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

/
/
g

Test String

Code Generator

Language

Generated Code

package main import ( "regexp" "fmt" ) func main() { var re = regexp.MustCompile(`box(?!-shadow) `) var str = `positive lookahead box(?=-shadow) https://youtu.be/aIEjh0YsxWA?t=309 // select box only if what comes after it IS -shadow box-sizing shape-shadow ------------------------------------------------------------------ negative lookahead box(?!-shadow) // select box only if what comes after it IS NOT shadow box-sizing shape-shadow ------------------------------------------------------------------ negative look behind (?<!jeffery).+ https://youtu.be/aIEjh0YsxWA?t=212 // this string cannot come before the @ jeffrey@envato.com joe@envato.com ------------------------------------------------------------------ positive look behind (?<=box-)sizing https://youtu.be/aIEjh0YsxWA?t=337 // only want to select 'sizing' if what comes before it is 'box' // select sizing as long as what comes before it is 'box' box-sizing shape-sizing ------------------------------------------------------------------ negative look behind (?<!box-)sizing // anything can come before it except 'box' box-sizing shape-sizing ----------------------------------------------------------------- positive lookahead @.+(?=\.[a-z]{2,4}) // Matches a group after your main expression without including it in the result wilson@gmail.com frank@france.fr joe@paris.france ` 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/