Regular Expressions 101

Explanation

Pro

1st Alternative(?<=\D|^)(?=\d{8,12}\D|$)(\d{3})[\s,-]?\[\s,-]\K\d{4}

Positive Lookbehind(?<=\D|^)

1st Alternative\D

\Dany character that's not a digit

2nd Alternative^

^start of line

Positive Lookahead(?=\d{8,12}\D|$)

1st Alternative\d{8,12}\D

\d{8,12}a digit, repeated between 8 and 12 times

\Dany character that's not a digit

2nd Alternative$

$end of line

Group 1(\d{3})

\d{3}a digit, repeated exactly 3 times

Character Class[\s,-]?

?matches at most one character from the set below:

\sany whitespace character

,the literal , (44₁₀ / 54₈ / 2C₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\[the literal [ (91₁₀ / 133₈ / 5B₁₆)

\sany whitespace character

,-]the literal text ,-]

\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match

\d{4}a digit, repeated exactly 4 times

2nd Alternative(?<=\D|^)(?=\d{12}|\d{9}\D|$)\d{5}

Positive Lookbehind(?<=\D|^)

1st Alternative\D

\Dany character that's not a digit

2nd Alternative^

^start of line

Positive Lookahead(?=\d{12}|\d{9}\D|$)

1st Alternative\d{12}

\d{12}a digit, repeated exactly 12 times

2nd Alternative\d{9}\D

\d{9}a digit, repeated exactly 9 times

\Dany character that's not a digit

3rd Alternative$

$end of line

\d{5}a digit, repeated exactly 5 times

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

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Unit Test Summary

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Quick Reference

25 tokens

Regular Expression

(?<=\D|^)(?=\d{8,12}\D|$)(\d{3})[\s,-]?\[\s,-]\K\d{4}|(?<=\D|^)(?=\d{12}|\d{9}\D|$)\d{5}

Unit Tests

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