Same Lua script works in Mac, Windows, but NOT Linux

It should behave the same in Linux, Mac, and Windows - there's been a recent change. What version were you running on Windows/Mac?

"When you say local tables, do you mean declare all the functions as "local"?"

When your script has this: "_G[funcName]", it's trying to access an entry in the Lua global table - an entry named whatever the variable funcName resolves to. ("_G" is the name of the global table)

"The functions are generated by python. I have python code writing to the Lua file lines like "function pkgExtract%s(buffer, offset)" %pkgID, which is the start of the function. Is this what you mean?"

You mean the Python code is writing something like this:

function pkgExtract0x0a01fe32(buffer, offset)
    -- do stuff
end

And it writes the above into the same Lua script file that has the code you posted in the question?

If so, then there's at least one problem: that doesn't actually create a global function named "pkgExtract0x0a01fe32" - i.e., it's not in the "_G" global table. Wireshark used to do that, but the code got changed recently to stop doing that. Instead, it creates a function of that name in the local file environment, meaning it's no longer global, and no longer put into the "_G" table. That was done to prevent Lua scripts from accidentally polluting the global table and affecting other scripts. (because people kept forgetting to use the word "local" before their variables and function definitions)

So change your Python code and the Lua code in your question to do this:

-- this is in your Lua file before the Python-generated code,
-- or Python generates one of these too (but only once)
local myfuncs = {}
– Python generates this
function myfuncs.pkgExtract0x0a01fe32(buffer, offset)
– do stuff
end
– presumably this is in your dissector function
local packageID_string = string.format("0x%08x", packageID)
local funcName = "pkgExtract" .. packageID_string
if myfuncs[funcName] ~= nil then
myfuncs[funcName](buffer, offset)
else
tree_payload:add(buffer(offset, pkg_payload_len), "Package ID not defined")
end

BTW, there’s no need to do the string.format() and concatenation thing… Lua’s table keys can be numbers. So you could do this instead:

– this is in your Lua file before the Python-generated code,
– or Python generates one of these too (but only once)
local myfuncs = {}

– Python generates this - note the '0x0a01fe32' is not
– in quotes, so it's a number key
myfuncs[0x0a01fe32] = function(buffer, offset)
– do stuff
end
– presumably this is in your dissector function
– the 'packageID' is a variable of a number, not a string
if myfuncs[packageID] ~= nil then
myfuncs[packageID](buffer, offset)
else
tree_payload:add(buffer(offset, pkg_payload_len), "Package ID not defined")
end