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

@"
"
gmnxs

Test String

Code Generator

Language

Generated Code

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @"(?mnxs-i) ^ (?!$) (?<Thousands> M{0,3} ) (?<Hundreds> ( (C(M|D)) (?!C) | D )? C{0,3} ) (?<Tens> ( (X(C|L)) (?!X) | L )? X{0,3} ) (?<Ones> ( (I(X|V)) (?!I) | V )? I{0,3} ) $"; string input = @"MMMDCCCLXXXVIII MMMCDXLIV 50 Valid I MMMCMXCIX MMDCLXXIV MCDXCIX CCCXVIII XCII MMMLXXXIV MMMCMLIII DCCXXX DCXCV CCXCV MMDCLX MDCCLXXVI CDXLV MMMCDXLII CMXXI MDCCCXC MMCCCXLVII MCMXXXVIII CDXCII MMMCMXXII DCXLVIII MCDLVI DCCLXXXIX MMXIV MCMXC CCCLXXI MDCCCXXI MMCMLIV MDCXVI MMCMXLV MCDLXXIX DCCCXIII CCXLVII MDCCCXCV MMCMLXXXVIII CDLX MMCDLIII CMXLV DCCXXII MMMDCCL CDXXVIII MMDXLII DCCCXCIX MMXLI CMXLIX MCDXXXIX 50 Invalid IIII VV LL DD XXXX CCCC MMMM IIV IIIV VX VL VC XD XM IL IC ID IM MCMC IXX XCC IIC CDM CDC MIM IXL ILX ICX IICM IIIC IIIM XIC XIXX XIXC IXXC CMCM CDCD XCXC XLXL MDCM DCD IXXL XLC VIX VID VIL IIVX IVXL MXLIVC CXM "; RegexOptions options = RegexOptions.Multiline | RegexOptions.ExplicitCapture | RegexOptions.IgnorePatternWhitespace | RegexOptions.Singleline; foreach (Match m in Regex.Matches(input, pattern, options)) { Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index); } } }

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 C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx