Reading a text file located on the computer with NodeMCU using Lua

Question

My problem is about reading a text file (which is located in my computer) in the NodeMCU development kit. I am able to read the file content in Ubuntu terminal using a Lua script. Here I am sharing the code that I have been using for reading. Both are working pretty well in the Ubuntu terminal.

First one:

local open = io.open
local function read_file(path)
local file = open(path, "rb") -- r read mode and b binary mode
if not file then return nil end
local content = file:read "*a" -- *a or *all reads the whole file
file:close()
return content

Second one:

local fileContent = read_file("output.txt");
print (fileContent);

function file_exists(file)
  local f = io.open(file, "rb")
  if f then f:close() end
  return f ~= nil
end

-- get all lines from a file, returns an empty 
-- list/table if the file does not exist
function lines_from(file)
  if not file_exists(file) then return {} end
  lines = {}
  for line in io.lines(file) do 
    lines[#lines + 1] = line
  end
  return lines
end

-- tests the functions above
local file = 'output.txt'
local lines = lines_from(file)

-- print all line numbers and their contents
for k,v in pairs(lines) do
  print('line[' .. k .. ']', v)
end

My problem occurs when I have sent the code to NodeMCU, using Esplorer to send the code in. But the error occurs like this:

attempt to index global 'io' (a nil value)
stack traceback:
    applicationhuff.lua:5: in function 'file_exists'
    applicationhuff.lua:13: in function 'lines_from'
    applicationhuff.lua:23: in main chunk
    [C]: in function 'dofile'
    stdin:1: in main chunk

My general purpose is actually to read this datas and publish it to a Mosquitto Broker via MQTT protocol. I am new to these topics. If anyone can handle my problem it will be appreciated. Thanks for your help...

Answer 1

NodeMCU does not have an io library. Therefore you get an error for indexing io, which is a nil value.

No offense, but sometimes I wonder how you guys actually manage to find your way to StackOverflow and even write some code without knowing how to do basic web research.

https://nodemcu.readthedocs.io/en/master/en/lua-developer-faq/

The firmware has replaced some standard Lua modules that don't align well with the SDK structure with ESP8266-specific versions. For example, the standard io and os libraries don't work, but have been largely replaced by the NodeMCU node and file libraries.

https://nodemcu.readthedocs.io/en/master/en/modules/file/

The file module provides access to the file system and its individual files.

I hope that's enough help...