Regular expression special Symbols (Metacharacters)

-

 Regular expression special Symbols (Metacharacters): -

  • Special characters are characters with a special meaning in regular expressions.

 

1) [ ] (square brackets): -

  • It represents a set of characters.
  • We can also specify a range of characters using – (hyphen) inside the square brackets.
  • Example:

                                [abc] will match "a", "b", or "c".

                                [0,3] is same as [0 1 2 3]

                                [a-c] is same as [a b c]

  • We can also invert the character class using ^ (caret) symbol.

                                [^0-3] means any number except 0, 1 , 2 , or 3.

                                [^a-c] means any character except a , b , or c.

        Example: -


        output: -

        



2) \ (Backslash): -

  • In Python, the backslash (\) is called an escape character.
  • It is used to insert special characters into a string that cannot be typed directly.
  •      \d → Matches any digit (0–9).
    • Example: "\d+" matches "123", "45".

  • \w → Matches any word (alphanumeric) character ((a-z, A-Z,) - letters, (0-9) digits, ( _ ) underscore).
  • \s → Matches any whitespace character (space, tab, newline).

        Example: -


      output: -


3) . (dot): -

  • It matches only any single character except for newline character (\n).
  • Example: "c.t" matches "cat", "cut", "cot".

 Example: -       


output: -



4) ^ (caret): -

  • It matches the beginning of a string and checks whether the string ends with given character or characters or not.
  • Example: ^Hello matches "Hello World" but not "Say Hello".

            Example: -


                    output: -


5) $ (dollar): -

  • It matches the end of a string and checks whether the string starts with given character or characters or not.
  • Example: world$ matches "Hello world".

            Example: -


output: -



6) *(asterisk): -

  • It matches zero or more occurrences with * symbol.
  • ab*c will be matched for the string ac, abc, dabc etc. but will not be matched for abdc because b is not followed by c.
  • Example: "go*" matches "g", "goo", "google".

            Example: -


            output: -


7) + (plus): -

  • It matches one or more occurrences with + symbol.
  • ab+c will be matched for the string abc , abbc , dabc, but will not matchwd for ac , abdc because there is no b in ac and b is not followed by c in abdc.
  • Example: "go+" matches "go", "goo", but not "g".

            Example: -


                output: -



8) ? (question mark): -

  • It matches zero or one occurrence with ? symbol.
  • a?b → Matches "b" or "ab", but not "aab".
  • Example: "colou?r" matches "color" and "colour".

            Example: -

            output: -



- Hyphen within a character set indicates a range. [a-z] matches any lowercase letter.

| Pipe acts as an "OR" operator. (cat|dog) matches either "cat" or "dog".


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