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

Generated Code

const regex = /(?<!```html\s*)(<link href=.*?)(?=^\s*$)/gmis; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?<!```html\\s*)(<link href=.*?)(?=^\\s*$)', 'gmis') const str = ` # 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> `; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

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 JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions