Regular Expressions 101

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/
^([1-9]|0[1-9]|1[012])([-\/.])([1-9]|0[1-9]|[12][0-9]|3[01])\2(\d{4})$|^(\d{4})([-\/.])([1-9]|0[1-9]|[12][0-9]|3[01])\6([1-9]|0[1-9]|[12][0-9]|3[01])$
/
1st Alternative
^([1-9]|0[1-9]|1[012])([-\/.])([1-9]|0[1-9]|[12][0-9]|3[01])\2(\d{4})$
^ asserts position at start of the string
1st Capturing Group
([1-9]|0[1-9]|1[012])
1st Alternative
[1-9]
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)
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)
3rd 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 Capturing Group
([-\/.])
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 4710 (2F16 or 578) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
3rd Capturing Group
([1-9]|0[1-9]|[12][0-9]|3[01])
1st Alternative
[1-9]
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)
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)
3rd 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)
4th 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)
\2 matches the same text as most recently matched by the 2nd capturing group
4th Capturing Group
(\d{4})
\d
matches a digit (equivalent to [0-9])
{4} matches the previous token exactly 4 times
$ asserts position at the end of the string
2nd Alternative
^(\d{4})([-\/.])([1-9]|0[1-9]|[12][0-9]|3[01])\6([1-9]|0[1-9]|[12][0-9]|3[01])$
^ asserts position at start of the string
5th Capturing Group
(\d{4})
\d
matches a digit (equivalent to [0-9])
{4} matches the previous token exactly 4 times
6th Capturing Group
([-\/.])
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 4710 (2F16 or 578) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
7th Capturing Group
([1-9]|0[1-9]|[12][0-9]|3[01])
1st Alternative
[1-9]
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)
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)
3rd 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)
4th 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)
\6 matches the same text as most recently matched by the 6th capturing group
8th Capturing Group
([1-9]|0[1-9]|[12][0-9]|3[01])
1st Alternative
[1-9]
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)
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)
3rd 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)
4th 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)
$ asserts position at the end of the string
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/

Test String