Regular Expressions 101

^start of line

Group 1((?(1)b\1|a))+

+repeats the group contents below at least once:

Condition(?(1)b\1|a)

Uses the first branch if group 1 matched

If the condition is true, match this branch:b\1

bthe literal b (98₁₀ / 142₈ / 62₁₆) (case sensitive)

\1the text saved by group 1

Otherwise, match this branch:a

athe literal a (97₁₀ / 141₈ / 61₁₆) (case sensitive)

$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.

25 tokens

Regular Expression

^((?(1)b\1|a))+$

New

a
aba
ababba
ababbabbba
ababbabbbabbbba
ababbabbbabbbbabbbbba

abba
abbba
aa
abbaa
aabb
abababa
ababbba
abbaba

a
aba
ababba
ababbabbba
ababbabbbabbbba
ababbabbbabbbbabbbbba

abba
abbba
aa
abbaa
aabb
abababa
ababbba
abbaba