Add fallback to tmpfile for use in cases where user's relying on
[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
f675dbe5 20hesitate to drop a line to vmsperl@newman.upenn.edu.
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.
124For this reason, you shouldn't nest the source directory
125too deeply in your directory structure, lest you eccedd RMS'
126maximum of 8 levels of subdirectory in a filespec. (You
127can use rooted logical names to get another 8 levels of
128nesting, if you can't place the files near the top of
129the physical directory structure.)
e518068a 130
131VMS support for this process in the current release of Perl
132is sufficient to handle most extensions. However, it does
133not yet recognize extra libraries required to build shareable
134images which are part of an extension, so these must be added
135to the linker options file for the extension by hand. For
136instance, if the F<PGPLOT> extension to Perl requires the
137F<PGPLOTSHR.EXE> shareable image in order to properly link
138the Perl extension, then the line C<PGPLOTSHR/Share> must
139be added to the linker options file F<PGPLOT.Opt> produced
140during the build process for the Perl extension.
141
142By default, the shareable image for an extension is placed
bbce6d69 143F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
e518068a 144installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
bbce6d69 145F<VMS_AXP>, and I<Extname> is the name of the extension, with
146each C<::> translated to C<.>). (See the MakeMaker documentation
147for more details on installation options for extensions.)
4e592037 148However, it can be manually placed in any of several locations:
bbce6d69 149 - the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
150 of one of the directories in C<@INC> (where I<PVers>
151 is the version of Perl you're using, as supplied in C<$]>,
152 with '.' converted to '_'), or
748a9306 153 - one of the directories in C<@INC>, or
154 - a directory which the extensions Perl library module
155 passes to the DynaLoader when asking it to map
156 the shareable image, or
157 - F<Sys$Share> or F<Sys$Library>.
158If the shareable image isn't in any of these places, you'll need
159to define a logical name I<Extshortname>, where I<Extshortname>
160is the portion of the extension's name after the last C<::>, which
161translates to the full file specification of the shareable image.
162
4e592037 163=head1 File specifications
748a9306 164
4e592037 165=head2 Syntax
a0d0e21e 166
748a9306 167We have tried to make Perl aware of both VMS-style and Unix-
a0d0e21e 168style file specifications wherever possible. You may use
169either style, or both, on the command line and in scripts,
170but you may not combine the two styles within a single fle
1c9f8daa 171specification. VMS Perl interprets Unix pathnames in much
172the same way as the CRTL (I<e.g.> the first component of
173an absolute path is read as the device name for the
174VMS file specification). There are a set of functions
175provided in the C<VMS::Filespec> package for explicit
176interconversion between VMS and Unix syntax; its
177documentation provides more details.
178
179Filenames are, of course, still case-insensitive. For
180consistency, most Perl routines return filespecs using
181lower case letters only, regardless of the case used in
182the arguments passed to them. (This is true only when
183running under VMS; Perl respects the case-sensitivity
184of OSs like Unix.)
a0d0e21e 185
748a9306 186We've tried to minimize the dependence of Perl library
a0d0e21e 187modules on Unix syntax, but you may find that some of these,
188as well as some scripts written for Unix systems, will
189require that you use Unix syntax, since they will assume that
4e592037 190'/' is the directory separator, I<etc.> If you find instances
748a9306 191of this in the Perl distribution itself, please let us know,
a0d0e21e 192so we can try to work around them.
193
4e592037 194=head2 Wildcard expansion
195
196File specifications containing wildcards are allowed both on
aa779de1 197the command line and within Perl globs (e.g. <CE<lt>*.cE<gt>>). If
4e592037 198the wildcard filespec uses VMS syntax, the resultant
199filespecs will follow VMS syntax; if a Unix-style filespec is
200passed in, Unix-style filespecs will be returned.
201
aa779de1 202In both cases, VMS wildcard expansion is performed. (csh-style
203wildcard expansion is available if you use C<File::Glob::glob>.)
