Something

  if [ -z "$DEFWM" -o "x$DEFWM" = "xgnome-wm" ]; then
      
      if /usr/bin/xdpyinfo | /usr/bin/grep -q '^vendor release number: *70000001'; then
          if [ -x /usr/bin/compiz ]; then
              if [ -z "$SMID" ]; then
                  exec /usr/bin/compiz --replace --sm-disable glib gconf
              else
                  exec /usr/bin/compiz --replace --sm-client-id $SMID glib gconf
              fi
          fi
      fi
      
    for wm in $KNOWN_WM ; do
      IFS=":"
      for dir in $PATH ; do
	if [ -x "$dir/$wm" ] ; then
	  WINDOW_MANAGER="$dir/$wm"
    	  break 2
	fi
      done
      IFS=$OLDIFS
    done
  else
    WINDOW_MANAGER=$DEFWM
  fi
  IFS=$OLDIFS
fi