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 = /^\s*(?!.*?_.*?)(?!(?:[\d\w]+?\.)?\-[\w\d\.\-]*?)(?![\w\d]+?\-\.(?:[\d\w\.\-]+?))(?=[\w\d])(?=[\w\d\.\-]*?\.+[\w\d\.\-]*?)(?![\w\d\.\-]{254})(?!(?:\.?[\w\d\-\.]*?[\w\d\-]{64,}\.)+?)[\w\d\.\-]+?(?<![\w\d\-\.]*?\.[\d]+?)(?<=[\w\d\-]{2,})(?<![\w\d\-]{25})(\s*,\s*(?!.*?_.*?)(?!(?:[\d\w]+?\.)?\-[\w\d\.\-]*?)(?![\w\d]+?\-\.(?:[\d\w\.\-]+?))(?=[\w\d])(?=[\w\d\.\-]*?\.+[\w\d\.\-]*?)(?![\w\d\.\-]{254})(?!(?:\.?[\w\d\-\.]*?[\w\d\-]{64,}\.)+?)[\w\d\.\-]+?(?<![\w\d\-\.]*?\.[\d]+?)(?<=[\w\d\-]{2,})(?<![\w\d\-]{25}))*$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^\\s*(?!.*?_.*?)(?!(?:[\\d\\w]+?\\.)?\\-[\\w\\d\\.\\-]*?)(?![\\w\\d]+?\\-\\.(?:[\\d\\w\\.\\-]+?))(?=[\\w\\d])(?=[\\w\\d\\.\\-]*?\\.+[\\w\\d\\.\\-]*?)(?![\\w\\d\\.\\-]{254})(?!(?:\\.?[\\w\\d\\-\\.]*?[\\w\\d\\-]{64,}\\.)+?)[\\w\\d\\.\\-]+?(?<![\\w\\d\\-\\.]*?\\.[\\d]+?)(?<=[\\w\\d\\-]{2,})(?<![\\w\\d\\-]{25})(\\s*,\\s*(?!.*?_.*?)(?!(?:[\\d\\w]+?\\.)?\\-[\\w\\d\\.\\-]*?)(?![\\w\\d]+?\\-\\.(?:[\\d\\w\\.\\-]+?))(?=[\\w\\d])(?=[\\w\\d\\.\\-]*?\\.+[\\w\\d\\.\\-]*?)(?![\\w\\d\\.\\-]{254})(?!(?:\\.?[\\w\\d\\-\\.]*?[\\w\\d\\-]{64,}\\.)+?)[\\w\\d\\.\\-]+?(?<![\\w\\d\\-\\.]*?\\.[\\d]+?)(?<=[\\w\\d\\-]{2,})(?<![\\w\\d\\-]{25}))*$', 'gm') const str = `# REGEX for domains separated by comas and sapces: #longest domain - 253 - add one character a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl #3 longest domains a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl,a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl,a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl #4 longest domains with spaces a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl ,a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl , a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl , a22bcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopdasdqrstuvwxylkjlkjlk.pl #spaces everywhere al.pl , a.pl, b.com , asdf.asdf google.com google.com,shakalaka.bu shakalaka.com.pl g.co a.13B 12312412412..cor xn--stackoverflow.com stackoverflow.xn--com xn--d1ai6ai.xn--p1ai 1.2.3.4.5.com , 12.34.pl x.XN--VERMGENSBERATUNG-PWB ## List of invalid domains: http://google.com http://www.google.com dot. space com under_score.com underscore.c_om -dash.com dash-.com sub.-dash.com sub-.dash.com -.com -com .com com mx.gmail.com. mkyong.t.t.c mkyong,com mkyong.com/users a.123 x.XN--VERMGENSBERATUNG-PWBB abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkk.com www.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkk.co.uk abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.comm example.c `; // 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