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

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "(?mnxs-i)\n" + "^\n" + "(?!$)\n" + "(?<Thousands>\n" + " M{0,3}\n" + ")\n" + "(?<Hundreds>\n" + " (\n" + " (C(M|D))\n" + " (?!C)\n" + " |\n" + " D\n" + " )?\n" + " C{0,3}\n" + ")\n" + "(?<Tens>\n" + " (\n" + " (X(C|L))\n" + " (?!X)\n" + " |\n" + " L\n" + " )?\n" + " X{0,3}\n" + ")\n" + "(?<Ones>\n" + " (\n" + " (I(X|V))\n" + " (?!I)\n" + " |\n" + " V\n" + " )?\n" + " I{0,3}\n" + ")\n" + "$"; final String string = "MMMDCCCLXXXVIII\n" + "MMMCDXLIV\n\n" + "50 Valid\n" + "I\n" + "MMMCMXCIX\n" + "MMDCLXXIV\n" + "MCDXCIX\n" + "CCCXVIII\n" + "XCII\n" + "MMMLXXXIV\n" + "MMMCMLIII\n" + "DCCXXX\n" + "DCXCV\n" + "CCXCV\n" + "MMDCLX\n" + "MDCCLXXVI\n" + "CDXLV\n" + "MMMCDXLII\n" + "CMXXI\n" + "MDCCCXC\n" + "MMCCCXLVII\n" + "MCMXXXVIII\n" + "CDXCII\n" + "MMMCMXXII\n" + "DCXLVIII\n" + "MCDLVI\n" + "DCCLXXXIX\n" + "MMXIV\n" + "MCMXC\n" + "CCCLXXI\n" + "MDCCCXXI\n" + "MMCMLIV\n" + "MDCXVI\n" + "MMCMXLV\n" + "MCDLXXIX\n" + "DCCCXIII\n" + "CCXLVII\n" + "MDCCCXCV\n" + "MMCMLXXXVIII\n" + "CDLX\n" + "MMCDLIII\n" + "CMXLV\n" + "DCCXXII\n" + "MMMDCCL\n" + "CDXXVIII\n" + "MMDXLII\n" + "DCCCXCIX\n" + "MMXLI\n" + "CMXLIX\n" + "MCDXXXIX\n\n" + "50 Invalid\n" + "IIII\n" + "VV\n" + "LL\n" + "DD\n" + "XXXX\n" + "CCCC\n" + "MMMM\n" + "IIV\n" + "IIIV\n" + "VX\n" + "VL\n" + "VC\n" + "XD\n" + "XM\n" + "IL\n" + "IC\n" + "ID\n" + "IM\n" + "MCMC\n" + "IXX\n" + "XCC\n" + "IIC\n" + "CDM\n" + "CDC\n" + "MIM\n" + "IXL\n" + "ILX\n" + "ICX\n" + "IICM\n" + "IIIC\n" + "IIIM\n" + "XIC\n" + "XIXX\n" + "XIXC\n" + "IXXC\n" + "CMCM\n" + "CDCD\n" + "XCXC\n" + "XLXL\n" + "MDCM\n" + "DCD\n" + "IXXL\n" + "XLC\n" + "VIX\n" + "VID\n" + "VIL\n" + "IIVX\n" + "IVXL\n" + "MXLIVC\n" + "CXM\n"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE | Pattern.COMMENTS | Pattern.DOTALL); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html