Regular Expressions 101

Save & Share

  • Regex Version: ver. 1
  • Update Regex
    ctrl+⇧+s
  • Save new Regex
    ctrl+s
  • Add to Community Library

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8
  • .NET 7.0 (C#)
  • Rust
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests

Tools

Sponsors
There are currently no sponsors. Become a sponsor today!
An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
gm

Test String

Code Generator

Language

Generated Code

const regex = /(?i)<a\s+href="(?:https?:\/\/)?(?:w{3}\.)?(?:[^"\/]*\.)?([a-z0-9_-]+\.[a-z0-9_-]{2,6})(\/[^"]*)?"[^>]*>(?!.*\1.*)(?:https?:\/\/)?(?:w{3}\.)?(?:[^"\/]*\.)?([a-z0-9_-]+\.[a-z0-9_-]{2,6})(\/[^"]*)?.*?<\/a>/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?i)<a\\s+href="(?:https?:\\\/\\\/)?(?:w{3}\\.)?(?:[^"\\\/]*\\.)?([a-z0-9_-]+\\.[a-z0-9_-]{2,6})(\\\/[^"]*)?"[^>]*>(?!.*\\1.*)(?:https?:\\\/\\\/)?(?:w{3}\\.)?(?:[^"\\\/]*\\.)?([a-z0-9_-]+\\.[a-z0-9_-]{2,6})(\\\/[^"]*)?.*?<\\\/a>', 'gm') const str = `<a href="http://www.test1.net/dir1/index.html" target="_blank">test1.net/admin</a> <-- NOT MATCH <a href="https://test2.com">THIS SITE</a> <-- NOT MATCH <a href="https://subdomain.test3.org">test2.org</a> <-- MATCH <a href="http://www2.test4.com" target="_blank">https://global.test4.com/index.html</a> <-- NOT MATCH <a href="http://eu.test5.com">https://evil.com/eu.test5.com/</a> <-- MATCH <a href="http://eu.site6.com/index.html" target="_blank">https://eu.evil.com</a> <-- MATCH <a href="https://site7.com/">http://www.site7.com/123/test</a> <-- NOT MATCH`; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

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