I bet is not perl emitting this message; it comes or from your own script or by some module you use. Infact all messages emitted by perl itself are in perldiag and nothing similar to what you received is there.

L*

PS meh! since you provided some more info I won the bet: look here

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