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]
  • Character class intersection
    [\w&&[^\d]]
  • 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
Processing...

Test String

Code Generator

Language

Generated Code

import re regex = re.compile(r"^[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})$", flags=re.MULTILINE) test_str = ("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") matches = regex.finditer(test_str) for match_num, match in enumerate(matches, start=1): print(f"Match {match_num} was found at {match.start()}-{match.end()}: {match.group()}") for group_num, group in enumerate(match.groups(), start=1): print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")

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 Python, please visit: https://docs.python.org/3/library/re.html