Regular Expressions 101

Group 1(^|\s+)

1st Alternative^

^start of string

2nd Alternative\s+

\s+any whitespace character, repeated at least once

Group 2(\S*)

\S*any non-whitespace character, repeated any number of times

Group 3(($|\s+)\2)+

+repeats the group contents below at least once:

Group 4($|\s+)

1st Alternative$

$end of string, or before its final line terminator

2nd Alternative\s+

\s+any whitespace character, repeated at least once

\2the text saved by group 2

Global pattern flags

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

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

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(^|\s+)(\S*)(($|\s+)\2)+

She left LEft leFT LEFTnow