4e592037 204If the wildcard filespec contains a device or directory
205specification, then the resultant filespecs will also contain
206a device and directory; otherwise, device and directory
207information are removed. VMS-style resultant filespecs will
208contain a full device and directory, while Unix-style
209resultant filespecs will contain only as much of a directory
210path as was present in the input filespec. For example, if
211your default directory is Perl_Root:[000000], the expansion
212of C<[.t]*.*> will yield filespecs like
213"perl_root:[t]base.dir", while the expansion of C<t/*/*> will
214yield filespecs like "t/base.dir". (This is done to match
215the behavior of glob expansion performed by Unix shells.)
216
217Similarly, the resultant filespec will contain the file version
218only if one was present in the input filespec.
219
220=head2 Pipes
221
222Input and output pipes to Perl filehandles are supported; the
223"file name" is passed to lib$spawn() for asynchronous
224execution. You should be careful to close any pipes you have
225opened in a Perl script, lest you leave any "orphaned"
226subprocesses around when Perl exits.
227
228You may also use backticks to invoke a DCL subprocess, whose
229output is used as the return value of the expression. The
aa779de1 230string between the backticks is handled as if it were the
231argument to the C<system> operator (see below). In this case,
232Perl will wait for the subprocess to complete before continuing.
4e592037 233
234=head1 PERL5LIB and PERLLIB
235
236The PERL5LIB and PERLLIB logical names work as documented L<perl>,
237except that the element separator is '|' instead of ':'. The
238directory specifications may use either VMS or Unix syntax.
239
240=head1 Command line
241
242=head2 I/O redirection and backgrounding
a0d0e21e 243
244Perl for VMS supports redirection of input and output on the
245command line, using a subset of Bourne shell syntax:
55497cff 246
a0d0e21e 247 <F<file> reads stdin from F<file>,
248 >F<file> writes stdout to F<file>,
249 >>F<file> appends stdout to F<file>,
748a9306 250 2>F<file> writes stderr to F<file>, and
a0d0e21e 251 2>>F<file> appends stderr to F<file>.
252
253In addition, output may be piped to a subprocess, using the
254character '|'. Anything after this character on the command
255line is passed to a subprocess for execution; the subprocess
748a9306 256takes the output of Perl as its input.
a0d0e21e 257
258Finally, if the command line ends with '&', the entire
259command is run in the background as an asynchronous
260subprocess.
261
4e592037 262=head2 Command line switches
a0d0e21e 263
4e592037 264The following command line switches behave differently under
265VMS than described in L<perlrun>. Note also that in order
266to pass uppercase switches to Perl, you need to enclose
267them in double-quotes on the command line, since the CRTL
268downcases all unquoted strings.
a0d0e21e 269
55497cff 270=over 4
271
edc7bc49 272=item -i
273
274If the C<-i> switch is present but no extension for a backup
275copy is given, then inplace editing creates a new version of
276a file; the existing copy is not deleted. (Note that if
277an extension is given, an existing file is renamed to the backup
278file, as is the case under other operating systems, so it does
279not remain as a previous version under the original filename.)
280
4e592037 281=item -S
a0d0e21e 282
4e592037 283If the C<-S> switch is present I<and> the script name does
284not contain a directory, then Perl translates the logical
285name DCL$PATH as a searchlist, using each translation as
286a directory in which to look for the script. In addition,
287if no file type is specified, Perl looks in each directory
288for a file matching the name specified, with a blank type,
289a type of F<.pl>, and a type of F<.com>, in that order.
a0d0e21e 290
4e592037 291=item -u
748a9306 292
4e592037 293The C<-u> switch causes the VMS debugger to be invoked
294after the Perl program is compiled, but before it has
295run. It does not create a core dump file.
