Regular Expressions 101

Pro

^start of line

Negative Lookahead(?!\d*(\d)\d*(?:(\d)\d*\1\d*\2|\1\d*(\d)\d*\3)|0)

1st Alternative\d*(\d)\d*(?:(\d)\d*\1\d*\2|\1\d*(\d)\d*\3)

\d*a digit, repeated any number of times

Group 1(\d)

\da digit

\d*a digit, repeated any number of times

Non-Capturing Group(?:(\d)\d*\1\d*\2|\1\d*(\d)\d*\3)

1st Alternative(\d)\d*\1\d*\2

Group 2(\d)

\da digit

\d*a digit, repeated any number of times

\1the text saved by group 1

\d*a digit, repeated any number of times

\2the text saved by group 2

2nd Alternative\1\d*(\d)\d*\3

\1the text saved by group 1

\d*a digit, repeated any number of times

Group 3(\d)

\da digit

\d*a digit, repeated any number of times

\3the text saved by group 3

2nd Alternative0

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Positive Lookahead(?=\d*(\d).*\4)

\d*a digit, repeated any number of times

Group 4(\d)

\da digit

.*any character (except for line terminators), repeated any number of times

\4the text saved by group 4

\d{10}a digit, repeated exactly 10 times

$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

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27 tokens

^(?!\d*(\d)\d*(?:(\d)\d*\1\d*\2|\1\d*(\d)\d*\3)|0)(?=\d*(\d).*\4)\d{10}$

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