In addition to the advice by others: Something is wrong with 
        if ($block->match($row[$i])){
            print "IP address: $row[$i] is inside $block\n";
        }
        else{
            print "IP address: $row is not inside $block\n";
        }

[download]
in the "if" branch, you print $row[$i], while in the "else" branch, you print $row - no wonder your output contains blatant lies as e.g. "IP address: 192.168.1.1 is not inside 192.168.1.0/27" …
I suggest something like 
        print "IP address: $row[$i] is ";
        if ($block->match($row[$i])){
            print "inside";
        }
        else{
            print "outside";
        }
        print " $block\n";

[download]
Of course, this isn't ideal either, but less error prone.

In reply to Re: Use of uninitialized value $i in bitwise and (&) at <Netmask.pm> by soonix
in thread Use of uninitialized value $i in bitwise and (&) at <Netmask.pm> by dotowwxo

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