748a9306 296
55497cff 297=back
298
748a9306 299=head1 Perl functions
a0d0e21e 300
301As of the time this document was last revised, the following
748a9306 302Perl functions were implemented in the VMS port of Perl
a0d0e21e 303(functions marked with * are discussed in more detail below):
304
4fdae800 305 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
a0d0e21e 306 caller, chdir, chmod, chown, chomp, chop, chr,
c07a80fd 307 close, closedir, cos, crypt*, defined, delete,
4e592037 308 die, do, dump*, each, endpwent, eof, eval, exec*,
309 exists, exit, exp, fileno, fork*, getc, getlogin,
310 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
311 grep, hex, import, index, int, join, keys, kill*,
312 last, lc, lcfirst, length, local, localtime, log, m//,
313 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
c07a80fd 314 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
4fdae800 315 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
a0d0e21e 316 require, reset, return, reverse, rewinddir, rindex,
e518068a 317 rmdir, s///, scalar, seek, seekdir, select(internal),
318 select (system call)*, setpwent, shift, sin, sleep,
319 sort, splice, split, sprintf, sqrt, srand, stat,
320 study, substr, sysread, system*, syswrite, tell,
321 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
322 undef, unlink*, unpack, untie, unshift, use, utime*,
323 values, vec, wait, waitpid*, wantarray, warn, write, y///
a0d0e21e 324
325The following functions were not implemented in the VMS port,
326and calling them produces a fatal error (usually) or
327undefined behavior (rarely, we hope):
328
4e592037 329 chroot, dbmclose, dbmopen, fcntl, flock,
c07a80fd 330 getpgrp, getppid, getpriority, getgrent, getgrgid,
331 getgrnam, setgrent, endgrent, ioctl, link, lstat,
332 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
333 semget, semop, setpgrp, setpriority, shmctl, shmget,
bf99883d 334 shmread, shmwrite, socketpair, symlink, syscall
335
336The following functions are available on Perls compiled with Dec C 5.2 or
337greater and running VMS 7.0 or greater
338
339 truncate
a0d0e21e 340
341The following functions may or may not be implemented,
342depending on what type of socket support you've built into
748a9306 343your copy of Perl:
4e592037 344
a0d0e21e 345 accept, bind, connect, getpeername,
346 gethostbyname, getnetbyname, getprotobyname,
347 getservbyname, gethostbyaddr, getnetbyaddr,
348 getprotobynumber, getservbyport, gethostent,
349 getnetent, getprotoent, getservent, sethostent,
350 setnetent, setprotoent, setservent, endhostent,
351 endnetent, endprotoent, endservent, getsockname,
c07a80fd 352 getsockopt, listen, recv, select(system call)*,
353 send, setsockopt, shutdown, socket
a0d0e21e 354
55497cff 355=over 4
a0d0e21e 356
357=item File tests
358
748a9306 359The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
360C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
361advertised. The return values for C<-r>, C<-w>, and C<-x>
362tell you whether you can actually access the file; this may
363not reflect the UIC-based file protections. Since real and
364effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
365and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
366Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
367C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
368VMS, and the values returned by these tests reflect whatever
369your CRTL C<stat()> routine does to the equivalent bits in the
370st_mode field. Finally, C<-d> returns true if passed a device
371specification without an explicit directory (e.g. C<DUA1:>), as
372well as if passed a directory.
373
4e592037 374Note: Some sites have reported problems when using the file-access
375tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
376Specifically, since DFS does not currently provide access to the
377extended file header of files on remote volumes, attempts to
378examine the ACL fail, and the file tests will return false,
379with C<$!> indicating that the file does not exist. You can
380use C<stat> on these files, since that checks UIC-based protection
381only, and then manually check the appropriate bits, as defined by
382your C compiler's F<stat.h>, in the mode value it returns, if you
383need an approximation of the file's protections.
384
4fdae800 385=item backticks
386
387Backticks create a subprocess, and pass the enclosed string
388to it for execution as a DCL command. Since the subprocess is
389created directly via C<lib$spawn()>, any valid DCL command string
390may be specified.
391
748a9306 392=item binmode FILEHANDLE
393
1c9f8daa 394The C<binmode> operator will attempt to insure that no translation
395of carriage control occurs on input from or output to this filehandle.
