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perlvms - VMS-specific documentation for Perl
Gathered below are notes describing details of Perl 5's behavior on VMS. They are a supplement to the regular Perl 5 documentation, so we have focussed on the ways in which Perl 5 functions differently under VMS than it does under Unix, and on the interactions between Perl and the rest of the operating system. We haven't tried to duplicate complete descriptions of Perl features from the main Perl documentation, which can be found in the [.pod] subdirectory of the Perl distribution.
We hope these notes will save you from confusion and lost sleep when writing Perl scripts on VMS. If you find we've missed something you think should appear here, please don't hesitate to drop a line to vmsperl@perl.org.
Directions for building and installing Perl 5 can be found in the file README.vms in the main source directory of the Perl distribution..
During the installation process, three Perl images are produced. Miniperl.Exe is an executable image which contains all of the basic functionality of Perl, but cannot take advantage of Perl extensions. It is used to generate several files needed to build the complete Perl and various extensions. Once you've finished installing Perl, you can delete this image.
Most of the complete Perl resides in the shareable image PerlShr.Exe, which provides a core to which the Perl executable image and all Perl extensions are linked. You should place this image in Sys$Share, or define the logical name PerlShr to translate to the full file specification of this image. It should be world readable. (Remember that if a user has execute only access to PerlShr, VMS will treat it as if it were a privileged shareable image, and will therefore require all downstream shareable images to be INSTALLed, etc.)
Finally, Perl.Exe is an executable image containing the main entry point for Perl, as well as some initialization code. It should be placed in a public directory, and made world executable. In order to run Perl with command line arguments, you should define a foreign command to invoke this image.
Perl extensions are packages which provide both XS and Perl code
to add new functionality to perl. (XS is a meta-language which
simplifies writing C code which interacts with Perl, see
the perlxs manpage for more details.) The Perl code for an
extension is treated like any other library module - it's
made available in your script through the appropriate
use or require statement, and usually defines a Perl
package containing the extension.
The portion of the extension provided by the XS code may be
connected to the rest of Perl in either of two ways. In the
static configuration, the object code for the extension is
linked directly into PerlShr.Exe, and is initialized whenever
Perl is invoked. In the dynamic configuration, the extension's
machine code is placed into a separate shareable image, which is
mapped by Perl's DynaLoader when the extension is used or
required in your script. This allows you to maintain the
extension as a separate entity, at the cost of keeping track of the
additional shareable image. Most extensions can be set up as either
static or dynamic.
The source code for an extension usually resides in its own
directory. At least three files are generally provided:
Extshortname.xs (where Extshortname is the portion of
the extension's name following the last ::), containing
the XS code, Extshortname.pm, the Perl library module
for the extension, and Makefile.PL, a Perl script which uses
the MakeMaker library modules supplied with Perl to generate
a Descrip.MMS file for the extension.
Since static extensions are incorporated directly into
PerlShr.Exe, you'll have to rebuild Perl to incorporate a
new extension. You should edit the main Descrip.MMS or Makefile
you use to build Perl, adding the extension's name to the ext
macro, and the extension's object file to the extobj macro.
You'll also need to build the extension's object file, either
by adding dependencies to the main Descrip.MMS, or using a
separate Descrip.MMS for the extension. Then, rebuild
PerlShr.Exe to incorporate the new code.
Finally, you'll need to copy the extension's Perl library
module to the [.Extname] subdirectory under one
of the directories in @INC, where Extname is the name
of the extension, with all :: replaced by . (e.g.
the library module for extension Foo::Bar would be copied
to a [.Foo.Bar] subdirectory).
In general, the distributed kit for a Perl extension includes a file named Makefile.PL, which is a Perl program which is used to create a Descrip.MMS file which can be used to build and install the files required by the extension. The kit should be unpacked into a directory tree not under the main Perl source directory, and the procedure for building the extension is simply
$ perl Makefile.PL ! Create Descrip.MMS
$ mmk ! Build necessary files
$ mmk test ! Run test code, if supplied
$ mmk install ! Install into public Perl tree
N.B. The procedure by which extensions are built and tested creates several levels (at least 4) under the directory in which the extension's source files live. For this reason if you are running a version of VMS prior to V7.1 you shouldn't nest the source directory too deeply in your directory structure lest you exceed RMS' maximum of 8 levels of subdirectory in a filespec. (You can use rooted logical names to get another 8 levels of nesting, if you can't place the files near the top of the physical directory structure.)
