Get back the output of os.execute in Lua

Question

When I do an "os.execute" in Lua, a console quickly pops up, executes the command, then closes down. But is there some way of getting back the console output only using the standard Lua libraries?

Answer 1

I think you want this http://pgl.yoyo.org/luai/i/io.popen io.popen. But it's not always compiled in.

Answer 2

If you have io.popen, then this is what I use:

function os.capture(cmd, raw)
  local f = assert(io.popen(cmd, 'r'))
  local s = assert(f:read('*a'))
  f:close()
  if raw then return s end
  s = string.gsub(s, '^%s+', '')
  s = string.gsub(s, '%s+$', '')
  s = string.gsub(s, '[\n\r]+', ' ')
  return s
end

If you don't have io.popen, then presumably popen(3) is not available on your system, and you're in deep yoghurt. But all unix/mac/windows Lua ports will have io.popen.

Answer 3

I don't know about Lua specifically but you can generally run a command as:

comd >comd.txt 2>&1

to capture the output and error to the file comd.txt, then use the languages file I/O functions to read it in.

That's how I'd do it if the language itself didn't provide for capturing stanard output and error.