Regular Expression - how to find text within particular if blocks?

Question

Hello,

I'm new to regular expressions and would like to use one to search through our source control to find text within a block of code that follows a particular enum value. I.e.:

/(\/{2}\@debug)(.|\s)*?(\/{2}\@end-debug).*/
var junk = dontWantThis if (junk) {dont want this} if ( **myEnumValue** ) **{ var yes = iWantToFindThis if (true) { var yes2 = iWantThisToo } }**
var junk2 = dontWantThis if (junk) {dont want this}  
var stuff = dontWantThis if (junk) {dont want this} if ( enumValue ) { wantToFindThis }
var stuff = iDontWantThis if (junk) {iDontWantThisEither}

I know I can use (\{(/?[^\>]+)\}) to find if blocks, but I only want the first encompassing block of code that follows the enum value I'm looking for. I've also notice that using (\{(/?[^\>]+)\}) gives me the first { and last }, it doesn't group the subsequent {}.

Thank you!
Tim

Answer 1

Regexps simply can't handle this kind of stuff. For this you'll need a parser and scanner.

Answer 2

As others hint at, it's mathematically impossible to do with with regular expressions (at least in general; you might be able to get it to work if you have highly specialized cases). Try using a combination of lex and awk to get the desired results if you want to stick with standard Unix tools, or just go to Perl, Python, Ruby, etc. and build up the lexical parsing you need.

Answer 3

While nesting is a problem, you could use backtracking and lookahead to effectively count your matching braces or quotes. This is not strictly part of a regular expression but has been added to many regex libraries, such as the one in .NET, perl, and java; probably more. I wouldn't recommend that you go this route, as you should find it easier to lexically parse this. But if you do try this as a quick fix, absolutely collect a few test cases and run them through regexbuddy or expresso.