Currency Regular Expression

Question

I think I created a working regular expression for what I need. Just wondering if anyone can break it or see a shorter way to write it.

The regular expression shoul

Answer 1

You can express "between one and six digits; comma before the last three digits is optional" a bit more tersely as \d{1,3}(,?\d{3})?. This also allows you to include only two copies of (\.\d{1,2})?: one for positive and one for negative, instead of one for positive-without-comma, one for positive-with-comma, etc.

Also, \d{1,2} can be shortened slightly to \d\d?, though I'm not sure if that's an improvement.

So, barring some notation like (?(1)) to test if a backreference is set, here's the shortest version I see:

^(\$?\d{1,3}(,?\d{3})?(\.\d\d?)?|\(\$?\d{1,3}(,?\d{3})?(\.\d\d?)?\))$

One perhaps-undesirable aspect of your regex, and of this one, is that they will allow something like $00,012.7, even though no one uses leading zeroes that way. You can address that by requiring the first digit to be nonzero, and then adding a special case to handle $0 and (0.12) and so on:

^(\$?(0|[1-9]\d{0,2}(,?\d{3})?)(\.\d\d?)?|\(\$?(0|[1-9]\d{0,2}(,?\d{3})?)(\.\d\d?)?\))$

Edited to add: using a lookahead assertion like F.J suggests in his/her answer, the latter can be shortened to:

^(?!\(.*[^)]$|[^(].*\)$)\(?\$?(0|[1-9]\d{0,2}(,?\d{3})?)(\.\d\d?)?\)?$