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^((a{1,4}|a?b|ba){1,3}|(a{1,3}|b){1,4}|((a{2,3}|b){2}|aaba|abaa){2})$

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gm

^ asserts position at start of a line

1st Capturing Group

((a{1,4}|a?b|ba){1,3}|(a{1,3}|b){1,4}|((a{2,3}|b){2}|aaba|abaa){2})

1st Alternative

(a{1,4}|a?b|ba){1,3}

2nd Capturing Group

(a{1,4}|a?b|ba){1,3}

{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)

A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data

1st Alternative

a{1,4}

a

matches the character a with index 972nd Alternative

a?b

a

matches the character a with index 97b matches the character b with index 98_{10} (62_{16} or 142_{8}) literally (case sensitive)

3rd Alternative

ba

ba

matches the characters ba literally (case sensitive)2nd Alternative

(a{1,3}|b){1,4}

3rd Capturing Group

(a{1,3}|b){1,4}

{1,4} matches the previous token between 1 and 4 times, as many times as possible, giving back as needed (greedy)

A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data

1st Alternative

a{1,3}

a

matches the character a with index 972nd Alternative

b

b matches the character b with index 98_{10} (62_{16} or 142_{8}) literally (case sensitive)

3rd Alternative

((a{2,3}|b){2}|aaba|abaa){2}

4th Capturing Group

((a{2,3}|b){2}|aaba|abaa){2}

{2} matches the previous token exactly 2 times

A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data

1st Alternative

(a{2,3}|b){2}

5th Capturing Group

(a{2,3}|b){2}

{2} matches the previous token exactly 2 times A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data

1st Alternative

a{2,3}

a

matches the character a with index 972nd Alternative

b

b matches the character b with index 98_{10} (62_{16} or 142_{8}) literally (case sensitive)

2nd Alternative

aaba

aaba

matches the characters aaba literally (case sensitive)3rd Alternative

abaa

abaa

matches the characters abaa literally (case sensitive)$ asserts position at the end of a line

Global pattern flags

g modifier: **g**lobal. All matches (don't return after first match)

m modifier: **m**ulti line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)

Your regular expression does not match the subject string.Try launching the debugger to find out why.

/

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gm

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