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
  • 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

/
/
gm

Test String

Code Generator

Language

Generated Code

const regex = /(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]', 'gm') const str = `Valid domain name matching. Vote for it: http://stackoverflow.com/a/30007882/697313 Sample text for testing: abcdefghijklmnopqrstuvwxyz.ABCDEFGHIJKLMNOPQRSTUVWXYZ 0123456789 +-.,!@#\$%^&*();\\\\/|<>\\"\\' 12345 -98.7 3.141 .6180 9,000 +42 555.123.4567 +1-(800)-555-2468 foodemo.net bar.ba.test.co.uk www.demo.com http://foo.co.uk/ http://regexr.com/foo.html?q=bar g.com g-.com com.g -g.com xn--d1ai6ai.xn--p1ai xn-fsqu00a.xn-0zwm56d xn--stackoverflow.com stackoverflow.xn--com stackoverflow.co.uk google.com.au -0-0o.com 0-0o_.com (underscore not allowed) a.net -a.dot 0-0o.com 0-oz.co.uk 0-tension.com.br 0-wh-ao14-0.com-com.net a-1234567890-1234567890-1234567890-1234567890-1234567890-1234-z.eu.us a-1234567890-1234567890-1234567890-1234567890-1234567890-12345-z.eu.us (too long) List of valid domain names: www.google.com google.com mkyong123.com mkyong-info.com sub.mkyong.com sub.mkyong-info.com mkyong.com.au g.co mkyong.t.t.co List of invalid domain names, and why: mkyong.t.t.c – Tld must between 2 and 6 long mkyong,com – Comma is not allow mkyong – No Tld mkyong.123 , Tld not allow digit (can easily fix for this) .com – Must start with [A-Za-z0-9] mkyong.com/users – No Tld -mkyong.com – Cannot begin with a hyphen - mkyong-.com – Cannot end with a hyphen - sub.-mkyong.com – Cannot begin with a hyphen - sub.mkyong-.com – Cannot end with a hyphen - `; // 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