#!/usr/bin/perl
use warnings;
use strict;

my $mask1 = 0b1101_1101;
my $mask2 = 0b0010_0010;

printf " \$mask1 = %b\n", $mask1;

#Use bitwise NOT to flip all the bits.
printf "~\$mask1 = %b\n\n", ~$mask1;

#use bitwise OR to set bit(s) but keep original values for all other bits.

my $value = 0b1010_1000; 

printf "  %b \$value\n| %b \$mask1\n----------\n  %b\n\n\n", $value, $mask1, $value | $mask1;
printf "  %b \$value\n| %08b \$mask2\n----------\n  %b\n\n\n", $value, $mask2, $value | $mask2;

#use bitwise AND to clear bit(s) but keep original values for all other bits.

printf "  %b \$value\n& %b \$mask1\n----------\n  %b\n\n\n", $value, $mask1, $value & $mask1;
printf "  %b \$value\n& %08b \$mask2\n----------\n  %08b\n", $value, $mask2, $value & $mask2;

#If you just want to test the value of a bit then clearing the other bits 
#  lets you test the value for the remaining one.

__END__
 $mask1 = 11011101
~$mask1 = 1111111111111111111111111111111111111111111111111111111100100010

  10101000 $value
| 11011101 $mask1
----------
  11111101


  10101000 $value
| 00100010 $mask2
----------
  10101010


  10101000 $value
& 11011101 $mask1
----------
  10001000


  10101000 $value
& 00100010 $mask2
----------
  00100000