patch@32028 POD updates for VMS
[p5sagit/p5-mst-13.2.git] / vms / perlvms.pod
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e518068a 1=head1 NAME
2
3perlvms - VMS-specific documentation for Perl
4
5=head1 DESCRIPTION
a0d0e21e 6
748a9306 7Gathered below are notes describing details of Perl 5's
8behavior on VMS. They are a supplement to the regular Perl 5
9documentation, so we have focussed on the ways in which Perl
105 functions differently under VMS than it does under Unix,
11and on the interactions between Perl and the rest of the
a0d0e21e 12operating system. We haven't tried to duplicate complete
748a9306 13descriptions of Perl features from the main Perl
a0d0e21e 14documentation, which can be found in the F<[.pod]>
748a9306 15subdirectory of the Perl distribution.
a0d0e21e 16
17We hope these notes will save you from confusion and lost
748a9306 18sleep when writing Perl scripts on VMS. If you find we've
a0d0e21e 19missed something you think should appear here, please don't
9bc98430 20hesitate to drop a line to vmsperl@perl.org.
a0d0e21e 21
4e592037 22=head1 Installation
23
24Directions for building and installing Perl 5 can be found in
25the file F<README.vms> in the main source directory of the
26Perl distribution..
27
e518068a 28=head1 Organization of Perl Images
748a9306 29
e518068a 30=head2 Core Images
748a9306 31
32During the installation process, three Perl images are produced.
33F<Miniperl.Exe> is an executable image which contains all of
34the basic functionality of Perl, but cannot take advantage of
35Perl extensions. It is used to generate several files needed
36to build the complete Perl and various extensions. Once you've
37finished installing Perl, you can delete this image.
38
39Most of the complete Perl resides in the shareable image
40F<PerlShr.Exe>, which provides a core to which the Perl executable
41image and all Perl extensions are linked. You should place this
42image in F<Sys$Share>, or define the logical name F<PerlShr> to
43translate to the full file specification of this image. It should
44be world readable. (Remember that if a user has execute only access
45to F<PerlShr>, VMS will treat it as if it were a privileged shareable
46image, and will therefore require all downstream shareable images to be
47INSTALLed, etc.)
48
49
50Finally, F<Perl.Exe> is an executable image containing the main
51entry point for Perl, as well as some initialization code. It
52should be placed in a public directory, and made world executable.
53In order to run Perl with command line arguments, you should
54define a foreign command to invoke this image.
55
56=head2 Perl Extensions
57
58Perl extensions are packages which provide both XS and Perl code
59to add new functionality to perl. (XS is a meta-language which
60simplifies writing C code which interacts with Perl, see
2ceaccd7 61L<perlxs> for more details.) The Perl code for an
748a9306 62extension is treated like any other library module - it's
63made available in your script through the appropriate
64C<use> or C<require> statement, and usually defines a Perl
65package containing the extension.
66
67The portion of the extension provided by the XS code may be
68connected to the rest of Perl in either of two ways. In the
69B<static> configuration, the object code for the extension is
70linked directly into F<PerlShr.Exe>, and is initialized whenever
71Perl is invoked. In the B<dynamic> configuration, the extension's
72machine code is placed into a separate shareable image, which is
73mapped by Perl's DynaLoader when the extension is C<use>d or
74C<require>d in your script. This allows you to maintain the
75extension as a separate entity, at the cost of keeping track of the
76additional shareable image. Most extensions can be set up as either
77static or dynamic.
78
79The source code for an extension usually resides in its own
80directory. At least three files are generally provided:
81I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
82the extension's name following the last C<::>), containing
83the XS code, I<Extshortname>F<.pm>, the Perl library module
84for the extension, and F<Makefile.PL>, a Perl script which uses
85the C<MakeMaker> library modules supplied with Perl to generate
86a F<Descrip.MMS> file for the extension.
87
e518068a 88=head2 Installing static extensions
748a9306 89
90Since static extensions are incorporated directly into
91F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
92new extension. You should edit the main F<Descrip.MMS> or F<Makefile>
93you use to build Perl, adding the extension's name to the C<ext>
94macro, and the extension's object file to the C<extobj> macro.
95You'll also need to build the extension's object file, either
96by adding dependencies to the main F<Descrip.MMS>, or using a
97separate F<Descrip.MMS> for the extension. Then, rebuild
98F<PerlShr.Exe> to incorporate the new code.
99
100Finally, you'll need to copy the extension's Perl library
101module to the F<[.>I<Extname>F<]> subdirectory under one
102of the directories in C<@INC>, where I<Extname> is the name
103of the extension, with all C<::> replaced by C<.> (e.g.
104the library module for extension Foo::Bar would be copied
105to a F<[.Foo.Bar]> subdirectory).
106
e518068a 107=head2 Installing dynamic extensions
108
109In general, the distributed kit for a Perl extension includes
110a file named Makefile.PL, which is a Perl program which is used
111to create a F<Descrip.MMS> file which can be used to build and
112install the files required by the extension. The kit should be
c07a80fd 113unpacked into a directory tree B<not> under the main Perl source
e518068a 114directory, and the procedure for building the extension is simply
115
e518068a 116 $ perl Makefile.PL ! Create Descrip.MMS
117 $ mmk ! Build necessary files
118 $ mmk test ! Run test code, if supplied
119 $ mmk install ! Install into public Perl tree
120
c07a80fd 121I<N.B.> The procedure by which extensions are built and
122tested creates several levels (at least 4) under the
123directory in which the extension's source files live.
d7f8936a 124For this reason if you are running a version of VMS prior
773da73d 125to V7.1 you shouldn't nest the source directory
126too deeply in your directory structure lest you exceed RMS'
c07a80fd 127maximum of 8 levels of subdirectory in a filespec. (You
128can use rooted logical names to get another 8 levels of
129nesting, if you can't place the files near the top of
130the physical directory structure.)
e518068a 131
132VMS support for this process in the current release of Perl
133is sufficient to handle most extensions. However, it does
134not yet recognize extra libraries required to build shareable
135images which are part of an extension, so these must be added
136to the linker options file for the extension by hand. For
137instance, if the F<PGPLOT> extension to Perl requires the
138F<PGPLOTSHR.EXE> shareable image in order to properly link
139the Perl extension, then the line C<PGPLOTSHR/Share> must
140be added to the linker options file F<PGPLOT.Opt> produced
141during the build process for the Perl extension.
142
773da73d 143By default, the shareable image for an extension is placed in
144the F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
e518068a 145installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
bbce6d69 146F<VMS_AXP>, and I<Extname> is the name of the extension, with
147each C<::> translated to C<.>). (See the MakeMaker documentation
148for more details on installation options for extensions.)
