Debugging regex from the CLI
Just stumbled across this obvious solution from the why didn’t I realize this earlier? department. GNU grep makes an great regex debugger!
The secret is combining
-P (for perlre) with
--color to color the matched pattern. For example:
% echo -e '123\n123.123' | grep -P '^\d+(?!\.\d)' 123 123.123 % echo -e '123\n123.123' | grep -P '^\d+(?![\.\d])' 123