3 perlvms - VMS-specific documentation for Perl
7 Gathered below are notes describing details of Perl 5's
8 behavior on VMS. They are a supplement to the regular Perl 5
9 documentation, so we have focussed on the ways in which Perl
10 5 functions differently under VMS than it does under Unix,
11 and on the interactions between Perl and the rest of the
12 operating system. We haven't tried to duplicate complete
13 descriptions of Perl features from the main Perl
14 documentation, which can be found in the F<[.pod]>
15 subdirectory of the Perl distribution.
17 We hope these notes will save you from confusion and lost
18 sleep when writing Perl scripts on VMS. If you find we've
19 missed something you think should appear here, please don't
20 hesitate to drop a line to vmsperl@genetics.upenn.edu.
24 Directions for building and installing Perl 5 can be found in
25 the file F<README.vms> in the main source directory of the
28 =head1 Organization of Perl Images
32 During the installation process, three Perl images are produced.
33 F<Miniperl.Exe> is an executable image which contains all of
34 the basic functionality of Perl, but cannot take advantage of
35 Perl extensions. It is used to generate several files needed
36 to build the complete Perl and various extensions. Once you've
37 finished installing Perl, you can delete this image.
39 Most of the complete Perl resides in the shareable image
40 F<PerlShr.Exe>, which provides a core to which the Perl executable
41 image and all Perl extensions are linked. You should place this
42 image in F<Sys$Share>, or define the logical name F<PerlShr> to
43 translate to the full file specification of this image. It should
44 be world readable. (Remember that if a user has execute only access
45 to F<PerlShr>, VMS will treat it as if it were a privileged shareable
46 image, and will therefore require all downstream shareable images to be
50 Finally, F<Perl.Exe> is an executable image containing the main
51 entry point for Perl, as well as some initialization code. It
52 should be placed in a public directory, and made world executable.
53 In order to run Perl with command line arguments, you should
54 define a foreign command to invoke this image.
56 =head2 Perl Extensions
58 Perl extensions are packages which provide both XS and Perl code
59 to add new functionality to perl. (XS is a meta-language which
60 simplifies writing C code which interacts with Perl, see
61 L<perlapi> for more details.) The Perl code for an
62 extension is treated like any other library module - it's
63 made available in your script through the appropriate
64 C<use> or C<require> statement, and usually defines a Perl
65 package containing the extension.
67 The portion of the extension provided by the XS code may be
68 connected to the rest of Perl in either of two ways. In the
69 B<static> configuration, the object code for the extension is
70 linked directly into F<PerlShr.Exe>, and is initialized whenever
71 Perl is invoked. In the B<dynamic> configuration, the extension's
72 machine code is placed into a separate shareable image, which is
73 mapped by Perl's DynaLoader when the extension is C<use>d or
74 C<require>d in your script. This allows you to maintain the
75 extension as a separate entity, at the cost of keeping track of the
76 additional shareable image. Most extensions can be set up as either
79 The source code for an extension usually resides in its own
80 directory. At least three files are generally provided:
81 I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
82 the extension's name following the last C<::>), containing
83 the XS code, I<Extshortname>F<.pm>, the Perl library module
84 for the extension, and F<Makefile.PL>, a Perl script which uses
85 the C<MakeMaker> library modules supplied with Perl to generate
86 a F<Descrip.MMS> file for the extension.
88 =head2 Installing static extensions
90 Since static extensions are incorporated directly into
91 F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
92 new extension. You should edit the main F<Descrip.MMS> or F<Makefile>
93 you use to build Perl, adding the extension's name to the C<ext>
94 macro, and the extension's object file to the C<extobj> macro.
95 You'll also need to build the extension's object file, either
96 by adding dependencies to the main F<Descrip.MMS>, or using a
97 separate F<Descrip.MMS> for the extension. Then, rebuild
98 F<PerlShr.Exe> to incorporate the new code.
100 Finally, you'll need to copy the extension's Perl library
101 module to the F<[.>I<Extname>F<]> subdirectory under one
102 of the directories in C<@INC>, where I<Extname> is the name
103 of the extension, with all C<::> replaced by C<.> (e.g.
104 the library module for extension Foo::Bar would be copied
105 to a F<[.Foo.Bar]> subdirectory).