4e592037 149However, it can be manually placed in any of several locations:
773da73d 150
151=over 4
152
153=item *
154
155the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
156of one of the directories in C<@INC> (where I<PVers>
157is the version of Perl you're using, as supplied in C<$]>,
158with '.' converted to '_'), or
159
160=item *
161
162one of the directories in C<@INC>, or
163
164=item *
165
166a directory which the extensions Perl library module
167passes to the DynaLoader when asking it to map
168the shareable image, or
169
170=item *
171
172F<Sys$Share> or F<Sys$Library>.
173
174=back
175
748a9306 176If the shareable image isn't in any of these places, you'll need
177to define a logical name I<Extshortname>, where I<Extshortname>
178is the portion of the extension's name after the last C<::>, which
179translates to the full file specification of the shareable image.
180
4e592037 181=head1 File specifications
748a9306 182
4e592037 183=head2 Syntax
a0d0e21e 184
748a9306 185We have tried to make Perl aware of both VMS-style and Unix-
a0d0e21e 186style file specifications wherever possible. You may use
187either style, or both, on the command line and in scripts,
39aca757 188but you may not combine the two styles within a single file
1c9f8daa 189specification. VMS Perl interprets Unix pathnames in much
190the same way as the CRTL (I<e.g.> the first component of
191an absolute path is read as the device name for the
192VMS file specification). There are a set of functions
193provided in the C<VMS::Filespec> package for explicit
194interconversion between VMS and Unix syntax; its
195documentation provides more details.
196
9296fdfa 197Perl is now in the process of evolving to follow the setting of
fb38d079 198the DECC$* feature logical names in the interpretation of UNIX pathnames.
9296fdfa 199This is still a work in progress.
200
201For handling extended characters, and case sensitivity, as long as
202DECC$POSIX_COMPLIANT_PATHNAMES, DECC$FILENAME_UNIX_REPORT, and
203DECC$FILENAME_UNIX_ONLY are not set, then the older Perl behavior
204for conversions of file specifications from UNIX to VMS is followed,
fb38d079 205except that VMS paths with concealed rooted logical names are now
9296fdfa 206translated correctly to UNIX paths.
207
208With those features set, then new routines may handle the translation,
209because some of the rules are different. The presence of ./.../
210in a UNIX path is no longer translated to the VMS [...]. It will
211translate to [.^.^.^.]. To be compatible with what MakeMaker expects,
212if a VMS path can not be translated to a UNIX path when unixify
213is called, it is passed through unchanged. So unixify("[...]") will
214return "[...]".
215
216The handling of extended characters will also be better with the
217newer translation routines. But more work is needed to fully support
218extended file syntax names. In particular, at this writing Pathtools
219can not deal with directories containing some extended characters.
220
221There are several ambiguous cases where a conversion routine can not
222determine if an input filename is in UNIX format or in VMS format,
223since now both VMS UNIX file specifications can have characters in
224them that could be mistaken for syntax delimiters of the other type.
225So some pathnames simply can not be used in a mode that allows either
226type of pathname to be present.
227
228Perl will tend to assume that an ambiguous filename is in UNIX format.
229
230Allowing "." as a version delimiter is simply incompatible with
231determining if a pathname is already VMS format or UNIX with the
232extended file syntax. There is no way to know if "perl-5.8.6" that
233TAR produces is a UNIX "perl-5.8.6" or a VMS "perl-5.8;6" when
234passing it to unixify() or vmsify().
235
236The DECC$FILENAME_UNIX_REPORT or the DECC$FILENAME_UNIX_ONLY logical
237names control how Perl interprets filenames.
238
239The DECC$FILENAME_UNIX_ONLY setting has not been tested at this time.
240Perl uses traditional OpenVMS file specifications internally and in
241the test harness, so this mode may have limited use, or require more
242changes to make usable.
243
244Everything about DECC$FILENAME_UNIX_REPORT should be assumed to apply
245to DECC$FILENAME_UNIX_ONLY mode. The DECC$FILENAME_UNIX_ONLY differs
246in that it expects all filenames passed to the C runtime to be already
247in UNIX format.
248
249Again, currently most of the core Perl modules have not yet been updated
250to understand that VMS is not as limited as it use to be. Fixing that
251is a work in progress.
252
253The logical name DECC$POSIX_COMPLIANT_PATHNAMES is new with the
254RMS Symbolic Link SDK. This version of Perl does not support it being set.
255
256
257Filenames are case-insensitive on VAX, and on ODS-2 formatted
258volumes on ALPHA and I64.
259
260On ODS-5 volumes filenames are case preserved and on newer
261versions of OpenVMS can be optionally case sensitive.
262
263On ALPHA and I64, Perl is in the process of being changed to follow the
264process case sensitivity setting to report if the file system is case
265sensitive.
266
267Perl programs should not assume that VMS is case blind, or that
268filenames will be in lowercase.
269
270Programs should use the File::Spec:case_tolerant setting to determine
271the state, and not the $^O setting.
272
273For consistency, when the above feature is clear and when not
fb38d079 274otherwise overridden by DECC feature logical names, most Perl routines
9296fdfa 275return file specifications using lower case letters only,
276regardless of the case used in the arguments passed to them.
277(This is true only when running under VMS; Perl respects the
278case-sensitivity of OSs like Unix.)
a0d0e21e 279
748a9306 280We've tried to minimize the dependence of Perl library
a0d0e21e 281modules on Unix syntax, but you may find that some of these,
282as well as some scripts written for Unix systems, will
283require that you use Unix syntax, since they will assume that
4e592037 284'/' is the directory separator, I<etc.> If you find instances
748a9306 285of this in the Perl distribution itself, please let us know,
a0d0e21e 286so we can try to work around them.
287
9296fdfa 288Also when working on Perl programs on VMS, if you need a syntax
289in a specific operating system format, then you need to either
290check the appropriate DECC$ feature logical, or call a conversion
291routine to force it to that format.
292
4e592037 293=head2 Wildcard expansion
294
295File specifications containing wildcards are allowed both on
07698885 296the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). If
4e592037 297the wildcard filespec uses VMS syntax, the resultant
298filespecs will follow VMS syntax; if a Unix-style filespec is
299passed in, Unix-style filespecs will be returned.
