Im trying to capture a string of upper case characters but want to ignore if there is a lower case letter after the upper case letter
For example
for the string ABC ABC ABC ABc it should capture ABC ABC ABC only because theres a lower case 'c' after the last AB
I tried ([A-Z ]+) which captures ABC ABC ABC AB,
How do i add a negative lookahead in this context?
Try putting [A-Z]\b at the end, to ensure that the match ends at a word boundary to the right of a word, without matching unnecessary spaces either. Note that there's no need for a capturing group here, you can leave that out entirely.
[A-Z ]+[A-Z]\b
https://regex101.com/r/j8Arzu/13
If the capital-letter substring may start with a space, then use the same technique at the beginning of the string - lead with \b[A-Z]:
\b[A-Z][A-Z ]*[A-Z]\b
If you additionally may have only a single character matched, then put the second and third character sets [A-Z ]*[A-Z] into an optional group:
\b[A-Z](?:[A-Z ]*[A-Z])?\b