With bash, the printf builtin has an additional format specifier %q, which prints the corresponding argument in a friendly way:
In addition to the standard printf(1) formats, %b causes printf to expand backslash escape sequences in the corresponding argument (except that \c terminates output, backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits), and %q causes printf to output the corresponding argument in a format that can be reused as shell input.
So you can do something like this:
printf %q "$VARIABLE"
printf %q "$(my_command)"
to get the contents of a variable or a command's output in a format which is safe to pass in as input again (i.e. spaces escaped). For example:
$ printf "%q\n" "foo bar"
foo\ bar
(I added a newline just so it'll be pretty in an interactive shell.)