773da73d 300Similar to the behavior of wildcard globbing for a Unix shell,
301one can escape command line wildcards with double quotation
302marks C<"> around a perl program command line argument. However,
303owing to the stripping of C<"> characters carried out by the C
304handling of argv you will need to escape a construct such as
305this one (in a directory containing the files F<PERL.C>, F<PERL.EXE>,
306F<PERL.H>, and F<PERL.OBJ>):
307
308 $ perl -e "print join(' ',@ARGV)" perl.*
309 perl.c perl.exe perl.h perl.obj
310
311in the following triple quoted manner:
312
313 $ perl -e "print join(' ',@ARGV)" """perl.*"""
314 perl.*
4e592037 315
773da73d 316In both the case of unquoted command line arguments or in calls
317to C<glob()> VMS wildcard expansion is performed. (csh-style
aa779de1 318wildcard expansion is available if you use C<File::Glob::glob>.)
4e592037 319If the wildcard filespec contains a device or directory
320specification, then the resultant filespecs will also contain
321a device and directory; otherwise, device and directory
322information are removed. VMS-style resultant filespecs will
323contain a full device and directory, while Unix-style
324resultant filespecs will contain only as much of a directory
325path as was present in the input filespec. For example, if
326your default directory is Perl_Root:[000000], the expansion
327of C<[.t]*.*> will yield filespecs like
328"perl_root:[t]base.dir", while the expansion of C<t/*/*> will
329yield filespecs like "t/base.dir". (This is done to match
330the behavior of glob expansion performed by Unix shells.)
331
332Similarly, the resultant filespec will contain the file version
333only if one was present in the input filespec.
334
9296fdfa 335
4e592037 336=head2 Pipes
337
338Input and output pipes to Perl filehandles are supported; the
339"file name" is passed to lib$spawn() for asynchronous
340execution. You should be careful to close any pipes you have
341opened in a Perl script, lest you leave any "orphaned"
342subprocesses around when Perl exits.
343
344You may also use backticks to invoke a DCL subprocess, whose
345output is used as the return value of the expression. The
aa779de1 346string between the backticks is handled as if it were the
347argument to the C<system> operator (see below). In this case,
348Perl will wait for the subprocess to complete before continuing.
4e592037 349
376ae1f1 350The mailbox (MBX) that perl can create to communicate with a pipe
351defaults to a buffer size of 512. The default buffer size is
1506e54c 352adjustable via the logical name PERL_MBX_SIZE provided that the
376ae1f1 353value falls between 128 and the SYSGEN parameter MAXBUF inclusive.
354For example, to double the MBX size from the default within
1506e54c 355a Perl program, use C<$ENV{'PERL_MBX_SIZE'} = 1024;> and then
376ae1f1 356open and use pipe constructs. An alternative would be to issue
357the command:
358
359 $ Define PERL_MBX_SIZE 1024
360
361before running your wide record pipe program. A larger value may
362improve performance at the expense of the BYTLM UAF quota.
363
4e592037 364=head1 PERL5LIB and PERLLIB
365
39aca757 366The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
4e592037 367except that the element separator is '|' instead of ':'. The
368directory specifications may use either VMS or Unix syntax.
369
17d4810c 370=head1 The Perl Forked Debugger
371
372The Perl forked debugger places the debugger commands and output in a
373separate X-11 terminal window so that commands and output from multiple
374processes are not mixed together.
375
376Perl on VMS supports an emulation of the forked debugger when Perl is
377run on a VMS system that has X11 support installed.
378
379To use the forked debugger, you need to have the default display set to an
380X-11 Server and some environment variables set that Unix expects.
381
382The forked debugger requires the environment variable C<TERM> to be C<xterm>,
383and the environment variable C<DISPLAY> to exist. C<xterm> must be in
384lower case.
385
386 $define TERM "xterm"
387
388 $define DISPLAY "hostname:0.0"
389
390Currently the value of C<DISPLAY> is ignored. It is recommended that it be set
391to be the hostname of the display, the server and screen in UNIX notation. In
392the future the value of DISPLAY may be honored by Perl instead of using the
393default display.
394
395It may be helpful to always use the forked debugger so that script I/O is
396separated from debugger I/O. You can force the debugger to be forked by
397assigning a value to the logical name <PERLDB_PIDS> that is not a process
398identification number.
399
400 $define PERLDB_PIDS XXXX
401
402
9c1171d1 403=head1 PERL_VMS_EXCEPTION_DEBUG
404
405The PERL_VMS_EXCEPTION_DEBUG being defined as "ENABLE" will cause the VMS
406debugger to be invoked if a fatal exception that is not otherwise
407handled is raised. The purpose of this is to allow debugging of
408internal Perl problems that would cause such a condition.
409
410This allows the programmer to look at the execution stack and variables to
411find out the cause of the exception. As the debugger is being invoked as
412the Perl interpreter is about to do a fatal exit, continuing the execution
413in debug mode is usally not practical.
414
415Starting Perl in the VMS debugger may change the program execution
416profile in a way that such problems are not reproduced.
417
418The C<kill> function can be used to test this functionality from within
419a program.
420
421In typical VMS style, only the first letter of the value of this logical
422name is actually checked in a case insensitive mode, and it is considered
423enabled if it is the value "T","1" or "E".
424
425This logical name must be defined before Perl is started.
426
4e592037 427=head1 Command line
428
429=head2 I/O redirection and backgrounding
a0d0e21e 430
431Perl for VMS supports redirection of input and output on the
432command line, using a subset of Bourne shell syntax:
55497cff 433
773da73d 434=over 4
07698885 435
436=item *
437
438C<E<lt>file> reads stdin from C<file>,
439
440=item *
441
442C<E<gt>file> writes stdout to C<file>,
443
444=item *
445
446C<E<gt>E<gt>file> appends stdout to C<file>,
447
448=item *
449
2fde0ff0 450C<2E<gt>file> writes stderr to C<file>,
07698885 451
452=item *
453
2fde0ff0 454C<2E<gt>E<gt>file> appends stderr to C<file>, and
455
456=item *
457
458C<< 2>&1 >> redirects stderr to stdout.
07698885 459
460=back
a0d0e21e 461
462In addition, output may be piped to a subprocess, using the
463character '|'. Anything after this character on the command
464line is passed to a subprocess for execution; the subprocess
748a9306 465takes the output of Perl as its input.
a0d0e21e 466
467Finally, if the command line ends with '&', the entire
468command is run in the background as an asynchronous
469subprocess.
470
4e592037 471=head2 Command line switches
a0d0e21e 472
4e592037 473The following command line switches behave differently under
474VMS than described in L<perlrun>. Note also that in order
475to pass uppercase switches to Perl, you need to enclose
476them in double-quotes on the command line, since the CRTL
477downcases all unquoted strings.
a0d0e21e 478
9296fdfa 479On newer 64 bit versions of OpenVMS, a process setting now
480controls if the quoting is needed to preserve the case of
481command line arguments.
