Regular Expressions 101

^start of line

_?optionally matches the literal _ (95₁₀ / 137₈ / 5F₁₆)

Negated Character Class[^_\n]+

+matches at least one character outside the set below:

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

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

Non-Capturing Group(?:_[^_\n]+)*

*repeats the group contents below any number of times:

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Negated Character Class[^_\n]+

+matches at least one character outside the set below:

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

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

Non-Capturing Group(?:__\d+)?

?repeats the group contents below at most once:

__the literal text __

\d+a digit, repeated at least once

$end of line

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

^_?[^_\n]+(?:_[^_\n]+)*(?:__\d+)?$

New

foo_bar__2
foo
foo--$%^##
$%^#
foo__42
_foo_bar__32
foo_
f__o__2
_
foo___2
foo__xzy