I think you are looking for a carriage return (without line feed):

sub do_stuff {
  sleep 2; # for the sake of the example ..
}

$|=1; # turn off buffering, or you may never see what you write ...

my @v = (1, 3, 10, 20);
while (@v) {
  printf "\r%2d", shift @v;
  do_stuff();
}
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