1. A method comprising: receiving an input string; receiving a regular expression; converting, by a system comprising a hardware processor, the regular expression into a plurality of automata to extract submatches of substrings in the input string, wherein the extracting comprises: using a first automaton of the plurality of automata to determine whether the input string is in a language described by the regular expression, and to process the input string; and using states of the first automaton in a second automaton of the plurality of automata to extract the submatches; and identifying, by the system, a source of an issue in a network in response to the submatches.