Javascript regex: dynamic capture group

Question

I'm trying to wrap my mind around regex for the first time.

For the string

I want you to MATCH THIS, you bastard regex, but also MATCH X THIS and yeah,
MATCH X X X THIS too.

Basically, a starting pattern, an end pattern and an arbitrary number of a pattern inbetween.

So I'd like a myregex.exec string to successively return

["MATCH", "THIS"]
["MATCH", "X", "THIS"]
["MATCH", "X", "X", "X", "THIS"]

I've tried variations of this

/(MATCH)\s+(X)?\s+(THIS)/

but no cigar...

So do you want to match all the white space delimitted upper case words? — npinti
– npinti, Commented Jul 15, 2015 at 8:27
This is partially answered in stackoverflow.com/questions/5018487/… - see Tim Picker's comment. Short answer: in some flavours of Regex you can ask for multiple captures of the same group. But not in javascript. — yu_sha
– yu_sha, Commented Jul 15, 2015 at 8:29
Having said that - you can group all of it in one group and then split. — yu_sha
– yu_sha, Commented Jul 15, 2015 at 8:48

MT0 · Accepted Answer · 2015-07-15 08:47:38Z

2

You can use the regular expression to match the entire expression:

/MATCH\s+(?:X\s+)*THIS/g

To get it into an array of terms/words you can then use String.split() like this:

var out = document.getElementById( "out" );

function parse( string ){
  var re = /MATCH\s+(?:X\s+)*THIS/g;
  var matches = (string.match( re ) || [])
                  .map( function(m){ return m.split( /\s+/ ); } );
  out.innerHTML = JSON.stringify( matches );
}

parse( document.getElementById( "in" ).value );

textarea { width: 100%; }

<textarea id="in" onchange="parse( this.value )">I want you to MATCH THIS, you bad regex, but also MATCH X THIS and yeah, MATCH X X X THIS too.</textarea>
<p id="out"/>

answered Jul 15, 2015 at 8:47

MT0

173k12 gold badges70 silver badges136 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Joe · Accepted Answer · 2015-07-15 08:36:44Z

1

Try putting the \s+ into the optional group with *:

/(MATCH)\s+(?:(X)\s)*(THIS)/g

Note the g modifier to get all matches.

edited Jul 15, 2015 at 8:36

answered Jul 15, 2015 at 8:28

Joe

9371 gold badge12 silver badges28 bronze badges

2 Comments

Marek Over a year ago

(?:(X)) would never have done that. A capture group in a non-capture group ... weird. Doesn't work for MATCH X X X THIS, but apparently that don't work in JavaScript...

MT0 Over a year ago

Will match multiple Xs but will only ever return a single X as a capture group using RegExp.exec() - and for MATCH THIS it will return an empty capture group for the Xs.

Collectives™ on Stack Overflow

Javascript regex: dynamic capture group

2 Answers 2

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related