You might be able to do that with Port.open and then receive messages coming from it and send them to the liveview process.

port.exs

defmodule Command do
  def exec(cmd, args) do
    path = System.find_executable(cmd)
    port = Port.open({:spawn_executable, path}, [:binary, :exit_status, args: args, line: 1000])
    loop(port)
  end

  defp loop(port) do
    receive do
      {^port, {:data, data}} ->
        IO.inspect(data: data)
        loop(port)

      {^port, {:exit_status, exit_status}} ->
        IO.inspect(exit_status: exit_status)
    end
  end
end

Command.exec("cat", ["port.exs"])

> elixir port.exs
[data: {:eol, "defmodule Command do"}]
[data: {:eol, "  def exec(cmd, args) do"}]
[data: {:eol, "    path = System.find_executable(cmd)"}]
[
  data: {:eol,
   "    port = Port.open({:spawn_executable, path}, [:binary, :exit_status, args: args, line: 1000])"}
]
[data: {:eol, "    loop(port)"}]
[data: {:eol, "  end"}]
[data: {:eol, ""}]
[data: {:eol, "  defp loop(port) do"}]
[data: {:eol, "    receive do"}]
[data: {:eol, "      {^port, {:data, data}} ->"}]
[data: {:eol, "        IO.inspect(data: data)"}]
[data: {:eol, "        loop(port)"}]
[data: {:eol, ""}]
[data: {:eol, "      {^port, {:exit_status, exit_status}} ->"}]
[data: {:eol, "        IO.inspect(exit_status: exit_status)"}]
[data: {:eol, "    end"}]
[data: {:eol, "  end"}]
[data: {:eol, "end"}]
[data: {:eol, ""}]
[data: {:eol, "Command.exec(\"cat\", [\"port.exs\"])"}]
[exit_status: 0]

There’re some on https://saleyn.github.io/erlexec/

I’d recommend looking into exexec | Hex (which wraps the erlexec Erlang library) especially if the command you want to run are not written to conform to the behavior that Port expects.