Attempt to index ? (A nil value)

Hey there! I'm trying to make a bootloader, and I want to detect all .bmf on /dev, but line 83 gives me: "Attempt to index ? (a nil value)". I've been trying to troubleshoot the error, and I think it may be that fs.open is returning nil, but if that code gets to run, it means there is a file. Thanks in advance

local function toLines(readall)
  local t = {}
  local function helper(line) table.insert(t, line) return "" end
  helper((readall:gsub("(.-]\r?\n", helper)))
  return t
end

local function s(str, char)
  sep = sep or "%s"
  local l={}
  for str in string.gmatch(str, "(.-)("..sep..")") do
	table.insert(l,str)
  end
  return t
end


function sW(str, start)
  return string.sub(str,1,string.len(Start))==Start
end
function eW(str, ends)
  return ends=='' or string.sub(str, -string.len(ends))==ends
end

bmflist = {}
seltable = {1}

fsl = fs.list("/dev")

for _,fse in ipairs(fsl) do
  print(fse) --Debug print
  if eW(fse, ".bmf") then
	bmf = fs.open(fse, "r") -- Debug print (THIS errors)
	bmflist[fse] = {["rf"] = bmf} -- THIS errors
	print(bmf.readAll())
	bmflines = toLines(bmf.readAll())
	for line in bmflines do
	  if sW(line, "-- entryName:") then
		sline = s(line, ':')
		bmflist[fse]["en"] = sline[2]
		if sline[2] == "Shutdown" then
		  table.insert(seltable, 2)
		else table.insert(seltable, 0) end
	  elseif sW(line, "-- description:") then
		sline = s(line, ':')
		bmflist[fse]["dc"] = sline[2]
	  elseif sW(line, "-- bmf:end") then break end
	end
  end
  bmf.close()
  term.setCursorPos(1,19)
  if bmflist == {} then error("> No .bmf files found.") end
  for k,v in bmflist do if v["en"] == nil then error("> .bmf file not registered.") end end
end

the error should give a file name too, which file name did it give?

also the code you gave doesn't have 80+ lines.

if all else fails then add a few print statements throughout your code, the error is between the last one which gets printed and the first one which didn't

Happened with me, in my disk lock here is the fix
use shell.resolve
Like this:

resolvedPath = shell.resolve("hellothere.lua")
hwnd = fs.open(resolvedPath, "r")
if hwnd then
dataContains = hwnd.readAll()
hwnd.close()
print("Recieved: " ..dataContains ..".")
else
print("Failed to open the file!")
error()
end

The code has a filename and has 100+ lines, just want to keep it secret. Thanks Meit! The Code worked, but now I have another problem.

bmflines = toLines(bmf.readAll())

for line in bmflines do -- Error here
          if sW(line, "-- entryName:") then
                sline = s(line, ':')
                bmflist[fse]["en"] = sline[2]
                if sline[2] == "Shutdown" then
                  table.insert(seltable, 2)
                else table.insert(seltable, 0) end
          elseif sW(line, "-- description:") then
                sline = s(line, ':')
                bmflist[fse]["dc"] = sline[2]
          elseif sW(line, "-- bmf:end") then break end
        end

(Same code as above, full code above). Now it says Attempt to call table…

Attempt to call table means that you are using a table as a function which doesn't have a meta-method for that (don't worry if you don't understand that last bit)

for x in y do expects y to be an iterator function, try looking at this: https://www.lua.org/pil/7.3.html

Instead of creating bmflines and trying to iterate on that, I think this would achieve what you want. However I'm not sure if it'll work on a file that is already opened with a handle (haven't ever tried that)…

for line in io.lines(fse) do
  ...
end