396Since this involves reopening the file and then restoring its
397file position indicator, if this function returns FALSE, the
398underlying filehandle may no longer point to an open file, or may
399point to a different position in the file than before C<binmode>
400was called.
401
402Note that C<binmode> is generally not necessary when using normal
403filehandles; it is provided so that you can control I/O to existing
404record-structured files when necessary. You can also use the
405C<vmsfopen> function in the VMS::Stdio extension to gain finer
406control of I/O to files and devices with different record structures.
a0d0e21e 407
c07a80fd 408=item crypt PLAINTEXT, USER
409
410The C<crypt> operator uses the C<sys$hash_password> system
411service to generate the hashed representation of PLAINTEXT.
412If USER is a valid username, the algorithm and salt values
413are taken from that user's UAF record. If it is not, then
414the preferred algorithm and a salt of 0 are used. The
415quadword encrypted value is returned as an 8-character string.
416
417The value returned by C<crypt> may be compared against
418the encrypted password from the UAF returned by the C<getpw*>
419functions, in order to authenticate users. If you're
420going to do this, remember that the encrypted password in
421the UAF was generated using uppercase username and
422password strings; you'll have to upcase the arguments to
423C<crypt> to insure that you'll get the proper value:
424
425 sub validate_passwd {
426 my($user,$passwd) = @_;
427 my($pwdhash);
428 if ( !($pwdhash = (getpwnam($user))[1]) ||
429 $pwdhash ne crypt("\U$passwd","\U$name") ) {
430 intruder_alert($name);
431 }
432 return 1;
433 }
434
4e592037 435=item dump
436
437Rather than causing Perl to abort and dump core, the C<dump>
438operator invokes the VMS debugger. If you continue to
439execute the Perl program under the debugger, control will
440be transferred to the label specified as the argument to
441C<dump>, or, if no label was specified, back to the
442beginning of the program. All other state of the program
443(I<e.g.> values of variables, open file handles) are not
444affected by calling C<dump>.
445
748a9306 446=item exec LIST
a0d0e21e 447
748a9306 448The C<exec> operator behaves in one of two different ways.
449If called after a call to C<fork>, it will invoke the CRTL
450C<execv()> routine, passing its arguments to the subprocess
451created by C<fork> for execution. In this case, it is
452subject to all limitations that affect C<execv()>. (In
a0d0e21e 453particular, this usually means that the command executed in
454the subprocess must be an image compiled from C source code,
455and that your options for passing file descriptors and signal
456handlers to the subprocess are limited.)
457
748a9306 458If the call to C<exec> does not follow a call to C<fork>, it
459will cause Perl to exit, and to invoke the command given as
460an argument to C<exec> via C<lib$do_command>. If the argument
aa779de1 461begins with '@' or '$' (other than as part of a filespec), then it
a0d0e21e 462is executed as a DCL command. Otherwise, the first token on
463the command line is treated as the filespec of an image to
464run, and an attempt is made to invoke it (using F<.Exe> and
465the process defaults to expand the filespec) and pass the
8012a33e 466rest of C<exec>'s argument to it as parameters. If the token
467has no file type, and matches a file with null type, then an
468attempt is made to determine whether the file is an executable
469image which should be invoked using C<MCR> or a text file which
470should be passed to DCL as a command procedure.
a0d0e21e 471
748a9306 472You can use C<exec> in both ways within the same script, as
473long as you call C<fork> and C<exec> in pairs. Perl
474keeps track of how many times C<fork> and C<exec> have been
475called, and will call the CRTL C<execv()> routine if there have
476previously been more calls to C<fork> than to C<exec>.
a0d0e21e 477
478=item fork
479
748a9306 480The C<fork> operator works in the same way as the CRTL
481C<vfork()> routine, which is quite different under VMS than
482under Unix. Specifically, while C<fork> returns 0 after it
483is called and the subprocess PID after C<exec> is called, in
a0d0e21e 484both cases the thread of execution is within the parent
485process, so there is no opportunity to perform operations in
748a9306 486the subprocess before calling C<exec>.
a0d0e21e 487
748a9306 488In general, the use of C<fork> and C<exec> to create
a0d0e21e 489subprocess is not recommended under VMS; wherever possible,
748a9306 490use the C<system> operator or piped filehandles instead.
