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

/
/
gm

Test String

Code Generator

Language

Generated Code

const regex = /^(?:(?:(?:0?[13578]|1[02])(\/)31)\1|(?:(?:0?[1,3-9]|1[0-2])(\/)(?:29|30)\2))(?:(?:19|[2-9]\d)\d{2})$|^(?:0?2(\/)29\3(?:(?:(?:19|20)(?:0[048]|[2468][048]|[13579][26]))))$|^(?:(?:0?[1-9])|(?:1[0-2]))(\/)(?:0?[1-9]|1\d|2[0-8])\4(?:(?:19|[0-9]\d)?\d{2})$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^(?:(?:(?:0?[13578]|1[02])(\\\/)31)\\1|(?:(?:0?[1,3-9]|1[0-2])(\\\/)(?:29|30)\\2))(?:(?:19|[2-9]\\d)\\d{2})$|^(?:0?2(\\\/)29\\3(?:(?:(?:19|20)(?:0[048]|[2468][048]|[13579][26]))))$|^(?:(?:0?[1-9])|(?:1[0-2]))(\\\/)(?:0?[1-9]|1\\d|2[0-8])\\4(?:(?:19|[0-9]\\d)?\\d{2})$', 'gm') const str = `1/1/2019 2/29/2020 1/31/00 2/29/2000 3/31/2019 2/29/2020 7/23/1999 7/31/1999 7/28/1999 7/21/1999 7/5/1964 7/21/2000 2/29/1900 6/5/1999 5/5/1999 4/4/1999 3/3/1999 2/2/1999 2/29/1996 2/29/2000 1/1/1954 1/1/1985 3/31/2019 1/29/2010 10/21/1967`; // 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