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

/
/
g

Test String

Code Generator

Language

Generated Code

const regex = /(?<src_host>\w+\.\w+:\d{2})\s(?<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\D{1,6}(?<date_time>[^ ]+)\s(?<GMT_offset>[^ ]+)\]\s"(?<action>(GET|POST|HEAD|TRACE|PUT|DELETE|CONNECT))\s(?<hash_url>[^ ]+)\s(?<protocol>[^\"]+)\"\s(?<code>\d{1,3})\s(?<size>[^ ]+)\s\"(?<referrer>[^ ]+)\"\s\"(?<user_agent>[^ ]+.+)\"/g; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?<src_host>\\w+\\.\\w+:\\d{2})\\s(?<src_ip>\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3})\\D{1,6}(?<date_time>[^ ]+)\\s(?<GMT_offset>[^ ]+)\\]\\s"(?<action>(GET|POST|HEAD|TRACE|PUT|DELETE|CONNECT))\\s(?<hash_url>[^ ]+)\\s(?<protocol>[^\\"]+)\\"\\s(?<code>\\d{1,3})\\s(?<size>[^ ]+)\\s\\"(?<referrer>[^ ]+)\\"\\s\\"(?<user_agent>[^ ]+.+)\\"', 'g') const str = `google.com:80 212.111.203.171 - - [02/Mar/2015:10:27:04 +0000] "GET /css/style.css HTTP/1.1" 304 138 "http://google.com" "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36"`; // 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