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 in the F<[.Lib.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>, followed by the Perl version number, and I<Extname>
146 is the name of the extension, with each C<::> translated to C<.>).
147 However, it can be manually placed in any of several locations:
148 - the F<[.Lib.Auto.>I<Extname>F<]> subdirectory of one of
149 the directories in C<@INC>, or
150 - one of the directories in C<@INC>, or
151 - a directory which the extensions Perl library module
152 passes to the DynaLoader when asking it to map
153 the shareable image, or
154 - F<Sys$Share> or F<Sys$Library>.
155 If the shareable image isn't in any of these places, you'll need
156 to define a logical name I<Extshortname>, where I<Extshortname>
157 is the portion of the extension's name after the last C<::>, which
158 translates to the full file specification of the shareable image.
160 =head1 File specifications
164 We have tried to make Perl aware of both VMS-style and Unix-
165 style file specifications wherever possible. You may use
166 either style, or both, on the command line and in scripts,
167 but you may not combine the two styles within a single fle
168 specification. VMS Perl interprets Unix pathnames in much
169 the same way as the CRTL (I<e.g.> the first component of
170 an absolute path is read as the device name for the
171 VMS file specification). There are a set of functions
172 provided in the C<VMS::Filespec> package for explicit
173 interconversion between VMS and Unix syntax; its
174 documentation provides more details.
176 Filenames are, of course, still case-insensitive. For
177 consistency, most Perl routines return filespecs using
178 lower case letters only, regardless of the case used in
179 the arguments passed to them. (This is true only when
180 running under VMS; Perl respects the case-sensitivity
183 We've tried to minimize the dependence of Perl library
184 modules on Unix syntax, but you may find that some of these,
185 as well as some scripts written for Unix systems, will
186 require that you use Unix syntax, since they will assume that
187 '/' is the directory separator, I<etc.> If you find instances
188 of this in the Perl distribution itself, please let us know,
189 so we can try to work around them.
191 =head2 Wildcard expansion
193 File specifications containing wildcards are allowed both on
194 the command line and within Perl globs (e.g. <CE<lt>*.cE<gt>>). If
195 the wildcard filespec uses VMS syntax, the resultant
196 filespecs will follow VMS syntax; if a Unix-style filespec is
197 passed in, Unix-style filespecs will be returned.
199 If the wildcard filespec contains a device or directory
200 specification, then the resultant filespecs will also contain
201 a device and directory; otherwise, device and directory
202 information are removed. VMS-style resultant filespecs will
203 contain a full device and directory, while Unix-style
204 resultant filespecs will contain only as much of a directory
205 path as was present in the input filespec. For example, if
206 your default directory is Perl_Root:[000000], the expansion
207 of C<[.t]*.*> will yield filespecs like
208 "perl_root:[t]base.dir", while the expansion of C<t/*/*> will
209 yield filespecs like "t/base.dir". (This is done to match
210 the behavior of glob expansion performed by Unix shells.)
212 Similarly, the resultant filespec will contain the file version
213 only if one was present in the input filespec.
217 Input and output pipes to Perl filehandles are supported; the
218 "file name" is passed to lib$spawn() for asynchronous
219 execution. You should be careful to close any pipes you have
220 opened in a Perl script, lest you leave any "orphaned"
221 subprocesses around when Perl exits.
223 You may also use backticks to invoke a DCL subprocess, whose
224 output is used as the return value of the expression. The
225 string between the backticks is passed directly to lib$spawn
226 as the command to execute. In this case, Perl will wait for
227 the subprocess to complete before continuing.
229 =head1 PERL5LIB and PERLLIB
231 The PERL5LIB and PERLLIB logical names work as documented L<perl>,
232 except that the element separator is '|' instead of ':'. The
233 directory specifications may use either VMS or Unix syntax.
237 =head2 I/O redirection and backgrounding
239 Perl for VMS supports redirection of input and output on the
240 command line, using a subset of Bourne shell syntax:
241 <F<file> reads stdin from F<file>,
242 >F<file> writes stdout to F<file>,
243 >>F<file> appends stdout to F<file>,
244 2>F<file> writes stderr to F<file>, and
245 2>>F<file> appends stderr to F<file>.
