Re: shouldn't prompt printing be smarter?

[Francesco Montorsi]

Hi Bob,
        thanks for looking into this!

Bob Proulx ha scritto:
> Francesco Montorsi wrote:
> >    I think you all have encountered this: do a "cat somefile" where 
> > "somefile" is a text file _without_ a final newline. You'll see the 
> > prompt is printed both at the end of the text printed by 'cat' and then, 
> > also at the beginning of that same line.
>
> I cannot reproduce your reported behavior.  I think there must also be
> some interaction with your environment.  I only see the prompt once.
interesting. I've always seen that problem since I started using Linux 
some year ago and finally decided today to report it. I always thought 
it was a known issue not classified as "bug" or something similar.

> > I'm attaching a screenshot which should make it clear.
>
> What is your PROMPT_COMMAND set to?
PROMPT_COMMAND='echo -ne "\033]0;${PWD/$HOME/~}\007"'

>  If your PROMPT_COMMAND is also
> printing out PS1 then that would possibly create the situation that
> you describe.  What is your PS1 set to? 
PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ 
'
what is it btw?

> > I think it would be great if bash before printing the prompt could do a 
> > simple check: if the cursor is not positioned in the first column of the 
> > terminal, then prepend the prompt with a newline.
>
> I think that bash shouldn't try to ask the terminal where the cursor
> is because that I believe would react badly on many terminals.
>
> While use of 'cat' as a file dumper is certainly a time honored
> tradition it is not the purpose of the program.  The purpose of the
> cat program is to concatenate files and it does that exactly without
> adding a newline to the end if one does not exist.
>
> To avoid the problem with files without a trailing newline it is
> better to use more or less or most or other pagers that are designed
> to deal with terminal screens.  Use of cat to browse files is a
> power-user mentality that says that you know what you are doing and
> are driving the machine at that level.  Therefore when the file does
> not have a trailing newline it is expected that you will deal with it.
ok, but this problem does not only happen with "cat". It happens with 
_any_ program which does not print a newline:

if test.c is:

#include <stdio.h>
int main()
{
        printf("Hello world without final newline");
        return 0;
}

then:

frm@ubuntu:~$ gcc -o test test.c
frm@ubuntu:~$ ./test
frm@ubuntu:~$ thout final newlinefrm@ubuntu:~$
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

same weird behaviour I see when using cat with non-newline-ended files.

Interestly, if the main() just returns 0 and does not printf() anything, 
then the prompt is correctly printed...

Francesco