Regular Expressions 101

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  • Unit Tests (18)

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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 = /\b(?:(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9]))\b/g; // Alternative syntax using RegExp constructor // const regex = new RegExp('\\b(?:(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9]))\\b', 'g') const str = `This REGULAR EXPRESSION is just for searching for dotted decimal IPv4 Adresses. Unlike a shorter one, this one is made for seeing the numbers in seperate Mach-groups-thingy. I also included some unit tests.. But i think they are not needed. Below are some tests: Valid: 0.0.0.0 1.2.3.4 127.0.0.1 8.8.4.4 8.8.8.8 255.255.255.255 249.0.0.1 0.1.255.254 98.139.180.149 69.89.31.226 Invalid: 999.999.999 290.250.2.6 256.259.20.255 Texts: Google DNS Server IP is 8.8.8.8. As a alternative you can use 8.8.4.4. The IP 127.0.0.1 (also known as localhost) is a 'loopback' IP-Adress, pointing to your computer. Example pinging: Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. Alle Rechte vorbehalten. C:\\Users\\Example>ping google.com Pinging google.com [212.6.83.44] with 32 bytes of data: Reply from 212.6.83.44: bytes=32 time=42ms TTL=59 Reply from 212.6.83.44: bytes=32 time=55ms TTL=59 Reply from 212.6.83.44: bytes=32 time=35ms TTL=59 Reply from 212.6.83.44: bytes=32 time=27ms TTL=59 Ping statistics for 212.6.83.44: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 27ms, Maximum = 55ms, Average = 39ms C:\\Users\\Example>`; // 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