On Mon, Nov 10, 2008 at 08:34:31PM +0100, Ralf Wildenhues wrote:
> * Paolo Bonzini wrote on Mon, Nov 10, 2008 at 12:07:12PM CET:
> > [...] we could use a shell function like
> >
> > func_fallback_echo()
> > {
> > cat <<_LTEOF
> > $1 (or $*)
> > _LTEOF
> > }
>
> IIRC then it would have to be something like this:
>
> func_fallback_echo()
> {
> eval 'cat <<_LTEOF
> $*
> _LTEOF'
> }
>
> in order to prevent some shells from expanding $* already at function
> definition time; but I don't remember for certain. And IIRC I learned
> this on your pages, Sven, but cannot find it any more now.
You probably remembered "http://www.in-ulm.de/~mascheck/bourne/common.html";?
The problem is not the body of the here-doc ($* above); the body would just
be contained literally in a tempfile and it's not expanded prematurely.
But the premature tempfile definition itself can cause harm, because it
might get lost:
In traditional Bourne shells and in some cases in ksh88 up to ksh88g,
the above (variant without eval) fails like
"/tmp/sh123456: cannot open"
in:
(sleep 1; func_fallback_echo) &
(sleep just guarantees that the parent exits first)
I don't expect to see such a call in libtool/autoconf...
But also worth to mentiont: A subshell or another script called must
not redefine or unset func_fallback_echo if the original definition
made use of a tempfile. The redefinition/unset fails, and the definition
is lost for the parent. Again, this can be fixed with eval.
(The above are just those problems i stumbled over when doing
intensive Usenet research. I cannot tell whether there are other
potential problems, but otherwise it always looked safe to me.)
Cheers, Sven
