Regular Expressions 101

^start of line

Group 1((?:.(?=.*\n(\2?.)))*?X.*\n)

Non-Capturing Group(?:.(?=.*\n(\2?.)))*?

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

.any character (except for line terminators)

Positive Lookahead(?=.*\n(\2?.))

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

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

Group 2(\2?.)

\2?optionally matches the text saved by group 2

.any character (except for line terminators)

Xthe literal X (88₁₀ / 130₈ / 58₁₆) (case sensitive)

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

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

\2?optionally matches the text saved by group 2

.any character (except for line terminators)

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

^((?:.(?=.*\n(\2?.)))*?X.*\n)\2?.

New

X.........
..........

...X......
..........

..X.......
..........

.......X..
..........

.........X
..........

$1$2Y

X.........
..........

...X......
..........

..X.......
..........

.......X..
..........

.........X
..........