perl script to check what environment variables a program actually needs to run

env-necessary.pl

#! /usr/bin/env perl
use POSIX ":sys_wait_h";

my @untested = keys %ENV;

sub choose {
    return splice @untested, rand @untested, 1;
}

sub works {
    my $pid = fork;
    unless ($pid) { exec @ARGV or die "couldn't exec"; }
    my $limit = time + 3;
    do { return $? == 0 if waitpid($pid, WNOHANG) == $pid; } while time < $limit;
    kill 'TERM', $pid;
    return 1;
}

my @necessary;

sub status {
    print @untested . " elements to go, " . @necessary . " needed\n";
}

while (@untested) {
    status;
    my $var = choose;
    my $val = delete $ENV{$var};
    next if works;
    push @necessary, $var;
    $ENV{$var} = $val;
}

print "@necessary";