概述

urfavecli 的使用文档中关于从外部资源文件读取参数的说明比较模糊，从github的issues中也看到用户提到这个问题并提了PR，但现在这个版本依然没有更新，其实只是需要更新一下文档。

问题

There is a separate package altsrc that adds support for getting flag values from other file input sources.

Currently supported input source formats:

YAML JSON TOML

In order to get values for a flag from an alternate input source the following code would be added to wrap an existing cli.Flag like below:

altsrc.NewIntFlag(&cli.IntFlag{Name: “test”})

Initialization must also occur for these flags. Below is an example initializing getting data from a yaml file below.

command.Before = altsrc.InitInputSourceWithContext(command.Flags, NewYamlSourceFromFlagFunc(“load”))

The code above will use the “load” string as a flag name to get the file name of a yaml file from the cli.Context. It will then use that file name to initialize the yaml input source for any flags that are defined on that command. As a note the “load” flag used would also have to be defined on the command flags in order for this code snippet to work.

Currently only YAML, JSON, and TOML files are supported but developers can add support for other input sources by implementing the altsrc.InputSourceContext for their given sources.

Here is a more complete sample of a command using YAML support:

package main

import (
  "fmt"
  "os"

  "github.com/urfave/cli/v2"
  "github.com/urfave/cli/v2/altsrc"
)

func main() {
  flags := []cli.Flag{
    altsrc.NewIntFlag(&cli.IntFlag{Name: "test"}),
    &cli.StringFlag{Name: "load"},
  }

  app := &cli.App{
    Action: func(c *cli.Context) error {
      fmt.Println("--test value.*default: 0")
      return nil
    },
    Before: altsrc.InitInputSourceWithContext(flags, altsrc.NewYamlSourceFromFlagFunc("load")),
    Flags: flags,
  }

  app.Run(os.Args)
}

这段代码的意思实际做了3件事实现读取配置文件。

  1. 创建一个load的字符串参数，用于传递文件名的参数
  2. 创建一个test的整形参数，用于保存从配置文件中读取的内容
  3. 调用altsrc的读取功能装载

由于原版文档并没有提供运行的方式，以及参数的输出，开始读完不知道发生了什么 简而言之就是使用一个名字是load的参数，传入文件名，并在文件中读取名为test的参数

解决方法

加入运行的指令

go run main.go --load ./app.yml

从名为app.yml的文件中读取参数test

app.yml:

test: 123

在运行的Action中加入参数test的输出

package main

import (
  "fmt"
  "os"

  "github.com/urfave/cli/v2"
  "github.com/urfave/cli/v2/altsrc"
)

func main() {
  flags := []cli.Flag{
    altsrc.NewIntFlag(&cli.IntFlag{Name: "test"}),
    &cli.StringFlag{Name: "load"},
  }

  app := &cli.App{
    Action: func(c *cli.Context) error {
      fmt.Println("test: ", c.Int("test"))
      return nil
    },
    Before: altsrc.InitInputSourceWithContext(flags, altsrc.NewYamlSourceFromFlagFunc("load")),
    Flags: flags,
  }

  app.Run(os.Args)
}

原来的：

fmt.Println("–test value.*default: 0")

替换为：

fmt.Println(“test: “, c.Int(“test”))

配置文件取值覆盖

因为读取配置文件是发生在参数载入之前，所以可以通过在命令行上赋值覆盖在配置文件中的取值

go run main.go --test 1 --load ./app.yml
test:  1

参考资料