Regular Expressions 101

Save & Share

Flavor

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

Function

  • Match
  • Substitution
  • List
  • Unit Tests
/
^(0?\d|[1][0-2])\/(0?[1-9]|[0-2]\d|[3][0-1])\/(\d{2})(?:(?:\s(0?[1-9]|1[012])\:([0-5]\d)(?:\s(AM|PM))?)?)$
/
gm
^ asserts position at start of a line
1st Capturing Group
(0?\d|[1][0-2])
1st Alternative
0?\d
0
matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
\d matches a digit (equivalent to [0-9])
2nd Alternative
[1][0-2]
Match a single character present in the list below
[1]
1 matches the character 1 with index 4910 (3116 or 618) literally (case sensitive)
Match a single character present in the list below
[0-2]
0-2 matches a single character in the range between 0 (index 48) and 2 (index 50) (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
2nd Capturing Group
(0?[1-9]|[0-2]\d|[3][0-1])
1st 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)
2nd Alternative
[0-2]\d
Match a single character present in the list below
[0-2]
0-2 matches a single character in the range between 0 (index 48) and 2 (index 50) (case sensitive)
\d matches a digit (equivalent to [0-9])
3rd Alternative
[3][0-1]
Match a single character present in the list below
[3]
3 matches the character 3 with index 5110 (3316 or 638) literally (case sensitive)
Match a single character present in the list below
[0-1]
0-1 matches a single character in the range between 0 (index 48) and 1 (index 49) (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
3rd Capturing Group
(\d{2})
\d
matches a digit (equivalent to [0-9])
{2} matches the previous token exactly 2 times
Non-capturing group
(?:(?:\s(0?[1-9]|1[012])\:([0-5]\d)(?:\s(AM|PM))?)?)
Non-capturing group
(?:\s(0?[1-9]|1[012])\:([0-5]\d)(?:\s(AM|PM))?)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\s matches any whitespace character (equivalent to [\r\n\t\f\v ])
4th Capturing Group
(0?[1-9]|1[012])
1st 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)
2nd 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)
\: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
5th Capturing Group
([0-5]\d)
Match a single character present in the list below
[0-5]
0-5 matches a single character in the range between 0 (index 48) and 5 (index 53) (case sensitive)
\d matches a digit (equivalent to [0-9])
Non-capturing group
(?:\s(AM|PM))?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\s matches any whitespace character (equivalent to [\r\n\t\f\v ])
6th Capturing Group
(AM|PM)
1st Alternative
AM
AM
matches the characters AM literally (case sensitive)
2nd Alternative
PM
PM
matches the characters PM literally (case sensitive)
$ asserts position at the end of a line
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