247 In addition, output may be piped to a subprocess, using the
248 character '|'. Anything after this character on the command
249 line is passed to a subprocess for execution; the subprocess
250 takes the output of Perl as its input.
252 Finally, if the command line ends with '&', the entire
253 command is run in the background as an asynchronous
256 =head2 Command line switches
258 The following command line switches behave differently under
259 VMS than described in L<perlrun>. Note also that in order
260 to pass uppercase switches to Perl, you need to enclose
261 them in double-quotes on the command line, since the CRTL
262 downcases all unquoted strings.
266 If the C<-S> switch is present I<and> the script name does
267 not contain a directory, then Perl translates the logical
268 name DCL$PATH as a searchlist, using each translation as
269 a directory in which to look for the script. In addition,
270 if no file type is specified, Perl looks in each directory
271 for a file matching the name specified, with a blank type,
272 a type of F<.pl>, and a type of F<.com>, in that order.
276 The C<-u> switch causes the VMS debugger to be invoked
277 after the Perl program is compiled, but before it has
278 run. It does not create a core dump file.
280 =head1 Perl functions
282 As of the time this document was last revised, the following
283 Perl functions were implemented in the VMS port of Perl
284 (functions marked with * are discussed in more detail below):
286 file tests*, abs, alarm, atan, binmode*, bless,
287 caller, chdir, chmod, chown, chomp, chop, chr,
288 close, closedir, cos, crypt*, defined, delete,
289 die, do, dump*, each, endpwent, eof, eval, exec*,
290 exists, exit, exp, fileno, fork*, getc, getlogin,
291 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
292 grep, hex, import, index, int, join, keys, kill*,
293 last, lc, lcfirst, length, local, localtime, log, m//,
294 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
295 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
296 qx//, quotemeta, rand, read, readdir, redo, ref, rename,
297 require, reset, return, reverse, rewinddir, rindex,
298 rmdir, s///, scalar, seek, seekdir, select(internal),
299 select (system call)*, setpwent, shift, sin, sleep,
300 sort, splice, split, sprintf, sqrt, srand, stat,
301 study, substr, sysread, system*, syswrite, tell,
302 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
303 undef, unlink*, unpack, untie, unshift, use, utime*,
304 values, vec, wait, waitpid*, wantarray, warn, write, y///
306 The following functions were not implemented in the VMS port,
307 and calling them produces a fatal error (usually) or
308 undefined behavior (rarely, we hope):
310 chroot, dbmclose, dbmopen, fcntl, flock,
311 getpgrp, getppid, getpriority, getgrent, getgrgid,
312 getgrnam, setgrent, endgrent, ioctl, link, lstat,
313 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
314 semget, semop, setpgrp, setpriority, shmctl, shmget,
315 shmread, shmwrite, socketpair, symlink, syscall, truncate
317 The following functions may or may not be implemented,
318 depending on what type of socket support you've built into
321 accept, bind, connect, getpeername,
322 gethostbyname, getnetbyname, getprotobyname,
323 getservbyname, gethostbyaddr, getnetbyaddr,
324 getprotobynumber, getservbyport, gethostent,
325 getnetent, getprotoent, getservent, sethostent,
326 setnetent, setprotoent, setservent, endhostent,
327 endnetent, endprotoent, endservent, getsockname,
328 getsockopt, listen, recv, select(system call)*,
329 send, setsockopt, shutdown, socket
334 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
335 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
336 advertised. The return values for C<-r>, C<-w>, and C<-x>
337 tell you whether you can actually access the file; this may
338 not reflect the UIC-based file protections. Since real and
339 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
340 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
341 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
342 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
343 VMS, and the values returned by these tests reflect whatever
344 your CRTL C<stat()> routine does to the equivalent bits in the
345 st_mode field. Finally, C<-d> returns true if passed a device
346 specification without an explicit directory (e.g. C<DUA1:>), as
347 well as if passed a directory.
