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

r"
"
gm

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 = "(?i)(?=(((\\()?(red|gold|silver|king)( pack)?(\\))?)|((70|83|84|100|120)(s|'s)?)))((((\\()?(red|gold|silver|king)( pack)?(\\))? )?((70|83|84|100|120)(s|'s)? )?)(\\bbox\\b))"; final String string = "Python does not support conditionals using lookaround, even though Python does support lookaround outside conditionals. Instead of a conditional like (?(?=regex)then|else), you can alternate two opposite lookarounds: (?=regex)then|(?!regex)else.\n\n" + "https://www.regular-expressions.info/lookaround.html\n" + "https://www.regular-expressions.info/conditional.html\n\n" + "LOOKAHEAD to see if EITHER pattern1 or pattern2 exists\n" + "pattern1 = ((\\()?(red|gold|silver|king)( pack)?(\\))?)\n" + "pattern2 = ((70|83|84|100|120)(s|'s)?)\n" + "IF one of the patterns exists in the string, THEN look for \n" + "pattern1 box\n" + "pattern2 box\n" + "pattern1 pattern2 box\n" + " \n" + "IS NOT cases - things that I do NOT want to match\n" + "box\n" + " box\n" + "Marlboro Box - this is a perfect example of a NOT case - I do NOT want to match this string\n" + "OR maybe I do ... ARGH - NO I do not want to match BOX!!\n" + "moving box - example that I NEVER want to match ... ARGHHH\n" + "junk 's matchbox car\n" + "matchboxracer\n" + "boxer - we NEVER think about the NOT cases ... lol mitch and I fought about this for years. recently he meantioned the NEED for NOT\n\n" + "IS cases - aka - things that I WANT TO MATCH\n\n" + "Marlboro 100's Box\n" + "Marlboro Gold Pack 100's Box\n" + "Marlboro Special Blend (Gold Pack) 100's Box\n" + "Marlboro Silver Pack Box\n" + "Marlboro Special Blend (Red Pack) 100s Box\n" + "Pall Mall RED 100 BOX\n" + "Marlboro Special Blend (Gold Pack) Box\n\n\n\n\n"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); 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