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-z0-9]+[A-Z]?)*)$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^[A-Z](([a-z0-9]+[A-Z]?)*)$', 'gm') const str = `ABCD ABCDE snake_case camelCase 2PascalCase streamIOIO gREATERDtha MdeADFAFdsADFads DeviceSNSD AabcABCD AabcABCDabcABCD ABabcABCD ABabcABCDabcABCD ABCabcABCD ABCabcABCDabcABCDabcABCDabcABCD ABCDabcABCD ABCDabcABCDabcABCDabcABCDabcABCD HTMLParser ABabcABCDbcABC ABCDabcABC ABCDabcAB ABCDabcA AaABC AabcABCabcABC MoeADFdsADFads ABCabcABC ABCabcAB ABabcABC ABabcAB AabcAB ABCabcABCabcA ABCabcA AabcABC AB ABC StreamIO IOStream DeviceID DeviceSNS IbsReleaseTestVerificationRegressioNSuite CamelCA CamelCa_1 Camel01CC01 HELLO ContextHTMLParser CreateAMode CreateBMode PacalCasePacalCasePacalCasePacalCasePacalCasePacalCase A Aabc123 Context PascalCase Pascal2Case PascalCaseA Pascal2CaseA ModeA Mode2A Mode2A2 Mode2A2A MadeEasy WonderFul AndMe HtmlParser H AaA Camel01C Camel01c01 Camel01C01 Camel0a1c1 Camel0a1C1 Camel0ac1b1C1 CamelC CamelC1 CamelCa1 IbsReleaseTestVerificationRegressionSuite IbsReleaseTestVerificationRegressioN XmlHttpRequest NewCustomerId InnerStopwatch SupportsIpv6OnIos YouTubeImporter YoutubeImporter Affine3D`; // 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