107 =head2 Installing dynamic extensions
109 In general, the distributed kit for a Perl extension includes
110 a file named Makefile.PL, which is a Perl program which is used
111 to create a F<Descrip.MMS> file which can be used to build and
112 install the files required by the extension. The kit should be
113 unpacked into a directory tree B<not> under the main Perl source
114 directory, and the procedure for building the extension is simply
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
121 I<N.B.> The procedure by which extensions are built and
122 tested creates several levels (at least 4) under the
123 directory in which the extension's source files live.
124 For this reason, you shouldn't nest the source directory
125 too deeply in your directory structure, lest you eccedd RMS'
126 maximum of 8 levels of subdirectory in a filespec. (You
127 can use rooted logical names to get another 8 levels of
128 nesting, if you can't place the files near the top of
129 the physical directory structure.)
131 VMS support for this process in the current release of Perl
132 is sufficient to handle most extensions. However, it does
133 not yet recognize extra libraries required to build shareable
134 images which are part of an extension, so these must be added
135 to the linker options file for the extension by hand. For
136 instance, if the F<PGPLOT> extension to Perl requires the
137 F<PGPLOTSHR.EXE> shareable image in order to properly link
138 the Perl extension, then the line C<PGPLOTSHR/Share> must
139 be added to the linker options file F<PGPLOT.Opt> produced
140 during the build process for the Perl extension.
142 By default, the shareable image for an extension is placed
143 F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
144 installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
145 F<VMS_AXP>, and I<Extname> is the name of the extension, with
146 each C<::> translated to C<.>). (See the MakeMaker documentation
147 for more details on installation options for extensions.)
148 However, it can be manually placed in any of several locations:
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
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>.
158 If the shareable image isn't in any of these places, you'll need
159 to define a logical name I<Extshortname>, where I<Extshortname>
160 is the portion of the extension's name after the last C<::>, which
161 translates to the full file specification of the shareable image.
163 =head1 File specifications
167 We have tried to make Perl aware of both VMS-style and Unix-
168 style file specifications wherever possible. You may use
169 either style, or both, on the command line and in scripts,
170 but you may not combine the two styles within a single fle
171 specification. VMS Perl interprets Unix pathnames in much
172 the same way as the CRTL (I<e.g.> the first component of
173 an absolute path is read as the device name for the
174 VMS file specification). There are a set of functions
175 provided in the C<VMS::Filespec> package for explicit
176 interconversion between VMS and Unix syntax; its
177 documentation provides more details.
179 Filenames are, of course, still case-insensitive. For
180 consistency, most Perl routines return filespecs using
181 lower case letters only, regardless of the case used in
182 the arguments passed to them. (This is true only when
183 running under VMS; Perl respects the case-sensitivity
186 We've tried to minimize the dependence of Perl library
187 modules on Unix syntax, but you may find that some of these,
188 as well as some scripts written for Unix systems, will
189 require that you use Unix syntax, since they will assume that
190 '/' is the directory separator, I<etc.> If you find instances
191 of this in the Perl distribution itself, please let us know,
192 so we can try to work around them.
194 =head2 Wildcard expansion
196 File specifications containing wildcards are allowed both on
197 the command line and within Perl globs (e.g. <CE<lt>*.cE<gt>>). If
198 the wildcard filespec uses VMS syntax, the resultant
199 filespecs will follow VMS syntax; if a Unix-style filespec is
200 passed in, Unix-style filespecs will be returned.
202 If the wildcard filespec contains a device or directory
203 specification, then the resultant filespecs will also contain
204 a device and directory; otherwise, device and directory
205 information are removed. VMS-style resultant filespecs will
206 contain a full device and directory, while Unix-style
207 resultant filespecs will contain only as much of a directory
208 path as was present in the input filespec. For example, if
209 your default directory is Perl_Root:[000000], the expansion
210 of C<[.t]*.*> will yield filespecs like
211 "perl_root:[t]base.dir", while the expansion of C<t/*/*> will
212 yield filespecs like "t/base.dir". (This is done to match
213 the behavior of glob expansion performed by Unix shells.)
215 Similarly, the resultant filespec will contain the file version
216 only if one was present in the input filespec.
220 Input and output pipes to Perl filehandles are supported; the
221 "file name" is passed to lib$spawn() for asynchronous
222 execution. You should be careful to close any pipes you have
223 opened in a Perl script, lest you leave any "orphaned"
224 subprocesses around when Perl exits.
226 You may also use backticks to invoke a DCL subprocess, whose
227 output is used as the return value of the expression. The
228 string between the backticks is passed directly to lib$spawn
229 as the command to execute. In this case, Perl will wait for
230 the subprocess to complete before continuing.
