How to implement a basic Lua function in Conky?

Question

I am trying to add a function to my Conky which prints the length of a string for debug purposes. The code, inside a file called test.lua, is pretty trivial:

function test(word)
return string.len(word)
end

...and I load it like this. In my conky.config section I have:

lua_load = '/home/xvlaze/test.lua',
lua_draw_hook_pre = 'test'

...in the conky.text section I have:

${lua test "fooo"}

...where test is the name of the function and fooo the string to test.

The expected result should be a printed 4 in Conky, but instead of that I get:

conky: llua_do_call: function conky_test execution failed: /home/xvlaze/test.lua:2: attempt to index a nil value (local 'string')
conky: llua_getstring: function conky_test didn't return a string, result discarded

I have browsed through the documentation, but I can't find anything. Does anybody know where the failure is?

Frankly calling your parameter `string`, just the same as the regular `string` library can't really end well. — Bartek Banachewicz, Jul 28 '17 at 09:18
@xvlaze Is that your entire script? It looks like you have a variable named `string` that is overriding the string library (maybe you did `string = 'this'`)? — DavisDude, Jul 29 '17 at 18:34
UPDATE: found the solution and wrote a little explanation. I'll update when I can. — xvlaze, Aug 06 '17 at 15:11

xvlaze · Accepted Answer · 2017-08-16T10:10:14.910

Several guidances on how to implement functions in Conky:

First of all: YOU MUST USE conky_ BEFORE YOUR FUNCTION'S NAME. Otherwise, you will get the following error when running your Conky:
```
attempt to call a nil value
```
Secondly: YOU MUST ALWAYS RETURN A VALUE. I don't mind repeating it - it is crucial. Otherwise, you will get:
```
function foobar didn't return a string, result discarded
function_result
```
...in your terminal, and your Conky will be left empty of values related to your extra code. Nothing will be printed regarding your function.

Last but not least: YOU MUST ALWAYS CALL YOUR FUNCTION LIKE:

lua_load = '/path/to/function.lua',
-- Whatever content...
${lua function_name function_parameter1 function_parameterN} -- In case you use more than one parameter.

In summary, a dummy function template could be:

MAIN FILE (conky.conf):

conky.config = {
    -- Whatever content... Lua styled comments.
    lua_load = '/path/to/function.lua',
}

conky.text = [[
    # Whatever content... In this section comments are started with '#'!    
    ${lua function_name parameter}
]]

FUNCTION FILE:

function conky_function_name(parameter)
    -- Whatever content... Remember this is Lua, not conky.text syntax. Always use '--' comments!
    return whatever -- No return, no party. A function MUST always return something!
end

not working right now.is there anything missing?? should `function.lua` be executable? — nyxee, Mar 08 '21 at 06:02

How to implement a basic Lua function in Conky?

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