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
"
^([0-9]{2})(.|\/|\s)([0-9]{2})(.|\/|\s)([0-9]{4}|[0-9]{2})
"
gm
^ asserts position at start of a line
1st Capturing Group
([0-9]{2})
Match a single character present in the list below
[0-9]
{2} matches the previous token exactly 2 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
2nd Capturing Group
(.|\/|\s)
1st Alternative
.
. matches any character (except for line terminators)
2nd Alternative
\/
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
3rd Alternative
\s
\s matches any whitespace character (equivalent to [\r\n\t\f\v  ])
3rd Capturing Group
([0-9]{2})
Match a single character present in the list below
[0-9]
{2} matches the previous token exactly 2 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
4th Capturing Group
(.|\/|\s)
1st Alternative
.
. matches any character (except for line terminators)
2nd Alternative
\/
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
3rd Alternative
\s
\s matches any whitespace character (equivalent to [\r\n\t\f\v  ])
5th Capturing Group
([0-9]{4}|[0-9]{2})
1st Alternative
[0-9]{4}
Match a single character present in the list below
[0-9]
{4} matches the previous token exactly 4 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
2nd Alternative
[0-9]{2}
Match a single character present in the list below
[0-9]
{2} matches the previous token exactly 2 times
0-9 matches 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.

Regular Expression
No Match

r"
"
gm

Test String