VMS support for this process in the current release of Perl
is sufficient to handle most extensions. However, it does
not yet recognize extra libraries required to build shareable
images which are part of an extension, so these must be added
to the linker options file for the extension by hand. For
instance, if the PGPLOT extension to Perl requires the
PGPLOTSHR.EXE shareable image in order to properly link
the Perl extension, then the line PGPLOTSHR/Share must
be added to the linker options file PGPLOT.Opt produced
during the build process for the Perl extension.
By default, the shareable image for an extension is placed in
the [.lib.site_perl.autoArch.Extname] directory of the
installed Perl directory tree (where Arch is VMS_VAX or
VMS_AXP, and Extname is the name of the extension, with
each :: translated to .). (See the MakeMaker documentation
for more details on installation options for extensions.)
However, it can be manually placed in any of several locations:
the [.Lib.Auto.Arch$PVersExtname] subdirectory
of one of the directories in @INC (where PVers
is the version of Perl you're using, as supplied in $],
with '.' converted to '_'), or
one of the directories in @INC, or
a directory which the extensions Perl library module passes to the DynaLoader when asking it to map the shareable image, or
Sys$Share or Sys$Library.
If the shareable image isn't in any of these places, you'll need
to define a logical name Extshortname, where Extshortname
is the portion of the extension's name after the last ::, which
translates to the full file specification of the shareable image.
We have tried to make Perl aware of both VMS-style and Unix-
style file specifications wherever possible. You may use
either style, or both, on the command line and in scripts,
but you may not combine the two styles within a single file
specification. VMS Perl interprets Unix pathnames in much
the same way as the CRTL (e.g. the first component of
an absolute path is read as the device name for the
VMS file specification). There are a set of functions
provided in the VMS::Filespec package for explicit
interconversion between VMS and Unix syntax; its
documentation provides more details.
Filenames are, of course, still case-insensitive. For consistency, most Perl routines return filespecs using lower case letters only, regardless of the case used in the arguments passed to them. (This is true only when running under VMS; Perl respects the case-sensitivity of OSs like Unix.)
We've tried to minimize the dependence of Perl library modules on Unix syntax, but you may find that some of these, as well as some scripts written for Unix systems, will require that you use Unix syntax, since they will assume that '/' is the directory separator, etc. If you find instances of this in the Perl distribution itself, please let us know, so we can try to work around them.
File specifications containing wildcards are allowed both on
the command line and within Perl globs (e.g. <*.c>). If
the wildcard filespec uses VMS syntax, the resultant
filespecs will follow VMS syntax; if a Unix-style filespec is
passed in, Unix-style filespecs will be returned.
Similar to the behavior of wildcard globbing for a Unix shell,
one can escape command line wildcards with double quotation
marks " around a perl program command line argument. However,
owing to the stripping of " characters carried out by the C
handling of argv you will need to escape a construct such as
this one (in a directory containing the files PERL.C, PERL.EXE,
PERL.H, and PERL.OBJ):
$ perl -e "print join(' ',@ARGV)" perl.*
perl.c perl.exe perl.h perl.obj
in the following triple quoted manner:
$ perl -e "print join(' ',@ARGV)" """perl.*"""
perl.*
In both the case of unquoted command line arguments or in calls
to glob() VMS wildcard expansion is performed. (csh-style
wildcard expansion is available if you use File::Glob::glob.)
If the wildcard filespec contains a device or directory
specification, then the resultant filespecs will also contain
a device and directory; otherwise, device and directory
information are removed. VMS-style resultant filespecs will
contain a full device and directory, while Unix-style
resultant filespecs will contain only as much of a directory
path as was present in the input filespec. For example, if
your default directory is Perl_Root:[000000], the expansion
of [.t]*.* will yield filespecs like
``perl_root:[t]base.dir'', while the expansion of t/*/* will
yield filespecs like ``t/base.dir''. (This is done to match
the behavior of glob expansion performed by Unix shells.)
Similarly, the resultant filespec will contain the file version only if one was present in the input filespec.
Input and output pipes to Perl filehandles are supported; the ``file name'' is passed to lib$spawn() for asynchronous execution. You should be careful to close any pipes you have opened in a Perl script, lest you leave any ``orphaned'' subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose
output is used as the return value of the expression. The
string between the backticks is handled as if it were the
argument to the system operator (see below). In this case,
Perl will wait for the subprocess to complete before continuing.
