Awesome

erlsh

Family of functions and ports involving interacting with the system shell, paths and external programs.

Reason why not os:cmd/1:

> Email = "hacker+/somepath&reboot#@example.com". % this is a valid email!
> os:cmd(["mkdir -p ", Email]).
% path clobbering and a reboot may happen here!

Examples with erlsh:run/1,2,3,4, erlsh:oneliner/1,2, erlsh_path:escape/1:

> erlsh:oneliner("uname -v"). % oneliner/1,2 funs do not include newlines
{done,0,
      <<"Darwin Kernel Version 12.4.0: Wed May  1 17:57:12 PDT 2013; root:xnu-2050.24.15~1/RELEASE_X86_64">>}

> erlsh:oneliner("git describe --always").
{done,128,<<"fatal: Not a valid object name HEAD">>}

> erlsh:oneliner("git describe --always", "/tank/proger/vxz/otp").
{done,0,<<"OTP_R16B01">>}

> erlsh:run(["git", "clone", "https://github.com/proger/darwinkit.git"], binary, "/tmp").
{done,0,<<"Cloning into 'darwinkit'...\n">>}

> UserUrl = "https://github.com/proger/darwinkit.git".
"https://github.com/proger/darwinkit.git"
> erlsh:run(["git", "clone", UserUrl], binary, "/tmp").
{done,128,
      <<"fatal: destination path 'darwinkit' already exists and is not an empty directory.\n">>}

> Path = erlsh_path:escape("email+=/subdir@example.com").
"email+=%2Fsubdir@example.com"

> erlsh:oneliner(["touch", filename:join("/tmp/", Path)]).
{done,0,<<>>}

> erlsh:run(["ifconfig"], "/tmp/output.log", "/tank/proger/vxz/otp").
{done,0,"/tmp/output.log"}

% cat /tmp/output.log
>>> {{2013,8,28},{8,39,14}} /sbin/ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	options=3<RXCSUM,TXCSUM>
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
	inet 127.0.0.1 netmask 0xff000000
	inet6 ::1 prefixlen 128
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	ether 7c:d1:c3:e9:24:65
	inet6 fe80::7ed1:c3ff:fee9:2465%en0 prefixlen 64 scopeid 0x4
	inet 192.168.63.163 netmask 0xfffffc00 broadcast 192.168.63.255
	media: autoselect
	status: active
p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304
	ether 0e:d1:c3:e9:24:65
	media: autoselect
	status: inactive
>>> {{2013,8,28},{8,39,14}} exit status: 0

fdlink port

Consider a case of spawning a port that does not actually read its standard input (e.g. socat that bridges AF_UNIX with AF_INET):

# pstree -A -a $(pgrep make)
make run
  `-sh -c...
      `-beam.smp -- -root /usr/lib/erlang -progname erl -- -home /root -- -pa ebin -config run/sys.config -eval[ok = application:
          |-socat tcp-listen:32133,reuseaddr,bind=127.0.0.1 unix-connect:/var/run/docker.sock
          `-16*[{beam.smp}]

If you terminate the node, beam will close the port but the process will still remain alive (thus, it will leak).

To mitigate this issue, you can use fdlink that will track stdin availability for you:

# pstree -A -a $(pgrep make)
make run
  `-sh -c...
      `-beam.smp -- -root /usr/lib/erlang -progname erl -- -home /root -- -pa ebin -config run/sys.config -eval[ok = application:
          |-fdlink /usr/bin/socat tcp-listen:32133,reuseaddr,bind=127.0.0.1 unix-connect:/var/run/docker.sock
          |   `-socat tcp-listen:32133,reuseaddr,bind=127.0.0.1 unix-connect:/var/run/docker.sock
          `-16*[{beam.smp}]

Using fdlink is easy:

> Fdlink = erlsh:fdlink_executable().               % make sure your app dir is setup correctly
> Fdlink = filename:join("./priv", "fdlink").       % in case you're running directly from erlsh root

> erlang:open_port({spawn_executable, Fdlink}, [stream, exit_status, {args, ["/usr/bin/socat"|RestOfArgs]}).

fdlink will also close the standard input of its child process.