Basic LUA problems - lua

I'm using ComputerCraft, a Minecraft mod that adds computers, monitors, modems and so on, which can be programmed using Lua scripts.
http://www.computercraft.info/wiki/Main_Page
While running my script I get this error: "bios:171: bad argument: string expected, got nil".
I dont understand because it says line 171 even though my code doesn't exceed 30 lines.. Can somebody explain?
monitor = peripheral.wrap("right")
monitor.clear()
monitor.setCursorPos(1, 1)
monitor.setTextScale(1)
monitor.write("Current mode:")
monitor.setCursorPos(1, 3)
monitor.write("furnace")
redstone.setOutput("back", false)
print("blablabla")
write()
if input == ja then
print("k")
redstone.setOutput("back", true)
monitor.clear()
monitor.setCursorPos(1, 1)
monitor.write("blabla")
else
print("u sux")
end
help would be highly appreciated.

You invoked an error in bios.lua which implements functions you can use in your script. Like write.
If we take a look into bios.lua we see that line 171 is actually part of the implementation of write.
It says: while string.len(sText) > 0 do, where sText
is the input argument to function write( sText ) in line 154.
There is no proper error handling or default value for the case that sText is nil. The programmer did a sloppy job here.
In that case string.len(sText) in line 171 will causes the error you received.
In order to fix that you have to either remove the empty call to write, which is equivalent to write(nil) or you have to provide some input string.
write("something") will not cause any error. If you want to print an empty string just call write("").

Related

"function arguments expected near 'levelc'" when using LOVE

I'm currently trying to make a level loading system for a game.
function love.filedropped(file)
ofile=io.open(file:getFilename(),"r")
io.input(ofile)
file:close
levelc=io.read()
for i=1,levelc do
levels[i]=io.read()
print levels[i]
end
levelc should be the first line of the file, and file:getFilename is the file to open (path included) the project gives an error message on startup, and i've used a similar structure before, but for an output. The error is at line 30, which is the levelc=io.read().
I've tried changing the name of the file pointer (it was "f" before, now "ofile") and i've tried using io.read("*l") instead of io.read() but same result.
EDITS:
-this is a love.filedropped(file)
-i need to open other files from a .txt later and i don't really understand how do do that
The parameter given by love.filedropped is a DroppedFile.
In your case helpful could be File:lines().
For example:
function love.filedropped(file)
-- Open for reading
file:open("r")
-- Iterate over the lines
local i = 0
for line in file:lines() do
i = i + 1
levels[i] = line
print(i, levels[i]) -- Notice the parentheses missing in your code
end
-- Close the file
file:close()
end
Notice that love2d usually only allows reading/writing files within the save or working directory. Dropped files are an exception.
Unrelated to this answer but things I noticed in your code:
Use locals, oFile should be local
file:close() required parentheses as its a function call
Same for the print
The filedropped callback has no end
You mentioned reading other files too, to do so, you can either:
Use love.filesystem.newFile and a similar approach as before
The recommended one-liner love.filesystem.lines

I'm using ComputerCraft, a minecraft mod that adds computers, modems, and other peripherals. In this mod, you can write code using Lua

This is my first time using Lua, and with following a tutorial, Im making a chat program, allowing two players to send and receive messages to each other. The receiving is called chatreceive.lua. The script is:
rednet.open("right")
sender, message = rednet.receive()
print("computer " .. sender .. " has sent :")
print(message)
I keep getting an error saying
chatreceive.lua:3: attempt to concatenate global 'sender' (a nil value)
Any solutions? Ive been trying for a while now
That means that the variable 'sender' was nil. This probably means that there was some sort of error with rednet. You should add a lot of checks to make sure your programs don't fail in critical situations:
if sender==nil then
print("SENDER IS NIL!!!")
end
Also, what version of CC are you using? You shoud be more specific, to get better answers...

Catch back trace information without exit

I'm trying to run a series of tests and collect some meta data on each test. If there is an error during one of the tests, I would like to save the back trace information but not to exit the script. For example:
-- Example program
for _, v in ipairs(tests) do
--check some results of function calls
if v == nil then
--error("function X failed") no exit
--save back trace to variable/file
-- continue with program
end
end
I'm not currently aware if it is possible in lua to tell the function error()
not to stop after creating the back trace. Any thoughts on how to do this?
debug.traceback ([thread,] [message [, level]]) (source) is what you're looking for. You can write a function that 1. gets a traceback 2. opens a file 3. writes the traceback to the file 4. closes the file.
In that case you'd have to use a level of 2, since 0 would be the debug.traceback function, 1 would be the function calling it (i.e. your function) and 2 the funcion calling that one. message could be your error code. Then you just override the error function locally in your script and you're done; calling error will just log the error and not exit the program.
EDIT: You can also override error globally, if you want, but that might lead to unexpected results if something goes terribly wrong somewhere else (code that you didn't write yourself) and the program continues nonetheless.
You'd be better off with a construct like this:
if os.getenv 'DEBUG' then
my_error = function()
-- what I explained above
end
else
my_error = error
end
and just use my_error in all the places where you'd usually use error.

