Regular Expressions 101

^start of line

Condition(?(?=#).*\n(.)|(?(?=.#).*\n.(.)|(?(?=..#).*\n..(.)|(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#)))))))

Uses the first branch if the lookaround matches

Positive Lookahead(?=#)

#the literal # (35₁₀ / 43₈ / 23₁₆)

If the condition is true, match this branch:.*\n(.)

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

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

Group 1(.)

.any character (except for line terminators)

Otherwise, match this branch:(?(?=.#).*\n.(.)|(?(?=..#).*\n..(.)|(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))))))

Condition(?(?=.#).*\n.(.)|(?(?=..#).*\n..(.)|(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))))))

Uses the first branch if the lookaround matches

Positive Lookahead(?=.#)

.any character (except for line terminators)

#the literal # (35₁₀ / 43₈ / 23₁₆)

If the condition is true, match this branch:.*\n.(.)

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

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

.any character (except for line terminators)

Group 2(.)

.any character (except for line terminators)

Otherwise, match this branch:(?(?=..#).*\n..(.)|(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#)))))

Condition(?(?=..#).*\n..(.)|(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#)))))

Uses the first branch if the lookaround matches

Positive Lookahead(?=..#)

.any character (except for line terminators)

.any character (except for line terminators)

#the literal # (35₁₀ / 43₈ / 23₁₆)

If the condition is true, match this branch:.*\n..(.)

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

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

.any character (except for line terminators)

.any character (except for line terminators)

Group 3(.)

.any character (except for line terminators)

Otherwise, match this branch:(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))))

Condition(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))))

Uses the first branch if the lookaround matches

Positive Lookahead(?=...#)

.any character (except for line terminators)

.any character (except for line terminators)

.any character (except for line terminators)

#the literal # (35₁₀ / 43₈ / 23₁₆)

If the condition is true, match this branch:.*\n...(.)

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

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

.any character (except for line terminators)

.any character (except for line terminators)

.any character (except for line terminators)

Group 4(.)

.any character (except for line terminators)

Otherwise, match this branch:(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#)))

Condition(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#)))

Uses the first branch if the lookaround matches

Positive Lookahead(?=^....#)

^start of line

.any character (except for line terminators)

.any character (except for line terminators)

.any character (except for line terminators)

.any character (except for line terminators)

#the literal # (35₁₀ / 43₈ / 23₁₆)

If the condition is true, match this branch:.*\n....(.)

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

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

.any character (except for line terminators)

.any character (except for line terminators)

.any character (except for line terminators)

.any character (except for line terminators)

Group 5(.)

.any character (except for line terminators)

Otherwise, match this branch:(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))

Condition(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))

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

$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.(.)|(?(?=..#).*\n..(.)|(?(?=...#).*\n...(.)|(?(?=^....#).*\n....(.)|(?(?=^.{5}#).*\n.{5}(.)|(?(?=^.{6}#).*\n.{6}(.)|#))))))).*$

New

#AB
xyz
A#B
xyz
X#ZEAKBLA
123456789
XIZEAK#LA
123456789