I recently had occasion to want to start an IEx session from an Elixir script. Here’s how I was able to do it.

Method 1

Here’s a quick test script:

run.exs

:shell.start_interactive({IEx, :start, []})

System.no_halt(true)

System.no_halt(true) is needed so that the interactive session doesn’t die when the process running the script ends. You could also use the elixir command with the --no-halt option instead to achieve the same effect.

When we run this script with just elixir (instead of iex), we should still see an interactive IEx session start.

$ elixir run.exs
Erlang/OTP 26 [erts-14.1] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.6) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)>

Method 2

While researching, I found another way that works, but it’s even more obscure than the above method.

:user_drv.start_shell(%{initial_shell: {IEx, :start, []}})

I can’t find documentation for user_drv, I had to browse the code directly.