Re: ${prefix} expansion in configure.ac ?

[Philippe Trottier]

Stepan Kasal wrote:

> Hi,
>
> On Mon, Feb 07, 2005 at 03:40:02PM +0200, Philippe Trottier wrote:
>  
>
> > here is something I have noticed, exec_prefix is set to NONE until the 
> > end of the config script... now I am thinking to see if it is set at 
> > NONE and if it is then set exec_prefix to ${prefix}, and put it back to 
> > NONE afterward ... does that make any sense ?
> >    
>
> if it's set to NONE, it means it hasn't been given on the command line.
> Perhaps a macro below will execute
>
>         test $exec_prefix = NONE
>  
Yes that I noticed...

> to see whether a value was given or not.  I don't want to destroy this
> information, so I restore the previous state.
>
> It would be also possible to do something like:
>
> test "x$prefix" = xNONE &&  prefix=$ac_default_prefix
> test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'
> eval eval ac_define_dir="\"\\\"$1\\\"\""
> test -d "$ac_define_dir" dnl
>
> or even:
>
> test "x$prefix" = xNONE &&  prefix=$ac_default_prefix
> test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'
> eval eval test -d "\"\\\"$1\\\"\"" dnl
>
> But please note that I had to change the value assigned to exec_prefix,
> and I had to add one more `eval' on that account.
>  
But why is it not set at the beginning just like ${prefix} is a good 
question ...

> The reason is that in the generated Makefiles, you should see:
>
>         exec_prefix = ${prefix}
>
> not the value of $prefix.  This subtle difference enables the following:
>
>         make prefix=...
>
> which should change both prefix and exec_prefix variables.
>
> To sum up, I think the solution with restoring NONEs is the cleanest way.
>  
setting the exec_prefix in the beginning of configure.ac would still 
allow the exec_prefix to be set at make stage (I think ?) any other 
reasons why it should be left to NONE till the end ? non- Unix platforms 
maybe ?

The other solution is not to touch it at all, but I do not know if with 
my clumsy use of sed is dangerous or not... then I have been trying to 
understand the disable and enable trouble in this case, it does seem to 
work very nicely, at least for me ...

    AC_MSG_CHECKING([Library directory at])
    if test "${exec_prefix}" = "NONE" ; then
        eval test -d `echo $libdir | sed 's,exec_prefix,prefix,'` &&
        eval LDFLAGS="-L`echo $libdir | sed 's,exec_prefix,prefix,'` 
$LDFLAGS" &&
   else
        eval test -d $libdir &&
        eval LDFLAGS="-L$libdir $LDFLAGS" &&
   fi
   AC_MSG_RESULT($libdir)


I know I should rebraket everything to make it clean again ... I know I 
am not the only one trying to do the same thing, so I'll keep it 
complete ...

Phil