You won't get much better than the foreach solution, which has the advantage of being easy to read. You could use grep to select the keys: $hash{$_} = "boom_$1" for grep /abc_(.*)_ghi/, keys %hash;

I think the way you generate your data is a bit to complex to be turned into a readable map generation: my %hash = { /abc_(.*)_ghi/ ? ($_ => "boom_$1") : ($_ => 1) } @list_of_keys; wouldn't work so well with the two (or more) separate conditions, or wouldn't be as readable as your current solution.