Regular Expressions 101

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/
(?<!\d[- \/.])(?<!\d)(3[01]|[12][0-9]|0?[1-9])[- \/.](1[012]|0?[1-9])[- \/.](?:\d{2})?(\d?\d)(?![- \/.]?\d)
/
g
Negative Lookbehind
(?<!\d[- \/.])
Assert that the Regex below does not match
\d matches a digit (equivalent to [0-9])
Match a single character present in the list below
[- \/.]
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Negative Lookbehind
(?<!\d)
Assert that the Regex below does not match
\d matches a digit (equivalent to [0-9])
1st Capturing Group
(3[01]|[12][0-9]|0?[1-9])
1st Alternative
3[01]
3 matches the character 3 with index 5110 (3316 or 638) literally (case sensitive)
Match a single character present in the list below
[01]
01
matches a single character in the list 01 (case sensitive)
2nd Alternative
[12][0-9]
Match a single character present in the list below
[12]
12
matches a single character in the list 12 (case sensitive)
Match a single character present in the list below
[0-9]
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
3rd Alternative
0?[1-9]
0
matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
Match a single character present in the list below
[1-9]
1-9 matches a single character in the range between 1 (index 49) and 9 (index 57) (case sensitive)
Match a single character present in the list below
[- \/.]
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
2nd Capturing Group
(1[012]|0?[1-9])
1st Alternative
1[012]
1 matches the character 1 with index 4910 (3116 or 618) literally (case sensitive)
Match a single character present in the list below
[012]
012
matches a single character in the list 012 (case sensitive)
2nd Alternative
0?[1-9]
0
matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
Match a single character present in the list below
[1-9]
1-9 matches a single character in the range between 1 (index 49) and 9 (index 57) (case sensitive)
Match a single character present in the list below
[- \/.]
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Non-capturing group
(?:\d{2})?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\d
matches a digit (equivalent to [0-9])
{2} matches the previous token exactly 2 times
3rd Capturing Group
(\d?\d)
\d
matches a digit (equivalent to [0-9])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\d matches a digit (equivalent to [0-9])
Negative Lookahead
(?![- \/.]?\d)
Assert that the Regex below does not match
Match a single character present in the list below
[- \/.]
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\d matches a digit (equivalent to [0-9])
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
g

Test String