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

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"^ *[^\s]+( +[^\s]+)*$" test_str = ("# UFIS : User-Friendly and Instant Installer System\n\n" "# Each comment starts with '#' and ends with a new line.\n" "# Each statement is written in one line.\n" "# Commands' and built-in variables' names are always uppercase.\n" "# A custom variable name must have at least one lowercase character and must begin with a letter or the underscore (_).\n\n" "LET APP_NAME = \"MyApp\"\n" "LET APP_VERSION = \"1.0.0\"\n\n" "LET a = MATERIAL \"folderx/\"\n" "a -= \"test.exe\"\n" "a -= \"main.exe\"\n" "a += MATERIAL \"folderz/\"\n" "a += MATERIAL \"README.md\"\n\n" "LET b = MATERIAL \"folderx/test.exe\"\n\n" "LET c = MATERIAL \"folderx/main.exe\"\n\n" "IF INSTALLING\n" " LET iAcceptLicense = INPUT CHECKBOX \"Accept [license](https://myapp.com/license)\" MANDATORY\n" " IF iAcceptLicense == FALSE\n" " QUIT\n" " ENDIF\n\n" " LET iLanguage = INPUT CHOICES \"Vietnamese\" OR \"English\" DEFAULT \"English\" MANDATORY\n\n" " LET INSTALL_DIR = INPUT DIRECTORY \"Installation directory\" POSTFIX \"/${APP_NAME}\" DEFAULT PROGRAM_FILES\n" " LET iInstallTest = INPUT CHECKBOX \"Install test.exe\" DEFAULT FALSE\n" " LET iCreateDesktopShortcut = INPUT CHECKBOX \"Create desktop shortcut\" DEFAULT TRUE\n" " LET iLaunchAtStartup = INPUT CHECKBOX \"Launch program at startup\" DEFAULT TRUE\n\n" " INSTALL a AND c TO INSTALL_DIR # the same as \"${INSTALL_DIR}\"\n\n" " IF iInstallTest == TRUE\n" " INSTALL b TO INSTALL_DIR AS \"test_program.exe\"\n" " ENDIF\n\n" " IF iCreateDesktopShortcut == TRUE\n" " CREATE SHORTCUT FOR c IN DESKTOP_ALL_USERS\n" " ENDIF\n\n" " IF iLaunchAtStartup == TRUE\n" " RUN c AT STARTUP\n" " ENDIF\n" " \n" " WORK registry_work\n" " CREATE REGSZ \"HKEY_LOCAL_MACHINE/Software/${APP_NAME}\" VALUE \"1\"\n" " ENDWORK\n" " \n" " CPP\n" " #include <iostream>\n" " \n" " void entry() {\n" " std::cout << \"Not very intelligent\";\n" " }\n" " ENDCPP\n" " \n" " CALL entry\n\n" "ELIF RUNNING\n" " RUN c\n\n" "ELSE # UNINSTALLING\n" " UNDO ALL EXCEPT registry_work\n\n" "ENDIF\n") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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