Regular Expressions 101

Save & Share

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

/
/
gx

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

const regex = /<img\s+ (?=[^>]*\balt="(?<alt>[^>]*?)")? # optional alt attribute (?=[^>]*\bclass="(?<class>[^>]*?)")? # optional class attribute (?=[^>]*\bsrc="(?<src>[^>]*?)") # src attribute [^>]*\/>/g; // Alternative syntax using RegExp constructor // const regex = new RegExp('<img\\s+ (?=[^>]*\\balt="(?<alt>[^>]*?)")? # optional alt attribute (?=[^>]*\\bclass="(?<class>[^>]*?)")? # optional class attribute (?=[^>]*\\bsrc="(?<src>[^>]*?)") # src attribute [^>]*\\\/>', 'g') const str = `<img src="image.png" alt="test" style="zoom:55%;" /> <img class="big" src="image2.png" /> <img alt="test" src="image.png" style="zoom:55%;" /> <img src="image.png" class="small" style="zoom:55%;" alt="test" /> <img src="image.png" alt="test" style="zoom:55%;" /> <img src="image.png" alt="test" style="zoom:55%;" />`; const subst = `![${alt}](${src}){.${class}}`; // The substituted value will be contained in the result variable const result = str.replace(regex, subst); console.log('Substitution result: ', result);

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