use Scalar::Util qw( looks_like_number );

while( <> ) {
  next unless looks_like_number($_);
  chomp;
  $min = ! defined( $min ) || $min > $_ ? $_ : $min;
  $max = ! defined( $max ) || $max < $_ ? $_ : $max;
}
print "\nminimum number: $min\n";
print "maximum number: $max\n";