original pseudo-regex: test_%a%b
modified regex: test_(\d{2})(?{ $mv{a} = $^N })(\d{4})(?{ $mv{b} = $^N })

Matching on test_001022
Result:
        a => 00
        b => 1022
Matching on test_585381
No keys in hash.
No match.
Matching on test_389742
No keys in hash.
No match.
Matching on test_330104
No keys in hash.
No match.