482
55497cff 483=over 4
484
edc7bc49 485=item -i
486
487If the C<-i> switch is present but no extension for a backup
488copy is given, then inplace editing creates a new version of
489a file; the existing copy is not deleted. (Note that if
490an extension is given, an existing file is renamed to the backup
491file, as is the case under other operating systems, so it does
492not remain as a previous version under the original filename.)
493
4e592037 494=item -S
a0d0e21e 495
376ae1f1 496If the C<"-S"> or C<-"S"> switch is present I<and> the script
497name does not contain a directory, then Perl translates the
498logical name DCL$PATH as a searchlist, using each translation
499as a directory in which to look for the script. In addition,
4e592037 500if no file type is specified, Perl looks in each directory
501for a file matching the name specified, with a blank type,
502a type of F<.pl>, and a type of F<.com>, in that order.
a0d0e21e 503
4e592037 504=item -u
748a9306 505
4e592037 506The C<-u> switch causes the VMS debugger to be invoked
507after the Perl program is compiled, but before it has
508run. It does not create a core dump file.
748a9306 509
55497cff 510=back
511
748a9306 512=head1 Perl functions
a0d0e21e 513
514As of the time this document was last revised, the following
748a9306 515Perl functions were implemented in the VMS port of Perl
a0d0e21e 516(functions marked with * are discussed in more detail below):
517
4fdae800 518 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
a0d0e21e 519 caller, chdir, chmod, chown, chomp, chop, chr,
c07a80fd 520 close, closedir, cos, crypt*, defined, delete,
4e592037 521 die, do, dump*, each, endpwent, eof, eval, exec*,
41cbbefa 522 exists, exit, exp, fileno, getc, getlogin, getppid,
4e592037 523 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
524 grep, hex, import, index, int, join, keys, kill*,
525 last, lc, lcfirst, length, local, localtime, log, m//,
526 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
c07a80fd 527 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
4fdae800 528 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
a0d0e21e 529 require, reset, return, reverse, rewinddir, rindex,
e518068a 530 rmdir, s///, scalar, seek, seekdir, select(internal),
531 select (system call)*, setpwent, shift, sin, sleep,
532 sort, splice, split, sprintf, sqrt, srand, stat,
533 study, substr, sysread, system*, syswrite, tell,
534 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
535 undef, unlink*, unpack, untie, unshift, use, utime*,
536 values, vec, wait, waitpid*, wantarray, warn, write, y///
a0d0e21e 537
538The following functions were not implemented in the VMS port,
539and calling them produces a fatal error (usually) or
540undefined behavior (rarely, we hope):
541
41cbbefa 542 chroot, dbmclose, dbmopen, flock, fork*,
543 getpgrp, getpriority, getgrent, getgrgid,
c07a80fd 544 getgrnam, setgrent, endgrent, ioctl, link, lstat,
545 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
546 semget, semop, setpgrp, setpriority, shmctl, shmget,
bf99883d 547 shmread, shmwrite, socketpair, symlink, syscall
548
35b2760a 549The following functions are available on Perls compiled with Dec C
5505.2 or greater and running VMS 7.0 or greater:
bf99883d 551
552 truncate
a0d0e21e 553
35b2760a 554The following functions are available on Perls built on VMS 7.2 or
555greater:
556
557 fcntl (without locking)
558
a0d0e21e 559The following functions may or may not be implemented,
560depending on what type of socket support you've built into
748a9306 561your copy of Perl:
4e592037 562
a0d0e21e 563 accept, bind, connect, getpeername,
564 gethostbyname, getnetbyname, getprotobyname,
565 getservbyname, gethostbyaddr, getnetbyaddr,
566 getprotobynumber, getservbyport, gethostent,
567 getnetent, getprotoent, getservent, sethostent,
568 setnetent, setprotoent, setservent, endhostent,
569 endnetent, endprotoent, endservent, getsockname,
c07a80fd 570 getsockopt, listen, recv, select(system call)*,
571 send, setsockopt, shutdown, socket
a0d0e21e 572
9296fdfa 573The following function is available on Perls built on 64 bit OpenVMS 8.2
574with hard links enabled on an ODS-5 formatted build disk. If someone with
575an OpenVMS 7.3-1 system were to modify configure.com and test the results,
576this feature can be brought back to OpenVMS 7.3-1 and later. Hardlinks
577must be enabled on the build disk because if the build procedure sees
578this feature enabled, it uses it.
579
580 link
581
582The following functions are available on Perls built on 64 bit OpenVMS
5838.2 and can be implemented on OpenVMS 7.3-2 if someone were to modify
584configure.com and test the results. (While in the build, at the time
585of this writing, they have not been specifically tested.)
586
587 getgrgid, getgrnam, getpwnam, getpwuid,
588 setgrent, ttyname
589
590The following functions are available on Perls built on 64 bit OpenVMS 8.2
591and later. (While in the build, at the time of this writing, they have
592not been specifically tested.)
593
594 statvfs, socketpair
595
596The following functions are expected to soon be available on Perls built
597on 64 bit OpenVMS 8.2 or later with the RMS Symbolic link package. Use
598of symbolic links at this time effectively requires the
599DECC$POSIX_COMPLIANT_PATHNAMES to defined as 3, and operating in a
600DECC$FILENAME_UNIX_REPORT mode.
601
602 lchown, link, lstat, readlink, symlink
52e64fc8 603
55497cff 604=over 4
a0d0e21e 605
606=item File tests
607
748a9306 608The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
609C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
610advertised. The return values for C<-r>, C<-w>, and C<-x>
611tell you whether you can actually access the file; this may
612not reflect the UIC-based file protections. Since real and
613effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
614and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
615Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
616C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
617VMS, and the values returned by these tests reflect whatever
618your CRTL C<stat()> routine does to the equivalent bits in the
619st_mode field. Finally, C<-d> returns true if passed a device
620specification without an explicit directory (e.g. C<DUA1:>), as
621well as if passed a directory.
622
fb38d079 623There are DECC feature logical names AND ODS-5 volume attributes that
9296fdfa 624also control what values are returned for the date fields.
625
4e592037 626Note: Some sites have reported problems when using the file-access
627tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
628Specifically, since DFS does not currently provide access to the
629extended file header of files on remote volumes, attempts to
630examine the ACL fail, and the file tests will return false,
631with C<$!> indicating that the file does not exist. You can
632use C<stat> on these files, since that checks UIC-based protection
633only, and then manually check the appropriate bits, as defined by
634your C compiler's F<stat.h>, in the mode value it returns, if you
635need an approximation of the file's protections.
