3. Quotes

Quoted characters are expanded by own rules. A character following the escape character "\" is taken as literal. "\$" is taken as literal "$" instead of the beginning the start of a variable expansion:

$ echo \$USER
$USER

Only the sequence "\newline" has a special meaning. \newline is interpreted as line continuation:

$ echo 12\
34
1234

Single quoted strings are taken always literal:

$ echo '$USER'
$USER

Double quoted strings allow parameter expansion and command substitution:

$ echo "$(echo $USER)"
pa

"\" disables the special meaning of characters within double quotes:

$ echo "\"Oranges and lemons\""
"Oranges and lemons"

To translate special characters, ANSI-C Quoting can be used. Escape sequences between "$'...'" operator:

echo $'\n\t\\$USER'

	\$USER

will be translated according to the ANSI-C standard: \n - newline, \t - tab, \\ backslash.