The mailbox (MBX) that perl can create to communicate with a pipe
defaults to a buffer size of 512. The default buffer size is
adjustable via the logical name PERL_MBX_SIZE provided that the
value falls between 128 and the SYSGEN parameter MAXBUF inclusive.
For example, to double the MBX size from the default within
a Perl program, use $ENV{'PERL_MBX_SIZE'} = 1024; and then
open and use pipe constructs. An alternative would be to issue
the command:
$ Define PERL_MBX_SIZE 1024
before running your wide record pipe program. A larger value may improve performance at the expense of the BYTLM UAF quota.
The PERL5LIB and PERLLIB logical names work as documented in the perl manpage, except that the element separator is '|' instead of ':'. The directory specifications may use either VMS or Unix syntax.
Perl for VMS supports redirection of input and output on the command line, using a subset of Bourne shell syntax:
<file reads stdin from file,
>file writes stdout to file,
>>file appends stdout to file,
2>file writes stderr to file,
2>>file appends stderr to file, and
2>&1 redirects stderr to stdout.
In addition, output may be piped to a subprocess, using the character '|'. Anything after this character on the command line is passed to a subprocess for execution; the subprocess takes the output of Perl as its input.
Finally, if the command line ends with '&', the entire command is run in the background as an asynchronous subprocess.
The following command line switches behave differently under VMS than described in the perlrun manpage. Note also that in order to pass uppercase switches to Perl, you need to enclose them in double-quotes on the command line, since the CRTL downcases all unquoted strings.
If the -i switch is present but no extension for a backup
copy is given, then inplace editing creates a new version of
a file; the existing copy is not deleted. (Note that if
an extension is given, an existing file is renamed to the backup
file, as is the case under other operating systems, so it does
not remain as a previous version under the original filename.)
If the "-S" or -"S" switch is present and the script
name does not contain a directory, then Perl translates the
logical name DCL$PATH as a searchlist, using each translation
as a directory in which to look for the script. In addition,
if no file type is specified, Perl looks in each directory
for a file matching the name specified, with a blank type,
a type of .pl, and a type of .com, in that order.
The -u switch causes the VMS debugger to be invoked
after the Perl program is compiled, but before it has
run. It does not create a core dump file.
As of the time this document was last revised, the following Perl functions were implemented in the VMS port of Perl (functions marked with * are discussed in more detail below):
file tests*, abs, alarm, atan, backticks*, binmode*, bless,
caller, chdir, chmod, chown, chomp, chop, chr,
close, closedir, cos, crypt*, defined, delete,
die, do, dump*, each, endpwent, eof, eval, exec*,
exists, exit, exp, fileno, getc, getlogin, getppid,
getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
grep, hex, import, index, int, join, keys, kill*,
last, lc, lcfirst, length, local, localtime, log, m//,
map, mkdir, my, next, no, oct, open, opendir, ord, pack,
pipe, pop, pos, print, printf, push, q//, qq//, qw//,
qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
require, reset, return, reverse, rewinddir, rindex,
rmdir, s///, scalar, seek, seekdir, select(internal),
select (system call)*, setpwent, shift, sin, sleep,
sort, splice, split, sprintf, sqrt, srand, stat,
study, substr, sysread, system*, syswrite, tell,
telldir, tie, time, times*, tr///, uc, ucfirst, umask,
undef, unlink*, unpack, untie, unshift, use, utime*,
values, vec, wait, waitpid*, wantarray, warn, write, y///
The following functions were not implemented in the VMS port, and calling them produces a fatal error (usually) or undefined behavior (rarely, we hope):
chroot, dbmclose, dbmopen, flock, fork*,
getpgrp, getpriority, getgrent, getgrgid,
getgrnam, setgrent, endgrent, ioctl, link, lstat,
msgctl, msgget, msgsend, msgrcv, readlink, semctl,
semget, semop, setpgrp, setpriority, shmctl, shmget,
shmread, shmwrite, socketpair, symlink, syscall
The following functions are available on Perls compiled with Dec C 5.2 or greater and running VMS 7.0 or greater:
truncate
The following functions are available on Perls built on VMS 7.2 or greater:
fcntl (without locking)
The following functions may or may not be implemented, depending on what type of socket support you've built into your copy of Perl:
accept, bind, connect, getpeername,
gethostbyname, getnetbyname, getprotobyname,
getservbyname, gethostbyaddr, getnetbyaddr,
getprotobynumber, getservbyport, gethostent,
getnetent, getprotoent, getservent, sethostent,
setnetent, setprotoent, setservent, endhostent,
endnetent, endprotoent, endservent, getsockname,
getsockopt, listen, recv, select(system call)*,
send, setsockopt, shutdown, socket
The tests -b, -B, -c, -C, -d, -e, -f,
-o, -M, -s, -S, -t, -T, and -z work as
advertised. The return values for -r, -w, and -x
tell you whether you can actually access the file; this may
not reflect the UIC-based file protections. Since real and
effective UIC don't differ under VMS, -O, -R, -W,
and -X are equivalent to -o, -r, -w, and -x.
