I just saw this in an init script:
echo $"Stopping Apache"
What is that dollar-sign for?
My research so far:
I found this in the bash manual:
extquote
If set,
$'string'and$"string"quoting is performed within${parameter}expansions enclosed in double quotes. This option is enabled by default.
…but I’m not finding any difference between strings with and without the $ prefix:
$ echo "I am in $PWD"
I am in /var/shared/home/southworth/qed
$ echo $"I am in $PWD"
I am in /var/shared/home/southworth/qed
$ echo $"I am in ${PWD}"
I am in /var/shared/home/southworth/qed
$ echo "I am in ${PWD}"
I am in /var/shared/home/southworth/qed
$ echo 'I am in ${PWD}'
I am in ${PWD}
$ echo $'I am in ${PWD}'
I am in ${PWD}
$ echo $'I am in $PWD'
I am in $PWD
Answers:
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Method 1
There are two different things going on here, both documented in the bash manual
$’
Dollar-sign single quote is a special form of quoting:
Words of the form $’string’ are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard.
$”
Dollar-sign double-quote is for localization:
A double-quoted string preceded by a dollar sign (‘$’) will cause the string to be translated according to the current locale. If the current locale is C or POSIX, the dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted.
Method 2
When a string is expanded inside of $'', the escape sequences are interpreted. From the manpage:
Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard.
An easy example is the n escape sequence for a newline:
$ echo 'foon' foon $ echo $'foon' foo $
Note: You may get different results in other shells as echo may interpret escape sequences without providing options.
Method 3
You’re misinterpreting the manual. You’ll only see an effect when a $-quoted string is inside a ${parameter} expansion.
$ echo "${v:-'abncd'}"
'abncd'
$ echo "${v:-$'abncd'}"
ab
cd
Source and further reading: https://lists.gnu.org/archive/html/bug-bash/2005-10/msg00017.html
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0