Single and Double quotes.

-

Guidelines for quoting command arguments

\
prevent the shell from expanding any single special character.
' '
prevent the shell from expanding all special characters enclosed in this string except !.
" "
prevent the shell from expanding any enclosed special character except $, ` and !.



Single quotes limit substitution. We can place variables in double quoted text and the shell still performs substitution.

[me@linuxbox me]$ echo "My host name is $HOSTNAME."
My host name is linuxbox.

[me@linuxbox me]$ echo 'My host name is $HOSTNAME.'
My host name is $HOSTNAME.

Double quotes do not suppress the substitution of words that begin with "$" but they do suppress the expansion of wildcard characters. For example, try the following:

[me@linuxbox me]$ echo *
anaconda-ks.cfg clear.sh config.txt date_marker ftpftp1 list1 list2 list3 list4 list5 list6 post-install post-install.log script status textfile

 [me@linuxbox me]$ echo "*"
*

Quoting a single character

There is another quoting character you will encounter. It is the backslash. The backslash tells the shell to "ignore the next character." Here is an example:

[me@linuxbox me]$ echo "My host name is \$HOSTNAME."
My host name is $HOSTNAME.

By using the backslash, the shell ignored the "$" symbol. Since the shell ignored it, it did not perform the substitution on $HOSTNAME. Here is a more useful example:

[me@linuxbox me]$ echo "My host name is \"$HOSTNAME\"."
My host name is "linuxbox".

As you can see, using the \" sequence allows us to embed double quotes into our text.





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