How can a Regex match everything after group 1 unless group 1 pattern appears again on the same line?

Question

I'm having an issue understanding how I can capture everything after an optional prefix, unless, that prefix is displayed again. It would be nice to have the [FFFFFF] tag get matched a start over as group 1 vs being an optional additional group.

I'm new-ish to regex and I love the regex101.com site but this just appears to be above my level of understanding.

Expression:

(\[[0-9a-fA-F]{6}\])?(.*)

Sample Text

[00B800][!] Green - [004DB8] Blue does not match!!

[FFFFff][!] White

[e60000][!] Red

123456

Test string, another test abcdef

This is the result I'm attempting to get.

Link

https://regex101.com/r/z3CbHm/2/

Answer 1

You could use 2 capturing group, making the first group optional.

Then for the second group, match either until you see the next occurrence of the pattern \[[0-9a-fA-F]{6}\] or the end of the string.

(\[[0-9a-fA-F]{6}\])?(.+?)(?=\[[0-9a-fA-F]{6}\]|$)

Regex demo

If you want to omit possible leading whitespace chars for the second group:

(\[[0-9a-fA-F]{6}\])?(?:[^\S\r\n]*(.+?))(?=\[[0-9a-fA-F]{6}\]|$)

That will match

• (\[[0-9a-fA-F]{6}\])? Match the pattern in optional group 1
• (?: Non capture group
  • [^\S\r\n]* Match 0+ occurrences of a whitespace char except a newline
  • (.+?)Capture group 2, match 1+ occurrences of any char except a newline
• ) Close group
• (?= Positive lookhead, assert what is on the right is
  • \[[0-9a-fA-F]{6}\] Match the pattern
  • | Or
  • $ End of string
• ) Close lookahead

Regex demo