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
Processing...

Test String

Substitution
Processing...

Code Generator

Language

Generated Code

import re regex = re.compile(r"if\s*(\((?>[^()]|(?1))*\))(*SKIP)(*F)|(\w+)(\s*<=[^;]*)", flags=re.DOTALL) test_str = ("always @(posedge clk or negedge rst_n)\n" "if(!rst_n)begin\n" " d1 <= 0; //perl_comment_4\n" " //perl_comment_5\n" " d2 <= 1 //perl_comment_6\n" " + 2;\n" " end\n" "else if( d3 <= d4 && ( d5 <= 3 ) ) begin\n" " d6 <= d7 +\n" " (d8 <= d9 ? 1 : 0);\n" " //perl_comment_7\n" " d10 <= d11 <=\n" " d12\n" " + d13\n" " <= d14 ? 1 : 0;\n" " end") subst = "$2_yes$3" result = regex.sub(subst, test_str) if result: print(result)

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