Regular Expressions 101

1st Alternative(?*(.*)(.*+))(?=(?:((?(?=\2$).?))(21|(1|2(?3)2)(?3)(12)*(?3)(2|1(?3)1)))+(?3)$)\1\K.?(.*)

Non-Atomic Positive Lookahead(?*(.*)(.*+))

Group 1(.*)

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

Group 2(.*+)

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

Positive Lookahead(?=(?:((?(?=\2$).?))(21|(1|2(?3)2)(?3)(12)*(?3)(2|1(?3)1)))+(?3)$)

Non-Capturing Group(?:((?(?=\2$).?))(21|(1|2(?3)2)(?3)(12)*(?3)(2|1(?3)1)))+

+repeats the group contents below at least once:

Group 3((?(?=\2$).?))

Condition(?(?=\2$).?)

Uses the first branch if the lookaround matches

Positive Lookahead(?=\2$)

\2the text saved by group 2

$end of line

If the condition is true, match this branch:.?

.?optionally matches any character (except for line terminators)

Group 4(21|(1|2(?3)2)(?3)(12)*(?3)(2|1(?3)1))

1st Alternative21

21the literal text 21

2nd Alternative(1|2(?3)2)(?3)(12)*(?3)(2|1(?3)1)

Group 5(1|2(?3)2)

1st Alternative1

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2nd Alternative2(?3)2

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

(?3)calls group 3 as a subroutine

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

(?3)calls group 3 as a subroutine

Group 6(12)*

*repeats the group contents below any number of times:

12the literal text 12

(?3)calls group 3 as a subroutine

Group 7(2|1(?3)1)

1st Alternative2

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

2nd Alternative1(?3)1

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

(?3)calls group 3 as a subroutine

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

(?3)calls group 3 as a subroutine

$end of line

\1the text saved by group 1

\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match

.?optionally matches any character (except for line terminators)

Group 8(.*)

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

2nd Alternative(..)\9*\K.?

Group 9(..)

.any character (except for line terminators)

.any character (except for line terminators)

\9*the text saved by group 9, repeated any number of times

\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match

.?optionally matches 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

(?*(.*)(.*+))(?=(?:((?(?=\2$).?))(21|(1|2(?3)2)(?3)(12)*(?3)(2|1(?3)1)))+(?3)$)\1\K.?(.*)|(..)\9*\K.?

New

111
112
121
122
211
212
221
222
1111
1112
1121
1122
1211
1212
1221
1222
2111
2112
2121
2122
2211
2212
2221
2222
11111
11112
11121
11122
11211
11212
11221
11222
12111
12112
12121
12122
12211
12212
12221
12222
21111
21112
21121
21122
21211
21212
21221
21222
22111
22112
22121
22122
22211
22212
22221
22222
111111
111112
111121
111122
111211
111212
111221
111222
112111
112112
112121
112122
112211
112212
112221
112222
121111
121112
121121
121122
121211
121212
121221
121222
122111
122112
122121
122122
122211
122212
122221
122222
211111
211112
211121
211122
211211
211212
211221
211222
212111
212112
212121
212122
212211
212212
212221
212222
221111
221112
221121
221122
221211
221212
221221
221222
222111
222112
222121
222122
222211
222212
222221
222222
1111111
1111112
1111121
1111122
1111211
1111212
1111221
1111222
1112111
1112112
1112121
1112122
1112211
1112212
1112221
1112222
1121111
1121112
1121121
1121122
1121211
1121212
1121221
1121222
1122111
1122112
1122121
1122122
1122211
1122212
1122221
1122222
1211111
1211112
1211121
1211122
1211211
1211212
1211221
1211222
1212111
1212112
1212121
1212122
1212211
1212212
1212221
1212222
1221111
1221112
1221121
1221122
1221211
1221212
1221221
1221222
1222111
1222112
1222121
1222122
1222211
1222212
1222221
1222222
2111111
2111112
2111121
2111122
2111211
2111212
2111221
2111222
2112111
2112112
2112121
2112122
2112211
2112212
2112221
2112222
2121111
2121112
2121121
2121122
2121211
2121212
2121221
2121222
2122111
2122112
2122121
2122122
2122211
2122212
2122221
2122222
2211111
2211112
2211121
2211122
2211211
2211212
2211221
2211222
2212111
2212112
2212121
2212122
2212211
2212212
2212221
2212222
2221111
2221112
2221121
2221122
2221211
2221212
2221221
2221222
2222111
2222112
2222121
2222122
2222211
2222212
2222221
2222222

11111111
111111111
1111111111
11111111111
111111111111
1111111111111
11111111111111

22222222
222222222
2222222222
22222222222
222222222222
2222222222222
22222222222222

Substitution

$8 ${9:-3}