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 = /^((10|127)(\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|169\.254|192\.168|172\.(2[0-9]|1[6-9]|3[0-1]))(\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){2}$/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^((10|127)(\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|169\\.254|192\\.168|172\\.(2[0-9]|1[6-9]|3[0-1]))(\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){2}$', 'gm') const str = `Private ranges 10.0.0.0-10.255.255.255 127.0.0.0-127.255.255.255 169.254.0.0-169.254.255.255 172.16.0.0-172.31.255.255 192.168.0.0-192.168.255.255 -----OK----- 10.0.0.0 10.255.255.255 127.0.0.0 127.255.255.255 169.254.0.255 169.254.255.255 172.16.0.0 172.31.255.255 192.168.0.0 192.168.255.255 ------NOT OK------ 1.1.1.1 9.255.255.255 11.0.0.0 126.255.255.255 128.0.0.0 169.253.255.255 169.255.0.0 172.15.255.255 172.32.0.0 192.167.255.255 192.169.0.0`; // 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