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
/
^(?:(?:\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){3}(?:\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])$
/
mg
^ asserts position at start of a line
Non-capturing group
(?:(?:\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){3}
{3} matches the previous token exactly 3 times
Non-capturing group
(?:\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])
1st Alternative
\d
\d matches a digit (equivalent to [0-9])
2nd Alternative
[1-9]\d
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)
\d matches a digit (equivalent to [0-9])
3rd Alternative
1\d\d
1 matches the character 1 with index 4910 (3116 or 618) literally (case sensitive)
\d matches a digit (equivalent to [0-9])
\d matches a digit (equivalent to [0-9])
4th Alternative
2[0-4]\d
2 matches the character 2 with index 5010 (3216 or 628) literally (case sensitive)
Match a single character present in the list below
[0-4]
0-4 matches a single character in the range between 0 (index 48) and 4 (index 52) (case sensitive)
\d matches a digit (equivalent to [0-9])
5th Alternative
25[0-5]
25
matches the characters 25 literally (case sensitive)
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)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Non-capturing group
(?:\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])
1st Alternative
\d
\d matches a digit (equivalent to [0-9])
2nd Alternative
[1-9]\d
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)
\d matches a digit (equivalent to [0-9])
3rd Alternative
1\d\d
1 matches the character 1 with index 4910 (3116 or 618) literally (case sensitive)
\d matches a digit (equivalent to [0-9])
\d matches a digit (equivalent to [0-9])
4th Alternative
2[0-4]\d
2 matches the character 2 with index 5010 (3216 or 628) literally (case sensitive)
Match a single character present in the list below
[0-4]
0-4 matches a single character in the range between 0 (index 48) and 4 (index 52) (case sensitive)
\d matches a digit (equivalent to [0-9])
5th Alternative
25[0-5]
25
matches the characters 25 literally (case sensitive)
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)
$ asserts position at the end of a line
Global pattern flags
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
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

/
/
mg

Test String

Code Generator

Generated Code

Loading code sample...
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php