Regular Expressions 101

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/
^(0|[1-9]\d)\.(0|[1-9]\d)\.(0|[1-9]\d)(?:-((?:0|[1-9]\d|\d[a-zA-Z-][0-9a-zA-Z-])(?:\.(?:0|[1-9]\d|\d[a-zA-Z-][0-9a-zA-Z-]))*))?(?:\+([0-9a-zA-Z-](?:\.[0-9a-zA-Z-])*))?$
/
gm
^ asserts position at start of a line
1st Capturing Group
(0|[1-9]\d)
1st Alternative
0
0 matches the character 0 literally (case sensitive)
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])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . literally (case sensitive)
2nd Capturing Group
(0|[1-9]\d)
1st Alternative
0
0 matches the character 0 literally (case sensitive)
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])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . literally (case sensitive)
3rd Capturing Group
(0|[1-9]\d)
1st Alternative
0
0 matches the character 0 literally (case sensitive)
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])
Non-capturing group
(?:-((?:0|[1-9]\d|\d[a-zA-Z-][0-9a-zA-Z-])(?:\.(?:0|[1-9]\d|\d[a-zA-Z-][0-9a-zA-Z-]))*))?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
- matches the character - literally (case sensitive)
4th Capturing Group
((?:0|[1-9]\d|\d[a-zA-Z-][0-9a-zA-Z-])(?:\.(?:0|[1-9]\d|\d[a-zA-Z-][0-9a-zA-Z-]))*)
Non-capturing group
(?:\+([0-9a-zA-Z-](?:\.[0-9a-zA-Z-])*))?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\+ matches the character + literally (case sensitive)
5th Capturing Group
([0-9a-zA-Z-](?:\.[0-9a-zA-Z-])*)
$ 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.

Regular Expression
No Match

/
/
gm

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 JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions