Synchronous command execution in Lua

Question

I'd like to get data from an output when a system command is finished in Lua,
even while that command may take a few minutes to an end.
Obviously popen executes the command separately from the lua process.
Does anyone has an idea to solve this?

r = popen('command','r')
for line in r:lines() do
  print(line)
end

Answer 1

If the command uses buffered output (the default) then there's nothing you can do. Some commands (e.g., cat -u) have an option to use unbuffered output, but they're rare.