Regular Expressions 101

Pro

\ban ASCII word boundary

Group 1(\w+)

\w+any word character, repeated at least once

\ban ASCII word boundary

Negative Lookbehind(?<!\b\1\b.*\b\1\b)

\ban ASCII word boundary

\1the text saved by group 1

\ban ASCII word boundary

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

\ban ASCII word boundary

\1the text saved by group 1

\ban ASCII word boundary

Non-Capturing Group(?:(?!\b\1\b).)*?

*?repeats the group contents below any number of times:

Negative Lookahead(?!\b\1\b)

\ban ASCII word boundary

\1the text saved by group 1

\ban ASCII word boundary

.any character (except for line terminators)

\ban ASCII word boundary

\1the text saved by group 1

\ban ASCII word boundary

Negative Lookahead(?!.*\b\1\b)

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

\ban ASCII word boundary

\1the text saved by group 1

\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.

26 tokens

Regular Expression

\b(\w+)\b(?<!\b\1\b.*\b\1\b)(?:(?!\b\1\b).)*?\b\1\b(?!.*\b\1\b)

New

apple banana pineapple
apple banana apple pineapple
apple banana banana pineapple
apple banana apple pineapple apple
apple banana apple banana
apple banana banana apple pineapple apple

Substitution

apple banana pineapple
apple banana apple pineapple
apple banana banana pineapple
apple banana apple pineapple apple
apple banana apple banana
apple banana banana apple pineapple apple