[LTP] [PATCH v3 4/4] shell: fix echo -e bashisms, simplify code

[Peter Maydell]

On 1 December 2016 at 15:26, Cyril Hrubis <chrubis@suse.cz> wrote:
> Hi!
>> Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
>> -    echo "${ME}: Sending $SIGSHOW signal to $1's process(es)..."
>> -    echo -e "\\n\\n\\nYour current session has been terminated.\\n\\n\\n" | \
>> +    printf "${ME}: Sending $SIGSHOW signal to $1's process(es)...\n"
>> +    printf "\\n\\n\\nYour current session has been terminated.\\n\\n\\n\n" | \
>
> I'm a bit puzzled by the double backslashes here. I guess that the
> double backslash is reduced by shell to a single backslash and then
> echo/printf command gets just plain old \n in ARGV[].

Yes. In shell double-quoted text backslashes function as an escape
character when they precede any of $ ` " \ <newline>.
So "Hello\\n" becomes "Hello\n" as the executed command
sees it, and then printf/echo interpret \n as the newline.
You could also write that as 'Hello\n', since single-quotes don't
do backslash-escaping, or indeed as "Hello\n", since 'n' isn't
one of the handful of punctuation characters that need backslash
escapes inside double-quotes, and the shell is required not to
give backslash any special meaning if it isn't followed by one
of those. (This is why the first 'printf' in the bit I quote
above works even though it's just "${ME} ...\n" rather than \\n.)

Conclusion: those \\n could be tidied up to be just \n if you
want, but they're harmless.

thanks
-- PMM