636
4fdae800 637=item backticks
638
639Backticks create a subprocess, and pass the enclosed string
640to it for execution as a DCL command. Since the subprocess is
641created directly via C<lib$spawn()>, any valid DCL command string
642may be specified.
643
748a9306 644=item binmode FILEHANDLE
645
1c9f8daa 646The C<binmode> operator will attempt to insure that no translation
647of carriage control occurs on input from or output to this filehandle.
648Since this involves reopening the file and then restoring its
649file position indicator, if this function returns FALSE, the
650underlying filehandle may no longer point to an open file, or may
651point to a different position in the file than before C<binmode>
652was called.
653
654Note that C<binmode> is generally not necessary when using normal
655filehandles; it is provided so that you can control I/O to existing
656record-structured files when necessary. You can also use the
657C<vmsfopen> function in the VMS::Stdio extension to gain finer
658control of I/O to files and devices with different record structures.
a0d0e21e 659
c07a80fd 660=item crypt PLAINTEXT, USER
661
662The C<crypt> operator uses the C<sys$hash_password> system
663service to generate the hashed representation of PLAINTEXT.
664If USER is a valid username, the algorithm and salt values
665are taken from that user's UAF record. If it is not, then
666the preferred algorithm and a salt of 0 are used. The
667quadword encrypted value is returned as an 8-character string.
668
669The value returned by C<crypt> may be compared against
670the encrypted password from the UAF returned by the C<getpw*>
671functions, in order to authenticate users. If you're
672going to do this, remember that the encrypted password in
673the UAF was generated using uppercase username and
674password strings; you'll have to upcase the arguments to
675C<crypt> to insure that you'll get the proper value:
676
376ae1f1 677 sub validate_passwd {
678 my($user,$passwd) = @_;
679 my($pwdhash);
680 if ( !($pwdhash = (getpwnam($user))[1]) ||
681 $pwdhash ne crypt("\U$passwd","\U$name") ) {
682 intruder_alert($name);
683 }
684 return 1;
c07a80fd 685 }
c07a80fd 686
6ac6a52b 687
688=item die
689
690C<die> will force the native VMS exit status to be an SS$_ABORT code
691if neither of the $! or $? status values are ones that would cause
692the native status to be interpreted as being what VMS classifies as
693SEVERE_ERROR severity for DCL error handling.
694
52e64fc8 695When the future POSIX_EXIT mode is active, C<die>, the native VMS exit
696status value will have either one of the C<$!> or C<$?> or C<$^E> or
697the UNIX value 255 encoded into it in a way that the effective original
698value can be decoded by other programs written in C, including Perl
699and the GNV package. As per the normal non-VMS behavior of C<die> if
700either C<$!> or C<$?> are non-zero, one of those values will be
701encoded into a native VMS status value. If both of the UNIX status
702values are 0, and the C<$^E> value is set one of ERROR or SEVERE_ERROR
703severity, then the C<$^E> value will be used as the exit code as is.
704If none of the above apply, the UNIX value of 255 will be encoded into
705a native VMS exit status value.
706
707Please note a significant difference in the behavior of C<die> in
708the future POSIX_EXIT mode is that it does not force a VMS
709SEVERE_ERROR status on exit. The UNIX exit values of 2 through
710255 will be encoded in VMS status values with severity levels of
711SUCCESS. The UNIX exit value of 1 will be encoded in a VMS status
712value with a severity level of ERROR. This is to be compatible with
713how the VMS C library encodes these values.
714
715The minimum severity level set by C<die> in a future POSIX_EXIT mode
716may be changed to be ERROR or higher before that mode becomes fully active
717depending on the results of testing and further review. If this is
718done, the behavior of c<DIE> in the future POSIX_EXIT will close enough
719to the default mode that most DCL shell scripts will probably not notice
720a difference.
721
722See C<$?> for a description of the encoding of the UNIX value to
723produce a native VMS status containing it.
724
6ac6a52b 725
4e592037 726=item dump
727
728Rather than causing Perl to abort and dump core, the C<dump>
729operator invokes the VMS debugger. If you continue to
730execute the Perl program under the debugger, control will
731be transferred to the label specified as the argument to
732C<dump>, or, if no label was specified, back to the
733beginning of the program. All other state of the program
734(I<e.g.> values of variables, open file handles) are not
735affected by calling C<dump>.
736
748a9306 737=item exec LIST
a0d0e21e 738
41cbbefa 739A call to C<exec> will cause Perl to exit, and to invoke the command
740given as an argument to C<exec> via C<lib$do_command>. If the
741argument begins with '@' or '$' (other than as part of a filespec),
742then it is executed as a DCL command. Otherwise, the first token on
743the command line is treated as the filespec of an image to run, and
744an attempt is made to invoke it (using F<.Exe> and the process
745defaults to expand the filespec) and pass the rest of C<exec>'s
746argument to it as parameters. If the token has no file type, and
747matches a file with null type, then an attempt is made to determine
748whether the file is an executable image which should be invoked
749using C<MCR> or a text file which should be passed to DCL as a
750command procedure.
a0d0e21e 751
752=item fork
753
41cbbefa 754While in principle the C<fork> operator could be implemented via
755(and with the same rather severe limitations as) the CRTL C<vfork()>
756routine, and while some internal support to do just that is in
757place, the implementation has never been completed, making C<fork>
758currently unavailable. A true kernel C<fork()> is expected in a
759future version of VMS, and the pseudo-fork based on interpreter
760threads may be available in a future version of Perl on VMS (see
761L<perlfork>). In the meantime, use C<system>, backticks, or piped
762filehandles to create subprocesses.
748a9306 763
764=item getpwent
c07a80fd 765
748a9306 766=item getpwnam
c07a80fd 767
748a9306 768=item getpwuid
769
770These operators obtain the information described in L<perlfunc>,
771if you have the privileges necessary to retrieve the named user's
772UAF information via C<sys$getuai>. If not, then only the C<$name>,
773C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
774the login directory in VMS syntax, while the C<$comment> item
775contains the login directory in Unix syntax. The C<$gcos> item
776contains the owner field from the UAF record. The C<$quota>
777item is not used.
a0d0e21e 778
e518068a 779=item gmtime
780
781The C<gmtime> operator will function properly if you have a
782working CRTL C<gmtime()> routine, or if the logical name
783SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
784which must be added to UTC to yield local time. (This logical
785name is defined automatically if you are running a version of
786VMS with built-in UTC support.) If neither of these cases is
787true, a warning message is printed, and C<undef> is returned.
