sub timetill { # don't use prototypes
   local $| = 1; # will be restored on exit scope

   my $time = shift || return; # use "undef" to signal errors in Perl
   my $line = shift || " seconds until event";

   # why chomp?

   while($time > 0) {
       my $prompt = sprintf "%3d $line", $time;
       print $prompt;
       sleep 1;
       print "\b" x length $prompt; # no need to edit the function
       $time--;
   }
}