pokki, absolutely brilliant! ++ I needed to see this work myself and had Graph::Easy but couldn't duplicate. The CPAN install for Graph::Directed was easy (Win7 x64 / Strawberry 5.18.1) and I whipped this up based on your example:

#!perl
use strict;
use warnings;
use Graph::Directed;
my $graph = Graph::Directed->new;

while ( my $line = <DATA> ) {
    chomp $line;
    my ( $job, @deps ) = split( /,/, $line );
    for my $dep (@deps) {
        $graph->add_edge( $job, $dep );
    }
}

for my $job ( sort ( $graph->vertices ) ) {
    print "$job requires ";
    for ( sort ( $graph->all_successors($job) ) ) {
        print "$_ ";
    }
    print "\n";
}

__DATA__
job1,
job2,job1,
job3,job2
job4,job2
job5,job2,job4
job6,jobz
joba,job4,jobb
jobz,jobbc,job2
[download]

and outputs

job1 requires
job2 requires job1
job3 requires job1 job2
job4 requires job1 job2
job5 requires job1 job2 job4
job6 requires job1 job2 jobbc jobz
joba requires job1 job2 job4 jobb
jobb requires
jobbc requires
jobz requires job1 job2 jobbc
[download]