Re: printf bug(s?)

["Harald van Dijk" <truedfx@gentoo.org>]

Oliver Kiddle wrote:
> Harald van D?k wrote:
> 
>>When I run the command printf '%', zsh 4.2.5 gives me a segfault. It
> 
> 
> I can't reproduce the segfault on any system I have access to so perhaps
> it is platform specific. Your fix looks right so I'll commit it to
> CVS. Thanks.
> 
I`m using a rather plain Linux system (glibc 2,3,5, gcc 3.4.4), and in
the end zsh was configured with --prefix=$HOME/zsh --enable-zsh-debug,
nothing special. (I'm not sure on the original configuration.) It
doesn't always segfault since it depends on whatever happens to be in
memory after the format string. A pretty reliable way for me to get it
segfaulted is with for x in %; do printf $(echo $x); done on the command
line, or much more simply, zsh -c 'printf %'. However, even just
entering 'printf %' on the command line segfaulted for me sometimes.

Though it doesn't really matter; I guess it's good if you can't
reproduce it :) Thanks.

>>2:
>>
>>That segfault I noticed when I tried to run printf '\045'. I expected
>>this to print a single character '%', the same as printf '%%' would. zsh
>>instead treats it exactly as an ordinary % character. Is this a bug, or
> 
> 
> It's not a bug as such. Note that it is entirely consistent with how
> printf works from C. I think there was a brief discussion about it when
> printf was first added.
> 
> The current implementation makes it easier to share the \ handling code
> with echo. It just calls getkeystring() on the whole format
> specification first. I seem to remember that, at the time, a survey of
> how other printf implementations worked showed a complete mix so it
> seemed justifiable to take the lazy option. However, I would agree that
> your expected behaviour would probably be better.
> 
Oh, there are other printfs that behave the same? That I didn't know; in
that case, I may be better off avoiding using \045 anyway and just
replace it with %%...

>>" "\ddd", where ddd is a one, two, or three-digit octal number, shall
>>  be written as a byte with the numeric value specified by the octal
>>  number. "
> 
> 
> It's difficult to know whether it was intended by the wording or not.
> 
> However, that wording also means that \7 should output a bell character
> (you need \07 at the moment). Annoyingly, the specification for how \
> escapes work is subtly different for echo and printf. I think \c has a
> different definition too.
> 
Ah, right. As another example, \0007 should print a single character
with echo, but two ('\0' and '7') with printf '\0007'. However, printf
'%b' '\0007' should still print a single character...

> So what we probably need to do is have the printf code handle \ escapes
> itself at the same time as it scans through the specification looking
> for format specifiers.
> 
Either that, or you could modify getkeystring to be able to treat the
string the way a printf format string should be treated. That seems to
be a bit less work to me. Though, putting it with the % scanning would
mean being able to avoid %\nnn... printf '%\0163\n' 'Hello' works right
now, and modifying getkeystring would make printf '%\163\n' 'Hello' work.

But I'll be happy with whatever you decide to do.

> Oliver
> 
> 
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