scripty.lua

local function open_floating_terminal(command)
  local uis = vim.api.nvim_list_uis()
  local opts = {
    relative = 'editor';
    width = math.floor(uis[1].width * 50 / 100);
    height = math.floor(uis[1].height * 50 / 100);
    anchor = 'NW';
    style = 'minimal';
    focusable = false;
  }
  opts.col = math.floor((uis[1].width - opts.width) / 2)
  opts.row = math.floor((uis[1].height - opts.height) / 2)
  local bufnr = vim.api.nvim_create_buf(false, true)
  local winnr = vim.api.nvim_open_win(bufnr, true, opts)

  vim.api.nvim_call_function("termopen", {command})
  return bufnr, winnr
end

local function run_script(lines, start, starting_winnr)
  starting_winnr = starting_winnr or vim.api.nvim_get_current_win()
  for i = (start or 1), #lines do
    local line = lines[i]
    if line:match("^:!") then
      local command = line:sub(3)
      local bufnr, winnr = open_floating_terminal(command)
      vim.api.nvim_command("startinsert!")
      vim.api.nvim_buf_attach(bufnr, false, {
        on_detach = vim.schedule_wrap(function()
          run_script(lines, i+1, starting_winnr)
        end)
      })
      break
    else
      vim.api.nvim_set_current_win(starting_winnr)
      vim.api.nvim_win_set_cursor(starting_winnr, {i, 0})
      vim.api.nvim_command(line)
    end
  end
end

function run_file()
  run_script(vim.api.nvim_buf_get_lines(0, 0, -1, false))
end

Use by doing lua run_file() or for example creating a command which does that: command! Shell lua run_file().