How to insert file lines into table in lua

Question

I'm trying to make a Discord bot with lua and its going well so far, but I'm having a couple problems with the IO portion of lua. I'm trying to read a large list.txt file in lua and inserting each line into a table, but so far all of my attempts didn't work. Any advice?

Attempt #1 spits out nil:

local open = io.open
local function read_file(path)
    local file = open(path, "r") -- 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
end
local fileContent = read_file("list.txt")

local vga_files = {}
table.insert(vga_files, fileContent)

`for line in io.lines("list.txt") do table.insert(vga_files, line) end` — Egor Skriptunoff, Dec 27 '20 at 21:15

score 0 · Answer 1 · answered Dec 30 '20 at 17:59

I was not able to replicate your error running your code. Your code is valid, and is likely doing what you asked it to do.

here you tell the read_file function to return nil:

if not file then return nil end

So if the file is not found you will get nil. A good step in debugging would be to add a print in the body of this if statement and see if it is getting entered.

When you call read_file:

local fileContent = read_file("list.txt")

you pass in only a file name, this means lua will look for that where ever the code is being executed, and this location maybe different from what you expect.

I validated your code works by pointing the read at itself, and printing the result.

local open = io.open
local function read_file(path)
    local file = open(path, "r") -- 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
end

print(read_file("so_io_read_test.lua"))

Additionally to get the lines you should really used io.lines which creates an iterator that you can use in a for loop.

local vga_files = {}
for line in io.lines("list.txt") do 
    table.insert(vga_files, line)
end

Or alternatively you can read the file and then split the lines using gmatch.

local contents = read_file("so_io_read_test.lua")
for line in contents:gmatch("([^\n]+)") do
  table.insert(vga_files, line)
end

How to insert file lines into table in lua

1 Answers1