if [ ! -e $DATOS/modes/$PREFIJO ];
  then echo -n "Error: Mode $PREFIJO does not exist";
       c=$(find $DATOS/modes|wc -l)
       if((c <= 1));
       then echo ".";
       else echo ". Try one of:";
         for i in $DATOS/modes/*;
         do echo "  " $(basename $i);
         done;
       fi
       exit 1;
fi