ExCmd is an Elixir library to run and communicate with external programs with back-pressure mechanism. It makes use os backed stdio buffer for this.
Communication with external program using
Port is not demand driven. So
it is easy to run into memory issues when the size of the data we are
writing or reading from the external program is large. ExCmd tries to
solve this problem by making better use of os backed stdio buffers
and providing demand-driven interface to write and read from external
program. It can be used to stream data through an external
program. For example, streaming a video through ffmpeg to serve a
web request.
Getting audio out of a video stream is as simple as
ExCmd.stream!(~w(ffmpeg -i pipe:0 -f mp3 pipe:1), input: File.stream!("music_video.mkv", [], 65336))
|> Stream.into(File.stream!("music.mp3"))
|> Stream.run()- Unlike beam ports, ExCmd puts back pressure on the external program
- Stream abstraction
- No separate shim installation required
- Ships pre-built binaries for MacOS, Windows, Linux
- Proper program termination. No more zombie process
- Ability to close stdin and wait for output (with ports one can not selectively close stdin)
ExCmd.stream!(~w(curl ifconfig.co))
|> Enum.into("")Binary as input
ExCmd.stream!(~w(cat), input: "Hello World")
|> Enum.into("")
# => "Hello World"ExCmd.stream!(~w(base64), input: <<1, 2, 3, 4, 5>>)
|> Enum.into("")
# => "AQIDBAU=\n"List of binary as input
ExCmd.stream!(~w(cat), input: ["Hello ", "World"])
|> Enum.into("")
# => "Hello World"iodata as input
ExCmd.stream!(~w(base64), input: [<<1, 2,>>, [3], [<<4, 5>>]])
|> Enum.into("")
# => "AQIDBAU=\n"If you want pipes and globs, you can spawn shell process and pass your pipeline as argument
cmd = "echo 'foo bar' | base64"
ExCmd.stream!(["sh", "-c", cmd])
|> Enum.into("")
# => "Zm9vIGJhcgo=\n"Read stream documentation for information about parameters.
Check out Exile which is an alternative solution based on NIF without middleware overhead
def deps do
[
{:ex_cmd, "~> x.x.x"}
]
end