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
Result:
	a => 58
	b => 5381
Matching on test_389742
Result:
	a => 38
	b => 9742
Matching on test_330104
Result:
	a => 33
	b => 0104