Simple Regular Expression matching - Currency

Just need a regular expression to match a currency entered by a user.

The acceptable formats for $100.00 would be:

100.00
100.0
100.
100

I am using this regular expression:

/\d+(\.\d{0,2})?/

But it's letting by things like:

100....
100....00

Being a novice in expression matching, I'm not sure where I'm going wrong.

I thought putting \. would ask for exactly one '.'

This may be of help...

100....
100....00

For both of these, it matches the \d+ part (with 100). After that it looks for \.\d{0,2} but fails. However it sees the ?, realises that the last bit is optional and returns true.

Make use of the 'start' and 'end' characters (^ and $ respectively). Also, use a non-capturing group (?:blah) rather than (blah) - it's more efficient if you don't want to refer to them later, which it seems you don't in this case. Rewritten:

// max character length $99,888,777,666,555.4444
// same as 99888777666555.4444

^[$]?([0-9][0-9]?([,][0-9]{3}){0,4}([.][0-9]{0,4})?)$|^[$]?([0-9]{1,14})?([.][0-9]{1,4})$|^[$]?[0-9]{1,14}$