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perlvms - VMS-specific documentation for Perl |
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@newman.upenn.edu.
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, 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
[.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<*.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.
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 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:
<F<file> reads stdin from F<file>,
>F<file> writes stdout to F<file>,
>>F<file> appends stdout to F<file>,
2>F<file> writes stderr to F<file>, and
2>>F<file> appends stderr to F<file>.
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.
-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 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 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, 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
-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 $! indicating that the file does not exist. You can
use stat on these files, since that checks UIC-based protection
only, and then manually check the appropriate bits, as defined by
your
C compiler's stat.h, in the mode value it returns, if you
need an approximation of the file's protections.
lib$spawn(), any valid
DCL command string
may be specified.
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 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
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 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 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.
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 $quota
item is not used.
gmtime operator will function properly if you have a
working
CRTL gmtime() routine, or if the logical name
SYS$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 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
$FORCEX, which is ignored by
supervisor-mode images like
DCL.)
Also, negative signal values don't do anything special under VMS; they're just converted to the corresponding positive value.
backticks above.
select is not available at all. If socket
support is present, then the system call version of
select functions only for file descriptors attached
to sockets. It will not provide information about regular
files or pipes, since the
CRTL select() routine does not
provide this functionality.
st_dev and st_ino fields of a struct stat. Perl
tries its best, though, and the values it uses are pretty unlikely
to be the same for two different files. We can't guarantee this,
though, so caveat scriptor.
system operator creates a subprocess, and passes its
arguments to the subprocess for execution as a
DCL command.
Since the subprocess is created directly via lib$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; 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 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 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 fork 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.
open() (see 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.
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.
%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 $ENV{name}, then Perl uses the translations of
PERL_ENV_TABLES as follows:
environ
array of key-value pairs, using name as the key. In most cases,
this contains only a few keys, but if Perl was invoked via the
C
exec[lv]e() function, as is the case for
CGI processing by some
HTTP servers, then the environ array may have been populated by
the calling program.
CLISYM_tells Perl to consult the CLI's
symbol tables, using name as the name of the symbol. When reading
an element of %ENV, the local symbol table is scanned first, followed
by the global symbol table.. The characters following CLISYM_ are
significant when an element of %ENV is set or deleted: if the
complete string is CLISYM_LOCAL, the change is made in the local
symbol table; otherwise the global symbol table is changed.
PERL_ENV_TABLES is translated once when Perl starts up; any changes
you make while Perl is running do not affect the behavior of %ENV.
If
PERL_ENV_TABLES is not defined, then Perl defaults to consulting
first the logical name tables specified by
LNM$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)
$! 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.
$!. Its numeric value
is the value of vaxc$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.
$? 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;
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.).
$?, 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.
$| 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 26-Feb-2000, for Perl 5, patchlevel 6.
Charles Bailey <bailey@cor.newman.upenn.edu> Dan Sugalski <dan@sidhe.org>
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perlvms - VMS-specific documentation for Perl |