my $data = 'abacad';  # slurp in whole file into scalar
my $pattern = 'a'; 

my $ds = unpack "B*", $data;
my $ps = unpack "B*", $pattern;

my $proof = '-' x length($ds);
my $x = 0;
while ( 1 ) {
    $x = index($ds,$ps,$x);
  last if $x == -1;
    print "Match at bit offset $x\n";
    # modify proof string to show match, could extract surrounding 
    # bits just as easily using our $x offset and substr() on $ds
    substr( $proof, $x, length($ps), $ps );
    $x++;   # move offset pointer to next bit to avoid endless loop
}

print "
Original: $ds
Matches:  $proof\n";

__DATA__
Match at bit offset 0
Match at bit offset 16
Match at bit offset 32

Original: 011000010110001001100001011000110110000101100100
Matches:  01100001--------01100001--------01100001--------