send hex variable via TCP socket

Question

Probably it's an easy thing, but I'm a Lua beginner...
I'm creating a very simple QSC QSYS plugin to control a projection server using KVL API. Server API is based on hex strings.
For example this command asks the server to load a the playlist with 9bf5455689ed4c019731c6dd3c071f0e uuid:

Controls["LoadSPL"].EventHandler = function()
    sock:Write(
        "\x06\x0e\x2b\x34\x02\x05\x01\x0a\x0e\x10\x01\x01\x01\x03\x09\x00\x83\x00\x00\x14\x00\x00\x00\x01\x9b\xf5\x45\x56\x89\xed\x4c\x01\x97\x31\xc6\xdd\x3c\x07\x1f\x0e"
    )
end

Now I need to be able to create a string with a variable UUID, according to the text indicated in a textbox (or a list of available UUIDs read from the server) in the user interface. I will concatenate this string to the fixed part of the command. How can I correctly make a string like
ad17fc696b49454db17d593db3e553e5 become
\xad\x17\xfc\x69\x6b\x49\x45\x4d\xb1\x7d\x59\x3d\xb3\xe5\x53\xe5?

Answer 1

Try this:

local input = "ad17fc696b49454db17d593db3e553e5"
local output = input:gsub("%w%w", function(s) return string.char(tonumber(s, 16)) end)

Explanation: this takes every pair of characters, interprets them as base 16 numeric string, and then takes the character with that number, and uses that to replace the original characters.

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EDIT: To make it clear what's going on, and why the other answers are wrong, backslash escape sequences like \xad are a feature of the Lua source code, in memory it's represented by a byte with value 173, just like A is represented by a byte with value 65. Trying to concatenate a literal backslash character with hexadecimal characters does not create an escape code. So the way to do that is manually with string.char.