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

/
/
g

Test String

Code Generator

Language

Generated Code

const regex = /(?<=[:=!?&,;|{\[\(\n])[\x09\x20]*(?:\/(?![*+?])(?:(?:[^\n\[\\\/]*+(?:\\\\)*+(?:\\\[|\\\/|\\(?!\[))?(\[)?)+(?(1)([^\n\]\\]*+(\\\\)*+(\\\]|\\(?!\]))?)*((?<!\\)\])?))*[^\n]*?(?<![^\\]\/)(?<![^\\]\\)\/)[gim]{0,3}[\x09\x20]*+(?![^}\]\),;:.\n])/g; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?<=[:=!?&,;|{\\[\\(\\n])[\\x09\\x20]*(?:\\\/(?![*+?])(?:(?:[^\\n\\[\\\\\\\/]*+(?:\\\\\\\\)*+(?:\\\\\\[|\\\\\\\/|\\\\(?!\\[))?(\\[)?)+(?(1)([^\\n\\]\\\\]*+(\\\\\\\\)*+(\\\\\\]|\\\\(?!\\]))?)*((?<!\\\\)\\])?))*[^\\n]*?(?<![^\\\\]\\\/)(?<![^\\\\]\\\\)\\\/)[gim]{0,3}[\\x09\\x20]*+(?![^}\\]\\),;:.\\n])', 'g') const str = `// Regular expressions r = /([\\\\/])?([^\\\\/]*)\$/; r = /([\\\\/])?([^\\\\:/]*)\$/; // коммент /abc\\[def\\[^\\s[\\]/]ghi/g.test(s);// здесь одна пара квадратных скобок! r = /\\//i; r = /[/\\*]/img; // коммент r = /[a-z]{5}/; r = /[a-z]{1,5}/; r = /([a-z])+/; r = /([a-z]{1,5})+/; r = /f([a-z])/; r = /f([a-z]+)*/; r = /a(b)c(d)/; r = /a(b)?c(d)+?/; r =(t|/\\*/.test(s)); r =(t|/\\*/); // коммент r =/./.test(s) && f(); r=/[a-z]/.test(s) && f(); var a = [/a\\/, \\/b/]; a=[/a/,/b/]; var o = { r: /./, x: 2 }; // коммент o={r:/./,x:2}; var x = a && /b/.test(s); x = a ? /b/ : /c/;// коммент x=a?/b/:/c/; x=a?/b\\\\/:/c\\/\\\\/; // коммент x=a?/b\\\\/:/c\\/\\\\/; // коммент x = !/a/.test(s); x = f(/./i); x=1*s.replace(/^[^\\d]*(\\d+).*\$/,'\$1')/2; /\\s\\n\\s+\\/\\/\\\\\\\\/.test(s)?f(null):f(/\\\\/); /\\s\\n\\s+\\/\\/\\\\\\\\/.test(s)?f(null):f(/\\\\fghj[\\[fghj\\]]kl/), /fght/; a=s.search(/\\s\\n\\s+\\/f\\//gi); r=/>\\.jjj\\n<\\s\\</ .exec(s); r=/ \\n \\s/g, t=/'/g ; // Not a regular expressions var n = 1/2;// коммент n = 1/2/3; n = 1/2/p; n = 1/(2/p); // коммент n = 1/this.n/3; n = 1/this.f(5+4)/3; n = 1/this.f(2/3); n = 1/2 + (function() { return 3/4; })(); n = 1/2*(this.x/3 + 2); n = 1/2*(this.x + 2/3); n =p/2,t=3/p; n = f(1/2) + f(3/2);`; // 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