788
789=item kill
790
39aca757 791In most cases, C<kill> is implemented via the CRTL's C<kill()>
e518068a 792function, so it will behave according to that function's
793documentation. If you send a SIGKILL, however, the $DELPRC system
10a676f8 794service is called directly. This insures that the target
e518068a 795process is actually deleted, if at all possible. (The CRTL's C<kill()>
796function is presently implemented via $FORCEX, which is ignored by
797supervisor-mode images like DCL.)
798
799Also, negative signal values don't do anything special under
800VMS; they're just converted to the corresponding positive value.
801
4fdae800 802=item qx//
803
804See the entry on C<backticks> above.
805
e518068a 806=item select (system call)
807
808If Perl was not built with socket support, the system call
809version of C<select> is not available at all. If socket
810support is present, then the system call version of
811C<select> functions only for file descriptors attached
812to sockets. It will not provide information about regular
813files or pipes, since the CRTL C<select()> routine does not
814provide this functionality.
815
748a9306 816=item stat EXPR
a0d0e21e 817
748a9306 818Since VMS keeps track of files according to a different scheme
819than Unix, it's not really possible to represent the file's ID
820in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
821tries its best, though, and the values it uses are pretty unlikely
822to be the same for two different files. We can't guarantee this,
823though, so caveat scriptor.
824
825=item system LIST
826
827The C<system> operator creates a subprocess, and passes its
a0d0e21e 828arguments to the subprocess for execution as a DCL command.
e518068a 829Since the subprocess is created directly via C<lib$spawn()>, any
aa779de1 830valid DCL command string may be specified. If the string begins with
831'@', it is treated as a DCL command unconditionally. Otherwise, if
832the first token contains a character used as a delimiter in file
833specification (e.g. C<:> or C<]>), an attempt is made to expand it
834using a default type of F<.Exe> and the process defaults, and if
835successful, the resulting file is invoked via C<MCR>. This allows you
836to invoke an image directly simply by passing the file specification
c93fa817 837to C<system>, a common Unixish idiom. If the token has no file type,
838and matches a file with null type, then an attempt is made to
839determine whether the file is an executable image which should be
840invoked using C<MCR> or a text file which should be passed to DCL
841as a command procedure.
842
843If LIST consists of the empty string, C<system> spawns an
a2293a43 844interactive DCL subprocess, in the same fashion as typing
c93fa817 845B<SPAWN> at the DCL prompt.
846
748a9306 847Perl waits for the subprocess to complete before continuing
4fdae800 848execution in the current process. As described in L<perlfunc>,
849the return value of C<system> is a fake "status" which follows
c6966fea 850POSIX semantics unless the pragma C<use vmsish 'status'> is in
1b0c4952 851effect; see the description of C<$?> in this document for more
852detail.
a0d0e21e 853
1c9f8daa 854=item time
855
856The value returned by C<time> is the offset in seconds from
85701-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
858to make life easier for code coming in from the POSIX/Unix world.
859
a0d0e21e 860=item times
861
748a9306 862The array returned by the C<times> operator is divided up
863according to the same rules the CRTL C<times()> routine.
a0d0e21e 864Therefore, the "system time" elements will always be 0, since
865there is no difference between "user time" and "system" time
39aca757 866under VMS, and the time accumulated by a subprocess may or may
a0d0e21e 867not appear separately in the "child time" field, depending on
748a9306 868whether L<times> keeps track of subprocesses separately. Note
869especially that the VAXCRTL (at least) keeps track only of
870subprocesses spawned using L<fork> and L<exec>; it will not
a2293a43 871accumulate the times of subprocesses spawned via pipes, L<system>,
748a9306 872or backticks.
873
16d20bd9 874=item unlink LIST
875
876C<unlink> will delete the highest version of a file only; in
877order to delete all versions, you need to say
39aca757 878
35b2760a 879 1 while unlink LIST;
39aca757 880
16d20bd9 881You may need to make this change to scripts written for a
882Unix system which expect that after a call to C<unlink>,
883no files with the names passed to C<unlink> will exist.
4633a7c4 884(Note: This can be changed at compile time; if you
885C<use Config> and C<$Config{'d_unlink_all_versions'}> is
886C<define>, then C<unlink> will delete all versions of a
887file on the first call.)
16d20bd9 888
889C<unlink> will delete a file if at all possible, even if it
890requires changing file protection (though it won't try to
891change the protection of the parent directory). You can tell
892whether you've got explicit delete access to a file by using the
893C<VMS::Filespec::candelete> operator. For instance, in order
894to delete only files to which you have delete access, you could
895say something like
4e592037 896
16d20bd9 897 sub safe_unlink {
898 my($file,$num);
899 foreach $file (@_) {
900 next unless VMS::Filespec::candelete($file);
901 $num += unlink $file;
902 }
903 $num;
904 }
4e592037 905
906(or you could just use C<VMS::Stdio::remove>, if you've installed
907the VMS::Stdio extension distributed with Perl). If C<unlink> has to
908change the file protection to delete the file, and you interrupt it
909in midstream, the file may be left intact, but with a changed ACL
910allowing you delete access.
16d20bd9 911
fb38d079 912This behavior of C<unlink> is to be compatible with POSIX behavior
913and not traditional VMS behavior.
914
748a9306 915=item utime LIST
916
941b3de1 917This operator changes only the modification time of the file (VMS
918revision date) on ODS-2 volumes and ODS-5 volumes without access
919dates enabled. On ODS-5 volumes with access dates enabled, the
920true access time is modified.
748a9306 921
922=item waitpid PID,FLAGS
923
39aca757 924If PID is a subprocess started by a piped C<open()> (see L<open>),
376ae1f1 925C<waitpid> will wait for that subprocess, and return its final status
926value in C<$?>. If PID is a subprocess created in some other way (e.g.
927SPAWNed before Perl was invoked), C<waitpid> will simply check once per
928second whether the process has completed, and return when it has. (If
929PID specifies a process that isn't a subprocess of the current process,
930and you invoked Perl with the C<-w> switch, a warning will be issued.)
35b2760a 931
932Returns PID on success, -1 on error. The FLAGS argument is ignored
933in all cases.
a0d0e21e 934
55497cff 935=back
936
a5f75d66 937=head1 Perl variables
938
55497cff 939The following VMS-specific information applies to the indicated
940"special" Perl variables, in addition to the general information
a2293a43 941in L<perlvar>. Where there is a conflict, this information
55497cff 942takes precedence.