491
492=item getpwent
c07a80fd 493
748a9306 494=item getpwnam
c07a80fd 495
748a9306 496=item getpwuid
497
498These operators obtain the information described in L<perlfunc>,
499if you have the privileges necessary to retrieve the named user's
500UAF information via C<sys$getuai>. If not, then only the C<$name>,
501C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
502the login directory in VMS syntax, while the C<$comment> item
503contains the login directory in Unix syntax. The C<$gcos> item
504contains the owner field from the UAF record. The C<$quota>
505item is not used.
a0d0e21e 506
e518068a 507=item gmtime
508
509The C<gmtime> operator will function properly if you have a
510working CRTL C<gmtime()> routine, or if the logical name
511SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
512which must be added to UTC to yield local time. (This logical
513name is defined automatically if you are running a version of
514VMS with built-in UTC support.) If neither of these cases is
515true, a warning message is printed, and C<undef> is returned.
516
517=item kill
518
519In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
520function, so it will behave according to that function's
521documentation. If you send a SIGKILL, however, the $DELPRC system
10a676f8 522service is called directly. This insures that the target
e518068a 523process is actually deleted, if at all possible. (The CRTL's C<kill()>
524function is presently implemented via $FORCEX, which is ignored by
525supervisor-mode images like DCL.)
526
527Also, negative signal values don't do anything special under
528VMS; they're just converted to the corresponding positive value.
529
4fdae800 530=item qx//
531
532See the entry on C<backticks> above.
533
e518068a 534=item select (system call)
535
536If Perl was not built with socket support, the system call
537version of C<select> is not available at all. If socket
538support is present, then the system call version of
539C<select> functions only for file descriptors attached
540to sockets. It will not provide information about regular
541files or pipes, since the CRTL C<select()> routine does not
542provide this functionality.
543
748a9306 544=item stat EXPR
a0d0e21e 545
748a9306 546Since VMS keeps track of files according to a different scheme
547than Unix, it's not really possible to represent the file's ID
548in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
549tries its best, though, and the values it uses are pretty unlikely
550to be the same for two different files. We can't guarantee this,
551though, so caveat scriptor.
552
553=item system LIST
554
555The C<system> operator creates a subprocess, and passes its
a0d0e21e 556arguments to the subprocess for execution as a DCL command.
e518068a 557Since the subprocess is created directly via C<lib$spawn()>, any
aa779de1 558valid DCL command string may be specified. If the string begins with
559'@', it is treated as a DCL command unconditionally. Otherwise, if
560the first token contains a character used as a delimiter in file
561specification (e.g. C<:> or C<]>), an attempt is made to expand it
562using a default type of F<.Exe> and the process defaults, and if
563successful, the resulting file is invoked via C<MCR>. This allows you
564to invoke an image directly simply by passing the file specification
8012a33e 565to C<system>, a common Unixish idiom. If the token has no file type,
566and matches a file with null type, then an attempt is made to
567determine whether the file is an executable image which should be
568invoked using C<MCR> or a text file which should be passed to DCL
569as a command procedure.
570
571If LIST consists of the empty string, C<system> spawns an
ee8c7f54 572interactive DCL subprocess, in the same fashion as typing
8012a33e 573B<SPAWN> at the DCL prompt.
574
748a9306 575Perl waits for the subprocess to complete before continuing
4fdae800 576execution in the current process. As described in L<perlfunc>,
577the return value of C<system> is a fake "status" which follows
578POSIX semantics; see the description of C<$?> in this document
579for more detail. The actual VMS exit status of the subprocess
580is available in C<$^S> (as long as you haven't used another Perl
581function that resets C<$?> and C<$^S> in the meantime).
a0d0e21e 582
1c9f8daa 583=item time
584
585The value returned by C<time> is the offset in seconds from
58601-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
587to make life easier for code coming in from the POSIX/Unix world.