Similarly, several other tests, including -A, -g, -k,
-l, -p, and -u, aren't particularly meaningful under
VMS, and the values returned by these tests reflect whatever
your CRTL stat() routine does to the equivalent bits in the
st_mode field. Finally, -d returns true if passed a device
specification without an explicit directory (e.g. DUA1:), as
well as if passed a directory.
Note: Some sites have reported problems when using the file-access
tests (-r, -w, and -x) on files accessed via DEC's DFS.
Specifically, since DFS does not currently provide access to the
extended file header of files on remote volumes, attempts to
examine the ACL fail, and the file tests will return false,
with $! indicating that the file does not exist. You can
use stat on these files, since that checks UIC-based protection
only, and then manually check the appropriate bits, as defined by
your C compiler's stat.h, in the mode value it returns, if you
need an approximation of the file's protections.
Backticks create a subprocess, and pass the enclosed string
to it for execution as a DCL command. Since the subprocess is
created directly via lib$spawn(), any valid DCL command string
may be specified.
The binmode operator will attempt to insure that no translation
of carriage control occurs on input from or output to this filehandle.
Since this involves reopening the file and then restoring its
file position indicator, if this function returns FALSE, the
underlying filehandle may no longer point to an open file, or may
point to a different position in the file than before binmode
was called.
Note that binmode is generally not necessary when using normal
filehandles; it is provided so that you can control I/O to existing
record-structured files when necessary. You can also use the
vmsfopen function in the VMS::Stdio extension to gain finer
control of I/O to files and devices with different record structures.
The crypt operator uses the sys$hash_password system
service to generate the hashed representation of PLAINTEXT.
If USER is a valid username, the algorithm and salt values
are taken from that user's UAF record. If it is not, then
the preferred algorithm and a salt of 0 are used. The
quadword encrypted value is returned as an 8-character string.
The value returned by crypt may be compared against
the encrypted password from the UAF returned by the getpw*
functions, in order to authenticate users. If you're
going to do this, remember that the encrypted password in
the UAF was generated using uppercase username and
password strings; you'll have to upcase the arguments to
crypt to insure that you'll get the proper value:
sub validate_passwd {
my($user,$passwd) = @_;
my($pwdhash);
if ( !($pwdhash = (getpwnam($user))[1]) ||
$pwdhash ne crypt("\U$passwd","\U$name") ) {
intruder_alert($name);
}
return 1;
}
Rather than causing Perl to abort and dump core, the dump
operator invokes the VMS debugger. If you continue to
execute the Perl program under the debugger, control will
be transferred to the label specified as the argument to
dump, or, if no label was specified, back to the
beginning of the program. All other state of the program
(e.g. values of variables, open file handles) are not
affected by calling dump.
A call to exec will cause Perl to exit, and to invoke the command
given as an argument to exec via lib$do_command. If the
argument begins with '@' or '$' (other than as part of a filespec),
then it is executed as a DCL command. Otherwise, the first token on
the command line is treated as the filespec of an image to run, and
an attempt is made to invoke it (using .Exe and the process
defaults to expand the filespec) and pass the rest of exec's
argument to it as parameters. If the token has no file type, and
matches a file with null type, then an attempt is made to determine
whether the file is an executable image which should be invoked
using MCR or a text file which should be passed to DCL as a
command procedure.
While in principle the fork operator could be implemented via
(and with the same rather severe limitations as) the CRTL vfork()
routine, and while some internal support to do just that is in
place, the implementation has never been completed, making fork
currently unavailable. A true kernel fork() is expected in a
future version of VMS, and the pseudo-fork based on interpreter
threads may be available in a future version of Perl on VMS (see
the perlfork manpage). In the meantime, use system, backticks, or piped
filehandles to create subprocesses.