943
944=over 4
945
a5f75d66 946=item %ENV
947
f675dbe5 948The operation of the C<%ENV> array depends on the translation
949of the logical name F<PERL_ENV_TABLES>. If defined, it should
950be a search list, each element of which specifies a location
951for C<%ENV> elements. If you tell Perl to read or set the
952element C<$ENV{>I<name>C<}>, then Perl uses the translations of
953F<PERL_ENV_TABLES> as follows:
954
955=over 4
956
957=item CRTL_ENV
958
959This string tells Perl to consult the CRTL's internal C<environ>
960array of key-value pairs, using I<name> as the key. In most cases,
961this contains only a few keys, but if Perl was invoked via the C
962C<exec[lv]e()> function, as is the case for CGI processing by some
963HTTP servers, then the C<environ> array may have been populated by
964the calling program.
965
966=item CLISYM_[LOCAL]
967
968A string beginning with C<CLISYM_>tells Perl to consult the CLI's
969symbol tables, using I<name> as the name of the symbol. When reading
970an element of C<%ENV>, the local symbol table is scanned first, followed
971by the global symbol table.. The characters following C<CLISYM_> are
972significant when an element of C<%ENV> is set or deleted: if the
973complete string is C<CLISYM_LOCAL>, the change is made in the local
39aca757 974symbol table; otherwise the global symbol table is changed.
f675dbe5 975
976=item Any other string
977
978If an element of F<PERL_ENV_TABLES> translates to any other string,
979that string is used as the name of a logical name table, which is
980consulted using I<name> as the logical name. The normal search
981order of access modes is used.
982
983=back
984
985F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
986you make while Perl is running do not affect the behavior of C<%ENV>.
987If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
988first the logical name tables specified by F<LNM$FILE_DEV>, and then
989the CRTL C<environ> array.
990
991In all operations on %ENV, the key string is treated as if it
992were entirely uppercase, regardless of the case actually
993specified in the Perl expression.
994
995When an element of C<%ENV> is read, the locations to which
996F<PERL_ENV_TABLES> points are checked in order, and the value
997obtained from the first successful lookup is returned. If the
998name of the C<%ENV> element contains a semi-colon, it and
999any characters after it are removed. These are ignored when
1000the CRTL C<environ> array or a CLI symbol table is consulted.
1001However, the name is looked up in a logical name table, the
1002suffix after the semi-colon is treated as the translation index
1003to be used for the lookup. This lets you look up successive values
1004for search list logical names. For instance, if you say
a5f75d66 1005
1006 $ Define STORY once,upon,a,time,there,was
1007 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
740ce14c 1008 _$ -e "{ print $ENV{'story;'.$i},' '}"
a5f75d66 1009
f675dbe5 1010Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
1011that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
1012is found, rather than a CLI symbol or CRTL C<environ> element with
1013the same name.
1014
3eeba6fb 1015When an element of C<%ENV> is set to a defined string, the
f675dbe5 1016corresponding definition is made in the location to which the
1017first translation of F<PERL_ENV_TABLES> points. If this causes a
1018logical name to be created, it is defined in supervisor mode.
3eeba6fb 1019(The same is done if an existing logical name was defined in
1020executive or kernel mode; an existing user or supervisor mode
1021logical name is reset to the new value.) If the value is an empty
1022string, the logical name's translation is defined as a single NUL
1023(ASCII 00) character, since a logical name cannot translate to a
1024zero-length string. (This restriction does not apply to CLI symbols
1025or CRTL C<environ> values; they are set to the empty string.)
f675dbe5 1026An element of the CRTL C<environ> array can be set only if your
1027copy of Perl knows about the CRTL's C<setenv()> function. (This is
1028present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
1029to see whether your copy of Perl was built with a CRTL that has this
1030function.)
39aca757 1031
3eeba6fb 1032When an element of C<%ENV> is set to C<undef>,
f675dbe5 1033the element is looked up as if it were being read, and if it is
1034found, it is deleted. (An item "deleted" from the CRTL C<environ>
1035array is set to the empty string; this can only be done if your
1036copy of Perl knows about the CRTL C<setenv()> function.) Using
1037C<delete> to remove an element from C<%ENV> has a similar effect,
1038but after the element is deleted, another attempt is made to
1039look up the element, so an inner-mode logical name or a name in
1040another location will replace the logical name just deleted.
3eeba6fb 1041In either case, only the first value found searching PERL_ENV_TABLES
1042is altered. It is not possible at present to define a search list
1043logical name via %ENV.
f675dbe5 1044
1045The element C<$ENV{DEFAULT}> is special: when read, it returns
1046Perl's current default device and directory, and when set, it
1047resets them, regardless of the definition of F<PERL_ENV_TABLES>.
1048It cannot be cleared or deleted; attempts to do so are silently
1049ignored.
b7b1864f 1050
1051Note that if you want to pass on any elements of the
1052C-local environ array to a subprocess which isn't
1053started by fork/exec, or isn't running a C program, you
1054can "promote" them to logical names in the current
1055process, which will then be inherited by all subprocesses,
1056by saying
1057
1058 foreach my $key (qw[C-local keys you want promoted]) {
376ae1f1 1059 my $temp = $ENV{$key}; # read from C-local array
1060 $ENV{$key} = $temp; # and define as logical name
b7b1864f 1061 }
1062
1063(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
1064Perl optimizer is smart enough to elide the expression.)
a5f75d66 1065
6be8f7a6 1066Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
1067a fatal error. This is equivalent to doing the following from DCL:
1068
1069 DELETE/LOGICAL *
1070
1071You can imagine how bad things would be if, for example, the SYS$MANAGER
fb38d079 1072or SYS$SYSTEM logical names were deleted.
4a0d0822 1073
740ce14c 1074At present, the first time you iterate over %ENV using
edc7bc49 1075C<keys>, or C<values>, you will incur a time penalty as all
1076logical names are read, in order to fully populate %ENV.
1077Subsequent iterations will not reread logical names, so they
1078won't be as slow, but they also won't reflect any changes
f675dbe5 1079to logical name tables caused by other programs.
1080
fb38d079 1081You do need to be careful with the logical names representing
1082process-permanent files, such as C<SYS$INPUT> and C<SYS$OUTPUT>.
1083The translations for these logical names are prepended with a
1084two-byte binary value (0x1B 0x00) that needs to be stripped off
1085if you wantto use it. (In previous versions of Perl it wasn't
1086possible to get the values of these logical names, as the null
1087byte acted as an end-of-string marker)
a5f75d66 1088
a5f75d66 1089=item $!
1090
1091The string value of C<$!> is that returned by the CRTL's
1092strerror() function, so it will include the VMS message for
1093VMS-specific errors. The numeric value of C<$!> is the
1094value of C<errno>, except if errno is EVMSERR, in which
1095case C<$!> contains the value of vaxc$errno. Setting C<$!>
4e592037 1096always sets errno to the value specified. If this value is
1097EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
1098that the string value of C<$!> won't reflect the VMS error
1099message from before C<$!> was set.
