directory on CPAN for information, and possibly |
688 | binaries, for the likes of: acorn, aos, atari, lynxos, HP-MPE/iX, riscos, |
689 | Tandem Guardian, vos, I<etc.> (yes we know that some of these OSes may fall |
690 | under the Unix category but we are not a standards body.) |
691 | |
692 | See also: |
693 | |
694 | =over 4 |
695 | |
696 | =item Atari, Guido Flohr's page C<http://stud.uni-sb.de/~gufl0000/> |
697 | |
698 | =item HP 300 MPE/iX C<http://www.cccd.edu/~markb/perlix.html> |
699 | |
700 | =item Novell Netware |
701 | |
702 | A free Perl 5 based PERL.NLM for Novell Netware is available from |
703 | C<http://www.novell.com/> |
704 | |
705 | =back |
706 | |
707 | |
708 | =head1 FUNCTION IMPLEMENTATIONS |
709 | |
710 | Listed below are functions unimplemented or implemented differently on |
711 | various platforms. Following each description will be, in parentheses, a |
712 | list of platforms that the description applies to. |
713 | |
714 | The list may very well be incomplete, or wrong in some places. When in |
715 | doubt, consult the platform-specific README files in the Perl source |
716 | distribution, and other documentation resources for a given port. |
717 | |
718 | Be aware, moreover, that even among Unix-ish systems there are variations, |
719 | and not all functions listed here are necessarily available, though |
720 | most usually are. |
721 | |
722 | For many functions, you can also query C<%Config>, exported by default |
723 | from C<Config.pm>. For example, to check if the platform has the C<lstat> |
724 | call, check C<$Config{'d_lstat'}>. See L<Config> for a full description |
725 | of available variables. |
726 | |
727 | |
728 | =head2 Alphabetical Listing of Perl Functions |
729 | |
730 | =over 8 |
731 | |
732 | =item -X FILEHANDLE |
733 | |
734 | =item -X EXPR |
735 | |
736 | =item -X |
737 | |
738 | C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories |
739 | and applications are executable, and there are no uid/gid |
740 | considerations. C<-o> is not supported. (S<Mac OS>) |
741 | |
742 | C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible, |
743 | which may not reflect UIC-based file protections. (VMS) |
744 | |
745 | C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>, |
746 | C<-x>, C<-o>. (S<Mac OS>, Win32, VMS) |
747 | |
748 | C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented. |
749 | (S<Mac OS>) |
750 | |
751 | C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful. |
752 | (Win32, VMS) |
753 | |
754 | C<-d> is true if passed a device spec without an explicit directory. |
755 | (VMS) |
756 | |
757 | C<-T> and C<-B> are implemented, but might misclassify Mac text files |
758 | with foreign characters; this is the case will all platforms, but |
759 | affects S<Mac OS> a lot. (S<Mac OS>) |
760 | |
761 | C<-x> (or C<-X>) determine if a file ends in one of the executable |
762 | suffixes. C<-S> is meaningless. (Win32) |
763 | |
764 | =item binmode FILEHANDLE |
765 | |
766 | Meaningless. (S<Mac OS>) |
767 | |
768 | Reopens file and restores pointer; if function fails, underlying |
769 | filehandle may be closed, or pointer may be in a different position. |
770 | (VMS) |
771 | |
772 | The value returned by C<tell> may be affected after the call, and |
773 | the filehandle may be flushed. (Win32) |
774 | |
775 | =item chmod LIST |
776 | |
777 | Only limited meaning. Disabling/enabling write permission is mapped to |
