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

/
/
igmx

Test String

Code Generator

Language

Generated Code

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @"<link(?=[^<>]*?opensearch)(?:[^h]+|h(?!ref))*+href=[""']?\K([^<>'""\s]+(?:\/(?!>)|\b))(?=[^<>]*>)"; string input = @"This should succeed: <link rel=""search"" type=""application/opensearchdescription+xml"" href=""http://example.com/tsr-opensearch/"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=""http://www.example.com/search.xml"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=""/search.xml"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=""search.xml"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href="".search.xml"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=""./search.xml"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href="".search.xml"" title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href='http://www.example.com/search.xml' title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml title="" /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml/> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/dsfdsf/search.xml /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml/ /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml/ /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://href.example.com/search.xml/ /> <link rel=""search"" type=""application/opensearchdescription+xml"" hre href=http://href.example.com/search.xml/ /> <link rel=""search"" type=""application/opensearchdescription+xml"" ref=""adfsf"" href=http://href.example.com/search.xml/ /> Should fail: <link rel=""stylesheet"" type=""text/css"" href=""theme.css""> <link rel=""search"" type=""application/opensearchdescription+xml"" href= http://www.example.com/search.xml /> <link rel=""search"" type=""application/opensearchdescription+xml"" href= http://www.example.com/search.xml> link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml> link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml /> <link rel=""search"" type=""application/opensearchdescription+xml"" href=http://www.example.com/search.xml"; RegexOptions options = RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.IgnorePatternWhitespace; foreach (Match m in Regex.Matches(input, pattern, options)) { Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index); } } }

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 C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx