Re: PATCH: Slightly improve printf %s

["Thorsten Dahlheimer" <tdahlheim@gmx.net>]

Wayne Davison wrote:
> On Mon, Aug 08, 2005 at 08:21:28PM +0200, Thorsten Dahlheimer wrote:
> > After I made this change, the test suite uncovered a bug (which I
> > introduced) in the handling of %b (and now %s) when no argument is
> > left, so the patch includes a fix for that, too.
> 
> I didn't see that fix in the patch.  I assume you're talking about
> this line (which is executed when the arg is missing):
> 
>         count += fprintf(fout, "%*c", width, ' ');
> 
> ... since that would output a single space, even when "width" is 0.  I
> changed the "else" that is in front of that line to "else if (width)",
> and it fixes the problem (I could have also changed the line to use
> fprintf(fout, "%*s", width, ""), but the former seems a litle more
> optimal).

Sorry, I attached the wrong diff (the one that I made before I discovered
that bug).  Anyway, the fix I made is exactly the one you've described.

> As for the change to how %s is handled, can you show me an example where
> this is needed?  In my simple tests, if a variable has a literal null in
> it, using either %b or %s to print it out with printf truncates the
> variable at the null (and, of course, a backslash-zero can be passed to
> %b to get a real null, but %s doesn't evaluate backslashes).

I don't know if it's really needed, but it would certainly be more
consistent.  Currently you get:

    % s=$'a\0b'

    % print -n $s |od -tx1
    0000000 61 00 62
    0000003

    % printf $s |od -tx1  
    0000000 61 00 62
    0000003

    % printf '%b' $s |od -tx1
    0000000 61 00 62
    0000003

    % printf '%s' $s |od -tx1
    0000000 61
    0000001

(Note that the behaviour of %b in this case changed as a consequence
of zsh-workers/21552, item 4.)  Given that the first three variants
treat the nul just like any other character, and the same is true
for the rest of zsh, I find the behaviour of %s a bit surprising.
I think it's conceivable that someone processes strings containing
nuls (say, captured output from 'find ... -print0' or the like) and
finally writes them out with print; this all works well with zsh.
Then they change the output command from 'print -nr -- "$s"' to
'printf "...%s..." ... "$s" ...' and get bitten.

Regards,
Thorsten Dahlheimer