778 | locking/unlocking the file. (S<Mac OS>) |
779 | |
780 | Only good for changing "owner" read-write access, "group", and "other" |
781 | bits are meaningless. (Win32) |
782 | |
783 | =item chown LIST |
784 | |
785 | Not implemented. (S<Mac OS>, Win32, Plan9) |
786 | |
787 | Does nothing, but won't fail. (Win32) |
788 | |
789 | =item chroot FILENAME |
790 | |
791 | =item chroot |
792 | |
793 | Not implemented. (S<Mac OS>, Win32, VMS, Plan9) |
794 | |
795 | =item crypt PLAINTEXT,SALT |
796 | |
797 | May not be available if library or source was not provided when building |
798 | perl. (Win32) |
799 | |
800 | =item dbmclose HASH |
801 | |
802 | Not implemented. (VMS, Plan9) |
803 | |
804 | =item dbmopen HASH,DBNAME,MODE |
805 | |
806 | Not implemented. (VMS, Plan9) |
807 | |
808 | =item dump LABEL |
809 | |
810 | Not useful. (S<Mac OS>) |
811 | |
812 | Not implemented. (Win32) |
813 | |
814 | Invokes VMS debugger. (VMS) |
815 | |
816 | =item exec LIST |
817 | |
818 | Not implemented. (S<Mac OS>) |
819 | |
820 | =item fcntl FILEHANDLE,FUNCTION,SCALAR |
821 | |
822 | Not implemented. (Win32, VMS) |
823 | |
824 | =item flock FILEHANDLE,OPERATION |
825 | |
826 | Not implemented (S<Mac OS>, VMS). |
827 | |
828 | Available only on Windows NT (not on Windows 95). (Win32) |
829 | |
830 | =item fork |
831 | |
832 | Not implemented. (S<Mac OS>, Win32, AmigaOS) |
833 | |
834 | =item getlogin |
835 | |
836 | Not implemented. (S<Mac OS>) |
837 | |
838 | =item getpgrp PID |
839 | |
840 | Not implemented. (S<Mac OS>, Win32, VMS) |
841 | |
842 | =item getppid |
843 | |
844 | Not implemented. (S<Mac OS>, Win32, VMS) |
845 | |
846 | =item getpriority WHICH,WHO |
847 | |
848 | Not implemented. (S<Mac OS>, Win32, VMS) |
849 | |
850 | =item getpwnam NAME |
851 | |
852 | Not implemented. (S<Mac OS>, Win32) |
853 | |
854 | =item getgrnam NAME |
855 | |
856 | Not implemented. (S<Mac OS>, Win32, VMS) |
857 | |
858 | =item getnetbyname NAME |
859 | |
860 | Not implemented. (S<Mac OS>, Win32, Plan9) |
861 | |
862 | =item getpwuid UID |
863 | |
864 | Not implemented. (S<Mac OS>, Win32) |
865 | |
866 | =item getgrgid GID |
867 | |
868 | Not implemented. (S<Mac OS>, Win32, VMS) |
869 | |
870 | =item getnetbyaddr ADDR,ADDRTYPE |
871 | |
872 | Not implemented. (S<Mac OS>, Win32, Plan9) |
873 | |
874 | =item getprotobynumber NUMBER |
875 | |
876 | Not implemented. (S<Mac OS>) |
877 | |
878 | =item getservbyport PORT,PROTO |
879 | |
880 | Not implemented. (S<Mac OS>) |
881 | |
882 | =item getpwent |
883 | |
884 | Not implemented. (S<Mac OS>, Win32) |
885 | |
886 | =item getgrent |
887 | |
888 | Not implemented. (S<Mac OS>, Win32, VMS) |
889 | |
890 | =item gethostent |
891 | |
892 | Not implemented. (S<Mac OS>, Win32) |
893 | |
894 | =item getnetent |
895 | |
896 | Not implemented. (S<Mac OS>, Win32, Plan9) |
897 | |
898 | =item getprotoent |
899 | |
900 | Not implemented. (S<Mac OS>, Win32, Plan9) |
901 | |
902 | =item getservent |
903 | |
904 | Not implemented. (Win32, Plan9) |
905 | |
906 | =item setpwent |
907 | |
908 | Not implemented. (S<Mac OS>, Win32) |
909 | |
910 | =item setgrent |
911 | |
912 | Not implemented. (S<Mac OS>, Win32, VMS) |
913 | |
914 | =item sethostent STAYOPEN |
915 | |
916 | Not implemented. (S<Mac OS>, Win32, Plan9) |
917 | |
918 | =item setnetent STAYOPEN |
919 | |
920 | Not implemented. (S<Mac OS>, Win32, Plan9) |
921 | |
922 | =item setprotoent STAYOPEN |
923 | |
924 | Not implemented. (S<Mac OS>, Win32, Plan9) |
925 | |