Lua error for WoW addon (Tukui)

I don't have a lot of coding experience, did some C a few years ago, so that helps, but Lua handles things a bit differently, so I can't keep track.
I sometimes (not always) get this error when a friend or guildy logs into the game:
Date: 2013-06-14 16:57:57
ID: -1
Error occured in: Global
Count: 4
Message: ..\AddOns\Tukui\scripts\chat.lua line 335:
attempt to concatenate upvalue 'classColor' (a nil value)
Debug:
[C]: ?
Tukui\scripts\chat.lua:335: AddMessage()
..\FrameXML\ChatFrame.lua:2755: ChatFrame_MessageEventHandler()
..\FrameXML\ChatFrame.lua:2491: ChatFrame_OnEvent()
...s\WIM\Libs\LibChatHandler-1.0\LibChatHandler-1.0.lua:281:
...s\WIM\Libs\LibChatHandler-1.0\LibChatHandler-1.0.lua:252
...s\WIM\Libs\LibChatHandler-1.0\LibChatHandler-1.0.lua:308:
...s\WIM\Libs\LibChatHandler-1.0\LibChatHandler-1.0.lua:296
I have to do a reload of the ui after this happens to be able to see chat text again for that person.
Line 335 in that .lua file is this:
text = replace(text, "^|Hplayer:(.+)|h%[(.+)%]|h", "|Hplayer:%1|h|cff"..classColor.."%2|r|h")
Now I've learned that the .. indicates the concatenate function, but that isn't really helping me.
I don't know if this is enough information, but if you need it I can post the whole local function or whatever else is required.
If it makes any difference, I'm running the 3.3.5a WoW client.
You are probably using a global that gets defined from some other addon in a now deterministic way
While the (classColor or "") will get you rid of the error, you should try and find why that variable (classColor) is sometimes defined and sometimes not. Maybe it happens only for certain classes?
A simple hack would be to just replace
..classColor..
with
..(classColor or "")..
where it will select a blank string when classColor has no value assigned to it.

Getting return status AND program output

I need to use Lua to run a binary program that may write something in its stdout and also returns a status code (also known as "exit status").
I searched the web and couldn't find something that does what I need. However I found out that in Lua:
os.execute() returns the status code
io.popen() returns a file handler that can be used to read process output
However I need both. Writing a wrapper function that runs both functions behind the scene is not an option because of process overhead and possibly changes in result on consecutive runs. I need to write a function like this:
function run(binpath)
...
return output,exitcode
end
Does anyone has an idea how this problem can be solved?
PS. the target system rung Linux.
With Lua 5.2 I can do the following and it works
-- This will open the file
local file = io.popen('dmesg')
-- This will read all of the output, as always
local output = file:read('*all')
-- This will get a table with some return stuff
-- rc[1] will be true, false or nil
-- rc[3] will be the signal
local rc = {file:close()}
I hope this helps!
I can't use Lua 5.2, I use this helper function.
function execute_command(command)
local tmpfile = '/tmp/lua_execute_tmp_file'
local exit = os.execute(command .. ' > ' .. tmpfile .. ' 2> ' .. tmpfile .. '.err')
local stdout_file = io.open(tmpfile)
local stdout = stdout_file:read("*all")
local stderr_file = io.open(tmpfile .. '.err')
local stderr = stderr_file:read("*all")
stdout_file:close()
stderr_file:close()
return exit, stdout, stderr
end
This is how I do it.
local process = io.popen('command; echo $?') -- echo return code of last run command
local lastline
for line in process:lines() do
lastline = line
end
print(lastline) -- the return code is the last line of output
If the last line has fixed length you can read it directly using file:seek("end", -offset), offset should be the length of the last line in bytes.
This functionality is provided in C by pclose.
Upon successful return, pclose() shall return the termination status
of the command language interpreter.
The interpreter returns the termination status of its child.
But Lua doesn't do this right (io.close always returns true). I haven't dug into these threads but some people are complaining about this brain damage.
http://lua-users.org/lists/lua-l/2004-05/msg00005.html
http://lua-users.org/lists/lua-l/2011-02/msg00387.html
If you're running this code on Win32 or in a POSIX environment, you could try this Lua extension: http://code.google.com/p/lua-ex-api/
Alternatively, you could write a small shell script (assuming bash or similar is available) that:
executes the correct executable, capturing the exit code into a shell variable,
prints a newline and terminal character/string onto standard out
prints the shell variables value (the exit code) onto standard out
Then, capture all the output of io.popen and parse backward.
Full disclosure: I'm not a Lua developer.
yes , your are right that os.execute() has returns and it's very simple if you understand how to run your command with and with out lua
you also may want to know how many variables it returns , and it might take a while , but i think you can try
local a, b, c, d, e=os.execute(-what ever your command is-)
for my example a is an first returned argument , b is the second returned argument , and etc.. i think i answered your question right, based off of what you are asking.

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