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

r"
"
gmi

Test String

Code Generator

Language

Generated Code

package main import ( "regexp" "fmt" ) func main() { var re = regexp.MustCompile(`(?mi)(?:^(\w{1,255}):(.{1,255})@|^)(?:(?:(?=\S{0,253}(?:$|:| ))((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z0-9]{1,63})))|localhost)(:\d{1,5})?`) var str = `Valid localhost addresses: localhost user:password@localhost:80 localhost:8080/path/to/page.html Valid IPv4 addresses: 10.10.0.1 192.168.0.1 192.168.0.1:8888 user:password@192.168.0.1:8888 user:password@192.168.0.1 Valid IPv6 addresses: // regex does not check for that, check here: http://vernon.mauery.com/content/projects/linux/ipv6_regex 100:: 100::ffff:ffff:ffff:ffff ::ffff:0.0.0.0 64:ff9b::0.0.0.0 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff fe80:: 2001:2f:ffff:ffff:ffff:ffff:ffff:ffff 2001:db8:: ::1 Valid domains: // all should work www.test.com www1.test.com www1.test.com:8080 test.com test-test.com test.com/path/to/page?var=1&var2=2 test.com:80 user:password@test.com user:password@test-test.com user:password@test.com/path/to/page user:password@test.com/path/to/page?var=1&var2=2 user:password@test.com:80 user:password@test.com:80/path/to/page?var=1&var2=2 Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.com user:password@Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.com user:password@Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.com:8080 Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.MaximumLengthOf63CharactersForATopLevelDomainWithoutTheDashes Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.MaximumLengthOf63CharactersForATopLevelDomainWithoutTheDashes:8888 user:password@Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.MaximumLengthOf63CharactersForATopLevelDomainWithoutTheDashes:8888 a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a // Maximum number of 127 suddomains, seperated by 126 dots Invalid domains: // should not work justLongGibberishBLABLABLA againButThisTimeWithNumbers12345675678797 ShouldNOTWorkBecauseOfTheDash-.com UrlLenghtIsValidButThisSubdomainIsTooLongMaximumForASubdomainIs63Characters.com This-Url-Has-Valid-Subdomains.But-The-Url-Length-In-General-Is-Too-Long.This-Means-Longer-Than-253-Characters-For-The-Complete-Url.Including-The-Top-Level-Domain-Itself.So-This-Line-Shouldnt-Be-Catched-By-The-Regex.Its-Exactly-One-Character-Too-Long1.com` for i, match := range re.FindAllString(str, -1) { fmt.Println(match, "found at index", i) } }

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/