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- PCRE2 (PHP >=7.3)
- PCRE (PHP <7.3)
- ECMAScript (JavaScript)
- Python 2.7
- Golang
- Java 8

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(?<=\d\-\d\-\d|\d.\d|\d.\d.\d.\d|\d.\d.\d).(?=\d)

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gm

Positive Lookbehind

(?<=\d\-\d\-\d|\d.\d|\d.\d.\d.\d|\d.\d.\d)

Assert that the Regex below matches

1st Alternative

\d\-\d\-\d

\d

matches a digit (equivalent to [0-9]){4} matches the previous token exactly 4 times

\- matches the character - literally (case sensitive)

\d

matches a digit (equivalent to [0-9]){2} matches the previous token exactly 2 times

\- matches the character - literally (case sensitive)

\d

matches a digit (equivalent to [0-9]){2} matches the previous token exactly 2 times

2nd Alternative

\d.\d

\d

matches a digit (equivalent to [0-9]){4} matches the previous token exactly 4 times

. matches any character (except for line terminators)

\d

matches a digit (equivalent to [0-9]){4} matches the previous token exactly 4 times

3rd Alternative

\d.\d.\d.\d

\d

matches a digit (equivalent to [0-9]){4} matches the previous token exactly 4 times

. matches any character (except for line terminators)

\d

matches a digit (equivalent to [0-9]){1} matches the previous token exactly one time (meaningless quantifier)

. matches any character (except for line terminators)

\d

matches a digit (equivalent to [0-9]){1} matches the previous token exactly one time (meaningless quantifier)

. matches any character (except for line terminators)

\d

matches a digit (equivalent to [0-9])4th Alternative

\d.\d.\d

\d

matches a digit (equivalent to [0-9]){4} matches the previous token exactly 4 times

. matches any character (except for line terminators)

\d

matches a digit (equivalent to [0-9]){2} matches the previous token exactly 2 times

. matches any character (except for line terminators)

\d

matches a digit (equivalent to [0-9]).

matches any character (except for line terminators)*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)

Positive Lookahead

(?=\d)

Assert that the Regex below matches

\d matches a digit (equivalent to [0-9])

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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