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
  • Match everything enclosed
    (?:...)
  • Capture everything enclosed
    (...)
  • 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

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "^[A-Z](([A-Z]{1,2}[a-z0-9]+)+([A-Z]{1,3}[a-z0-9]+)*[A-Z]{0,3}|([a-z0-9]+[A-Z]{0,3})*|[A-Z]{1,2})$"; final String string = "ABCD\n" + "ABCDE\n" + "snake_case\n" + "camelCase\n" + "2PascalCase\n" + "streamIOIO\n" + "gREATERDtha\n" + "MdeADFAFdsADFads\n" + "DeviceSNSD\n" + "AabcABCD\n" + "AabcABCDabcABCD\n" + "ABabcABCD\n" + "ABabcABCDabcABCD\n" + "ABCabcABCD\n" + "ABCabcABCDabcABCDabcABCDabcABCD\n" + "ABCDabcABCD\n" + "ABCDabcABCDabcABCDabcABCDabcABCD\n" + "HTMLParser\n" + "ContextHTMLParser\n" + "ABabcABCDbcABC\n" + "ABCDabcABC\n" + "ABCDabcAB\n" + "ABCDabcA\n" + "CamelCa_1\n" + "HELLO\n" + "AaABC\n" + "PacalCasePacalCasePacalCasePacalCasePacalCasePacalCase\n" + "AabcABCabcABC\n" + "MoeADFdsADFads\n" + "ABCabcABC\n" + "ABCabcAB\n" + "ABabcABC\n" + "ABabcAB\n" + "AabcAB\n" + "ABCabcABCabcA\n" + "ABCabcA\n" + "Aabc123\n" + "AabcABC\n" + "A\n" + "AB\n" + "ABC\n" + "StreamIO\n" + "IOStream\n" + "DeviceID\n" + "DeviceSNS\n" + "Context\n" + "PascalCase\n" + "Pascal2Case\n" + "PascalCaseA\n" + "Pascal2CaseA\n" + "ModeA\n" + "Mode2A\n" + "Mode2A2\n" + "Mode2A2A\n" + "CreateAMode\n" + "CreateBMode\n" + "MadeEasy\n" + "WonderFul\n" + "AndMe\n" + "HtmlParser\n" + "H\n" + "AaA\n" + "Camel01C\n" + "Camel01c01\n" + "Camel01C01\n" + "Camel01CC01\n" + "Camel0a1c1\n" + "Camel0a1C1\n" + "Camel0ac1b1C1\n" + "CamelC\n" + "CamelC1\n" + "CamelCA\n" + "CamelCa1\n" + "IbsReleaseTestVerificationRegressionSuite\n" + "IbsReleaseTestVerificationRegressioNSuite\n" + "IbsReleaseTestVerificationRegressioN\n" + "XmlHttpRequest\n" + "NewCustomerId\n" + "InnerStopwatch\n" + "SupportsIpv6OnIos\n" + "YouTubeImporter\n" + "YoutubeImporter\n" + "Affine3D"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); 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