Regular Expressions 101

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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
  • Match everything enclosed
    (?:...)
  • Capture everything enclosed
    (...)
  • 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

Generated Code

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @/ <p>(\s*)(<a(.*)>)?(\s*)(https?:\/\/)?(w{3}\.)?(youtube\.com|youtu\.be)\/(watch\?v=|embed\/)?([A-Za-z0-9-_]{11})(\S*)(\s*)(<\/a>)?(\s*)<\/p> /; string input = @"No protocol: <p>youtube.com/watch?v=dQw4w9WgXcQ</p> <p>www.youtube.com/watch?v=dQw4w9WgXcQ</p> HTTP or HTTPS: <p>http://youtube.com/watch?v=dQw4w9WgXcQ</p> <p>http://www.youtube.com/watch?v=dQw4w9WgXcQ</p> <p>https://youtube.com/watch?v=dQw4w9WgXcQ</p> <p>https://www.youtube.com/watch?v=dQw4w9WgXcQ</p> With or without “www” <p>https://youtube.com/watch?v=dQw4w9WgXcQ</p> <p>https://www.youtube.com/watch?v=dQw4w9WgXcQ</p> Youtu.be short links <p>youtu.be/LQaehcfXvK0</p> <p>https://youtu.be/LQaehcfXvK0</p> Embed Urls: <p>http://www.youtube.com/embed/dQw4w9WgXcQ</p> URLs with extra parameters: <p>https://www.youtube.com/watch?v=LQaehcfXvK0&feature=youtu.be</p> <p>https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=RDdQw4w9WgXcQ&start_radio=1&t=1</p> This URL won’t actually work on YouTube, but it works here, which is somewhat odd? And yet doesn't seem harmful. <p>youtu.be/embed/dQw4w9WgXcQ</p> Paragraph tags on separate lines with arbitrary whitespace: <p> www.youtube.com/embed/u8pCsfT1gDU </p> <p> https://youtube.com/watch?v=dQw4w9WgXcQ </p> <p> http://www.youtube.com/embed/dQw4w9WgXcQ </p> <p> youtube.com/watch?v=dQw4w9WgXcQ </p> Paragraph tags with any other text in them, besides the URL: <p>This shouldn’t work: https://youtube.com/watch?v=dQw4w9WgXcQ</p> <p>https://youtube.com/watch?v=dQw4w9WgXcQ nor this</p> <p> https://youtube.com/watch?v=dQw4w9WgXcQ also not this </p> Paragraph tags with links added by markdown-it: <p><a href=""https://www.youtube.com/watch?v=dQw4w9WgXcQ"">https://www.youtube.com/watch?v=dQw4w9WgXcQ</a></p> <p> <a href=""https://www.youtube.com/watch?v=dQw4w9WgXcQ?something"" class=""something"" id=""whatever""> youtube.com/watch?v=dQw4w9WgXcQ?foo=bar&whatever </a> </p> "; foreach (Match m in Regex.Matches(input, pattern)) { 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