These operators obtain the information described in the perlfunc manpage,
if you have the privileges necessary to retrieve the named user's
UAF information via sys$getuai. If not, then only the $name,
$uid, and $gid items are returned. The $dir item contains
the login directory in VMS syntax, while the $comment item
contains the login directory in Unix syntax. The $gcos item
contains the owner field from the UAF record. The $quota
item is not used.
The gmtime operator will function properly if you have a
working CRTL gmtime() routine, or if the logical name
SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
which must be added to UTC to yield local time. (This logical
name is defined automatically if you are running a version of
VMS with built-in UTC support.) If neither of these cases is
true, a warning message is printed, and undef is returned.
In most cases, kill is implemented via the CRTL's kill()
function, so it will behave according to that function's
documentation. If you send a SIGKILL, however, the $DELPRC system
service is called directly. This insures that the target
process is actually deleted, if at all possible. (The CRTL's kill()
function is presently implemented via $FORCEX, which is ignored by
supervisor-mode images like DCL.)
Also, negative signal values don't do anything special under VMS; they're just converted to the corresponding positive value.
See the entry on backticks above.
If Perl was not built with socket support, the system call
version of select is not available at all. If socket
support is present, then the system call version of
select functions only for file descriptors attached
to sockets. It will not provide information about regular
files or pipes, since the CRTL select() routine does not
provide this functionality.
Since VMS keeps track of files according to a different scheme
than Unix, it's not really possible to represent the file's ID
in the st_dev and st_ino fields of a struct stat. Perl
tries its best, though, and the values it uses are pretty unlikely
to be the same for two different files. We can't guarantee this,
though, so caveat scriptor.
The system operator creates a subprocess, and passes its
arguments to the subprocess for execution as a DCL command.
Since the subprocess is created directly via lib$spawn(), any
valid DCL command string may be specified. If the string begins with
'@', it is treated as a DCL command unconditionally. Otherwise, if
the first token contains a character used as a delimiter in file
specification (e.g. : or ]), an attempt is made to expand it
using a default type of .Exe and the process defaults, and if
successful, the resulting file is invoked via MCR. This allows you
to invoke an image directly simply by passing the file specification
to system, a common Unixish idiom. If the token has no file type,
and matches a file with null type, then an attempt is made to
determine whether the file is an executable image which should be
invoked using MCR or a text file which should be passed to DCL
as a command procedure.
If LIST consists of the empty string, system spawns an
interactive DCL subprocess, in the same fashion as typing
SPAWN at the DCL prompt.
Perl waits for the subprocess to complete before continuing
execution in the current process. As described in the perlfunc manpage,
the return value of system is a fake ``status'' which follows
POSIX semantics unless the pragma use vmsish 'status' is in
effect; see the description of $? in this document for more
detail.
The value returned by time is the offset in seconds from
01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
to make life easier for code coming in from the POSIX/Unix world.
The array returned by the times operator is divided up
according to the same rules the CRTL times() routine.
Therefore, the ``system time'' elements will always be 0, since
there is no difference between ``user time'' and ``system'' time
under VMS, and the time accumulated by a subprocess may or may
not appear separately in the ``child time'' field, depending on
whether times keeps track of subprocesses separately. Note
especially that the VAXCRTL (at least) keeps track only of
subprocesses spawned using the fork manpage and exec; it will not
accumulate the times of subprocesses spawned via pipes, system,
or backticks.
unlink will delete the highest version of a file only; in
order to delete all versions, you need to say
1 while unlink LIST;
You may need to make this change to scripts written for a
Unix system which expect that after a call to unlink,
no files with the names passed to unlink will exist.
(Note: This can be changed at compile time; if you
use Config and $Config{'d_unlink_all_versions'} is
define, then unlink will delete all versions of a
file on the first call.)
unlink will delete a file if at all possible, even if it
requires changing file protection (though it won't try to
change the protection of the parent directory). You can tell
whether you've got explicit delete access to a file by using the
VMS::Filespec::candelete operator. For instance, in order
to delete only files to which you have delete access, you could
say something like
sub safe_unlink {
my($file,$num);
foreach $file (@_) {
next unless VMS::Filespec::candelete($file);
$num += unlink $file;
}
$num;
}
(or you could just use VMS::Stdio::remove, if you've installed
the VMS::Stdio extension distributed with Perl). If unlink has to
change the file protection to delete the file, and you interrupt it
in midstream, the file may be left intact, but with a changed ACL
allowing you delete access.
