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 (14)

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

/
/
ix

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "\\b(\n" + " # MAC address like xx:xx:xx:xx:xx:xx\n" + " [0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}:[0-9a-f]{2}\n" + " |\n" + " # MAC address like xx-xx-xx-xx-xx-xx\n" + " [0-9a-f]{2}-[0-9a-f]{2}-[0-9a-f]{2}-[0-9a-f]{2}-[0-9a-f]{2}-[0-9a-f]{2}\n" + " |\n" + " # MAC address like xxxx.xxxx.xxxx\n" + " [0-9a-f]{4}\\.[0-9a-f]{4}\\.[0-9a-f]{4}\n" + " |\n" + " # IPv4 address in dotted-quad format\n" + " # Not a lot of value for our needs in checking range of each octet\n" + " # Need to be more mindful of performance here anyway.\n" + " \\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\n" + ")\\b"; final String string = "192.168.1.2\n" + "10.0.0.0\n" + "ff:ff:ff:ff:ff:ff\n" + "FF-FF-FF-FF-FF-FF\n" + "FFFF.FFFF.FFFF\n" + "ffff.ffff.ffff\n" + "blah127.0.0.1haha\n" + "foo127.0.0.1\n\n\n"; final String subst = "\\1"; final Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE | Pattern.COMMENTS); final Matcher matcher = pattern.matcher(string); // The substituted value will be contained in the result variable final String result = matcher.replaceFirst(subst); System.out.println("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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html