Regex to consume between two groups where the second group is optional

Question

I have the following strings:

Sally: Hello there #line:34de2f
Bob: How are you today?

These strings have three parts to them...

• The "name"; Sally: and Bob:
• The "text"; Hello there and How are you today?
• An optional "line identifier"; #line:34de2f

I want to grab the "text" between the "name" and the optional "line identifier" using a regex.

This seems like what negative lookaheads are for:

(?<=:).*?(?!#line:.*)$

But this still captures the "line identifier".

The following works, but I do not want to actually capture the "line identifier":

(?<=:).*?(#line:.*)?$

Answer 1

You may try using

(?<=:\s).*?(?=\s*#line:.*|$)

See this regex demo. Details:

• (?<=:\s) - a location immediately preceded with : and a whitespace
• .*? - any 0 or more chars other than line break chars, as few as possible
• (?=\s*#line:.*|$) - a location immediately followed with 0+ whitespaces, #line: string or end of string.

You may also use

:\s*(.*?)(?:\s*#line:.*)?$

See the regex demo. Get the contents in Group 1.

Details

• :\s* - a colon and then 0 or more whitespaces
• (.*?) - Capturing group #1: any zero or more chars other than line break chars, as few as possible
• (?:\s*#line:.*)? - an optional sequence of
  • \s* - 0+ whitespaces
  • #line: - a literal #line: string
  • .* - any zero or more chars other than line break chars, as many as possible
• $ - end of string.