use Graph::Directed;
my $graph = Graph::Directed->new;

# Building the graph.  In this example, edges are directed from a job to a dependency.

while (my $line = $file->getline) {
    my ($job, @deps) = split(/,/, $line);
    foreach my $dep (@deps) {
        # adds both $job and $dep as nodes in the graph if they don't exist already
        $graph->add_edge($job, $dep);
    }
}

# What does job FOO require?
say "FOO requires $_" foreach $graph->all_successors('FOO');

# Who requires FOO?
say "FOO is required by $_" foreach $graph->all_predecessors('FOO');

# Jobs that do not have prerequisites.
say "$_ can be executed right now!" foreach $graph->sink_vertices;

# Somebody messed up here:
say "A job requires itself!" if $graph->has_a_cycle;