So you basically want

my $bob = 123.456
print &my_format($bob) . "\n";
[download]

to return 123456 What happens on 12345.6789 Do you want
12345678
or
12345679 ?
Or do you want something else? Assuming the last case is correct...

$bob = 123.4567;
print &print_fixed($bob). "\n";
exit 0;
sub print_fixed {
  my $num = shift;
  my $ipart = int($num);
  my $dpart = sprintf("%.3f",$num);
  my ($frac_part) = $dpart=~ /\.(\S*)/;
  return $ipart . $frac_part;
}
[download]

does what you want. You can specify arbitary decimal places by passing in a second arg and replacing sprintf("%.3f",$num); with sprintf("%.$dec_places",$num);
Crulx