232 =head1 PERL5LIB and PERLLIB
234 The PERL5LIB and PERLLIB logical names work as documented L<perl>,
235 except that the element separator is '|' instead of ':'. The
236 directory specifications may use either VMS or Unix syntax.
240 =head2 I/O redirection and backgrounding
242 Perl for VMS supports redirection of input and output on the
243 command line, using a subset of Bourne shell syntax:
245 <F<file> reads stdin from F<file>,
246 >F<file> writes stdout to F<file>,
247 >>F<file> appends stdout to F<file>,
248 2>F<file> writes stderr to F<file>, and
249 2>>F<file> appends stderr to F<file>.
251 In addition, output may be piped to a subprocess, using the
252 character '|'. Anything after this character on the command
253 line is passed to a subprocess for execution; the subprocess
254 takes the output of Perl as its input.
256 Finally, if the command line ends with '&', the entire
257 command is run in the background as an asynchronous
260 =head2 Command line switches
262 The following command line switches behave differently under
263 VMS than described in L<perlrun>. Note also that in order
264 to pass uppercase switches to Perl, you need to enclose
265 them in double-quotes on the command line, since the CRTL
266 downcases all unquoted strings.
272 If the C<-i> switch is present but no extension for a backup
273 copy is given, then inplace editing creates a new version of
274 a file; the existing copy is not deleted. (Note that if
275 an extension is given, an existing file is renamed to the backup
276 file, as is the case under other operating systems, so it does
277 not remain as a previous version under the original filename.)
281 If the C<-S> switch is present I<and> the script name does
282 not contain a directory, then Perl translates the logical
283 name DCL$PATH as a searchlist, using each translation as
284 a directory in which to look for the script. In addition,
285 if no file type is specified, Perl looks in each directory
286 for a file matching the name specified, with a blank type,
287 a type of F<.pl>, and a type of F<.com>, in that order.
291 The C<-u> switch causes the VMS debugger to be invoked
292 after the Perl program is compiled, but before it has
293 run. It does not create a core dump file.
297 =head1 Perl functions
299 As of the time this document was last revised, the following
300 Perl functions were implemented in the VMS port of Perl
301 (functions marked with * are discussed in more detail below):
303 file tests*, abs, alarm, atan, binmode*, bless,
304 caller, chdir, chmod, chown, chomp, chop, chr,
305 close, closedir, cos, crypt*, defined, delete,
306 die, do, dump*, each, endpwent, eof, eval, exec*,
307 exists, exit, exp, fileno, fork*, getc, getlogin,
308 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
309 grep, hex, import, index, int, join, keys, kill*,
310 last, lc, lcfirst, length, local, localtime, log, m//,
311 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
312 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
313 qx//, quotemeta, rand, read, readdir, redo, ref, rename,
314 require, reset, return, reverse, rewinddir, rindex,
315 rmdir, s///, scalar, seek, seekdir, select(internal),
316 select (system call)*, setpwent, shift, sin, sleep,
317 sort, splice, split, sprintf, sqrt, srand, stat,
318 study, substr, sysread, system*, syswrite, tell,
319 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
320 undef, unlink*, unpack, untie, unshift, use, utime*,
321 values, vec, wait, waitpid*, wantarray, warn, write, y///
323 The following functions were not implemented in the VMS port,
324 and calling them produces a fatal error (usually) or
325 undefined behavior (rarely, we hope):
327 chroot, dbmclose, dbmopen, fcntl, flock,
328 getpgrp, getppid, getpriority, getgrent, getgrgid,
329 getgrnam, setgrent, endgrent, ioctl, link, lstat,
330 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
331 semget, semop, setpgrp, setpriority, shmctl, shmget,
332 shmread, shmwrite, socketpair, symlink, syscall, truncate
334 The following functions may or may not be implemented,
335 depending on what type of socket support you've built into
338 accept, bind, connect, getpeername,
339 gethostbyname, getnetbyname, getprotobyname,
340 getservbyname, gethostbyaddr, getnetbyaddr,
341 getprotobynumber, getservbyport, gethostent,
342 getnetent, getprotoent, getservent, sethostent,
343 setnetent, setprotoent, setservent, endhostent,
344 endnetent, endprotoent, endservent, getsockname,
345 getsockopt, listen, recv, select(system call)*,
346 send, setsockopt, shutdown, socket
352 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
353 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
354 advertised. The return values for C<-r>, C<-w>, and C<-x>
355 tell you whether you can actually access the file; this may
356 not reflect the UIC-based file protections. Since real and
357 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
358 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
359 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
360 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
361 VMS, and the values returned by these tests reflect whatever
362 your CRTL C<stat()> routine does to the equivalent bits in the
363 st_mode field. Finally, C<-d> returns true if passed a device
364 specification without an explicit directory (e.g. C<DUA1:>), as
365 well as if passed a directory.
