WRT this reply:

grep {
    croak "This doesn't look like start-end\n" unless /(.*)-(.*)/;
    push @a, $1;
    push @b, $2;
} @cidr;
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I've seen map (mis)used in place of a for-loop before (although I've never understood the attraction of this unclean practice), but never grep. Purely to satisfy my idle curiosity, can anyone speculate on the rationale for this odd syntactic tic? Why not just

for (@cidr) {
    croak "This doesn't look like start-end\n" unless /(.*)-(.*)/;
    push @a, $1;
    push @b, $2;
    }
[download]