Question

If I have a string like this (from a Wiki-markup) that I need to parse in Java:

this link (is [[ inParen ]] and) (this) one is [[ notInParen ]]

I’d like to use regex to extract the texts inside the [[ ]] but not if they are inside parentheses. For example, in the example above it should return:

notInParen

But ignore:

inParen and this

… since they are inside parentheses. I can find the parentheses and the brackets separately no problem:

.*\(.*?\).* and .*?\[\[(.*?\]\].*

…but can’t figure out how to find the [[ ]], look around for parentheses, and ignore. Thanks!

Answer 1

This is a fine regex

\(.*?\)|\[\[(.*?)]]

Your desired match will be in group 1

FYI, to make it better perform you can minimize backtracking by replacing the lazy match with a negated character class.

In Java this becomes

String ResultString = null;
try {
    Pattern regex = Pattern.compile("\\(.*?\\)|\\[\\[(.*?)\\]\\]", Pattern.DOTALL | Pattern.MULTILINE);
    Matcher regexMatcher = regex.matcher(subjectString);
    if (regexMatcher.find()) {
        ResultString = regexMatcher.group(1);
    } 
} catch (PatternSyntaxException ex) {
    // Syntax error in the regular expression
}

Note that group 1 will be empty for the cases the first part of the alternation did match.