349 Note: Some sites have reported problems when using the file-access
350 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
351 Specifically, since DFS does not currently provide access to the
352 extended file header of files on remote volumes, attempts to
353 examine the ACL fail, and the file tests will return false,
354 with C<$!> indicating that the file does not exist. You can
355 use C<stat> on these files, since that checks UIC-based protection
356 only, and then manually check the appropriate bits, as defined by
357 your C compiler's F<stat.h>, in the mode value it returns, if you
358 need an approximation of the file's protections.
360 =item binmode FILEHANDLE
362 The C<binmode> operator will attempt to insure that no translation
363 of carriage control occurs on input from or output to this filehandle.
364 Since this involves reopening the file and then restoring its
365 file position indicator, if this function returns FALSE, the
366 underlying filehandle may no longer point to an open file, or may
367 point to a different position in the file than before C<binmode>
370 Note that C<binmode> is generally not necessary when using normal
371 filehandles; it is provided so that you can control I/O to existing
372 record-structured files when necessary. You can also use the
373 C<vmsfopen> function in the VMS::Stdio extension to gain finer
374 control of I/O to files and devices with different record structures.
376 =item crypt PLAINTEXT, USER
378 The C<crypt> operator uses the C<sys$hash_password> system
379 service to generate the hashed representation of PLAINTEXT.
380 If USER is a valid username, the algorithm and salt values
381 are taken from that user's UAF record. If it is not, then
382 the preferred algorithm and a salt of 0 are used. The
383 quadword encrypted value is returned as an 8-character string.
385 The value returned by C<crypt> may be compared against
386 the encrypted password from the UAF returned by the C<getpw*>
387 functions, in order to authenticate users. If you're
388 going to do this, remember that the encrypted password in
389 the UAF was generated using uppercase username and
390 password strings; you'll have to upcase the arguments to
391 C<crypt> to insure that you'll get the proper value:
393 sub validate_passwd {
394 my($user,$passwd) = @_;
396 if ( !($pwdhash = (getpwnam($user))[1]) ||
397 $pwdhash ne crypt("\U$passwd","\U$name") ) {
398 intruder_alert($name);
405 Rather than causing Perl to abort and dump core, the C<dump>
406 operator invokes the VMS debugger. If you continue to
407 execute the Perl program under the debugger, control will
408 be transferred to the label specified as the argument to
409 C<dump>, or, if no label was specified, back to the
410 beginning of the program. All other state of the program
411 (I<e.g.> values of variables, open file handles) are not
412 affected by calling C<dump>.
416 The C<exec> operator behaves in one of two different ways.
417 If called after a call to C<fork>, it will invoke the CRTL
418 C<execv()> routine, passing its arguments to the subprocess
419 created by C<fork> for execution. In this case, it is
420 subject to all limitations that affect C<execv()>. (In
421 particular, this usually means that the command executed in
422 the subprocess must be an image compiled from C source code,
423 and that your options for passing file descriptors and signal
424 handlers to the subprocess are limited.)
426 If the call to C<exec> does not follow a call to C<fork>, it
427 will cause Perl to exit, and to invoke the command given as
428 an argument to C<exec> via C<lib$do_command>. If the argument
429 begins with a '$' (other than as part of a filespec), then it
430 is executed as a DCL command. Otherwise, the first token on
431 the command line is treated as the filespec of an image to
432 run, and an attempt is made to invoke it (using F<.Exe> and
433 the process defaults to expand the filespec) and pass the
434 rest of C<exec>'s argument to it as parameters.
436 You can use C<exec> in both ways within the same script, as
437 long as you call C<fork> and C<exec> in pairs. Perl
438 keeps track of how many times C<fork> and C<exec> have been
439 called, and will call the CRTL C<execv()> routine if there have
440 previously been more calls to C<fork> than to C<exec>.
444 The C<fork> operator works in the same way as the CRTL
445 C<vfork()> routine, which is quite different under VMS than
446 under Unix. Specifically, while C<fork> returns 0 after it
447 is called and the subprocess PID after C<exec> is called, in
448 both cases the thread of execution is within the parent
449 process, so there is no opportunity to perform operations in
450 the subprocess before calling C<exec>.