367 Note: Some sites have reported problems when using the file-access
368 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
369 Specifically, since DFS does not currently provide access to the
370 extended file header of files on remote volumes, attempts to
371 examine the ACL fail, and the file tests will return false,
372 with C<$!> indicating that the file does not exist. You can
373 use C<stat> on these files, since that checks UIC-based protection
374 only, and then manually check the appropriate bits, as defined by
375 your C compiler's F<stat.h>, in the mode value it returns, if you
376 need an approximation of the file's protections.
378 =item binmode FILEHANDLE
380 The C<binmode> operator will attempt to insure that no translation
381 of carriage control occurs on input from or output to this filehandle.
382 Since this involves reopening the file and then restoring its
383 file position indicator, if this function returns FALSE, the
384 underlying filehandle may no longer point to an open file, or may
385 point to a different position in the file than before C<binmode>
388 Note that C<binmode> is generally not necessary when using normal
389 filehandles; it is provided so that you can control I/O to existing
390 record-structured files when necessary. You can also use the
391 C<vmsfopen> function in the VMS::Stdio extension to gain finer
392 control of I/O to files and devices with different record structures.
394 =item crypt PLAINTEXT, USER
396 The C<crypt> operator uses the C<sys$hash_password> system
397 service to generate the hashed representation of PLAINTEXT.
398 If USER is a valid username, the algorithm and salt values
399 are taken from that user's UAF record. If it is not, then
400 the preferred algorithm and a salt of 0 are used. The
401 quadword encrypted value is returned as an 8-character string.
403 The value returned by C<crypt> may be compared against
404 the encrypted password from the UAF returned by the C<getpw*>
405 functions, in order to authenticate users. If you're
406 going to do this, remember that the encrypted password in
407 the UAF was generated using uppercase username and
408 password strings; you'll have to upcase the arguments to
409 C<crypt> to insure that you'll get the proper value:
411 sub validate_passwd {
412 my($user,$passwd) = @_;
414 if ( !($pwdhash = (getpwnam($user))[1]) ||
415 $pwdhash ne crypt("\U$passwd","\U$name") ) {
416 intruder_alert($name);
423 Rather than causing Perl to abort and dump core, the C<dump>
424 operator invokes the VMS debugger. If you continue to
425 execute the Perl program under the debugger, control will
426 be transferred to the label specified as the argument to
427 C<dump>, or, if no label was specified, back to the
428 beginning of the program. All other state of the program
429 (I<e.g.> values of variables, open file handles) are not
430 affected by calling C<dump>.
434 The C<exec> operator behaves in one of two different ways.
435 If called after a call to C<fork>, it will invoke the CRTL
436 C<execv()> routine, passing its arguments to the subprocess
437 created by C<fork> for execution. In this case, it is
438 subject to all limitations that affect C<execv()>. (In
439 particular, this usually means that the command executed in
440 the subprocess must be an image compiled from C source code,
441 and that your options for passing file descriptors and signal
442 handlers to the subprocess are limited.)
444 If the call to C<exec> does not follow a call to C<fork>, it
445 will cause Perl to exit, and to invoke the command given as
446 an argument to C<exec> via C<lib$do_command>. If the argument
447 begins with a '$' (other than as part of a filespec), then it
448 is executed as a DCL command. Otherwise, the first token on
449 the command line is treated as the filespec of an image to
450 run, and an attempt is made to invoke it (using F<.Exe> and
451 the process defaults to expand the filespec) and pass the
452 rest of C<exec>'s argument to it as parameters.
454 You can use C<exec> in both ways within the same script, as
455 long as you call C<fork> and C<exec> in pairs. Perl
456 keeps track of how many times C<fork> and C<exec> have been
457 called, and will call the CRTL C<execv()> routine if there have
458 previously been more calls to C<fork> than to C<exec>.
462 The C<fork> operator works in the same way as the CRTL
463 C<vfork()> routine, which is quite different under VMS than
464 under Unix. Specifically, while C<fork> returns 0 after it
465 is called and the subprocess PID after C<exec> is called, in
466 both cases the thread of execution is within the parent
467 process, so there is no opportunity to perform operations in
468 the subprocess before calling C<exec>.
