REGEX - Combining positive lookaheads with conditionals?

Question

Got another one for you here! I've been fiddling for a while but I'm getting lost. I think the maybe the key to acheiving this is in combining conditionals with positive lookaheads?

I want to always find the start of a string. I've called it "MatchMe!" in the example but in reality it can be anything. Part 1, Part 2, Part 3 and Part 4 are always the same (well not the same but I can regex these reliably)

Is there a way to try and do a positive lookahead with Part 1, if that doesn't exist, try a positive lookahead with Part 2, and if that doesn't exist try a positive lookahead with Part 3, and lastly try the same with Part 4? Or am I overcomplicating things

My lousy attempt is here but it gives an idea of my problem :-)

https://regex101.com/r/TvgXXB/1

Many thanks again!

Maybe [`^.*?(?=\s*(?:Part1|Part2|Part3|Part4))`](https://regex101.com/r/TvgXXB/3)? — Wiktor Stribiżew, Aug 15 '18 at 20:11
Yeah, apologies. It's been a long day. Wiktor's regex should work for you then. — Paolo, Aug 15 '18 at 20:12
You closed capturing group too early. Move it to the end and use a *beginning of string / line* anchor. — revo, Aug 15 '18 at 20:15
Thanks guys! That was much simpler than I thought! :D I really need to read up on my anchors! — UnluckyForSome9, Aug 15 '18 at 20:15

score 2 · Answer 1 · answered Aug 15 '18 at 20:22

You may use

^.*?(?=\s*(?:Part1|Part2|Part3|Part4))

See the regex demo

Details

^ - start of string
.*? - any 0+ chars, other than line break chars, as few as possible
(?=\s*(?:Part1|Part2|Part3|Part4)) - a location in string that, immediately to the right of it, is followed with
- \s* - 0+ whitespaces
- (?:Part1|Part2|Part3|Part4) - either of the alternatives listed in the non-capturing group.

REGEX - Combining positive lookaheads with conditionals?

1 Answers1