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

/
/
gmux

Test String

Code Generator

Language

Generated Code

const regex = /^( # Match only leap years \d\d[2468][048] # multiple of four but not 100 |\d\d[13579][26] # ... |\d\d0[48] # ... |[02468][048]00 # multiple of four hundred |[13579][26]00 # ... )$/gmu; // Alternative syntax using RegExp constructor // const regex = new RegExp('^( # Match only leap years \\d\\d[2468][048] # multiple of four but not 100 |\\d\\d[13579][26] # ... |\\d\\d0[48] # ... |[02468][048]00 # multiple of four hundred |[13579][26]00 # ... )$', 'gmu') const str = `^( \\d\\d[2468][048]|\\d\\d[13579][26]|\\d\\d0[48]| # multiple of four but not 100 [02468][048]00 |[13579][26]00 # multiple of four hundred ) // accept: multiple of four () 0004 0008 0012 0016 0020 0024 0028 0032 0036 0040 0044 0048 0052 0056 0060 0064 0068 0072 0076 0080 0084 0088 0092 0096 1560 2004 2008 2012 2016 2020 2024 2028 2032 2036 2040 2044 9996 // accept: Multiple of 400 0000 0400 0800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400 6800 7200 7600 8000 8400 8800 9200 9600 // REJECT: Not a multiple of four 0101 0102 0103 1537 1538 2001 2002 2003 2021 2022 2023 2025 2026 2027 2029 2030 2031 2033 2034 2035 2037 2038 2039 2041 2042 2043 9997 9998 9999 // REJECT: Multiple of 100 but not 400 0100 0200 0300 0500 0600 0700 0900 1000 1100 1500 2100 2200 2300 2500 2600 2700 2900 3000 3100 3300 3400 3500 3700 // REJECT: Negative dates not accepted (malformed) -2000 -0400 -0100 -0004 // REJECT: Out of range date per RFC 3339 10000 `; // 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