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 (18)

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

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "\\b(?:(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9]))\\b"; final String string = "This REGULAR EXPRESSION is just for searching for dotted decimal IPv4 Adresses.\n" + "Unlike a shorter one, this one is made for seeing the numbers in seperate Mach-groups-thingy.\n" + "I also included some unit tests.. But i think they are not needed.\n\n" + "Below are some tests:\n\n" + "Valid:\n" + "0.0.0.0\n" + "1.2.3.4\n" + "127.0.0.1\n" + "8.8.4.4\n" + "8.8.8.8\n" + "255.255.255.255\n" + "249.0.0.1\n" + "0.1.255.254\n" + "98.139.180.149\n" + "69.89.31.226\n\n\n" + "Invalid:\n" + "999.999.999\n" + "290.250.2.6\n" + "256.259.20.255\n\n\n" + "Texts:\n" + "Google DNS Server IP is 8.8.8.8. As a alternative you can use 8.8.4.4. \n" + "The IP 127.0.0.1 (also known as localhost) is a 'loopback' IP-Adress, pointing to your computer.\n\n\n" + "Example pinging:\n" + " Microsoft Windows [Version 6.1.7601]\n" + " Copyright (c) 2009 Microsoft Corporation. Alle Rechte vorbehalten.\n" + " \n" + " C:\\Users\\Example>ping google.com\n" + " \n" + " Pinging google.com [212.6.83.44] with 32 bytes of data:\n" + " Reply from 212.6.83.44: bytes=32 time=42ms TTL=59\n" + " Reply from 212.6.83.44: bytes=32 time=55ms TTL=59\n" + " Reply from 212.6.83.44: bytes=32 time=35ms TTL=59\n" + " Reply from 212.6.83.44: bytes=32 time=27ms TTL=59\n" + " \n" + " Ping statistics for 212.6.83.44:\n" + " Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\n" + " Approximate round trip times in milli-seconds:\n" + " Minimum = 27ms, Maximum = 55ms, Average = 39ms\n" + " \n" + " C:\\Users\\Example>"; final Pattern pattern = Pattern.compile(regex); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(i)); } } } }

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