Question

I have several hex-values that I try to write to a file. It seems that Lua doesn’t support that out of the box, since they are all treated as strings instead of values. I figured I would have to break up a longer hex-value, for example AABBCC into AA, BB, CC and use string.char() on all of their decimal values consecutively to get the job done.

Is there a built in function that allows me to write such values directly without converting them first? I used escape characters such as “0xAA” and “\xAA”, but those didn’t work out.

Edit: Let me give you an example. I’m looking at a test file in a hex editor:

00000000  00  00  00  00  00  00  ......

And I want to write to it in the following fashion with the string “AABBCC”:

00000000  AA  BB  CC  00  00  00  ......

What I get though with the escape characters is:

00000000  41  41  42  42  43  43  AABBCC

Answer 1

I use the following functions to convert between a hex string and a “raw binary”:

function string.fromhex(str)
    return (str:gsub('..', function (cc)
        return string.char(tonumber(cc, 16))
    end))
end

function string.tohex(str)
    return (str:gsub('.', function (c)
        return string.format('%02X', string.byte(c))
    end))
end

They can be used as follows:

("Hello world!"):tohex()               --> 48656C6C6F20776F726C6421
("48656C6C6F20776F726C6421"):fromhex() --> Hello world!