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perlvms (1)
>> perlvms (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
perlvms (1) ( Разные man: Команды и прикладные программы пользовательского уровня )
NAME
perlvms - VMS-specific documentation for Perl
DESCRIPTION
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 [email protected].
Installation
Directions for building and installing Perl 5 can be found
in the file README.vms in the main source directory of the
Perl distribution..
Organization of Perl Images
CoreImages
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.
PerlExtensions
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 `use'd or `require'd 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.
Installingstaticextensions
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).
Installingdynamicextensions
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,
you shouldn't nest the source directory too deeply in your
directory structure, lest you eccedd 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
[.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.
File specifications
Syntax
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 fle
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.
Wildcardexpansion
File specifications containing wildcards are allowed both on
the command line and within Perl globs (e.g. <C<*.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.
In both cases, 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.
Pipes
Input and output pipes to Perl filehandles are supported;
the "file name" is passed to lib$spawn() for asynchronous
execution. You should be careful to close any pipes you
have opened in a Perl script, lest you leave any "orphaned"
subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose
output is used as the return value of the expression. The
string between the backticks is handled as if it were the
argument to the `system' operator (see below). In this
case, Perl will wait for the subprocess to complete before
continuing.
PERL5LIB and PERLLIB
The PERL5LIB and PERLLIB logical names work as documented
the perl manpage, except that the element separator is '|'
instead of ':'. The directory specifications may use either
VMS or Unix syntax.
Command line
I/Oredirectionandbackgrounding
Perl for VMS supports redirection of input and output on the
command line, using a subset of Bourne shell syntax:
<FCommand lineswitches
The following command line switches behave differently under
VMS than described in the perlrun manpage. Note also that
in order to pass uppercase switches to Perl, you need to
enclose them in double-quotes on the command line, since the
CRTL downcases all unquoted strings.
-i If the `-i' switch is present but no extension for a
backup copy is given, then inplace editing creates a new
version of a file; the existing copy is not deleted.
(Note that if an extension is given, an existing file is
renamed to the backup file, as is the case under other
operating systems, so it does not remain as a previous
version under the original filename.)
-S If the `-S' switch is present and the script name does
not contain a directory, then Perl translates the
logical name DCL$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.
-u 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.
Perl functions
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, fork*, getc, getlogin,
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, fcntl, flock,
getpgrp, getppid, 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 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
File tests
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 `$!'
indicating that the file does not exist. You can use
`stat' on these files, since that checks UIC-based
protection only, and then manually check the appropriate
bits, as defined by your C compiler's stat.h, in the
mode value it returns, if you need an approximation of
the file's protections.
backticks
Backticks create a subprocess, and pass the enclosed
string to it for execution as a DCL command. Since the
subprocess is created directly via `lib$spawn()', any
valid DCL command string may be specified.
binmode FILEHANDLE
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.
crypt PLAINTEXT, USER
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;
}
dump
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'.
exec LIST
The `exec' operator behaves in one of two different
ways. If called after a call to `fork', it will invoke
the CRTL `execv()' routine, passing its arguments to the
subprocess created by `fork' for execution. In this
case, it is subject to all limitations that affect
`execv()'. (In particular, this usually means that the
command executed in the subprocess must be an image
compiled from C source code, and that your options for
passing file descriptors and signal handlers to the
subprocess are limited.)
If the call to `exec' does not follow a call to `fork',
it 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.
You can use `exec' in both ways within the same script,
as long as you call `fork' and `exec' in pairs. Perl
keeps track of how many times `fork' and `exec' have
been called, and will call the CRTL `execv()' routine if
there have previously been more calls to `fork' than to
`exec'.
fork
The `fork' operator works in the same way as the CRTL
`vfork()' routine, which is quite different under VMS
than under Unix. Specifically, while `fork' returns 0
after it is called and the subprocess PID after `exec'
is called, in both cases the thread of execution is
within the parent process, so there is no opportunity to
perform operations in the subprocess before calling
`exec'.
In general, the use of `fork' and `exec' to create
subprocess is not recommended under VMS; wherever
possible, use the `system' operator or piped filehandles
instead.
getpwent
getpwnam
getpwuid
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.
gmtime
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.
kill
In most cases, `kill' 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 $FORCEX, which is
ignored by supervisor-mode images like DCL.)
