Environment Variable Setting

austinj has asked for the wisdom of the Perl Monks concerning the following question:

My ultimate goal would be to write a script in perl that accomplishes the same thing the following csh code does. I tried to simply source the csh code (located in the file sge_sigma.csh) but have since learned that this creates a child process and as such environment variables are not passed upstream. SO - I have been unsucessful in converting the following code from csh to perl.

#! /bin/csh

setenv SGE_ROOT /appl/lsf/grid_bins

set ARCH = `$SGE_ROOT/util/arch`
set DEFAULTMANPATH = `$SGE_ROOT/util/arch -m`
set MANTYPE = `$SGE_ROOT/util/arch -mt`

setenv SGE_CELL default
unsetenv SGE_QMASTER_PORT
unsetenv SGE_EXECD_PORT

# library path setting required only for architectures where RUNPATH i
+s not supported
if ( $?MANPATH == 1 ) then
   setenv MANPATH $SGE_ROOT/${MANTYPE}:$MANPATH
else
   setenv MANPATH $SGE_ROOT/${MANTYPE}:$DEFAULTMANPATH
endif

set path = ( $SGE_ROOT/bin/$ARCH $path )
switch ($ARCH)
case "sol*":
case "lx*":
   breaksw
case "*":
   set shlib_path_name = `$SGE_ROOT/util/arch -lib`
   if ( `eval echo '$?'$shlib_path_name` ) then
      set old_value = `eval echo '$'$shlib_path_name`
      setenv $shlib_path_name "$SGE_ROOT/lib/$ARCH":"$old_value"
   else
      setenv $shlib_path_name $SGE_ROOT/lib/$ARCH
   endif
   unset shlib_path_name
endsw
unset ARCH DEFAULTMANPATH MANTYPE old_value
[download]

so far I have

#!/usr/local/bin/perl -w

use strict;
use Switch;

$ENV{SGE_ROOT} = "/appl/lsf/grid_bins";

my $ARCH = $ENV{SGE_ROOT} . "/util/arch";
my $DEFAULTMANPATH = $ENV{SGE_ROOT} . "/util/arch -m";
my $MANTYPE = $ENV{SGE_ROOT} . "/util/arch -mt";

$ENV{SGE_CELL} = "default";
delete($ENV{SGE_QMASTER_PORT});
delete($ENV{SGE_EXECD_PORT});

# NEED HELP HERE
[download]

if there is a cleaner way to somehow "source" the csh file or any other suggestions I'm open to whatever. Thanks in advance for your help, Austin

Comment on Environment Variable Setting Select or Download Code

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Re: Environment Variable Setting by chrestomanci (Priest) on Apr 23, 2012 at 16:33 UTC
On unix, child processes inherit the environment from their parent, but any changes they make are not propagated back to the parent when the child quits. Your csh script works because it runs in the same process as your shell, so changes made in it remain after the script exits. The usual way to create a perl script that modifies the environment is to have it emit a shell script on stdout, and then eval the script's output. eg: eval `perl set_my_env.pl` The perl script just prints a series of `setenv NAME value` lines.	[reply] [d/l] [select]
Re: Environment Variable Setting by Corion (Patriarch) on Apr 23, 2012 at 16:30 UTC
See Get default login environment and also Shell, of which Shell::GetEnv and Shell::EnvImporter seem as if they do the same as that node (and its discussion).	[reply]
Re: Environment Variable Setting by aaron_baugher (Curate) on Apr 23, 2012 at 17:43 UTC
When you source a file in the shell, that actually does what you want -- it doesn't create a sub-shell, but interprets the file in the current shell, allowing it to change the environment. That's unlike running the script as an executable, which does fire up a new shell process, which is unable to change the environment of its parent. So `source sge_sigma.csh` should do what you want. Aaron B. My Woefully Neglected Blog, where I occasionally mention Perl.	[reply] [d/l]
Re^2: Environment Variable Setting by austinj (Acolyte) on Apr 23, 2012 at 19:03 UTC
this is only true within csh correct? I can't simply `source sge_sigma.csh;` Does perl have a "source" command? `system("source sge_sigma.csh");` doesn't work Thanks!	[reply] [d/l] [select]
Re^3: Environment Variable Setting by aaron_baugher (Curate) on Apr 23, 2012 at 21:14 UTC
If you're in a csh shell (or most other shells), then yes, entering `source sge_sigma.csh` at the command line will cause the contents of that file to be interpreted and take effect in the current shell. `bannor:~/work/perl/monks$ csh bannor:~/work/perl/monks> cat test.csh setenv MYTEST "This is a test." bannor:~/work/perl/monks> echo $MYTEST MYTEST: Undefined variable. bannor:~/work/perl/monks> source test.csh bannor:~/work/perl/monks> echo $MYTEST This is a test.` [download] You can't do this from within a Perl script, because it's a sub-process of the shell, so it can't change its parent's environment. To put it another way, you can change environment variables within a Perl script by use of the %ENV hash, and those will be inherited by any child processes that your Perl script spawns, but they can't go "upstream" to the parent process. Aaron B. My Woefully Neglected Blog, where I occasionally mention Perl.	[reply] [d/l] [select]
Re^4: Environment Variable Setting by Anonymous Monk on Apr 24, 2012 at 14:50 UTC