Quickest way to call a function with command line arguments?

Questions / Help
1

I have a module with a function that applies a transformation on a string e.g. (this is for an Advent of Code problem, where I need to do this often)

defmodule M do
  def f(some_string) do
    # apply transformation on some_string
  end
end

I need to run M.f with a string passed from the command line. What is the quickest way to do this?

Please note that

  • This script will never be deployed to production
  • I just need an easy way to call an Elixir function with some arguments from the command line

Option 1: escript

This is clean but requires some extra code (which Iā€™d like to avoid if possible):

# mix.exs

defmodule M.Mixfile do
  def project do
    [
      ...,
      escript: escript(),
      default_task: "escript.build",
    ]
  end
 
  defp escript do
    [main_module: M.CLI]
  end
end

# in m.ex

defmodule M do
  ...
end

defmodule M.CLI do
  def main(args) do
    string = hd(args)
    IO.puts M.f(string)
  end
end

Option 2: mix run

This requires a little extra typing ā€” I would like to move the IO.puts inside the code if possible. This approach avoids having to update mix.exs which is nice.

From the shell

%  mix run -e 'IO.puts M.f "some_user_string"'

Is there an easier / quicker way to do this?

2 Likes
2

Option 3: an *.exs

Just write an *.exs.

# foo.exs
defmodule M do
  def f(arg), do: IO.inspect arg
end

System.argv()
|> Enum.inspect(&M.f/1)

Then run it with elixir foo.exs print me

11 Likes
3

Perfect :slight_smile: Just what I needed. Thank you!

4

Just for reference, I ended up using a slightly tweaked syntax:

# foo.exs
defmodule M do
  def f(arg) do
    "transformed #{arg}"
  end
end

[arg1, arg2] = System.argv
IO.puts M.f(arg1)

This allows pattern matching for the command line args, and it fails when an incorrect number of args is specified.

4 Likes