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 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

/
/
gxJm

Test String

Code Generator

Language

Generated Code

$re = '/# SETTINGS (?<ANCHORED>){1} (?<NO_SIGN_DUP>){1} (?<PYTHON_POW>){1} (?<COMMENTS>){0} (?(ANCHORED)^(?&s)*) (?(DEFINE) (?<s>(?(COMMENTS)(?:\s+|\/\*[\s\S]*?\*\/|\/\/.*|\#.*)|\s+)) (?<sign>(?(NO_SIGN_DUP)(?<=(?<_>[\s\S]))(?!(?P=_)))[-+]) (?<base>\d+(?:\.\d*)?|\d*\.\d+) (?<exp>(?:[eE][+-]?\d+)) (?<num>(?&sign)?(?&base)(?&exp)?(?!\w)) (?<bracketed>\((?&s)*(?&expr)(?&s)*\)) (?<atom>(?&num)|(?&bracketed)) (?<pow>(?&atom)(?:(?&s)*(?(PYTHON_POW)(?:\^|\*\*)|\^)(?&s)*(?&pow))*) (?<mul>(?&pow)(?:(?&s)*[*\/](?&s)*(?&mul))*) (?<add>(?&mul)(?:(?&s)*[+-](?&s)*(?&add))*) (?<expr>(?&add)) ) (?&expr) (?(ANCHORED)(?&s)*$)/xJm'; $str = '0 :: 1 :: +1 :: -1 :: 1.e-1 :: 1e1 :: .1e+1 :: -6*((2**(2+4))/3) :: 0*0 :: 0+0 :: 0/0 :: 0^0 :: 0**0 :: 0-0 :: 5 - -2 :: 5- -2 :: 5+-2 :: .1 :: 1. :: 1.1 :: -2 :: 5 * (2 + 5 /* comment */ // ) - 1) INVALID: // Separated by :: to prevent parsing multiple examples . :: 1e :: 1e+ :: 1e- :: e2 :: + :: - :: 5 --2 '; preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0); // Print the entire match result var_dump($matches);

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 PHP, please visit: http://php.net/manual/en/ref.pcre.php