## Define a bit vector with positions 4 to 7 set to 1
my $bv1='';
vec($bv1,$_,1)=1 foreach (3..6);
dumpbv($bv1);

sub dumpbv
{
    my $bitv = shift @_;
    my $pos=0;
    foreach (split "",unpack("b*",$bitv)){
      print;
      $pos++;
    }
}