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-z][a-z]*(([A-Z][a-z]+)*[A-Z]?|([a-z]+[A-Z])*|[A-Z])$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^[a-z][a-z]*(([A-Z][a-z]+)*[A-Z]?|([a-z]+[A-Z])*|[A-Z])$', 'gm') const str = `affine3D lThan30DaysCount lessThan30DaysCount lessThan30DaysCountA greaterThan30LessThan60DaysCount greaterThan60LessThan90DaysCount greaterThan90DaysCount snake_case PascalCase 2PascalCase streamIOIO gREATERDtha modeADFAFdsADFads aBabcABCDabcABC modeADFdsADFads streamIO aBCabcABCabcA aBCabcA aabc123 aabcABC deviceSNS pathASNs dscpCP awsVPC deviceID gREA1 gREAt gREAtREAt cP3 a1 aABC a123 modeADFsADFads a1G modeADFads supportsIpv6OnIos pascal2Case pascal2CaseA mode2A mode2A2 mode2A2A createAMode createBMode hTMLParser hELLO camel01C camel01c01 camel01C01 camel01CC01 camel0a1c1 camel0a1C1 camel0ac1b1C1 camelC1 camelCA camelCa1 camelCa_1 ibsReleaseTestVerificationRegressioNSuite modeA pascalCaseA pascalCase madeEasy wonderFul andMe context htmlParser h aaA a ab abc abcd abcde camelCasE aGa camelCasecamelCasecamelCasecamelCasecamelCasecamelCase aG alphabet camelCase xmlHttpRequest newCustomerId innerStopwatch youTubeImporter youtubeImporter camelC ibsReleaseTestVerificationRegressionSuite ibsReleaseTestVerificationRegressioN`; // 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