Regular Expressions 101

^start of line

Negative Lookahead(?!.*\bCats\s+Dogs\b)

.*any character (except for line terminators), repeated any number of times

\ban ASCII word boundary

Catsthe literal text Cats (case sensitive)

\s+any whitespace character, repeated at least once

Dogsthe literal text Dogs (case sensitive)

\ban ASCII word boundary

.*?any character (except for line terminators), repeated any number of times

\ban ASCII word boundary

Dogsthe literal text Dogs (case sensitive)

\ban ASCII word boundary

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

^(?!.*\bCats\s+Dogs\b).*?\bDogs\b

New

My Dogs are happy
Dogs are humans best friend
This is invalid Cats   Dogs
The Dogs and Cats and Dogs and Dogs
The Dogs and Cats and Dogs and Cats Dogs

Substitution

My Dogs are happy
Dogs are humans best friend
This is invalid Cats   Dogs
The Dogs and Cats and Dogs and Dogs
The Dogs and Cats and Dogs and Cats Dogs