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

/
/
gm

Test String

Code Generator

Language

Generated Code

// include the latest version of the regex crate in your Cargo.toml extern crate regex; use regex::Regex; fn main() { let regex = Regex::new(r"(?m)([[:<:]]M*(C[MD]|D?C{0,3})(X[CL]|L?X{0,3})(I[VX]|V?I{0,3})[[:>:]])").unwrap(); let string = "### match ### I II III IV V VI VII VIII IX X XIII XIV XV XVIII XIX XXV XXVI XXVII XXVII XXIX XXX XXXIII XXXVIII XXXIX XL XLII XLV XLVIII XLIX L LI LII LIII LIV LV LVI LVII LVIII LIX LX LXVI LXIX LXXIX LXXXV LXXXVIII XC XCV XCVI XCVII XCIX C CI CV CIX CXI CXX CXXX CXXXVIII CXXXIX CXLII CL CLV CLVIII CLX CLXX CLXXX CXC CXCIII CXCVII CXCIX CC CCIII CCVIII CCIX CCXXV CCL CCLXXV CCCLXXV CD CDXXV CDL CDLXXV CDXC D DIX DCLXVI DCLXXV DCCCXXVIII CM CMLXXV M ML MCV MCCCL MD MDCCXXV MDCCCLXXV MCML MCMXCVIII MCMXCIX MM MMCCCXXV MMCDLXXV MMDL MMM MMMCCXXVIII MMMCCCXXVIII MMMD MMMCMXCV MMMCMXCVIII MMMCMXCIX MMMM MMMMMMMMMCMXCIX MMMMMMMMMMMDCCXXXII #### do not match #### VV VVX XVV IIII IIIII IVIVIV XIIX XXXXII VC IIXV IC CXIIL LVIXXX LIXXX XXXVIIII XXXVV MCVV MLTK IIV IIX IIL IIM IIC CCM CMD CMDB L0L LOL GG RAF WTF XIIIXCVIIVMC MMIXIII CCCXXXIIX MCMM MDCCLXXVIIII CCCD CCCXXXIIII MMMMXXXX"; // result will be an iterator over tuples containing the start and end indices for each match in the string let result = regex.captures_iter(string); for mat in result { println!("{:?}", mat); } }

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 Rust, please visit: https://docs.rs/regex/latest/regex/