452 In general, the use of C<fork> and C<exec> to create
453 subprocess is not recommended under VMS; wherever possible,
454 use the C<system> operator or piped filehandles instead.
462 These operators obtain the information described in L<perlfunc>,
463 if you have the privileges necessary to retrieve the named user's
464 UAF information via C<sys$getuai>. If not, then only the C<$name>,
465 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
466 the login directory in VMS syntax, while the C<$comment> item
467 contains the login directory in Unix syntax. The C<$gcos> item
468 contains the owner field from the UAF record. The C<$quota>
473 The C<gmtime> operator will function properly if you have a
474 working CRTL C<gmtime()> routine, or if the logical name
475 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
476 which must be added to UTC to yield local time. (This logical
477 name is defined automatically if you are running a version of
478 VMS with built-in UTC support.) If neither of these cases is
479 true, a warning message is printed, and C<undef> is returned.
483 In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
484 function, so it will behave according to that function's
485 documentation. If you send a SIGKILL, however, the $DELPRC system
486 service is is called directly. This insures that the target
487 process is actually deleted, if at all possible. (The CRTL's C<kill()>
488 function is presently implemented via $FORCEX, which is ignored by
489 supervisor-mode images like DCL.)
491 Also, negative signal values don't do anything special under
492 VMS; they're just converted to the corresponding positive value.
494 =item select (system call)
496 If Perl was not built with socket support, the system call
497 version of C<select> is not available at all. If socket
498 support is present, then the system call version of
499 C<select> functions only for file descriptors attached
500 to sockets. It will not provide information about regular
501 files or pipes, since the CRTL C<select()> routine does not
502 provide this functionality.
506 Since VMS keeps track of files according to a different scheme
507 than Unix, it's not really possible to represent the file's ID
508 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
509 tries its best, though, and the values it uses are pretty unlikely
510 to be the same for two different files. We can't guarantee this,
511 though, so caveat scriptor.
515 The C<system> operator creates a subprocess, and passes its
516 arguments to the subprocess for execution as a DCL command.
517 Since the subprocess is created directly via C<lib$spawn()>, any
518 valid DCL command string may be specified. If LIST consists
519 of the empty string, C<system> spawns an interactive DCL subprocess,
520 in the same fashion as typiing B<SPAWN> at the DCL prompt.
521 Perl waits for the subprocess to complete before continuing
522 execution in the current process.
526 The value returned by C<time> is the offset in seconds from
527 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
528 to make life easier for code coming in from the POSIX/Unix world.
532 The array returned by the C<times> operator is divided up
533 according to the same rules the CRTL C<times()> routine.
534 Therefore, the "system time" elements will always be 0, since
535 there is no difference between "user time" and "system" time
536 under VMS, and the time accumulated by subprocess may or may
537 not appear separately in the "child time" field, depending on
538 whether L<times> keeps track of subprocesses separately. Note
539 especially that the VAXCRTL (at least) keeps track only of
540 subprocesses spawned using L<fork> and L<exec>; it will not
541 accumulate the times of suprocesses spawned via pipes, L<system>,
546 C<unlink> will delete the highest version of a file only; in
547 order to delete all versions, you need to say
548 1 while (unlink LIST);
549 You may need to make this change to scripts written for a
550 Unix system which expect that after a call to C<unlink>,
551 no files with the names passed to C<unlink> will exist.
552 (Note: This can be changed at compile time; if you
553 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
554 C<define>, then C<unlink> will delete all versions of a
555 file on the first call.)
557 C<unlink> will delete a file if at all possible, even if it
558 requires changing file protection (though it won't try to
559 change the protection of the parent directory). You can tell
560 whether you've got explicit delete access to a file by using the
561 C<VMS::Filespec::candelete> operator. For instance, in order
562 to delete only files to which you have delete access, you could
568 next unless VMS::Filespec::candelete($file);
569 $num += unlink $file;
574 (or you could just use C<VMS::Stdio::remove>, if you've installed
575 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
576 change the file protection to delete the file, and you interrupt it
577 in midstream, the file may be left intact, but with a changed ACL
578 allowing you delete access.
