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

/
/

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

package main import ( "regexp" "fmt" ) func main() { var re = regexp.MustCompile(`(?i)(<a)(?=((?:[^>"']|"[^"]*"|'[^']*')*?\shref\s*=\s*(['"])\/mycms\/~\/link\.aspx\?_id=)([a-f0-9]{32})(&amp;_z=z\3(?:"[\S\s]*?"|'[\S\s]*?'|[^>]*?)+>))\s+(?:"[\S\s]*?"|'[\S\s]*?'|[^>]*?)+>`) var str = []byte(`<a hello world href="/mycms/~/link.aspx?_id=D9423CEFED254610A5DC6B096A297E17&amp;_z=z" class> ... </a> <img hello world src="/mycms/~/media/B1FB91AC357347BD84913D56B8791D03.ashx" alt="" width="690" height="202" /> `) var substitution = []byte("$1$2key{$4}$5") var count = 1 // negative counter is equivalent to global case (replace all) str = re.ReplaceAllStringFunc(str, func(s string) string { if count == 0 { return s } count -= 1 return re.ReplaceAllString(s, substitution) }) fmt.Println(string(str)) }

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/