Reserved Characters in Unix

Purdue Engineering Computer Network

Quoting disables a character's special meaning and allows it to be used literally as itself. The following characters have special meaning and must be quoted in order to use them literally.

;			Command separator
&			Background execution
(  )			Command grouping
|			Pipe
* ? [ ] ~		Filename metacharacters
{ }			String expansion characters. Usually don't require quoting.
> < & !			Redirection symbols
! ^			History substitution, quick substitution
" ' \			Using in quoting other characters
$			Variable substitution
newline space tab	Word separators

The characters below can be used for quoting:

" "			Everything between " and " is taken literally, except
			for the following characters that keep their 
			special meaning:
				$	Variable substitution will occur
				`	Command substitution will occur
				"	This marks the end of the double quote
				\	Escape next character
				!	The history character
				newline	The newline character
' '			Everything between ' and ' is taken literally except 
			for ! (history) and another ', and newline.
			
\			The character following a \ is taken literally. Use
			within " " to escape ", $ and `. Often used to escape
			itself, spaces, or newlines. Always needed to escape a
			history character (usually !).

Examples

% echo 'Single quotes "protect" double quotes'
Single quotes "protect" double quotes

% echo "Well, isn't that \"special\"?"
Well, isn't that "special"?

% echo "The value of \$x is $x"
The value of $x is 100