Negative lookahead to get last instance of a word

To get the last instance of abc from the below string

abcaaaaaaaabcbbbbabc111111abc22

use a regular expression negative lookahead that searches for abc not followed by any further abc. As Justin Cooney describes in his article, the syntax is:

abc(?!.*abc)

regular-expressions.info provides further information about negative and positive lookahead.

With negative lookahead, to match a q not followed by a u use q(?!u). Positive lookahead works the same. q(?=u) matches a q that is followed by a u, without making the u part of the match.