Also, negative signal values don't do anything special
under VMS; they're just converted to the corresponding
positive value.
qx//
See the entry on `backticks' above.
select (system call)
If Perl was not built with socket support, the system
call version of `select' is not available at all. If
socket support is present, then the system call version
of `select' functions only for file descriptors attached
to sockets. It will not provide information about
regular files or pipes, since the CRTL `select()'
routine does not provide this functionality.
stat EXPR
Since VMS keeps track of files according to a different
scheme than Unix, it's not really possible to represent
the file's ID in the `st_dev' and `st_ino' fields of a
`struct stat'. Perl tries its best, though, and the
values it uses are pretty unlikely to be the same for
two different files. We can't guarantee this, though,
so caveat scriptor.
system LIST
The `system' operator creates a subprocess, and passes
its arguments to the subprocess for execution as a DCL
command. Since the subprocess is created directly via
`lib$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
typiing 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; see the description of `$?' in this document
for more detail. The actual VMS exit status of the
subprocess is available in `$^S' (as long as you haven't
used another Perl function that resets `$?' and `$^S' in
the meantime).
time
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.
times
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
subprocess may or may not appear separately in the
"child time" field, depending on whether the times
manpage keeps track of subprocesses separately. Note
especially that the VAXCRTL (at least) keeps track only
of subprocesses spawned using the fork manpage and the
exec manpage; it will not accumulate the times of
suprocesses spawned via pipes, the system manpage, or
backticks.
unlink LIST
`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;
}
$num;
}
(or you could just use `VMS::Stdio::remove', if you've
installed the VMS::Stdio extension distributed with
Perl). If `unlink' has to change the file protection to
delete the file, and you interrupt it in midstream, the
file may be left intact, but with a changed ACL allowing
you delete access.
utime LIST
Since ODS-2, the VMS file structure for disk files, does
not keep track of access times, this operator changes
only the modification time of the file (VMS revision
date).
waitpid PID,FLAGS
If PID is a subprocess started by a piped the open
manpage, `waitpid' will wait for that subprocess, and
return its final status value. If PID is a subprocess
created in some other way (e.g. SPAWNed before Perl was
invoked), or is not a subprocess of the current process,
`waitpid' will check once per second whether the process
has completed, and when it has, will return 0. (If PID
specifies a process that isn't a subprocess of the
current process, and you invoked Perl with the `-w'
switch, a warning will be issued.)
The FLAGS argument is ignored in all cases.
Perl variables
The following VMS-specific information applies to the
indicated "special" Perl variables, in addition to the
general information in the perlvar manpage. Where there is
a conflict, this infrmation takes precedence.
%ENV
The operation of the `%ENV' array depends on the
translation of the logical name PERL_ENV_TABLES. If
defined, it should be a search list, each element of
which specifies a location for `%ENV' elements. If you
tell Perl to read or set the element `$ENV{'name`}',
then Perl uses the translations of PERL_ENV_TABLES as
follows:
CRTL_ENV
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.
CLISYM_[LOCAL]
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.
Any other string
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.)
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.
$^E This variable provides direct access to VMS status
values in vaxc$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 `$?' are
always 0 under VMS, since the termination status of a
process may or may not have been generated by an
exception. The next 8 bits are derived from severity
portion of the subprocess' exit status: if the severity
was success or informational, these bits are all 0;
otherwise, they contain the severity value shifted left
one bit. As a result, `$?' will always be zero if the
subprocess' exit status indicated successful completion,
and non-zero if a warning or error occurred. The actual
VMS exit status may be found in `$^S' (q.v.).
$^S Under VMS, this is the 32-bit VMS status value returned
by the last subprocess to complete. Unlink `$?', no
manipulation is done to make this look like a POSIX
wait(5) value, so it may be treated as a normal VMS
status value.
$| Setting `$|' 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.
Standard modules with VMS-specific differences
SDBM_File
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.
Revision date
This document was last updated on 26-Feb-2000, for Perl 5,
patchlevel 6.
