Question

I’ve been looking around and could not make this happen. I am not totally noob.

I need to get text delimited by (including) START and END that doesn’t contain START. Basically I can’t find a way to negate a whole word without using advanced stuff.

Example string:

abcSTARTabcSTARTabcENDabc

The expected result:

STARTabcEND

Not good:

STARTabcSTARTabcEND

I can’t use backward search stuff. I am testing my regex here: http://www.regextester.com

Thanks for any advice.

Answer 1

The really pedestrian solution would be START(([^S]|S*S[^ST]|ST[^A]|STA[^R]|STAR[^T])*(S(T(AR?)?)?)?)END. Modern regex flavors have negative assertions which do this more elegantly, but I interpret your comment about “backwards search” to perhaps mean you cannot or don’t want to use this feature.

Update: Just for completeness, note that the above is greedy with respect to the end delimiter. To only capture the shortest possible string, extend the negation to also cover the end delimiter — START(([^ES]|E*E[^ENS]|EN[^DS]|S*S[^STE]|ST[^AE]|STA[^RE]|STAR[^TE])*(S(T(AR?)?)?|EN?)?)END. This risks to exceed the torture threshold in most cultures, though.

Bug fix: A previous version of this answer had a bug, in that SSTART could be part of the match (the second S would match [^T], etc). I fixed this but by the addition of S in [^ST] and adding S* before the non-optional S to allow for arbitrary repetitions of S otherwise.