foreach my $z ( %abc) {
    push @ab, "-$z";    
}
[download]

foreach my $z (keys %abc) {
    push @ab, "-$z";    
}
[download]

Update 1:

In fact I misunderstood the question so much as to provide complete and utter drivel as a reply - doh!!!

Update 2:

Attempted to provide a more meaningful and possibly half-sensible, reply.