Regular Expressions 101

Pro

\ban ASCII word boundary

Positive Lookahead(?=[A-Z]{5}\b)

Character Class[A-Z]{5}

{5}matches exactly 5 characters from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\ban ASCII word boundary

Non-Capturing Group(?:\1|(?!\2)([B-Z])()|(?!\3)A())+

+repeats the group contents below at least once:

1st Alternative\1

\1the text saved by group 1

2nd Alternative(?!\2)([B-Z])()

Negative Lookahead(?!\2)

\2the text saved by group 2

Group 1([B-Z])

Character Class[B-Z]

B-Zone character from B (66₁₀) to Z (90₁₀) (case sensitive)

Group 2() — does not consume characters

3rd Alternative(?!\3)A()

Negative Lookahead(?!\3)

\3the text saved by group 3

Athe literal A (65₁₀ / 101₈ / 41₁₆) (case sensitive)

Group 3() — does not consume characters

\ban ASCII word boundary

\2the text saved by group 2

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

\b(?=[A-Z]{5}\b)(?:\1|(?!\2)([B-Z])()|(?!\3)A())+\b\2

New

BBABB -> true
ABBBB -> true
BABBB -> true
CCACC -> true
CCCCA -> true
AAAAA -> false (change "[B-Z]" to "[A-Z]" to match this)
CCBAB -> false
CCCAA -> false
ABCCB -> false
BACBB -> false