Since ODS-2, the VMS file structure for disk files, does not keep track of access times, this operator changes only the modification time of the file (VMS revision date).
If PID is a subprocess started by a piped open() (see the open manpage),
waitpid will wait for that subprocess, and return its final status
value in $?. If PID is a subprocess created in some other way (e.g.
SPAWNed before Perl was invoked), waitpid will simply check once per
second whether the process has completed, and return when it has. (If
PID specifies a process that isn't a subprocess of the current process,
and you invoked Perl with the -w switch, a warning will be issued.)
Returns PID on success, -1 on error. The FLAGS argument is ignored in all cases.
The following VMS-specific information applies to the indicated ``special'' Perl variables, in addition to the general information in the perlvar manpage. Where there is a conflict, this information takes precedence.
The operation of the %ENV array depends on the translation
of the logical name PERL_ENV_TABLES. If defined, it should
be a search list, each element of which specifies a location
for %ENV elements. If you tell Perl to read or set the
element $ENV{name}, then Perl uses the translations of
PERL_ENV_TABLES as follows:
This string tells Perl to consult the CRTL's internal environ
array of key-value pairs, using name as the key. In most cases,
this contains only a few keys, but if Perl was invoked via the C
exec[lv]e() function, as is the case for CGI processing by some
HTTP servers, then the environ array may have been populated by
the calling program.
A string beginning with CLISYM_tells Perl to consult the CLI's
symbol tables, using name as the name of the symbol. When reading
an element of %ENV, the local symbol table is scanned first, followed
by the global symbol table.. The characters following CLISYM_ are
significant when an element of %ENV is set or deleted: if the
complete string is CLISYM_LOCAL, the change is made in the local
symbol table; otherwise the global symbol table is changed.
If an element of PERL_ENV_TABLES translates to any other string, that string is used as the name of a logical name table, which is consulted using name as the logical name. The normal search order of access modes is used.
PERL_ENV_TABLES is translated once when Perl starts up; any changes
you make while Perl is running do not affect the behavior of %ENV.
If PERL_ENV_TABLES is not defined, then Perl defaults to consulting
first the logical name tables specified by LNM$FILE_DEV, and then
the CRTL environ array.
In all operations on %ENV, the key string is treated as if it were entirely uppercase, regardless of the case actually specified in the Perl expression.
When an element of %ENV is read, the locations to which
PERL_ENV_TABLES points are checked in order, and the value
obtained from the first successful lookup is returned. If the
name of the %ENV element contains a semi-colon, it and
any characters after it are removed. These are ignored when
the CRTL environ array or a CLI symbol table is consulted.
However, the name is looked up in a logical name table, the
suffix after the semi-colon is treated as the translation index
to be used for the lookup. This lets you look up successive values
for search list logical names. For instance, if you say
$ Define STORY once,upon,a,time,there,was
$ perl -e "for ($i = 0; $i <= 6; $i++) " -
_$ -e "{ print $ENV{'story;'.$i},' '}"
Perl will print ONCE UPON A TIME THERE WAS, assuming, of course,
that PERL_ENV_TABLES is set up so that the logical name story
is found, rather than a CLI symbol or CRTL environ element with
the same name.
When an element of %ENV is set to a defined string, the
corresponding definition is made in the location to which the
first translation of PERL_ENV_TABLES points. If this causes a
logical name to be created, it is defined in supervisor mode.
(The same is done if an existing logical name was defined in
executive or kernel mode; an existing user or supervisor mode
logical name is reset to the new value.) If the value is an empty
string, the logical name's translation is defined as a single NUL
(ASCII 00) character, since a logical name cannot translate to a
zero-length string. (This restriction does not apply to CLI symbols
or CRTL environ values; they are set to the empty string.)
An element of the CRTL environ array can be set only if your
copy of Perl knows about the CRTL's setenv() function. (This is
present only in some versions of the DECCRTL; check $Config{d_setenv}
to see whether your copy of Perl was built with a CRTL that has this
function.)
When an element of %ENV is set to undef,
the element is looked up as if it were being read, and if it is
found, it is deleted. (An item ``deleted'' from the CRTL environ
array is set to the empty string; this can only be done if your
copy of Perl knows about the CRTL setenv() function.) Using
delete to remove an element from %ENV has a similar effect,
but after the element is deleted, another attempt is made to
look up the element, so an inner-mode logical name or a name in
another location will replace the logical name just deleted.
