Date: Thu, 10 Jul 2008 13:54:46 +0930 From: Malcolm Kay <malcolm.kay@internode.on.net> To: freebsd-questions@freebsd.org Cc: Anton Shterenlikht <mexas@bristol.ac.uk> Subject: Re: snippet of configure script - explain please Message-ID: <200807101354.46321.malcolm.kay@internode.on.net> In-Reply-To: <20080709172513.GA51206@mech-cluster238.men.bris.ac.uk> References: <20080709172513.GA51206@mech-cluster238.men.bris.ac.uk>
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On Thu, 10 Jul 2008 02:55 am, Anton Shterenlikht wrote:
> I get errors building ports/graphviz on FBSD 6.3 on alpha.
> It seems the error is due to configure script erroneously
> deciding that there is no strncasecmp function on OS.
>
> Based on config.log:
>
> configure:9333: result: no
This probably the result for the previous check; probably strcasecmp
> configure:9253: checking for strncasecmp
>
> I think the following configure snippet is to blame.
> Could somebody explain, at least in general terms,
> what this piece of code does.
>
> many thanks
> anton
>
> 9249
> 9250 for ac_func in strcasecmp strncasecmp
> 9251 do
> 9252 as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
This is eqivalent to:
as_ac_var=ac_cv_func_strcasecmp
or:
as_ac_var=ac_cv_func_strncasecmp
depending on which time through the loop.
> 9253 { echo "$as_me:$LINENO: checking for $ac_func" >&5
> 9254 echo $ECHO_N "checking for $ac_func... $ECHO_C" >&6; }
These lines simplly write reports of one type or another (including to config.log ?)
The $ECHO_N and $ECHO_C are to cater for different versions of 'echo' wrt line feeds.
> 9255 if { as_var=$as_ac_var; eval "test \"\${$as_var+set}\" = set"; }; then
I find this line somewhat strange as I've not been able
to find documentation for the expansion of ${parameter+set} under the Bourne shell.
(nor bash, nor ksh)
*****************************************************
Presumably someone out there knows where to find it?
*****************************************************
But it seems that it returns "set" if "parameter" has been assigned a value and
null otherwise.
Unless strcasecmp, strncasecmp have already been checked one expects these will fail
so the 'else' section is executed.
> 9256 echo $ECHO_N "(cached) $ECHO_C" >&6
> 9257 else
> 9258 cat >conftest.$ac_ext <<_ACEOF
> 9259 /* confdefs.h. */
> 9260 _ACEOF
> 9261 cat confdefs.h >>conftest.$ac_ext
> 9262 cat >>conftest.$ac_ext <<_ACEOF
> 9263 /* end confdefs.h. */
This is the start of the build of a C program to test if the library function exists.
But we've barely started -- the guts of the check is still to come.
One would expect that if it does not exist the configuration would implement
some alternative action so even then I would not expect the built to fail.
> where
>
> as_tr_sh :
>
> 549 # Sed expression to map a string onto a valid variable name.
> 550 as_tr_sh="eval sed 'y%*+%pp%;s%[^_$as_cr_alnum]%_%g'"
>
> as_cr_alnum :
>
> 40 as_cr_alnum=$as_cr_Letters$as_cr_digits
>
> as_me :
>
> 132 # Name of the executable.
> 133 as_me=`$as_basename -- "$0" ||
>
> ECHO_N and ECHO_C :
>
> 474 ECHO_C= ECHO_N= ECHO_T=
> 475 case `echo -n x` in
> 476 -n*)
> 477 case `echo 'x\c'` in
> 478 *c*) ECHO_T=' ';; # ECHO_T is single tab character.
> 479 *) ECHO_C='\c';;
> 480 esac;;
> 481 *)
> 482 ECHO_N='-n';;
> 483 esac
>
>
Best of luck,
Malcolm Kay
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