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https://github.com/proger/erlsh

Erlang shell tools
https://github.com/proger/erlsh

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Erlang shell tools

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## erlsh



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



Reason why not `os:cmd/1`:



```erlang

> 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`:



```erlang

> 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+=/[email protected]").

"email+=%[email protected]"



> 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 mtu 16384

	options=3

	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1

	inet 127.0.0.1 netmask 0xff000000

	inet6 ::1 prefixlen 128

gif0: flags=8010 mtu 1280

stf0: flags=0<> mtu 1280

en0: flags=8863 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 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`):



``` shell

# 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:



``` shell

# 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:



```erlang

> 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.