In either case, only the first value found searching PERL_ENV_TABLES
is altered. It is not possible at present to define a search list
logical name via %ENV.
The element $ENV{DEFAULT} is special: when read, it returns
Perl's current default device and directory, and when set, it
resets them, regardless of the definition of PERL_ENV_TABLES.
It cannot be cleared or deleted; attempts to do so are silently
ignored.
Note that if you want to pass on any elements of the C-local environ array to a subprocess which isn't started by fork/exec, or isn't running a C program, you can ``promote'' them to logical names in the current process, which will then be inherited by all subprocesses, by saying
foreach my $key (qw[C-local keys you want promoted]) {
my $temp = $ENV{$key}; # read from C-local array
$ENV{$key} = $temp; # and define as logical name
}
(You can't just say $ENV{$key} = $ENV{$key}, since the
Perl optimizer is smart enough to elide the expression.)
Don't try to clear %ENV by saying %ENV = ();, it will throw
a fatal error. This is equivalent to doing the following from DCL:
DELETE/LOGICAL *
You can imagine how bad things would be if, for example, the SYS$MANAGER or SYS$SYSTEM logicals were deleted.
At present, the first time you iterate over %ENV using
keys, or values, you will incur a time penalty as all
logical names are read, in order to fully populate %ENV.
Subsequent iterations will not reread logical names, so they
won't be as slow, but they also won't reflect any changes
to logical name tables caused by other programs.
You do need to be careful with the logicals representing process-permanent
files, such as SYS$INPUT and SYS$OUTPUT. The translations for these
logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
stripped off if you want to use it. (In previous versions of Perl it wasn't
possible to get the values of these logicals, as the null byte acted as an
end-of-string marker)
The string value of $! is that returned by the CRTL's
strerror() function, so it will include the VMS message for
VMS-specific errors. The numeric value of $! is the
value of errno, except if errno is EVMSERR, in which
case $! contains the value of vaxc$errno. Setting $!
always sets errno to the value specified. If this value is
EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
that the string value of $! won't reflect the VMS error
message from before $! was set.
This variable provides direct access to VMS status values
in vaxc$errno, which are often more specific than the
generic Unix-style error messages in $!. Its numeric value
is the value of vaxc$errno, and its string value is the
corresponding VMS message string, as retrieved by sys$getmsg().
Setting $^E sets vaxc$errno to the value specified.
The ``status value'' returned in $? is synthesized from the
actual exit status of the subprocess in a way that approximates
POSIX wait(5) semantics, in order to allow Perl programs to
portably test for successful completion of subprocesses. The
low order 8 bits of $? are always 0 under VMS, since the
termination status of a process may or may not have been
generated by an exception. The next 8 bits are derived from
the severity portion of the subprocess' exit status: if the
severity was success or informational, these bits are all 0;
if the severity was warning, they contain a value of 1; if the
severity was error or fatal error, they contain the actual
severity bits, which turns out to be a value of 2 for error
and 4 for fatal error.
As a result, $? will always be zero if the subprocess' exit
status indicated successful completion, and non-zero if a
warning or error occurred. Conversely, when setting $? in
an END block, an attempt is made to convert the POSIX value
into a native status intelligible to the operating system upon
exiting Perl. What this boils down to is that setting $?
to zero results in the generic success value SS$_NORMAL, and
setting $? to a non-zero value results in the generic
failure status SS$_ABORT. See also exit in the perlport manpage.
The pragma use vmsish 'status' makes $? reflect the actual
VMS exit status instead of the default emulation of POSIX status
described above. This pragma also disables the conversion of
non-zero values to SS$_ABORT when setting $? in an END
block (but zero will still be converted to SS$_NORMAL).
Setting $| for an I/O stream causes data to be flushed
all the way to disk on each write (i.e. not just to
the underlying RMS buffers for a file). In other words,
it's equivalent to calling fflush() and fsync() from C.
SDBM_File works properly on VMS. It has, however, one minor difference. The database directory file created has a .sdbm_dir extension rather than a .dir extension. .dir files are VMS filesystem directory files, and using them for other purposes could cause unacceptable problems.
This document was last updated on 01-May-2002, for Perl 5, patchlevel 8.
Charles Bailey bailey@cor.newman.upenn.edu Craig Berry craigberry@mac.com Dan Sugalski dan@sidhe.org