Declare the external command-line tools your application needs.

Plenty of Elixir apps shell out — to ffmpeg, convert, pdftoppm, pandoc, pg_dump. When one of those is missing the failure usually surfaces as a System.cmd/3 crash deep inside a background job, at the moment a user was expecting something to work.

This declares them up front, checks whether they are actually installed, and turns "it broke" into "install ffmpeg".

Declaring

defmodule MyApp.Deps do
  use CliDeps

  tool :ffmpeg,
    version: ">= 6.0.0",
    args: ["-version"],
    install: [
      macos: "brew install ffmpeg",
      linux: "apt install ffmpeg",
      default: "https://ffmpeg.org/download.html"
    ]

  tool :convert,
    label: "ImageMagick",
    version: ">= 7.0.0",
    install: [macos: "brew install imagemagick"]
end

Using

MyApp.Deps.check(:ffmpeg)
#=> {:ok, "7.1.1"}

MyApp.Deps.check(:convert)
#=> {:error, :not_found}

MyApp.Deps.available?(:ffmpeg)
#=> true

MyApp.Deps.explain(:convert)
#=> "ImageMagick was not found on PATH. Install it with: brew install imagemagick"

MyApp.Deps.report()
#=> [%{name: :ffmpeg, ok?: true, result: {:ok, "7.1.1"}, message: "..."}, ...]

report/0 is meant for a status page, a health endpoint, or the mix cli_deps.check task, which exits non-zero when anything is missing and so works as a CI or container-build gate.

Caching

Results are cached for an hour, because whether ffmpeg is installed does not change between requests — but it does change between deploys, so entries expire rather than persisting for the life of the node. Override with use CliDeps, ttl: :timer.minutes(5), or ttl: :infinity to check once per boot. invalidate/0,1 clears entries after installing something.

What this does not do

It does not run your tools, and it does not install anything. Running a subprocess well — streaming, timeouts, not orphaning it when the VM dies — is its own problem, and MuonTrap, Rambo, and System.cmd/3 already solve it. This answers only "is it there, and is it new enough".