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

r"
"
gm

Test String

Substitution

Processing...

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"(?:^ *(?:/\*\*[^/\n]*\r?\n(?:[^/\n]*\r?\n)*[^/\n]*\*/ *|//.*)\r?\n)+(?: *[\r?\n])*#ifdef BUILD_FLAG\r?\n[\s\S]*?^#endif\r?\n" test_str = (" Code here\n" " and here\n\n" "//this is s comment block\n" "/**\n" "*and a nested comment block\n" "*/\n\n" "//-----------------------------------------------------------------------------\n" "// this comment block should not be captured\n" "//-----------------------------------------------------------------------------\n\n" "//-----------------------------------------------------------------------------\n" "// this whole comment block and the conditional block below should be captured\n" "//-----------------------------------------------------------------------------\n" "/**\n" " * @brief Some comment \n" " * \n" " xxxxx\n" " * @return \n" " */\n" "//-----------------------------------------------------------------------------\n" "#ifdef BUILD_FLAG\n" "...\n" "#endif\n\n" " More code\n" "More code\n\n" "//---------------------------------------------------------\n" "// this whole comment block and the conditional block below should be captured\n" "// --------------------------------------------------------\n" "#ifdef BUILD_FLAG\n" "...\n" "#endif\n\n" "More code\n\n" " //-------------------------------------------------------------------------\n" " /**\n" " * @name this whole block comment should be captured.\n" " * @{\n" " */\n\n" "#ifdef BUILD_FLAG\n" "...\n" "#endif\n") subst = "" # You can manually specify the number of replacements by changing the 4th argument result = re.sub(regex, subst, test_str, 0, re.MULTILINE) if result: print (result) # 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