commands.lua

local lfs = require 'lfs'

local commands = {}
setmetatable(commands, {__call = function(self, name, func, description)
  if func then
    self[name] = func
    table.insert(self, {name=name, description=description})
  else
    for index, command in ipairs(self) do
      print(command.name .. ': ' .. command.description)
    end
  end
end})

return commands

program

#!/usr/bin/env lua

require 'tasks'

local commands = require 'commands'

local command = commands[...]
if not command then
  commands()
else
  command(...)
end

tasks.lua

require 'commands' ('run', function(name, task, ...)
  if task == 'list' then
    -- TODO: Check if directory exists
    -- TODO: Tasks in folders
    for file in lfs.dir('tasks') do
      if file:sub(1,1)~='.' then
        print((file:gsub('.lua$', '')))
      end
    end
  elseif task then
    local file = io.open('tasks/'..task..'.lua')
    if not file then error("Task "..task.." not found!") end
    local code = load(file:read('*a'))
    file:close()
    return code(...)
  else
    print(name..' [task]: Runs a given task')
  end
end, 'Runs a task')