 |
Index for
Section 1 |
|
 |
Alphabetical
listing for P |
|
 |
Bottom of
page |
|
PERLVMS(1)
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
vmsperl@newman.upenn.edu.
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
Core Images
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
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.
Installing static extensions
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).
Installing dynamic extensions
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.
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 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.
Wildcard expansion
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 in the perl
manpage, except that the element separator is '|' instead of ':'. The
directory specifications may use either VMS or Unix syntax.
Command line
I/O redirection and backgrounding
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.
Command line switches
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" 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 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
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 a
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 subprocesses 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;
}
$num;
}
(or you could just use "VMS::Stdio::remove", if you've installed the
VMS::Stdio extension distributed with Perl). If "unlink" has to change
the file protection to delete the file, and you interrupt it in
midstream, the file may be left intact, but with a changed ACL allowing
you delete access.
utime LIST
Since ODS-2, the VMS file structure for disk files, does not keep track
of access times, this operator changes only the modification time of
the file (VMS revision date).
waitpid PID,FLAGS
If PID is a subprocess started by a piped "open()" (see the open
manpage), "waitpid" will wait for that subprocess, and return its final
status value. If PID is a subprocess created in some other way (e.g.
SPAWNed before Perl was invoked), or is not a subprocess of the current
process, "waitpid" will check once per second whether the process has
completed, and when it has, will return 0. (If PID specifies a process
that isn't a subprocess of the current process, and you invoked Perl
with the "-w" switch, a warning will be issued.)
The FLAGS argument is ignored in all cases.
Perl variables
The following VMS-specific information applies to the indicated "special"
Perl variables, in addition to the general information in the perlvar
manpage. Where there is a conflict, this information takes precedence.
%ENV
The operation of the "%ENV" array depends on the translation of the
logical name PERL_ENV_TABLES. If defined, it should be a search list,
each element of which specifies a location for "%ENV" elements. If you
tell Perl to read or set the element "$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.)
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.
$^E This variable provides direct access to VMS status values in
vaxc$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 "$?"
are always 0 under VMS, since the termination status of a process may
or may not have been generated by an exception. The next 8 bits are
derived from the severity portion of the subprocess' exit status: if
the severity was success or informational, these bits are all 0;
otherwise, they contain the severity value shifted left one bit. As a
result, "$?" 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.).
$^S Under VMS, this is the 32-bit VMS status value returned by the last
subprocess to complete. Unlike "$?", 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.
AUTHOR
Charles Bailey <bailey@cor.newman.upenn.edu> Dan Sugalski <dan@sidhe.org>
|
Index for
Section 1 |
|
|
Alphabetical
listing for P |
|
 |
Top of
page |
|