Matching multiple occurrences in javascript using a regex

Question

I am using Javascript and regex to parse some strings in "csv like flavour" with ; as separator. The regex I figured out so far is trying to get all the occurrences of a pattern like: "INTERESTING1 (INTERESTING2; INTERESTING3)".

The problems I am facing is that I can match only the last occurrence of the previous pattern in the whole string, whereas I would like to match all the occurring patterns. I have tried both the Javascript functions exec() and match() with or without some loops, but I can not figure out what's wrong with what I am doing?

var complexString = 'some boring stuff; some other boring stuff; interesting prefix (interesting inner stuff1; interesting inner stuff2; etc.); boring stuff; another interesting prefix (another interesting string 1; another interesting string 2; etc.)';
//var complexString = 'XXX';

// regex to apply
var roundBraketsRegex =  /.*;(.*)\((.*)\)/g; // string pattern: "INTERESTING1 (INTERESTING2; INTERESTING3)"
// array of matched groups
var matchesArray = roundBraketsRegex.exec(complexString);

var outputString = '';

if(matchesArray == null ) {
    outputString = 'NULL!!! ';
} 

// I have tried also the following commented line with stuff related to 
// while loops and functions like .exec() or .match()

//while ((matchesArray = roundBraketsRegex.match( complexString )) != null) {
outputString = outputString + ' ### ' + matchesArray[1] + ' ### ' + matchesArray[2] + ' ### NOT INTERESTED IN: ' + matchesArray[0];
//}


// print what has been found
console.log(document.getElementById('result'));
document.getElementById('result').innerHTML = outputString;

The output (I manually added some carriage returns here in Stackoverflow, just to get the string more readable):

### another interesting prefix 
### another interesting string 1; another interesting string 2; etc. 
### NOT INTERESTED IN: some boring stuff; some other boring stuff; interesting prefix (interesting inner stuff1; interesting inner stuff2; etc.); boring stuff; another interesting prefix (another interesting string 1; another interesting string 2; etc.)

Yeah, to add to what @hjpotter92 is saying, the problem is that your regex is matching everything at once because of the greedy .* If you use the non-greedy matcher .*? it will only match as much as it needs to — Jonathan Benn
– Jonathan Benn, Commented Jun 11, 2014 at 12:51

Jonathan Benn · Accepted Answer · 2014-06-16 17:20:23Z

1

The thing you need to understand about regular expressions is that multiple runs of the matcher will only find non-overlapping targets. If your regex is capturing too much, then you will not be able to find extra matches with additional runs.

Try this regular expression, which captures less:

([^;]+?)\s+\(([^\)]*)\)

It has two capturing groups, which grab the interesting prefix and the other interesting stuff in the brackets. Please note that you will need to use String.trim() on the results. Here is the regex explained on Regex 101.

Here is the final JavaScript solution, which includes the regex:

var complexString = 'some boring stuff; some other boring stuff; interesting prefix (interesting inner stuff1; interesting inner stuff2; etc.); boring stuff; another interesting prefix (another interesting string 1; another interesting string 2; etc.)';
var roundBraketsRegex =  /([^;]+?)\s+\(([^\)]*)\)/g;        
var matchesArray;
var i = 1;

while (matchesArray = roundBraketsRegex.exec(complexString)) {
    var group1 = matchesArray[1].trim();
    var group2 = matchesArray[2].trim();
    console.log("Match #" + i + " [1]: '" + group1 + "' [2]: '" + group2 + "'");
    ++i;
}

Here is the output from running the above:

Match #1 [1]: 'interesting prefix' [2]: 'interesting inner stuff1; interesting inner stuff2; etc.'
Match #2 [1]: 'another interesting prefix' [2]: 'another interesting string 1; another interesting string 2; etc.'

I hope that you find this helpful.

--Jonathan

edited Jun 16, 2014 at 17:20

answered Jun 11, 2014 at 13:01

Jonathan Benn

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2 Comments

TPPZ Over a year ago

That helped in narrowing down the prefix area before the round open bracket, however I need to find all the occurrences of the recurring pattern. I've played around with what suggested by @hjpotter (non greedy matchers) and I think that's close to what I would like to achieve.

Jonathan Benn Over a year ago

What I wrote should work for all occurrences, you just need to re-run the exec function until it returns null. I'm not feeling well today, but if you still haven't solved it by the time I'm back in the office I'll lend you a hand with the Javascript code

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