588
a0d0e21e 589=item times
590
748a9306 591The array returned by the C<times> operator is divided up
592according to the same rules the CRTL C<times()> routine.
a0d0e21e 593Therefore, the "system time" elements will always be 0, since
594there is no difference between "user time" and "system" time
595under VMS, and the time accumulated by subprocess may or may
596not appear separately in the "child time" field, depending on
748a9306 597whether L<times> keeps track of subprocesses separately. Note
598especially that the VAXCRTL (at least) keeps track only of
599subprocesses spawned using L<fork> and L<exec>; it will not
ee8c7f54 600accumulate the times of subprocesses spawned via pipes, L<system>,
748a9306 601or backticks.
602
16d20bd9 603=item unlink LIST
604
605C<unlink> will delete the highest version of a file only; in
606order to delete all versions, you need to say
607 1 while (unlink LIST);
608You may need to make this change to scripts written for a
609Unix system which expect that after a call to C<unlink>,
610no files with the names passed to C<unlink> will exist.
4633a7c4 611(Note: This can be changed at compile time; if you
612C<use Config> and C<$Config{'d_unlink_all_versions'}> is
613C<define>, then C<unlink> will delete all versions of a
614file on the first call.)
16d20bd9 615
616C<unlink> will delete a file if at all possible, even if it
617requires changing file protection (though it won't try to
618change the protection of the parent directory). You can tell
619whether you've got explicit delete access to a file by using the
620C<VMS::Filespec::candelete> operator. For instance, in order
621to delete only files to which you have delete access, you could
622say something like
4e592037 623
16d20bd9 624 sub safe_unlink {
625 my($file,$num);
626 foreach $file (@_) {
627 next unless VMS::Filespec::candelete($file);
628 $num += unlink $file;
629 }
630 $num;
631 }
4e592037 632
633(or you could just use C<VMS::Stdio::remove>, if you've installed
634the VMS::Stdio extension distributed with Perl). If C<unlink> has to
635change the file protection to delete the file, and you interrupt it
636in midstream, the file may be left intact, but with a changed ACL
637allowing you delete access.
16d20bd9 638
748a9306 639=item utime LIST
640
641Since ODS-2, the VMS file structure for disk files, does not keep
642track of access times, this operator changes only the modification
643time of the file (VMS revision date).
644
645=item waitpid PID,FLAGS
646
647If PID is a subprocess started by a piped L<open>, C<waitpid>
648will wait for that subprocess, and return its final
649status value. If PID is a subprocess created in some other way
650(e.g. SPAWNed before Perl was invoked), or is not a subprocess of
651the current process, C<waitpid> will check once per second whether
652the process has completed, and when it has, will return 0. (If PID
653specifies a process that isn't a subprocess of the current process,
654and you invoked Perl with the C<-w> switch, a warning will be issued.)
655
656The FLAGS argument is ignored in all cases.
a0d0e21e 657
55497cff 658=back
659
a5f75d66 660=head1 Perl variables
661
55497cff 662The following VMS-specific information applies to the indicated
663"special" Perl variables, in addition to the general information
ee8c7f54 664in L<perlvar>. Where there is a conflict, this information
55497cff 665takes precedence.
666
667=over 4
668
a5f75d66 669=item %ENV
670
f675dbe5 671The operation of the C<%ENV> array depends on the translation
672of the logical name F<PERL_ENV_TABLES>. If defined, it should
673be a search list, each element of which specifies a location
674for C<%ENV> elements. If you tell Perl to read or set the
675element C<$ENV{>I<name>C<}>, then Perl uses the translations of
676F<PERL_ENV_TABLES> as follows:
677
678=over 4
679
680=item CRTL_ENV
681
682This string tells Perl to consult the CRTL's internal C<environ>
683array of key-value pairs, using I<name> as the key. In most cases,
684this contains only a few keys, but if Perl was invoked via the C
685C<exec[lv]e()> function, as is the case for CGI processing by some
686HTTP servers, then the C<environ> array may have been populated by
687the calling program.
