I think you're misunderstanding the packet format. When you say that the representation is in "binary", it doesn't mean the binary representation that you get by doing unpack "B*"; it means that your data is packed as if it's in a binary structure. So you have the right operator (pack), you just have the wrong pack template.

I think that this will work for you:

    my $data = "LOGON USERNAME=NAME PASSWORD=PASS\0";
    my $packet = pack "CnCCNnn",
                2,                 ## sync byte
                length($data)+13,  ## message size
                13,                ## header size
                hex("4c"),         ## message type
                1,                 ## sequence ID
                0,                 ## protocol ID
                1;                 ## version number
    $packet .= $data;
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That pack template ("CnCCNnn") says to pack the list of values (the rest of the arguments to pack) in the following way:

• unsigned char value (1 byte)
• short in network order (2 bytes)
• unsigned char value (1 byte)
• unsigned char value (1 byte)
• long in network order (4 bytes)
• short in network order (2 bytes)
• short in network order (2 bytes)

This varies from your use of pack in two important ways. First, we no longer use 'unpack "B*"', because the point of that is to take a binary structure and make it into a human-readable string that looks like a sequence of bits. That's not what you want: you want to send the data to the server as a binary structure.

Second, you can't just use 'pack "N"'; that packs everything as a network-order long, which is 4 bytes. You don't want everything to be 4 bytes; some things are 1 byte, some are 2, some are 4. You have to vary you pack template depending on that.