CODEWITHSUNDEEP
processerlangoperating-system
regularfry
regularfry

Reputation: 3268

OS process management from Erlang

What's the best way to do OS process management from Erlang? I need to be able to spawn child OS processes, write to the child's stdin, read from both stdout and stderr, send kill signals, and get notified of exit codes. I don't see that this is possible with what's in erts.

I know about erlexec, but I don't know if it's stable or if anyone is actually using it in anger. Are there any other options, or is that the best?

Upvotes: 2

Views: 2432

Answers (2)

hdima
hdima

Reputation: 3637

In Erlang standard way to manage OS processes is ports.

Exit status of spawned OS process will be sent as a message if option exit_status added to open_port:

1> P = open_port({spawn, "/bin/ls unknown_file_name"}, [exit_status]).
#Port<0.486>
/bin/ls: cannot access unknown_file_name: No such file or directory
2> flush().
Shell got {#Port<0.486>,{exit_status,2}}
ok

Data can be written to stdin of spawned OS process by sending a message to port or by port_command function and stdout content will be sent as a message. (Note also {line, L} and {packet, N} options of open_port):

1> P = open_port({spawn, "/bin/cat"}, [stream, binary]).
#Port<0.486>
2> true = port_command(P, <<"data">>).
true
3> flush().
Shell got {#Port<0.486>,{data,<<"data">>}}
ok
4> true = port_close(P).
true

Stderr also can be redirected to stdout:

1> P = open_port({spawn, "/bin/ls unknown_file_name"}, [stderr_to_stdout, binary]).
#Port<0.486>
2> flush().
Shell got {#Port<0.486>,
    {data,<<"/bin/ls: cannot access unknown_file_name: No such file or directory\n">>}}
ok

However you can't send kill signals with ports but if you close port by sending a message to port or by calling port_close external process can exit by SIGPIPE signal.

Upvotes: 2

user177800
user177800

Reputation:

Port programs are the best way to do this. Port programs are safe and won't harm the Erlang VM, and if they crash or mis-behave can be killed and restarted like any other Erlang process.

Port Drivers are different and if they mis-behave can bring down the entire Erlang VM.

Upvotes: 3

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