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

/
/
x

Test String

Code Generator

Language

Generated Code

package main import ( "regexp" "fmt" ) func main() { var re = regexp.MustCompile(`(?(DEFINE) # JSON does not need backtracking if it's valid # so everything is atomic to prevent backtracking # regex is built per https://tools.ietf.org/html/rfc8259 (?<json>(?>\s*(?&object)\s*|\s*(?&array)\s*)) (?<object>(?>\{\s*(?>(?&member)(?>\s*,\s*(?&member))*)?\s*\})) (?<member>(?>(?&string)\s*:\s*(?&value))) (?<array>(?>\[\s*(?>(?&value)(?>\s*,\s*(?&value))*)?\s*\])) (?<value>(?>)false|null|true|(?&object)|(?&array)|(?&number)|(?&string)) (?<number>(?>-?(?>0|[1-9][0-9]*)(?>\.[0-9]+)?(?>[eE][-+]?[0-9]+)?)) (?<string>(?>"(?>\\(?>["\\\/bfnrt]|u[a-fA-F0-9]{4})|[^"\\\0-\x1F\x7F]+)*")) ) \A(?&json)\z `) var str = `[ "JSON Test Pattern pass1", {"object with 1 member":["array with 1 element"]}, {}, [], -42, true, false, null, { "integer": 1234567890, "real": -9876.543210, "e": 0.123456789e-12, "E": 1.234567890E+34, "": 23456789012E66, "zero": 0, "one": 1, "space": " ", "quote": "\"", "backslash": "\\", "controls": "\b\f\n\r\t", "slash": "/ & \/", "alpha": "abcdefghijklmnopqrstuvwyz", "ALPHA": "ABCDEFGHIJKLMNOPQRSTUVWYZ", "digit": "0123456789", "0123456789": "digit", "special": "\`1~!@#$%^&*()_+-={':[,]}|;.</>?", "hex": "\u0123\u4567\u89AB\uCDEF\uabcd\uef4A", "true": true, "false": false, "null": null, "array":[ ], "object":{ }, "address": "50 St. James Street", "url": "http://www.JSON.org/", "comment": "// /* <!-- --", "# -- --> */": " ", " s p a c e d " :[1,2 , 3 , 4 , 5 , 6 ,7 ],"compact":[1,2,3,4,5,6,7], "jsontext": "{\"object with 1 member\":[\"array with 1 element\"]}", "quotes": "&#34; \u0022 %22 0x22 034 &#x22;", "\/\\\"\uCAFE\uBABE\uAB98\uFCDE\ubcda\uef4A\b\f\n\r\t\`1~!@#$%^&*()_+-=[]{}|;:',./<>?" : "A key can be any string" }, 0.5 ,98.6 , 99.44 , 1066, 1e1, 0.1e1, 1e-1, 1e00,2e+00,2e-00 ,"rosebud"]` if len(re.FindStringIndex(str)) > 0 { fmt.Println(re.FindString(str),"found at index",re.FindStringIndex(str)[0]) } }

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 Golang, please visit: https://golang.org/pkg/regexp/