CODEWITHSUNDEEP
javascriptregex
Collin Chaffin
Collin Chaffin

Reputation: 942

Optional regex string/pattern sections with and without non-capturing groups

Here's what I'm trying to do: https://i.sstatic.net/Xj1CR.png

Simply take a URL with 3 groups, $1 not so important, $2 & $3 are but $2 is totally optional including (obviously) the corresponding backslash when present, which is all I am trying to make optional. I get that it can/should? be in a non-cap group, but does it HAVE to be? I've seen enough now seems to indicate it does not HAVE to be. If possible, I'd really like to have someone explain it so I can try to fully understand it, and not just get one possible working answer handed to me to simply copy, like some come here seeking.

Here's my regex string(s) tried and at best only currently matching second URL string with optional present:

^https:\/\/([a-z]{0,2})\.?blah\.com(?:\/)(.*)\/required\/B([A-Z0-9]{9}).*
^https:\/\/([a-z]{0,2})\.?blah\.com(\/)?(.*)\/required\/B([A-Z0-9]{9}).*
^https:\/\/([a-z]{0,2})\.?blah\.com(?:\/)?(.*)?\/required\/B([A-Z0-9]{9}).*

Here are the two URLs that I want to capture group 2 & 3, with 1 and 2 being optional, but $2 being the problem. I've tried all the strings above and have yet to get it to match the string when the optional is NOT present and I believe it must be due to the backslashes?

https://blah.com/required/B7BG0Z0GU1A
https://blah.com/optional/required/B7BG0Z0GU1A

Upvotes: 1

Views: 402

Answers (1)

Kobi
Kobi

Reputation: 138017

Making a part of the pattern optional is as simple as adding ?, and your last two attempts both work: https://regex101.com/r/RIKvYY/1

Your mistake is that your test is wrong - you are using ^ which matches the beginning of the string. You need to add the /m flag (multiline) to make it match the beginning of each line. This is the reason your patterns never match the second line...

Note that you're allowing two slashes (//required, for example). You can solve it by joining the first slash and the optional part to the same capturing group (of course, as long as you are using .* you can still match multiple slashes):

https:\/\/([a-z]{0,2})\.?blah\.com(?:\/(.*))?\/required\/B([A-Z0-9]{9}).*

Upvotes: 1

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