Regular Expressions 101

Group 1(\b\w+\b)

\ban ASCII word boundary

\w+any word character, repeated at least once

\ban ASCII word boundary

Positive 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

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(\b\w+\b)(?=.*\b\1\b)

New

hello world
hello world hello
hello ihello hellos
world world world world world
4545 xyz 4545 45 45
abc abcde abc abc
dollar$ euro dollar$