what is the purpose of $"string" in bash ?

marozsas · 10-27-2009, 07:22 AM

Hi !

What is the purpose of that '$' in front of an string, like in

Code:

echo $"usage: $0"

in bash scripts ?

You can see it all around in scripts at /etc/init.d but I was not able to figure out what is its purpose, neither found references to it in bash man page....

The only reference to it is indirect:
from bash man page:

Code:

extquote
        If  set,  $'string'  and  $"string"  quoting is performed within ${parameter} expansions enclosed in double quotes.
        This option is enabled by default.

GazL · 10-27-2009, 07:41 AM

I guess you didn't look hard enough. It's in the man-page fairly near the beginning, however, as the bash man-page is so big and ugly, I'll forgive you this once.

Code:

 Words  of the form $'string' are treated specially.  The word expands to string, with back-
       slash-escaped characters replaced as specified by the ANSI C  standard.   Backslash  escape
       sequences, if present, are decoded as follows:
              \a     alert (bell)
              \b     backspace
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \'     single quote
              \nnn   the eight-bit character whose value is the octal value nnn (one to three dig-
                     its)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one  or  two
                     hex digits)
              \cx    a control-x character

       The expanded result is single-quoted, as if the dollar sign had not been present.

       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.

marozsas · 10-27-2009, 10:29 AM

Thank you very much, dear GazL, to being a so nice and understanding Guru !

cheers,