582 Since ODS-2, the VMS file structure for disk files, does not keep
583 track of access times, this operator changes only the modification
584 time of the file (VMS revision date).
586 =item waitpid PID,FLAGS
588 If PID is a subprocess started by a piped L<open>, C<waitpid>
589 will wait for that subprocess, and return its final
590 status value. If PID is a subprocess created in some other way
591 (e.g. SPAWNed before Perl was invoked), or is not a subprocess of
592 the current process, C<waitpid> will check once per second whether
593 the process has completed, and when it has, will return 0. (If PID
594 specifies a process that isn't a subprocess of the current process,
595 and you invoked Perl with the C<-w> switch, a warning will be issued.)
597 The FLAGS argument is ignored in all cases.
599 =head1 Perl variables
603 Reading the elements of the %ENV array returns the
604 translation of the logical name specified by the key,
605 according to the normal search order of access modes and
606 logical name tables. If you append a semicolon to the
607 logical name, followed by an integer, that integer is
608 used as the translation index for the logical name,
609 so that you can look up successive values for search
610 list logical names. For instance, if you say
612 $ Define STORY once,upon,a,time,there,was
613 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
614 _$ -e "{ print $ENV{'foo'.$i},' '}"
616 Perl will print C<ONCE UPON A TIME THERE WAS>.
618 The %ENV keys C<home>, C<path>,C<term>, and C<user>
619 return the CRTL "environment variables" of the same
620 names, if these logical names are not defined. The
621 key C<default> returns the current default device
622 and directory specification, regardless of whether
623 there is a logical name DEFAULT defined..
625 Setting an element of %ENV defines a supervisor-mode logical
626 name in the process logical name table. C<Undef>ing or
627 C<delete>ing an element of %ENV deletes the equivalent user-
628 mode or supervisor-mode logical name from the process logical
629 name table. If you use C<undef>, the %ENV element remains
630 empty. If you use C<delete>, another attempt is made at
631 logical name translation after the deletion, so an inner-mode
632 logical name or a name in another logical name table will
633 replace the logical name just deleted. It is not possible
634 at present to define a search list logical name via %ENV.
636 In all operations on %ENV, the key string is treated as if it
637 were entirely uppercase, regardless of the case actually
638 specified in the Perl expression.
642 Since VMS status values are 32 bits wide, the value of C<$?>
643 is simply the final status value of the last subprocess to
644 complete. This differs from the behavior of C<$?> under Unix,
645 and under VMS' POSIX environment, in that the low-order 8 bits
646 of C<$?> do not specify whether the process terminated normally
647 or due to a signal, and you do not need to shift C<$?> 8 bits
648 to the right in order to find the process' exit status.
652 The string value of C<$!> is that returned by the CRTL's
653 strerror() function, so it will include the VMS message for
654 VMS-specific errors. The numeric value of C<$!> is the
655 value of C<errno>, except if errno is EVMSERR, in which
656 case C<$!> contains the value of vaxc$errno. Setting C<$!>
657 always sets errno to the value specified. If this value is
658 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
659 that the string value of C<$!> won't reflect the VMS error
660 message from before C<$!> was set.
664 This variable provides direct access to VMS status values
665 in vaxc$errno, which are often more specific than the
666 generic Unix-style error messages in C<$!>. Its numeric value
667 is the value of vaxc$errno, and its string value is the
668 corresponding VMS message string, as retrieved by sys$getmsg().
669 Setting C<$^E> sets vaxc$errno to the value specified.
673 Setting C<$|> for an I/O stream causes data to be flushed
674 all the way to disk on each write (I<i.e.> not just to
675 the underlying RMS buffers for a file). In other words,
676 it's equivalent to calling fflush() and fsync() from C.
680 This document was last updated on 28-Feb-1996, for Perl 5,
685 Charles Bailey bailey@genetics.upenn.edu