926 | =item setservent STAYOPEN |
927 | |
928 | Not implemented. (Plan9, Win32) |
929 | |
930 | =item endpwent |
931 | |
932 | Not implemented. (S<Mac OS>, Win32) |
933 | |
934 | =item endgrent |
935 | |
936 | Not implemented. (S<Mac OS>, Win32, VMS) |
937 | |
938 | =item endhostent |
939 | |
940 | Not implemented. (S<Mac OS>, Win32) |
941 | |
942 | =item endnetent |
943 | |
944 | Not implemented. (S<Mac OS>, Win32, Plan9) |
945 | |
946 | =item endprotoent |
947 | |
948 | Not implemented. (S<Mac OS>, Win32, Plan9) |
949 | |
950 | =item endservent |
951 | |
952 | Not implemented. (Plan9, Win32) |
953 | |
954 | =item getsockopt SOCKET,LEVEL,OPTNAME |
955 | |
956 | Not implemented. (S<Mac OS>, Plan9) |
957 | |
958 | =item glob EXPR |
959 | |
960 | =item glob |
961 | |
962 | Globbing built-in, but only C<*> and C<?> metacharacters are supported. |
963 | (S<Mac OS>) |
964 | |
965 | Features depend on external perlglob.exe or perlglob.bat. May be overridden |
966 | with something like File::DosGlob, which is recommended. (Win32) |
967 | |
968 | =item ioctl FILEHANDLE,FUNCTION,SCALAR |
969 | |
970 | Not implemented. (VMS) |
971 | |
972 | Available only for socket handles, and it does what the ioctlsocket() call |
973 | in the Winsock API does. (Win32) |
974 | |
975 | =item kill LIST |
976 | |
977 | Not implemented. (S<Mac OS>) |
978 | |
979 | Available only for process handles returned by the C<system(1, ...)> method of |
980 | spawning a process. (Win32) |
981 | |
982 | =item link OLDFILE,NEWFILE |
983 | |
984 | Not implemented. (S<Mac OS>, Win32, VMS) |
985 | |
986 | =item lstat FILEHANDLE |
987 | |
988 | =item lstat EXPR |
989 | |
990 | =item lstat |
991 | |
992 | Not implemented. (VMS) |
993 | |
994 | Return values may be bogus. (Win32) |
995 | |
996 | =item msgctl ID,CMD,ARG |
997 | |
998 | =item msgget KEY,FLAGS |
999 | |
1000 | =item msgsnd ID,MSG,FLAGS |
1001 | |
1002 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS |
1003 | |
1004 | Not implemented. (S<Mac OS>, Win32, VMS, Plan9) |
1005 | |
1006 | =item open FILEHANDLE,EXPR |
1007 | |
1008 | =item open FILEHANDLE |
1009 | |
1010 | The C<|> variants are only supported if ToolServer is installed. |
1011 | (S<Mac OS>) |
1012 | |
1013 | open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32) |
1014 | |
1015 | =item pipe READHANDLE,WRITEHANDLE |
1016 | |
1017 | Not implemented. (S<Mac OS>) |
1018 | |
1019 | =item readlink EXPR |
1020 | |
1021 | =item readlink |
1022 | |
1023 | Not implemented. (Win32, VMS) |
1024 | |
1025 | =item select RBITS,WBITS,EBITS,TIMEOUT |
1026 | |
1027 | Only implemented on sockets. (Win32) |
1028 | |
1029 | =item semctl ID,SEMNUM,CMD,ARG |
1030 | |
1031 | =item semget KEY,NSEMS,FLAGS |
1032 | |
1033 | =item semop KEY,OPSTRING |
1034 | |
1035 | Not implemented. (S<Mac OS>, Win32, VMS) |
1036 | |
1037 | =item setpgrp PID,PGRP |
1038 | |
1039 | Not implemented. (S<Mac OS>, Win32, VMS) |
1040 | |
1041 | =item setpriority WHICH,WHO,PRIORITY |
1042 | |
1043 | Not implemented. (S<Mac OS>, Win32, VMS) |
1044 | |
1045 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL |
1046 | |
1047 | Not implemented. (S<Mac OS>, Plan9) |
1048 | |
1049 | =item shmctl ID,CMD,ARG |
1050 | |
1051 | =item shmget KEY,SIZE,FLAGS |
1052 | |
1053 | =item shmread ID,VAR,POS,SIZE |
1054 | |
1055 | =item shmwrite ID,STRING,POS,SIZE |
1056 | |
1057 | Not implemented. (S<Mac OS>, Win32, VMS) |
1058 | |
1059 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL |
