Regular Expressions 101

Negative Lookbehind(?<!\d)

\da digit

Group 1(1(?>(?1))*2)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Atomic Group(?>(?1))*

*repeats the group contents below any number of times:

(?1)calls group 1 as a subroutine

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Negative Lookahead(?!\d)

\da digit

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.

Search reference

Regular Expression

(?<!\d)(1(?>(?1))*2)(?!\d)

New

111222222  112222  1111222
111222 1122 12 112222