How do you detect what OS you're running in Elixir?

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There might be some situations where you need to know which operating system your code is running on, especially if you're making your own mix tasks that need to work on different platforms. A common use case could be determining the location of a file to read it as config or maybe finding the correct application to launch. This can be achieved with the operating system module in Erlang.

It's as easy as :os.type(), running it on my M1 Mac I see the following output in IEx.

iex(1)> :os.type()
{:unix, :darwin}

From this I can see that my operating system is in the Unix family with the Osname, Darwin. On a Windows machine, you'd see :win32 as the Osfamily.

When would this be used?

Here's an example of how this is used in the ExDoc codebase.

defp browser_open(path) do
  {cmd, args, options} =
    case :os.type() do
      {:win32, _} ->
        dirname = Path.dirname(path)
        basename = Path.basename(path)
        {"cmd", ["/c", "start", basename], [cd: dirname]}

      {:unix, :darwin} ->
        {"open", [path], []}

      {:unix, _} ->
        {"xdg-open", [path], []}

  System.cmd(cmd, args, options)

See this snippet in the ExDoc codebase

This is an easy way to tailor this script to open the browser so it works on more platforms.


Seth Corker

A Fullstack Software Engineer working with React and Django. My main focus is JavaScript specialising in frontend UI with React. I like to explore different frameworks and technologies in my spare time. Learning languages (programming and real life) is a blast.