Regular Expressions 101

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  • Unit Tests (13)

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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

Code Generator

Language

Generated Code

package main import ( "regexp" "fmt" ) func main() { var re = regexp.MustCompile(`^(?!$)M{0,2}(?:M(?=CM(?:XC)?(?:IX)?$))?(?:C(?=M[^CD]*(?:XC)?[^CD]*$))?M?(?:C(?=D[^C]*(?:XC)?[^C]*$))?D?C{0,2}(?:C(?=XC(?:IX)?$))?(?:X(?=C[^X]*(?:IX)?[^X]*$)(?!.*L))?C?(?:X(?=L[^X]*(?:IX)?[^X]*$))?L?X{0,2}(?:X(?=IX$))?(?:I(?=[XV]$))?X?V?I{0,3}$`) var str = `I II XXIX XXXVIII IV XIV XXXIX LXXX XL CCCXCIX DCCCXCIX CDXC MMMCMIX MMMCMXCIX MMMCM (MMMCM)CMI (I)` 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/