470 In general, the use of C<fork> and C<exec> to create
471 subprocess is not recommended under VMS; wherever possible,
472 use the C<system> operator or piped filehandles instead.
480 These operators obtain the information described in L<perlfunc>,
481 if you have the privileges necessary to retrieve the named user's
482 UAF information via C<sys$getuai>. If not, then only the C<$name>,
483 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
484 the login directory in VMS syntax, while the C<$comment> item
485 contains the login directory in Unix syntax. The C<$gcos> item
486 contains the owner field from the UAF record. The C<$quota>
491 The C<gmtime> operator will function properly if you have a
492 working CRTL C<gmtime()> routine, or if the logical name
493 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
494 which must be added to UTC to yield local time. (This logical
495 name is defined automatically if you are running a version of
496 VMS with built-in UTC support.) If neither of these cases is
497 true, a warning message is printed, and C<undef> is returned.
501 In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
502 function, so it will behave according to that function's
503 documentation. If you send a SIGKILL, however, the $DELPRC system
504 service is is called directly. This insures that the target
505 process is actually deleted, if at all possible. (The CRTL's C<kill()>
506 function is presently implemented via $FORCEX, which is ignored by
507 supervisor-mode images like DCL.)
509 Also, negative signal values don't do anything special under
510 VMS; they're just converted to the corresponding positive value.
512 =item select (system call)
514 If Perl was not built with socket support, the system call
515 version of C<select> is not available at all. If socket
516 support is present, then the system call version of
517 C<select> functions only for file descriptors attached
518 to sockets. It will not provide information about regular
519 files or pipes, since the CRTL C<select()> routine does not
520 provide this functionality.
524 Since VMS keeps track of files according to a different scheme
525 than Unix, it's not really possible to represent the file's ID
526 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
527 tries its best, though, and the values it uses are pretty unlikely
528 to be the same for two different files. We can't guarantee this,
529 though, so caveat scriptor.
533 The C<system> operator creates a subprocess, and passes its
534 arguments to the subprocess for execution as a DCL command.
535 Since the subprocess is created directly via C<lib$spawn()>, any
536 valid DCL command string may be specified. If LIST consists
537 of the empty string, C<system> spawns an interactive DCL subprocess,
538 in the same fashion as typiing B<SPAWN> at the DCL prompt.
539 Perl waits for the subprocess to complete before continuing
540 execution in the current process.
544 The value returned by C<time> is the offset in seconds from
545 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
546 to make life easier for code coming in from the POSIX/Unix world.
550 The array returned by the C<times> operator is divided up
551 according to the same rules the CRTL C<times()> routine.
552 Therefore, the "system time" elements will always be 0, since
553 there is no difference between "user time" and "system" time
554 under VMS, and the time accumulated by subprocess may or may
555 not appear separately in the "child time" field, depending on
556 whether L<times> keeps track of subprocesses separately. Note
557 especially that the VAXCRTL (at least) keeps track only of
558 subprocesses spawned using L<fork> and L<exec>; it will not
559 accumulate the times of suprocesses spawned via pipes, L<system>,
564 C<unlink> will delete the highest version of a file only; in
565 order to delete all versions, you need to say
566 1 while (unlink LIST);
567 You may need to make this change to scripts written for a
568 Unix system which expect that after a call to C<unlink>,
569 no files with the names passed to C<unlink> will exist.
570 (Note: This can be changed at compile time; if you
571 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
572 C<define>, then C<unlink> will delete all versions of a
573 file on the first call.)
575 C<unlink> will delete a file if at all possible, even if it
576 requires changing file protection (though it won't try to
577 change the protection of the parent directory). You can tell
578 whether you've got explicit delete access to a file by using the
579 C<VMS::Filespec::candelete> operator. For instance, in order
580 to delete only files to which you have delete access, you could
586 next unless VMS::Filespec::candelete($file);
587 $num += unlink $file;
592 (or you could just use C<VMS::Stdio::remove>, if you've installed
593 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
594 change the file protection to delete the file, and you interrupt it
595 in midstream, the file may be left intact, but with a changed ACL
596 allowing you delete access.
600 Since ODS-2, the VMS file structure for disk files, does not keep
601 track of access times, this operator changes only the modification
602 time of the file (VMS revision date).
