Creating a Regex expression with a “not” condition for a specific substring

I have a use case where I am searching for a particular sub string in a string and if that particular string contains another particular sub string I want it to be rejected.

Ex:

1. pikachu_is_the_best_ever_in_the_world_go_pikachu
2. mew_is_the_best_ever_in_the_world_go_mew
3. raichu_is_the_best_ever_in_the_world_go_raichu

I want my Regex expression to pick up the string having the word "best" and not the word "mew", i.e the first and third string.

I have tried combining ^(.*best).*$ and ^((?!mew).)*$ into the below expressions and the second regex one only ignores words if "mew" is present in the start of the string.

^(.*best)((?!mew).).*$

And have tried

^((?!mew).)(.*best).*$

1 Answer

• Ctrl+F
• Find what: ^(?=.*best)(?:(?!mew).)*$
• check Wrap around
• check Regular expression
• DO NOT CHECK . matches newline
• Search in document

Explanation:

^ : start of line
(?= : positive lookahead .* : 0 or more any character but newline best : literally "best"
) : end lookahead
(?: : start non capture group (?! : negative lookahead, make sure we don't have mew : literally "mew" ) : end lookahead . : any character but newline
)* : group may appear 0 or more times
$ : end of line