How is %ENV copied by child processes ?

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

Maybe I'm touching some deep voodoo here, but how does one replace the version of %ENV that is used for child processes ? It seems like %ENV is just an ordinary hash, only with 'magic' scope, but the copy for forked processes isn't exactly what I expected :((

To put my question directly: how is %ENV copied by child processes ?

Some evil test code:

#!/usr/bin/perl

package Env::Tie;

use strict;
use Tie::Hash;
our @ISA = qw/Tie::StdHash/;

sub TIEHASH { bless $_[1] , $_[0] }
sub FETCH { $_[0]->{$_[1]} . '---BWUBUBWU' }
# The '---BWUBUBWU' of course being 
# dynamic generated content

package Test;

use strict;
sub print { print 'env home =', $ENV{HOME}, "\n" }

package main;

use strict;

print "Hic sunt leones\n";
print 'env home =', $ENV{HOME}, "\n";
print "lets go\n";

my %self = %ENV;
tie %ENV, 'Env::Tie', \%self;

print "tied ENV\n";
print 'env home =', $ENV{HOME}, "\n";

print "lets try it in an other package\n";
Test::print();

print "lets fork perl\n";
system(
    'perl', 
    '-e', 
    q{print 'env home =', $ENV{HOME}, "\n"} 
);

print "lets fork bash\n";
system(
    'bash', 
    '-c', 
    q{echo $HOME}
);

print "done\n";
[download]

The behaviour I'm looking for is that the forked processes use my modified ENV.

--
Jaap Karssenberg || Pardus (Larus)? <pardus@cpan.org>
>>>> Zoidberg: So many memories, so many strange fluids gushing out of patients' bodies.... <<<<

Comment on How is %ENV copied by child processes ? Download Code

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•Re: How is %ENV copied by child processes ? by merlyn (Sage) on Apr 21, 2003 at 17:58 UTC
The "copying" of a fork happens at a very low level, outside of user code space. You just end up with cloned pages. To change the `%ENV` of a child process, you have to do the fork yourself, then change the env before you exec the actual item. A skeleton of this looks like what I just posted in open-coding a system() operation. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^2: How is %ENV copied by child processes ? by Pardus (Pilgrim) on Apr 21, 2003 at 18:56 UTC
I thought of that option but I wanted to it make a module that could be used transparently. Considering the number of ways a perl program can be forked this won't be do-able :(( At least not without custom fork/system/.. routines. Well back to `use Env;` for me. -- Jaap Karssenberg \|\| Pardus (Larus)? <pardus@cpan.org> >>>> Zoidberg: So many memories, so many strange fluids gushing out of patients' bodies.... <<<<	[reply] [d/l]
Re: How is %ENV copied by child processes ? (untie) by tye (Sage) on Apr 21, 2003 at 20:36 UTC
You have to make your tied %ENV update the underlying %ENV which invokes the "magic" which calls putenv which updates the "real" environment of your process (which is what will be copied to the children). I don't see any use for appending '---BWUBUBWU' to the end of each environment value so I'll assume this is just a silly example. If you want to tell us what you are really trying to do, then someone will likely show you how to write code that actually does that. - tye	[reply]
Re^2: How is %ENV copied by child processes ? by Pardus (Pilgrim) on Apr 22, 2003 at 10:52 UTC
Well, one example would be incorporating the funtionality of the Env module for arrays, but then on an other level. An other example would be putting code refs in @PATH which do dynamical lookups. Allowing for the same kind of hooks as supported for @INC and %INC. But since I understand this is not a 'perl space' operation but lives in an other dimension of the OS, I just do the same stuff with some quick hacks. -- Jaap Karssenberg \|\| Pardus (Larus)? <pardus@cpan.org> >>>> Zoidberg: So many memories, so many strange fluids gushing out of patients' bodies.... <<<<	[reply]