Matching the Same Number of Chars that was Captured by a Previous Group

Question

Using regular expressions, is it possible to match a number of characters corresponding to the length of a previously captured group ?

I would like to match the following :

SomeLengthyPattern :
some_stuff         :
some_other_stuff   :

My idea was capturing SomeLengthyPattern and then using its length as a base to match some_stuff and some_other_stuff.

score 1 · Accepted Answer · edited May 23 '17 at 10:26

Surprisingly... Yes!

With a handful or regex engines, you can make sure that one token is matched the same number of times as a previous token.

In .NET, you can do it with balancing groups.
In PCRE and a few other, you can use what is known on this site as the Qtax trick. The requirement is that a capture Group must be able to contain a back-reference refer to itself.

Warning! These techniques are advanced. If you proceed further, your regex skills will improve tremendously.

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