688
689=item CLISYM_[LOCAL]
690
691A string beginning with C<CLISYM_>tells Perl to consult the CLI's
692symbol tables, using I<name> as the name of the symbol. When reading
693an element of C<%ENV>, the local symbol table is scanned first, followed
694by the global symbol table.. The characters following C<CLISYM_> are
695significant when an element of C<%ENV> is set or deleted: if the
696complete string is C<CLISYM_LOCAL>, the change is made in the local
697symbol table, otherwise the global symbol table is changed.
698
699=item Any other string
700
701If an element of F<PERL_ENV_TABLES> translates to any other string,
702that string is used as the name of a logical name table, which is
703consulted using I<name> as the logical name. The normal search
704order of access modes is used.
705
706=back
707
708F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
709you make while Perl is running do not affect the behavior of C<%ENV>.
710If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
711first the logical name tables specified by F<LNM$FILE_DEV>, and then
712the CRTL C<environ> array.
713
714In all operations on %ENV, the key string is treated as if it
715were entirely uppercase, regardless of the case actually
716specified in the Perl expression.
717
718When an element of C<%ENV> is read, the locations to which
719F<PERL_ENV_TABLES> points are checked in order, and the value
720obtained from the first successful lookup is returned. If the
721name of the C<%ENV> element contains a semi-colon, it and
722any characters after it are removed. These are ignored when
723the CRTL C<environ> array or a CLI symbol table is consulted.
724However, the name is looked up in a logical name table, the
725suffix after the semi-colon is treated as the translation index
726to be used for the lookup. This lets you look up successive values
727for search list logical names. For instance, if you say
a5f75d66 728
729 $ Define STORY once,upon,a,time,there,was
730 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
740ce14c 731 _$ -e "{ print $ENV{'story;'.$i},' '}"
a5f75d66 732
f675dbe5 733Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
734that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
735is found, rather than a CLI symbol or CRTL C<environ> element with
736the same name.
737
3eeba6fb 738When an element of C<%ENV> is set to a defined string, the
f675dbe5 739corresponding definition is made in the location to which the
740first translation of F<PERL_ENV_TABLES> points. If this causes a
741logical name to be created, it is defined in supervisor mode.
3eeba6fb 742(The same is done if an existing logical name was defined in
743executive or kernel mode; an existing user or supervisor mode
744logical name is reset to the new value.) If the value is an empty
745string, the logical name's translation is defined as a single NUL
746(ASCII 00) character, since a logical name cannot translate to a
747zero-length string. (This restriction does not apply to CLI symbols
748or CRTL C<environ> values; they are set to the empty string.)
f675dbe5 749An element of the CRTL C<environ> array can be set only if your
750copy of Perl knows about the CRTL's C<setenv()> function. (This is
751present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
752to see whether your copy of Perl was built with a CRTL that has this
753function.)
754
3eeba6fb 755When an element of C<%ENV> is set to C<undef>,
f675dbe5 756the element is looked up as if it were being read, and if it is
757found, it is deleted. (An item "deleted" from the CRTL C<environ>
758array is set to the empty string; this can only be done if your
759copy of Perl knows about the CRTL C<setenv()> function.) Using
760C<delete> to remove an element from C<%ENV> has a similar effect,
761but after the element is deleted, another attempt is made to
762look up the element, so an inner-mode logical name or a name in
763another location will replace the logical name just deleted.
3eeba6fb 764In either case, only the first value found searching PERL_ENV_TABLES
765is altered. It is not possible at present to define a search list
766logical name via %ENV.
f675dbe5 767
768The element C<$ENV{DEFAULT}> is special: when read, it returns
769Perl's current default device and directory, and when set, it
770resets them, regardless of the definition of F<PERL_ENV_TABLES>.
