Quoting

Remarks#

References

The POSIX ‘Shell Command Language’ section on ‘Quoting’

Single-Quotes

Single-quotes are literal strings, and the lack of escape characters means that the only character that can not occur inside of a single-quoted string is a single-quote.

$ echo '$var \$var \\$var \\\$var'
$var \$var \\$var \\\$var
$ echo '"quoted string"'
"quoted string"
$ echo 'var=$(echo $var)'
var=$(echo $var)

Double-Quotes

Double-quotes preserve all characters other than " terminator, $ expansions, ` command substitutions, and \ escapes of any of these characters (and newline removal). Note that the literal \ is preserved unless followed by a special character.

General escapes:

$ printf "\"quoted string\"\\n"
"quoted string"
$ printf "\`\`quoted string''\n"
``quoted string''
$ printf "four\\\\nthree\\\ntwo\\none\n"
four\nthree\ntwo
one
$ echo "var=\`echo \$var\`"
var=`echo $var`
$ echo "var=\$(echo \$var)"
var=$(echo $var)

Variable expansion:

$ var=variable echo "$var \$var \\$var \\\$var"
variable $var \variable \$var

Command substitution:

$ var=variable echo "var=`echo $var`"
var=variable
$ var=variable echo "var=$(echo $var)"
var=variable

Removing newlines:

$ echo "multi\
> -line"
multi-line

Escaping

\ escapes preserve the following character value, unless the following character is a newline in which case both the \ and the newline are removed.

Escaping special characters:

$ echo \"quoted text\"
"quoted text"
$ echo \`\`quoted text\'\'
``quoted text''
$ echo 'single-quotes inside of a '\''single-quoted'\'' string'
single-quotes inside of a 'single-quoted' string
$ printf format\ with\ %s spaces
format with spaces
$ printf %s\\n \$var
$var

Removing newlines:

$ echo multi\
> -line
multi-line