Regular Expressions 101

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  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python 2.7
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~
(0[1-9]|[12][0-9]|3[01])/(0[1-9]|1[012])/(19|20)[0-9]{2}
~
gm
1st Capturing Group
(0[1-9]|[12][0-9]|3[01])
1st Alternative
0[1-9]
0 matches the character 0 literally (case sensitive)
Match a single character present in the list below
[1-9]
1-9 a single character in the range between 1 (index 49) and 9 (index 57) (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 a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
3rd Alternative
3[01]
3 matches the character 3 literally (case sensitive)
Match a single character present in the list below
[01]
01 matches a single character in the list 01 (case sensitive)
/ matches the character / literally (case sensitive)
2nd Capturing Group
(0[1-9]|1[012])
1st Alternative
0[1-9]
0 matches the character 0 literally (case sensitive)
Match a single character present in the list below
[1-9]
1-9 a single character in the range between 1 (index 49) and 9 (index 57) (case sensitive)
2nd Alternative
1[012]
1 matches the character 1 literally (case sensitive)
Match a single character present in the list below
[012]
012 matches a single character in the list 012 (case sensitive)
/ matches the character / literally (case sensitive)
3rd Capturing Group
(19|20)
1st Alternative
19
19 matches the characters 19 literally (case sensitive)
2nd Alternative
20
20 matches the characters 20 literally (case sensitive)
Match a single character present in the list below
[0-9]{2}
{2} Quantifier — Matches exactly 2 times
0-9 a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi 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.

Regular Expression
No Match

~
~
gm

Test String