you need to assign the return value to something, as in my $status = my_sub( $my, $args );

read perlsub for more info.

Update: here's an example (adapted from perlsub)...

package return_test;

sub max 
{
    my $max = shift @_;
    foreach my $foo (@_) 
    {
        $max = $foo if $max < $foo;
    }
    return $max;
}

package main;

$bestday = return_test::max( $mon, $tue, $wed, $thu, $fri );
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~Particle *accelerates*