Getting return status AND program output

Question

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.

Answer 1

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.