Variable length look-behind

Question

Is there any elegant solution to build a variable length look-behind regex such as this one ?

/(?<=eat_(apple|pear|orange)_)today|yesterday/g;
         


        

Answer 1

Blog post found today, linked to me at #regex @ irc.freenode.org:

http://www.drregex.com/2019/02/variable-length-lookbehinds-actually.html

This article explains how to do a variable width look-behind in PCRE.

The solution would then be:

/(?=(?=(?'a'[\s\S]*))(?'b'eat_(?:apple|pear|orange)_(?=\k'a'\z)|(?<=(?=x^|(?&b))[\s\S])))today|yesterday/g

https://regex101.com/r/9DNpFj/1