771It cannot be cleared or deleted; attempts to do so are silently
772ignored.
b7b1864f 773
774Note that if you want to pass on any elements of the
775C-local environ array to a subprocess which isn't
776started by fork/exec, or isn't running a C program, you
777can "promote" them to logical names in the current
778process, which will then be inherited by all subprocesses,
779by saying
780
781 foreach my $key (qw[C-local keys you want promoted]) {
782 my $temp = $ENV{$key}; # read from C-local array
783 $ENV{$key} = $temp; # and define as logical name
784 }
785
786(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
787Perl optimizer is smart enough to elide the expression.)
a5f75d66 788
740ce14c 789At present, the first time you iterate over %ENV using
edc7bc49 790C<keys>, or C<values>, you will incur a time penalty as all
791logical names are read, in order to fully populate %ENV.
792Subsequent iterations will not reread logical names, so they
793won't be as slow, but they also won't reflect any changes
f675dbe5 794to logical name tables caused by other programs.
795
796You do need to be careful with the logicals representing process-permanent
797files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
798logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
799stripped off if you want to use it. (In previous versions of perl it wasn't
800possible to get the values of these logicals, as the null byte acted as an
801end-of-string marker)
a5f75d66 802
a5f75d66 803=item $!
804
805The string value of C<$!> is that returned by the CRTL's
806strerror() function, so it will include the VMS message for
807VMS-specific errors. The numeric value of C<$!> is the
808value of C<errno>, except if errno is EVMSERR, in which
809case C<$!> contains the value of vaxc$errno. Setting C<$!>
4e592037 810always sets errno to the value specified. If this value is
811EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
812that the string value of C<$!> won't reflect the VMS error
813message from before C<$!> was set.
814
815=item $^E
816
817This variable provides direct access to VMS status values
818in vaxc$errno, which are often more specific than the
819generic Unix-style error messages in C<$!>. Its numeric value
820is the value of vaxc$errno, and its string value is the
821corresponding VMS message string, as retrieved by sys$getmsg().
822Setting C<$^E> sets vaxc$errno to the value specified.
823
4fdae800 824=item $?
825
826The "status value" returned in C<$?> is synthesized from the
827actual exit status of the subprocess in a way that approximates
828POSIX wait(5) semantics, in order to allow Perl programs to
829portably test for successful completion of subprocesses. The
830low order 8 bits of C<$?> are always 0 under VMS, since the
831termination status of a process may or may not have been
832generated by an exception. The next 8 bits are derived from
833severity portion of the subprocess' exit status: if the
834severity was success or informational, these bits are all 0;
835otherwise, they contain the severity value shifted left one bit.
836As a result, C<$?> will always be zero if the subprocess' exit
837status indicated successful completion, and non-zero if a
838warning or error occurred. The actual VMS exit status may
839be found in C<$^S> (q.v.).
840
841=item $^S
842
843Under VMS, this is the 32-bit VMS status value returned by the
844last subprocess to complete. Unlink C<$?>, no manipulation
845is done to make this look like a POSIX wait(5) value, so it
846may be treated as a normal VMS status value.
847
4e592037 848=item $|
849
850Setting C<$|> for an I/O stream causes data to be flushed
851all the way to disk on each write (I<i.e.> not just to
852the underlying RMS buffers for a file). In other words,
853it's equivalent to calling fflush() and fsync() from C.
a5f75d66 854
55497cff 855=back
856
bf99883d 857=head1 Standard modules with VMS-specific differences
858
859=head2 SDBM_File
860
ee8c7f54 861SDBM_File works properly on VMS. It has, however, one minor
862difference. The database directory file created has a F<.sdbm_dir>
863extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
bf99883d 864directory files, and using them for other purposes could cause unacceptable
865problems.
866
748a9306 867=head1 Revision date
a0d0e21e 868
aa779de1 869This document was last updated on 26-Feb-2000, for Perl 5,
870patchlevel 6.
e518068a 871
872=head1 AUTHOR
873
aa779de1 874Charles Bailey <bailey@cor.newman.upenn.edu>
875Dan Sugalski <dan@sidhe.org>