Regular Expressions 101

Save & Share

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8
  • .NET 7.0 (C#)
  • Rust
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests

Tools

Sponsors
There are currently no sponsors. Become a sponsor today!
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 single character of: a, b, c or d
    [[ab][cd]]
  • 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]
  • Character class intersection
    [\w&&[^\d]]
  • 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

re = /^((?:[01][0-9]{0,2}|(?:2(?:5[0-5]{0,1}|[0-4][0-9]{0,1}|[6-9]{0,1}))|[3-9][0-9]{0,1})\.){3}(?:[01][0-9]{0,2}|(?:2(?:5[0-5]{0,1}|[0-4][0-9]{0,1}|[6-9]{0,1}))|[3-9][0-9]{0,1})$/m str = '000.12.12.034 01.1.1.1 121.234.12.12 23.45.12.56 000.12.234.23.23 666.666.23.23 .213.123.23.32 23.45.22.32. I.Am.not.an.ip 1.1.1.1 0.0.0.0 255.2.2.255 256.0.0.33 199.200.0.22 000 111 0 00 1 00 11 99 90 2 3 4 292 999 255 266 299 256 199 244 000.12.12.034 121.234.12.12 23.45.12.56 00.12.123.123123.123 122.23 Hello.IP ' # Print the match result str.scan(re) do |match| puts match.to_s end

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 Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html