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 = /^(.*?)(?:[._-]|(\())([a-z]{2,3})(?(2)\)|)(?:[_\W]forced)?$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^(.*?)(?:[._-]|(\\())([a-z]{2,3})(?(2)\\)|)(?:[_\\W]forced)?$', 'gm') const str = `name.eng name-eng name(eng) name(fri)_eng name(fri)(eng) name.eng.forced name(eng).forced name.(eng).forced name.fri.eng.forced name(fri).eng.forced name.(fri).eng_forced name-fri-eng.forced name_(fri)_eng.forced name(fri)_eng.forced name(friday)_eng_forced name(fri)(eng).forced I'm tying to extract the header and a 2 or 3 digit ISO 639 code from a string. The general format of a valid string is: header + <special char> + <2 or 3 digit code> + (<special char>forced) The last section <special character>forced is optional and may or may not be present but if present forced must be preceded with a special character (like . or _ or -) for it to be a considered a valid string. Examples of valid strings where the header and language code (eng) to be extracted are: name.eng name-eng name(eng) name(fri)_eng name(fri)(eng) name.eng.forced name(eng).forced name.(eng).forced name.fri.eng.forced name(fri).eng.forced name.(fri).eng_forced name-fri-eng.forced name_(fri)_eng.forced name(fri)_eng.forced name(friday)_eng_forced name(fri)(eng).forced nameeng nameeng.forced name.eng).forced name(fri)eng.forced name(friday).engforced name(fri)(eng)forced`; // 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