regex - 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 should validate the following...

• Dollar sign optional
• Negative numbers signified with parenthesis, not a minus
• If negative, dollar sign should be outside the parenthesis
• Commas are optional
• Max number is 999999.99
• Min number is (999999.99)
• Decimals do not have to be supplied, but if so, no more than two digits

So here are some examples of valid ones...

9
$9
$0.99
($999,999.99)
(999999)
($999999)
(999,999)
99,999.9

This is what I have come up with:

^$?(((d{1,6}(.d{1,2})?)|(d{1,3},d{3}(.d{1,2})?)|(((d{1,6}(.d{1,2})?)|(d{1,3},d{3}(.d{1,2})?)))))$

CORRECTION, my spec was wrong, if the dollar sign is used it must be INSIDE the parenthesis.

Answer 1

Here is one shorter alternative (56 chars to your 114), which will work in almost all regex flavors:

^$?(?=(.*)|[^()]*$)(?d{1,3}(,?d{3})?(.dd?)?)?$

Example: http://www.rubular.com/r/qtYHEVzVK7

Explanation:

^                # start of string anchor
$?              # optional '$'
(?=              # only match if inner regex can match (lookahead)
   (.*)          # both '(' and ')' are present
   |               # OR
   [^()]*$         # niether '(' or ')' are present
)                # end of lookaheand
(?              # optional '('
d{1,3}          # match 1 to 3 digits
(,?d{3})?       # optionally match another 3 digits, preceeded by an optional ','
(.dd?)?       # optionally match '.' followed by 1 or 2 digits
)?              # optional ')'
$                # end of string anchor