Matching Parantheses Using a regular expression

Question

I am trying to write a regular expression to match any string that satisfies the following criteria.

The string begins and ends with a matching pair of parentheses '(' ')'

There may be any number of parentheses within it.

For example my regex shud match :

( ( p(x)+q(x) ) . (p(x) * q(x) ) )

but not match

( p(x)+q(x) ) . ( p(x) * q(x) )

How do i write such a regex

Are you trying to say that all the internal parenthesis must match as well? If that is the case, I believe you would need to use a Push-Down-Automata instead of a regular expression to solve that, as a Finite-State-Automata (which define the space for a regex) does not allow for that type of a check. — aperkins, Sep 13 '10 at 16:11
To clarify my comment - if you are looking for a regex to solve a[n]b[n], where you have an equal number of a — aperkins, Sep 13 '10 at 16:11
dangit - stupid enter key - continuing: an equal number of a's and b's, then you would not be able to solve that general case with a regular expression. Based on what you have described, it seems like that is what you are looking for (in a variation, of course) which would require a PDA. — aperkins, Sep 13 '10 at 16:12
To clarify, i am assuming that in my input all parentheses match. The only issue is that i want to capture those strings where the very first '(' matches the last ')'. That is, something like ( ... ) — AnkurVj, Sep 13 '10 at 16:21
Now if i write a regex like ^\$.*\$$ _JavaStyle_ then i match also the strings of the form (..)(..) and not just ( .... ) — AnkurVj, Sep 13 '10 at 16:23
That is my point - if all of the parenthesis must match, then you have a situation where you want to prove that there are equal, matching elements of two characters - which is the equivalent of the a and b example I give earlier. — aperkins, Sep 13 '10 at 16:57

score 2 · Accepted Answer · edited May 23 '17 at 12:01

2

edited May 23 '17 at 12:01

Community

answered Sep 13 '10 at 16:20

Rodney Gitzel

Yep, as the accepted answer notes - this is a simple algorithmic problem, not really appropriate for regex. Thanks for the link. – aperkins Sep 13 '10 at 16:55

score 1 · Answer 2 · edited May 23 '17 at 12:04

1

Doing any sort of parsing like this using regular expressions is difficult and almost always a bad idea. See this answer to this question. Oh, the horror!

edited May 23 '17 at 12:04

Community

answered Sep 13 '10 at 16:29

Kelly S. French

2 Answers2