Is it possible to timeout a System.cmd(...)?

[Vince Marco]

I am building a DevOps tool that needs to execute OS commands.  Is it possible to timeout a System.cmd(...)?

Actually this is a redesign from a Java/Groovy tool, and one of the main draws is to move command execution to actors.  Is there a way to manage the timeout in the actor?  My main concern is a "hung" command that doesn't return.  It seems the actor would also be prevented from receiving msgs while stuck on the hung System.cmd(...).

Thanks in advance,

Vince

[Alexei Sholik]

Use ports instead. When you open a port, you get a pid. Your process will then receive output from the command as messages from that pid. So you could do something like the following:

port = Port.open(...)

{:os_pid, ospid} = Port.info(port, :os_pid)

# note that if the program terminated before the call to Port.info, you'll get :undefined back

receive do

  {^port, {:data, data}} -> ...

  after <timeout> ->

    System.cmd "kill #{ospid}"

end

If your program constantly produces output, you could fire a timer

{:ok, _} = :timer.send_after(1000, {:kill_this_process, ospid})

receive do
  {^port, {:data, data}} -> ...

  {:kill_this_process, ospid} ->

    System.cmd "kill #{ospid}"
end

---

To create a port that is somewhat equivalent to System.cmd, use this:

sh = :os.find_executable('sh')
command = "something something"
port = Port.open({:spawn_executable, sh}, [:stream, :binary, {:args, ["-c", command]}, :use_stdio, :stderr_to_stdout, :exit_status])

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Best regards
Alexei Sholik