Mac OS X Tiger in a Nutshell

Quoting

Quoting disables a character’s special meaning and allows it to be used literally, as itself. The following characters have special meaning to bash:

Table 5-17. Characters with special meaning in bash

Character	Meaning
;	Command separator
&	Background execution
()	Command grouping (enter a subshell)
{ }	Command block
|	Pipe
> < &	Redirection symbols
* ? [ ] ~ !	Filename metacharacters
" ' \	Used in quoting other characters
'	Command substitution
$	Variable substitution (or command substitution)
newline space tab	Word separators
#	Comment

The following characters can be used for quoting:

Table 5-18. Characters used for quoting in bash

Character	Action
""	Everything between " and " is taken literally, except for the following characters that keep their special meanings: $ Variable substitution will occur. ' Command substitution will occur. " This marks the end of the double quote.
''	Everything between ‘and’ is taken literally, except for another ‘.
\	The character following \ is taken literally. Use within " " to escape “, $, and ‘. Often used to escape itself, spaces, or newlines.

Examples

    $ echo 'Single quotes "protect" double quotes'
    Single quotes "protect" double quotes

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

    $ echo "You have 'ls | wc -l' files in 'pwd'"
    You have  43 files in /home/andy

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