Re: should a postinst script create config files?

[Manoj Srivastava <srivasta@debian.org>]

>>"Brian" == Brian May <bam@debian.org> writes:

 Brian> How does ucf work?

	Very well ;-)

	ucf is meant to be called from the postinst, with the format:
 ucf [options] <New file> <Destination>

	Now, since you control what the new file is called, you can
 use diff3 to create a merged/massaged version of the configuration
 file (Shipped in package: /usr/share/<pkg>/conf.old,
 /usr/share/<pkg>/conf, and /etc/pkg.conf is the dest). 

======================================================================
 if [ -e  /etc/pkg.conf ]; then
   rm -f /etc/pkg.conf.dpkg-new
   cp    /etc/pkg.conf  /etc/pkg.conf.dpkg-new
   diff3 -A /etc/pkg.conf.dpkg-new /usr/share/<pkg>/conf.old \
                                   /usr/share/<pkg>/conf >;
 fi

 ucf /etc/pkg.conf.dpkg-new /etc/pkg.conf
======================================================================

	See? Quite simply done. However, the success of this maneuver
 is predicated on you determining which version of the file is
 installed on the machine, and being able to use that information to
 use while generating the diff3. This rapidly gets complex. 

	Hmm. Heres how that'd work inside ucf (I am eliding how the
 variables are set and all)
----------------------------------------------------------------------
 if [ -e  /etc/pkg.conf ]; then
   if [ -e "$statedir/hashfile" ]; then
       lastsum=$(grep "[[:space:]]${dest_file}$" "$statedir/hashfile" | \
                      awk '{print $1;}' )
   fi

   if [ "X$lastsum" = "X" ]; then
       if [ -d "$old_conf_dir" ]; then
   	for file in ${old_mdsum_dir}/*; do
   	    oldsum=$(md5sum "$file");
   	    if [ "$oldsum" = "$lastsum"  ]; then
   #               Bingo! 
                   cp "$file" /usr/share/<pkg>/conf.old
                   break
   	    fi
   	done
       fi
   fi 
   rm -f /etc/pkg.conf.dpkg-new
   cp    /etc/pkg.conf  /etc/pkg.conf.dpkg-new
   diff3 -A /etc/pkg.conf.dpkg-new /usr/share/<pkg>/conf.old \
                                   /usr/share/<pkg>/conf >;
fi
----------------------------------------------------------------------

	If this seems like a worthwhile addition, I'll see if I can
 provide this functionality in the ucf package (namely, given a
 destination file name, and a directory of historical versions, a
 utility shall tell you which version corresponds to the last version
 installed; you can then runn diff3 or whatever on your own)

	manoj 
-- 
 System going down in 5 minutes.
Manoj Srivastava   <srivasta@debian.org>  <http://www.debian.org/%7Esrivasta/>
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