Regular Expressions 101

Pro

Group 1(numbers:(?:\n(?!999).+)*)

numbers:the literal text numbers: (case sensitive)

Non-Capturing Group(?:\n(?!999).+)*

*repeats the group contents below any number of times:

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

Negative Lookahead(?!999)

999the literal text 999

.+any character (except for line terminators), repeated at least once

Group 2(\n999)?

?repeats the group contents below at most once:

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

999the literal text 999

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

(numbers:(?:\n(?!999).+)*)(\n999)?

numbers:
32
45
999

56
or

numbers:
23
45

56