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

/
/
gmis

Test String

Code Generator

Language

Generated Code

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @"(?<!```html\s*)(<link href=.*?)(?=^\s*$)"; string input = @" # PATTERNS ## Style Blocks (2 patterns) - ***Matches:*** - All `<style> any code here </style> blocks that aren't preceded by ```css + any amount of optional whitespace >> NOTES FOR THE FOLLOWING PATTERN: • This requires the `regex` library, not Python's built-in-crap • This requires the `Single Line` (regex101) or `regex.DOTALL` (Python regex) flag ### Pattern: Old version (would have replaced all punctuation with `punctuation` from the string library) (?<!```css\s*)(\<style\>[\sa-z0-9\-\.\[\{\]\}:;#]+\<\/style\>) >> NOTES FOR THE FOLLOWING PATTERN: • This requires the `regex` library, not Python's built-in-crap • This requires the `Single Line` (regex101) or `regex.DOTALL` (Python regex) flag ### Pattern: Newest version (much better) (?<!```css\s*)(<style>.*?<\/style>) ## This does the same thing but for `<!DOCTYPE html> any code here </html>` >> NOTES FOR THE FOLLOWING PATTERN: • This requires the `regex` library, not Python's built-in-crap • This requires the `Single Line` (regex101) or `regex.DOTALL` (Python regex) flag ### Pattern: (?<!```html\s*)(<!DOCTYPE html>.*?<\/html>) ## This matches all blocks of code containing `<link href=>` up to, but not including, an empty line >> NOTES FOR THE FOLLOWING PATTERN: • This requires the `regex` library, not Python's built-in-crap • This requires the `Single Line` (regex101) or `regex.DOTALL` (Python regex) flag ### Pattern: (?<!```html\s*)(<link href=.*?)(?=^\s*$) <br> (><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><)(><) <br> # TEST TEXT <br> <style> .list-group-mine .list-group-item { background-color: black; color: white; border-top: 1px solid #0091b5; border-left-color: #fff; border-right-color: #fff; } .list-group-mine .list-group-item:hover { background-color: red; } </style> ```css <style> .list-group-mine .list-group-item { background-color: black; color: white; border-top: 1px solid #0091b5; border-left-color: #fff; border-right-color: #fff; } .list-group-mine .list-group-item:hover { background-color: red; } </style> ``` <link href=""https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css"" rel=""stylesheet"" integrity=""sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u"" crossorigin=""anonymous""> <div class=""list-group list-group-mine""> <a class=""list-group-item"" href=""https://bit.ly/3SICqay""><strong>Link to the SO Post</strong></a> <a class=""list-group-item"" href=""/path""><strong>Item 2</strong></a> <a class=""list-group-item"" href=""/path""><strong>Item 3</strong></a> </div> <br> ##### Before Bootstrap <!DOCTYPE html> <html lang=""en""> <head> <title>TABLE</title> </head> <body> <table> <thead> <tr> <th>Name</th> <th>Number</th> </tr> </thead> <tbody> <tr> <td>Malachi</td> <td>1-555-343-9867</td> </tr> <tr> <td>Steve</td> <td>1-555-734-8857</td> </tr> </tbody> </table> </body> </html> </br> <code style=""color: #f51686; font-weight: bold; font-size: 16pt;""> The HTML </code> ```html <!DOCTYPE html> <html lang=""en""> <head> <meta charset=""UTF-8"" /> <meta http-equiv=""X-UA-Compatible"" content=""IE=edge"" /> <meta name=""viewport"" content=""width=device-width, initial-scale=1.0"" /> <title>CSS Images</title> <link rel=""stylesheet"" href=""css/style.css"" /> </head> <body> <div class=""container""> <section class=""hero""> <figure class=""profile-pic-figure""> <img src=""img/profile-800x800.png"" alt=""profile"" width=""800"" height=""800"" title=""Profile Pic"" /> <figcaption class=""offscreen"">Pookie Scrumptious</figcaption> </figure> <h1 class=""h1""> <span class=""nowrap""> Hello 👋 </span> <span class=""nowrap""> I'm Pookie </span> </h1> </section> </div> </body> </html> ``` <br> <code style=""color: #f51686; font-weight: bold; font-size: 16pt;""> The CSS</code> "; RegexOptions options = RegexOptions.Multiline | RegexOptions.IgnoreCase | RegexOptions.Singleline; 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