Regular Expressions 101

Group 1(\n)?

?repeats the group contents below at most once:

\na line-feed (newline) character (ASCII 10)

Positive Lookahead(?=(^\N+$)(?(1)|(\n?)))

Group 2(^\N+$)

^start of line

\N+any non-newline character, repeated at least once

$end of line

Condition(?(1)|(\n?))

Uses the first branch if group 1 matched

If the condition is true, match this branch: — matches an empty string

Otherwise, match this branch:(\n?)

Group 3(\n?)

\n?optionally matches a line-feed (newline) character (ASCII 10)

Non-Capturing Group(?:\2\3(?=.*?^\2$)|((?<=(?=$\N|^\2$).))\2\3)

1st Alternative\2\3(?=.*?^\2$)

\2the text saved by group 2

\3the text saved by group 3

Positive Lookahead(?=.*?^\2$)

.*?any character, repeated any number of times

^start of line

\2the text saved by group 2

$end of line

2nd Alternative((?<=(?=$\N|^\2$).))\2\3

Group 4((?<=(?=$\N|^\2$).))

Positive Lookbehind(?<=(?=$\N|^\2$).)

Positive Lookahead(?=$\N|^\2$)

1st Alternative$\N

$end of line

\Nany non-newline character

2nd Alternative^\2$

^start of line

\2the text saved by group 2

$end of line

.any character

\2the text saved by group 2

\3the text saved by group 3

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

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

s modifier: single line. Allows a dot to match line terminators

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(\n)?(?=(^\N+$)(?(1)|(\n?)))(?:\2\3(?=.*?^\2$)|((?<=(?=$\N|^\2$).))\2\3)

Test String
New

bob
sally
george
bob
george
bob
sally
diego
dianora
diego

oh look
at my 
beatiful
beautiful
beauiful
beatiful
REGEX
IT'S REGEX TASTIC
REGEX
IS
BEATIFUL
beautifuyl

Regular Expression

Test StringNew

Test String
New