604 =item waitpid PID,FLAGS
606 If PID is a subprocess started by a piped L<open>, C<waitpid>
607 will wait for that subprocess, and return its final
608 status value. If PID is a subprocess created in some other way
609 (e.g. SPAWNed before Perl was invoked), or is not a subprocess of
610 the current process, C<waitpid> will check once per second whether
611 the process has completed, and when it has, will return 0. (If PID
612 specifies a process that isn't a subprocess of the current process,
613 and you invoked Perl with the C<-w> switch, a warning will be issued.)
615 The FLAGS argument is ignored in all cases.
619 =head1 Perl variables
621 The following VMS-specific information applies to the indicated
622 "special" Perl variables, in addition to the general information
623 in L<perlvar>. Where there is a conflict, this infrmation
630 Reading the elements of the %ENV array returns the
631 translation of the logical name specified by the key,
632 according to the normal search order of access modes and
633 logical name tables. If you append a semicolon to the
634 logical name, followed by an integer, that integer is
635 used as the translation index for the logical name,
636 so that you can look up successive values for search
637 list logical names. For instance, if you say
639 $ Define STORY once,upon,a,time,there,was
640 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
641 _$ -e "{ print $ENV{'story;'.$i},' '}"
643 Perl will print C<ONCE UPON A TIME THERE WAS>.
645 The %ENV keys C<home>, C<path>,C<term>, and C<user>
646 return the CRTL "environment variables" of the same
647 names, if these logical names are not defined. The
648 key C<default> returns the current default device
649 and directory specification, regardless of whether
650 there is a logical name DEFAULT defined..
652 Setting an element of %ENV defines a supervisor-mode logical
653 name in the process logical name table. C<Undef>ing or
654 C<delete>ing an element of %ENV deletes the equivalent user-
655 mode or supervisor-mode logical name from the process logical
656 name table. If you use C<undef>, the %ENV element remains
657 empty. If you use C<delete>, another attempt is made at
658 logical name translation after the deletion, so an inner-mode
659 logical name or a name in another logical name table will
660 replace the logical name just deleted. It is not possible
661 at present to define a search list logical name via %ENV.
663 At present, the first time you iterate over %ENV using
664 C<keys>, or C<values>, you will incur a time penalty as all
665 logical names are read, in order to fully populate %ENV.
666 Subsequent iterations will not reread logical names, so they
667 won't be as slow, but they also won't reflect any changes
668 to logical name tables caused by other programs. The C<each>
669 operator is special: it returns each element I<already> in
670 %ENV, but doesn't go out and look for more. Therefore, if
671 you've previously used C<keys> or C<values>, you'll see all
672 the logical names visible to your process, and if not, you'll
673 see only the names you've looked up so far. (This is a
674 consequence of the way C<each> is implemented now, and it
675 may change in the future, so it wouldn't be a good idea
676 to rely on it too much.)
678 In all operations on %ENV, the key string is treated as if it
679 were entirely uppercase, regardless of the case actually
680 specified in the Perl expression.
684 Since VMS status values are 32 bits wide, the value of C<$?>
685 is simply the final status value of the last subprocess to
686 complete. This differs from the behavior of C<$?> under Unix,
687 and under VMS' POSIX environment, in that the low-order 8 bits
688 of C<$?> do not specify whether the process terminated normally
689 or due to a signal, and you do not need to shift C<$?> 8 bits
690 to the right in order to find the process' exit status.
694 The string value of C<$!> is that returned by the CRTL's
695 strerror() function, so it will include the VMS message for
696 VMS-specific errors. The numeric value of C<$!> is the
697 value of C<errno>, except if errno is EVMSERR, in which
698 case C<$!> contains the value of vaxc$errno. Setting C<$!>
699 always sets errno to the value specified. If this value is
700 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
701 that the string value of C<$!> won't reflect the VMS error
702 message from before C<$!> was set.
706 This variable provides direct access to VMS status values
707 in vaxc$errno, which are often more specific than the
708 generic Unix-style error messages in C<$!>. Its numeric value
709 is the value of vaxc$errno, and its string value is the
710 corresponding VMS message string, as retrieved by sys$getmsg().
711 Setting C<$^E> sets vaxc$errno to the value specified.
715 Setting C<$|> for an I/O stream causes data to be flushed
716 all the way to disk on each write (I<i.e.> not just to
717 the underlying RMS buffers for a file). In other words,
718 it's equivalent to calling fflush() and fsync() from C.
724 This document was last updated on 28-Feb-1996, for Perl 5,
729 Charles Bailey bailey@genetics.upenn.edu