====== Unix/Linux Metacharacters ======

===== FILE NAME GENERATION CHARACTERS: =====

Will be interpreted by the **shell** **before** the command will be executed. The shell will look for matching file names in the current directory;the file name genera- tion characters on the command line will be replaced by the matching file names.

  ?     			any single character except a leading dot (as in .exrc)
  *     			zero or more characters except a leading dot
  [ ]   			specifies one position in the file name
  [0-9]   		inclusive range: one of the numbers 0-9
  [!0-9]                  exclusive range: any character but 0-9

**Examples:**

      $ echo .*                   all of the dotfiles in the current directory
      $ echo ?????		file names of 5 characters each, except dotfiles
      $ echo [a-z][0-9]?.org	file names of 7 characters each, starting with a
  				lower case letter and a number, ending with .org
      $ ls -l f*			long listing of file names starting with "f"

===== QUOTING (used to prevent shell metacharacter interpretation): =====

  '      '        single quotes  All metacharacters contained within single quotes
                                 will lose their special meaning.
                                 The shell won't interpret those metacharacters.
  \              	backslash      The metacharacter after the backslash will lose
                                 its special meaning.
  "      "       	double quotes  All metacharacters contained within double quotes
                                 will lose their special meaning except:
                                 $variable, ${variable}, `cmd`, $(cmd), \
  			       This means that the shell will still perform
                                 variable substitution and command substitution.

**Examples:**

       $ PS1='$PWD $ '	       prompt will show current value of PWD variable
       $ find . -name f\*        all file names with "f" in the current directory
       $ echo "$TERM;$PATH"      values of TERM and PATH variable separated by ";"

===== REGULAR EXPRESSIONS (used to construct search patterns in applications): =====

  .      			any single character
  *      			zero or more times the preceding character
  a*    			zero or more times "a"
  [ ]    			specifies one position in the search pattern
  [abcd]                  one of the characters "a", "b", "c" or "d"
  [A-Z]                   inclusive range: one upper case letter
  [^A-Z]                  exclusive range: any character but A-Z
  ^user                   the string "user" at the beginning of the line
  user$                   the string "user" at the end of the line

**Examples:**

      $ grep '^user' /etc/passwd	all lines starting with the string "user"
      $ ps -ef | grep 'root'	all processes of "root"
      $ vi f1
        :1,10s/[Aa]nd/OR/g	in lines 1 to 10 inclusively globally substitute
                                  the string "And" or "and" by "OR"

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