Question

I was posed an interesting question from a colleague for an operational pain point we currently have, and am curious if there’s anything out there (utility/library/algorithm) that might help automate this.

Say you have a list of literal values (in our cases, they are URLs). What we want to do is, based on this list, come up with a single regex that matches all of those literal items.

So, if my list is:

http://www.example.com
http://www.example.com/subdir
http://foo.example.com

The simplest answer is

^(http://www.example.com|http://www.example.com/subdir|http://foo.example.com)$

but this gets large for lots of data, and we have a length limit we’re trying to stay under.

Currently we manually write the regexes but this doesn’t scale very well nor is it a great use of anyone’s time. Is there a more automated way of decomposing the source data to come up with a length-optimal regex that matches all of the source values?

Answer 1

The Aho-Corasick matching algorithm constructs a finite automaton to match multiple strings. You could convert the automaton to its equivalent regex but it is simpler to use the automaton directly (this is what the algorithm does.)