1060 | |
1061 | Not implemented. (S<Mac OS>, Win32, VMS) |
1062 | |
1063 | =item stat FILEHANDLE |
1064 | |
1065 | =item stat EXPR |
1066 | |
1067 | =item stat |
1068 | |
1069 | mtime and atime are the same thing, and ctime is creation time instead of |
1070 | inode change time. (S<Mac OS>) |
1071 | |
1072 | device and inode are not meaningful. (Win32) |
1073 | |
1074 | device and inode are not necessarily reliable. (VMS) |
1075 | |
1076 | =item symlink OLDFILE,NEWFILE |
1077 | |
1078 | Not implemented. (Win32, VMS) |
1079 | |
1080 | =item syscall LIST |
1081 | |
1082 | Not implemented. (S<Mac OS>, Win32, VMS) |
1083 | |
1084 | =item system LIST |
1085 | |
1086 | Only implemented if ToolServer is installed. (S<Mac OS>) |
1087 | |
1088 | As an optimization, may not call the command shell specified in |
1089 | C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external |
1090 | process and immediately returns its process designator, without |
1091 | waiting for it to terminate. Return value may be used subsequently |
1092 | in C<wait> or C<waitpid>. (Win32) |
1093 | |
1094 | =item times |
1095 | |
1096 | Only the first entry returned is nonzero. (S<Mac OS>) |
1097 | |
1098 | "cumulative" times will be bogus. On anything other than Windows NT, |
1099 | "system" time will be bogus, and "user" time is actually the time |
1100 | returned by the clock() function in the C runtime library. (Win32) |
1101 | |
1102 | =item truncate FILEHANDLE,LENGTH |
1103 | |
1104 | =item truncate EXPR,LENGTH |
1105 | |
1106 | Not implemented. (VMS) |
1107 | |
1108 | =item umask EXPR |
1109 | |
1110 | =item umask |
1111 | |
1112 | Returns undef where unavailable, as of version 5.005. |
1113 | |
1114 | =item utime LIST |
1115 | |
1116 | Only the modification time is updated. (S<Mac OS>, VMS) |
1117 | |
1118 | May not behave as expected. (Win32) |
1119 | |
1120 | =item wait |
1121 | |
1122 | =item waitpid PID,FLAGS |
1123 | |
1124 | Not implemented. (S<Mac OS>) |
1125 | |
1126 | Can only be applied to process handles returned for processes spawned |
1127 | using C<system(1, ...)>. (Win32) |
1128 | |
1129 | =back |
1130 | |
1131 | |
1132 | =head1 AUTHORS / CONTRIBUTORS |
1133 | |
1134 | Chris Nandor E<lt>pudge@pobox.comE<gt>, |
1135 | Gurusamy Sarathy E<lt>gsar@umich.eduE<gt>, |
1136 | Peter Prymmer E<lt>pvhp@forte.comE<gt>, |
1137 | Tom Christiansen E<lt>tchrist@perl.comE<gt>, |
1138 | Nathan Torkington E<lt>gnat@frii.comE<gt>, |
1139 | Paul Moore E<lt>Paul.Moore@uk.origin-it.comE<gt>, |
1140 | Matthias Neercher E<lt>neeri@iis.ee.ethz.chE<gt>, |
1141 | Charles Bailey E<lt>bailey@genetics.upenn.eduE<gt>, |
1142 | Luther Huffman E<lt>lutherh@stratcom.comE<gt>, |
1143 | Gary Ng E<lt>71564.1743@CompuServe.COME<gt>, |
1144 | Nick Ing-Simmons E<lt>nick@ni-s.u-net.comE<gt>, |
1145 | Paul J. Schinder E<lt>schinder@pobox.comE<gt>, |
1146 | Tom Phoenix E<lt>rootbeer@teleport.comE<gt>, |
1147 | Hugo van der Sanden E<lt>h.sanden@elsevier.nlE<gt>, |
1148 | Dominic Dunlop E<lt>domo@vo.luE<gt>, |
1149 | Dan Sugalski E<lt>sugalskd@ous.eduE<gt>, |
1150 | Andreas J. Koenig E<lt>koenig@kulturbox.deE<gt>, |
1151 | Andrew M. Langmead E<lt>aml@world.std.comE<gt>, |
1152 | Andy Dougherty E<lt>doughera@lafcol.lafayette.eduE<gt>, |
1153 | Abigail E<lt>abigail@fnx.comE<gt>. |
1154 | |
1155 | This document is maintained by Chris Nandor. |
1156 | |
1157 | =head1 VERSION |
1158 | |
1159 | Version 1.23, last modified 10 July 1998. |
1160 | |