Basic_Metacharacters

  # . any single character except newline
  # * any number (including zero) of the single character that immediately
    preceeds it
  # [...] matches any one of the characters (known as a class) enclosed in
    the brackets.
    If the first character in the brackets is a ^ i.e. [^...] , this reverse
    the match, i.e. anything but the characters in the brackets
    A - specifies a range e.g. [a-z]
  # ^ As the first character of a regular expression matches the start of a
    line
  # \{n,m}\ matches a range of occurrences of the single character that
    preceeds it e.g. a\{4\} matches four a`s , a\{4,\} matches at lease 4 a`s
    , a\{4,8\} matches between 4 to 8 a`s.
  # \ Escape special meaning

Extended_Metacharacters

  # + matches one_or_more occurrences of character (or regular expression)
  # ? matches zero_or_one occurrences of character (or regular expression)
  # | matches either/or (alternation)
  # () groups regular expressions e.g. (abc)* matches " " , "abc " , "abcabc"
    etc.
  # {n,m} matches a range of occurrences of the single character that
    immediately precceds it

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