Regular Expressions 101

Pro

\ban ASCII word boundary

Positive Lookahead(?=[A-Z]{3}\b)

Character Class[A-Z]{3}

{3}matches exactly 3 characters from the set below:

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

\ban ASCII word boundary

A?optionally matches the literal A (65₁₀ / 101₈ / 41₁₆) (case sensitive)

Group 1([B-Z])

Character Class[B-Z]

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

A?optionally matches the literal A (65₁₀ / 101₈ / 41₁₆) (case sensitive)

\1the text saved by group 1

A?optionally matches the literal A (65₁₀ / 101₈ / 41₁₆) (case sensitive)

\ban ASCII word boundary

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]{3}\b)A?([B-Z])A?\1A?\b

New

BBA -> true
ABB -> true
BAB -> true
CCA -> true
AAA -> false (change "[B-Z]" to "[A-Z]" to match this)
CCB -> false
ABC -> false
BAC -> false
BBBA -> false (there have to be only two)
ABBB -> false (there have to be only two)
ABBA -> false (there has to be only one A)
BABA -> false (there has to be only one A)
BBAA -> false (there has to be only one A)