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 = /LIST\d+ LIST\d+\R((?!$)\S*(?: +\S+)?(?:\R|\Z))*?(?:(?:(\S+) +(?:\S*\R(?1)*\S* +)?\2\b\R?)|(?:\S+ (\S+)\R(?1)*\3\b))(?1)*/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('LIST\\d+ LIST\\d+\\R((?!$)\\S*(?: +\\S+)?(?:\\R|\\Z))*?(?:(?:(\\S+) +(?:\\S*\\R(?1)*\\S* +)?\\2\\b\\R?)|(?:\\S+ (\\S+)\\R(?1)*\\3\\b))(?1)*', 'gm') const str = `LIST1 LIST2 item1 item2 item3 item4 item5 item6 LIST3 LIST4 item1 item2 item4 item2 LIST5 LIST6 item1 item3 item2 item4 item5 item2 LIST7 LIST8 item1 itemA item2 itemB item3 itemC itemD item3 itemE`; // 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