最近看师父写的项目（项目是erlang项目，rebar3管理）中用到了Erlcron模块，仔细看了下是做定时任务用的，使用时只需要在项目主配置文件sys.config中配置相关定时任务的参数，然后整个项目启动是就可以实现需要定时的功能。

下面我们来看一下

一个开源项目，rebar3管理，扔在github上。

这是师父在项目说明文档中写的使用例子

Job = {{weekly, thu, {2, am}},
   {io, fwrite, ["It's 2 Thursday morning~n"]}}.
erlcron:cron(Job).

这样就完成了一个定时任务，很简单，每周二的上午2点在控制台打印："It's 2 Thursday morning" 这句话.

其中的job可以是这样的定义：

{{once, {3, 30, pm}},
    {io, fwrite, ["Hello, world!~n"]}}

{{once, {12, 23, 32}},
    {io, fwrite, ["Hello, world!~n"]}}

{{once, 3600},
    {io, fwrite, ["Hello, world!~n"]}}

{{daily, {every, {23, sec}, {between, {3, pm}, {3, 30, pm}}}},
    {io, fwrite, ["Hello, world!~n"]}}

{{daily, {3, 30, pm}},
    fun() -> io:fwrite("It's three thirty~n") end}

{{daily, [{1, 10, am}, {1, 07, 30, am}]},
    {io, fwrite, ["Bing~n"]}}

{{weekly, thu, {2, am}},
    {io, fwrite, ["It's 2 Thursday morning~n"]}}

{{weekly, wed, {2, am}},
    {fun() -> io:fwrite("It's 2 Wednesday morning~n") end}

{{weekly, fri, {2, am}},
    {io, fwrite, ["It's 2 Friday morning~n"]}}

{{monthly, 1, {2, am}},
    {io, fwrite, ["First of the month!~n"]}}

{{monthly, 4, {2, am}},
    {io, fwrite, ["Fourth of the month!~n"]}}

我基本已经做过测试了，大家也可以自己写个定时任务测试下。

如何使用

当此项目作为依赖时

1. 需要在主应用的rebar.config配置文件中添加上

{deps, [
  ......
  {erlcron, {git, "git://github.com/simonxu72/erlcron", {branch, "master"}}}
  ......
]}

2. .app.src文件中配置依赖

{applications,
      [
        ......
        erlcron,
        ......
      ]}

3. sys.config中配置

[
    {erlcron, [
        {crontab, [
            {{once, {3, 30, pm}}, {io, fwrite, ["Hello, world!~n"]}},

            {{once, {12, 23, 32}}, {io, fwrite, ["Hello, world!~n"]}},

            {{daily, {every, {23, sec}, {between, {3, pm}, {3, 30, pm}}}},
             {io, fwrite, ["Hello, world!~n"]}}

        ]}
    ]}
].

4.主项目用rebar3 shell中启动就可以了