Regex to match specific functions and their arguments in files

Question

I\'m working on a gettext javascript parser and I\'m stuck on the parsing regex.

I need to catch every argument passed to a specific method call _n( and

Answer 1

\(( |"(\\"|[^"])*"|'(\\'|[^'])*'|[^)"'])*?\)

This should get anything between a pair of parenthesis, ignoring parenthesis in quotes. Explanation:

\( // Literal open paren
    (
         | //Space or
        "(\\"|[^"])*"| //Anything between two double quotes, including escaped quotes, or
        '(\\'|[^'])*'| //Anything between two single quotes, including escaped quotes, or
        [^)"'] //Any character that isn't a quote or close paren
    )*? // All that, as many times as necessary
\) // Literal close paren

No matter how you slice it, regular expressions are going to cause problems. They're hard to read, hard to maintain, and highly inefficient. I'm unfamiliar with gettext, but perhaps you could use a for loop?

// This is just pseudocode.  A loop like this can be more readable, maintainable, and predictable than a regular expression.
for(int i = 0; i < input.length; i++) {
    // Ignoring anything that isn't an opening paren
    if(input[i] == '(') {
        String capturedText = "";
        // Loop until a close paren is reached, or an EOF is reached
        for(; input[i] != ')' && i < input.length; i++) {
            if(input[i] == '"') {
                // Loop until an unescaped close quote is reached, or an EOF is reached
                for(; (input[i] != '"' || input[i - 1] == '\\') && i < input.length; i++) {
                    capturedText += input[i];
                }
            }
            if(input[i] == "'") {
                // Loop until an unescaped close quote is reached, or an EOF is reached
                for(; (input[i] != "'" || input[i - 1] == '\\') && i < input.length; i++) {
                    capturedText += input[i];
                }
            }
            capturedText += input[i];
        }
        capture(capturedText);
    }
}

Note: I didn't cover how to determine if it's a function or just a grouping symbol. (ie, this will match a = (b * c)). That's complicated, as is covered in detail here. As your code gets more and more accurate, you get closer and closer to writing your own javascript parser. You might want to take a look at the source code for actual javascript parsers if you need that sort of accuracy.