1100
1101=item $^E
1102
1103This variable provides direct access to VMS status values
1104in vaxc$errno, which are often more specific than the
1105generic Unix-style error messages in C<$!>. Its numeric value
1106is the value of vaxc$errno, and its string value is the
1107corresponding VMS message string, as retrieved by sys$getmsg().
1108Setting C<$^E> sets vaxc$errno to the value specified.
1109
9296fdfa 1110While Perl attempts to keep the vaxc$errno value to be current, if
1111errno is not EVMSERR, it may not be from the current operation.
1112
4fdae800 1113=item $?
1114
1115The "status value" returned in C<$?> is synthesized from the
1116actual exit status of the subprocess in a way that approximates
1117POSIX wait(5) semantics, in order to allow Perl programs to
1118portably test for successful completion of subprocesses. The
1119low order 8 bits of C<$?> are always 0 under VMS, since the
1120termination status of a process may or may not have been
9296fdfa 1121generated by an exception.
1122
1123The next 8 bits contain the termination status of the program.
1124
1125If the child process follows the convention of C programs
1126compiled with the _POSIX_EXIT macro set, the status value will
1127contain the actual value of 0 to 255 returned by that program
1128on a normal exit.
1129
52e64fc8 1130With the _POSIX_EXIT macro set, the UNIX exit value of zero is
1131represented as a VMS native status of 1, and the UNIX values
1132from 2 to 255 are encoded by the equation:
1133
1134 VMS_status = 0x35a000 + (unix_value * 8) + 1.
1135
1136And in the special case of unix value 1 the encoding is:
1137
1138 VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
9296fdfa 1139
1140For other termination statuses, the severity portion of the
52e64fc8 1141subprocess' exit status is used: if the severity was success or
9296fdfa 1142informational, these bits are all 0; if the severity was
1143warning, they contain a value of 1; if the severity was
1144error or fatal error, they contain the actual severity bits,
52e64fc8 1145which turns out to be a value of 2 for error and 4 for severe_error.
1146Fatal is another term for the severe_error status.
9bc98430 1147
4fdae800 1148As a result, C<$?> will always be zero if the subprocess' exit
1149status indicated successful completion, and non-zero if a
9296fdfa 1150warning or error occurred or a program compliant with encoding
1151_POSIX_EXIT values was run and set a status.
1152
52e64fc8 1153How can you tell the difference between a non-zero status that is
1154the result of a VMS native error status or an encoded UNIX status?
1155You can not unless you look at the ${^CHILD_ERROR_NATIVE} value.
1156The ${^CHILD_ERROR_NATIVE} value returns the actual VMS status value
1157and check the severity bits. If the severity bits are equal to 1,
1158then if the numeric value for C<$?> is between 2 and 255 or 0, then
1159C<$?> accurately reflects a value passed back from a UNIX application.
1160If C<$?> is 1, and the severity bits indicate a VMS error (2), then
1161C<$?> is from a UNIX application exit value.
9296fdfa 1162
1163In practice, Perl scripts that call programs that return _POSIX_EXIT
52e64fc8 1164type status values will be expecting those values, and programs that
1165call traditional VMS programs will either be expecting the previous
1166behavior or just checking for a non-zero status.
9296fdfa 1167
52e64fc8 1168And success is always the value 0 in all behaviors.
9296fdfa 1169
fb38d079 1170When the actual VMS termination status of the child is an error,
52e64fc8 1171internally the C<$!> value will be set to the closest UNIX errno
1172value to that error so that Perl scripts that test for error
1173messages will see the expected UNIX style error message instead
1174of a VMS message.
fb38d079 1175
9296fdfa 1176Conversely, when setting C<$?> in an END block, an attempt is made
1177to convert the POSIX value into a native status intelligible to
1178the operating system upon exiting Perl. What this boils down to
1179is that setting C<$?> to zero results in the generic success value
1180SS$_NORMAL, and setting C<$?> to a non-zero value results in the
1181generic failure status SS$_ABORT. See also L<perlport/exit>.
4fdae800 1182
6ac6a52b 1183With the future POSIX_EXIT mode set, setting C<$?> will cause the
52e64fc8 1184new value to also be encoded into C<$^E> so that the either the
1185original parent or child exit status values of 0 to 255
1186can be automatically recovered by C programs expecting _POSIX_EXIT
1187behavior. If both a parent and a child exit value are non-zero, then it
1188will be assumed that this is actually a VMS native status value to
1189be passed through. The special value of 0xFFFF is almost a NOOP as
1190it will cause the current native VMS status in the C library to
1191become the current native Perl VMS status, and is handled this way
1192as consequence of it known to not be a valid native VMS status value.
1193It is recommend that only values in range of normal UNIX parent or
1194child status numbers, 0 to 255 are used.
6ac6a52b 1195
1b0c4952 1196The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
9bc98430 1197VMS exit status instead of the default emulation of POSIX status
1198described above. This pragma also disables the conversion of
1199non-zero values to SS$_ABORT when setting C<$?> in an END
1200block (but zero will still be converted to SS$_NORMAL).
4fdae800 1201
6ac6a52b 1202Do not use the pragma C<use vmsish 'status'> with the future
52e64fc8 1203POSIX_EXIT mode, as they are at times requesting conflicting
1204actions and the consequence of ignoring this advice will be
1205undefined to allow future improvements in the POSIX exit handling.
6ac6a52b 1206
4e592037 1207=item $|
1208
1209Setting C<$|> for an I/O stream causes data to be flushed
1210all the way to disk on each write (I<i.e.> not just to
1211the underlying RMS buffers for a file). In other words,
1212it's equivalent to calling fflush() and fsync() from C.
a5f75d66 1213
55497cff 1214=back
1215
bf99883d 1216=head1 Standard modules with VMS-specific differences
1217
1218=head2 SDBM_File
1219
270c2ced 1220SDBM_File works properly on VMS. It has, however, one minor
4a4eefd0 1221difference. The database directory file created has a F<.sdbm_dir>
1222extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
bf99883d 1223directory files, and using them for other purposes could cause unacceptable
1224problems.
1225
748a9306 1226=head1 Revision date
a0d0e21e 1227
9296fdfa 1228This document was last updated on 14-Oct-2005, for Perl 5,
9bc98430 1229patchlevel 8.
e518068a 1230
1231=head1 AUTHOR
1232
376ae1f1 1233Charles Bailey bailey@cor.newman.upenn.edu
1234Craig Berry craigberry@mac.com
1235Dan Sugalski dan@sidhe.org
9296fdfa 1236John Malmberg wb8tyw@qsl.net