Lua script via SSH with file io operations - ssh

Question

I am trying to run a script remotely (remote is server B). When I run the script locally on server A I get the expected results. When I run the script via SSH from server A to server B, I get the following error:
/usr/bin/ssh admin#server.domain.com "lua/rpi.init"
lua: lua/rpi.init:8: attempt to index upvalue 'logFile' (a nil value) stack traceback:
lua/rpi.init:8: in function 'logMsg'
lua/rpi.init:47: in main chunk
#!/usr/bin/env lua
local f = assert(io.popen("sudo netstat -a | grep ^tcp[^6] | grep LISTEN | grep [^0-9]22[0-9][0-9]", 'r'))
local ports22 = {}
local logFile
function logMsg(msg)
logFile = io.open("logs/pi.init.log", "a+")
logFile:write(os.date("%b %d %Y %X ") .. tostring(msg) .. "\n")
logFile:close()
end
function getPorts22()
logMsg("Getting available ports...")
while true do
line = f:read()
if line == nil then break end
port = string.sub(line, 40, 44)
table.insert(ports22, port)
end
f:close()
table.sort(ports22)
end
function getNextOpenPort22()
local openPort = 2222
if #ports22 == 0 then
logMsg("Returning port :" .. openPort)
return openPort
end
for i=1, #ports22 + 1 do
if tonumber(ports22[i]) == openPort then
openPort = openPort + 1
else
logMsg("Returning port: " .. openPort)
return openPort
end
end
end
function printPorts()
msg = table.concat(ports22, ", ")
logMsg("Found ports in use: " .. tostring(msg))
end
logMsg("Script called to run.")
getPorts22()
printPorts()
print(getNextOpenPort22())
Is it possible to run scripts via SSH (bash, lua or otherwise) and have them perform io operations on the remote machine?
Also, what is the best way to return values from the remote script to the local host? I return the value from my script by calling print() in order to have something for my local script to actual use.

Answer 1

You get this error because io.open calls returns a nil value and an error message. You may need to change this line logFile = io.open("logs/pi.init.log", "a+") to something like the following:
local logFile, err = io.open("logs/pi.init.log", "a+")
if not logFile then error(err, 2) end
This will print the error message when io.open call is not successful. In your case it may be caused by non-existent logs folder, insufficient permissions, or something else; the error message should point you in the right direction.