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
Processing...

Test String

Code Generator

Language

Generated Code

const regex = /^((a{1,4}|a?b|ba){1,3}|(a{1,3}|b){1,4}|((a{2,3}|b){2}|aaba|abaa){2})$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^((a{1,4}|a?b|ba){1,3}|(a{1,3}|b){1,4}|((a{2,3}|b){2}|aaba|abaa){2})$', 'gm') const str = `Allowed: aaaaaaaaaaaa aaaaaaaaaaa abaaaaab baaaaaba abaaaaba bbbb bababa ababab aabaabaa abaabaaa baaaaaab baaaaab baaaaaaaaa abaaaaaaaa aabaaaaaaa aaabaaaaaa aaaabaaaaa aaaaabaaaa aaaaaabaaa aaaaaaabaa aaaaaaaaba aaaaaaaaab baaaaaba abaaaaab babaaaaa ababaaaa aababaaa aaaababa aaaaabab baaaabaa abaaaaba aabaaaab baabaaaa abaabaaa aabaabaa aaabaaba baaaaba abaaaab babaaaa ababaaa aababaa aaababa abba abbb bababa bbaab abbab abaabb baaabaa abaaaba aabaaab baabaaa abaabaa abaabaa aabaaba Disallowed: aaaaaaaaaaaaa aabaabaaa aababab bbbba bbabb baaaaaaab`; // 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