How to use command line arguments in Go?

In the Go language, command line parameters are a very important way to pass input to the program and specify runtime behavior. Go provides a standard library flag to parse command line parameters. This article will introduce how to use command line parameters in Go.

What are command line parameters

Command line parameters are parameters passed to the program through the command line when the program is running, and are used to specify the behavior and input of the program when it is running. For example, the ls command in Linux can accept multiple command line parameters, such as -l to list detailed information, -a to show and hide Documents etc.

In Go, we can use os.Args to get all the command line arguments passed when the program is running. os.Args is a string slice, the first element is the name of the program, and the following elements are the command line parameters. For example:

package main

import (
    "fmt"
    "os"
)

func main() {
    fmt.Println(os.Args)
}

Run the program and pass in the two parameters hello and world:

$ go run main.go hello world

Output result:

[/tmp/go-build3065006307/b001/exe/main hello world]

As you can see, os.Args contains the name of the program and two command line parameters.

Use flag to parse command line parameters

Although we can obtain all command line parameters through os.Args, in actual development, we usually use more Flexible way to parse command line arguments. The Go standard library provides the flag package to parse command line parameters.

flagThe package provides three types of command line parameters: boolean, string and integer. These three parameters can be defined respectively through flag.Bool(), flag.String() and flag.Int().

The following is a simple example that defines a Boolean and a string command line parameter:

package main

import (
    "flag"
    "fmt"
)

func main() {
    // 定义命令行参数
    var (
        isVerbose bool
        name      string
    )
    flag.BoolVar(&isVerbose, "v", false, "verbose")
    flag.StringVar(&name, "name", "", "name of the user")

    // 解析命令行参数
    flag.Parse()

    // 输出命令行参数
    fmt.Printf("isVerbose=%v, name=%s
", isVerbose, name)
}

In the above example, we use flag.BoolVar() and flag.StringVar() define a Boolean and a string command line parameter respectively. These two functions have a total of four parameters:

1. The address of the variable used to store the command line parameter value;
2. The name of the command line parameter, which can be a single character or multiple characters Name;
3. Default value of command line parameters;
4. Description information of command line parameters.

After defining the command line parameters, you need to call the flag.Parse() function to parse the command line parameters.

Run the program and pass in the two command line parameters -v and -name="Alice":

$ go run main.go -v -name=Alice

Output results:

isVerbose=true, name=Alice

We can see that the flag package can easily parse command line parameters and store the values ​​into corresponding variables.

Customized command line parameters

In addition to using the three types of command line parameters provided by the flag package, we can also customize some types of command line parameters.

For example, we can define a drop-down box type command line parameter to let the user choose one from several options:

package main

import (
    "fmt"

    "github.com/AlecAivazis/survey/v2"
)

func main() {
    // 定义下拉框选项
    options := []string{"red", "blue", "green"}

    // 定义命令行参数
    var color string
    prompt := &survey.Select{
        Message: "Pick a color:",
        Options: options,
    }
    survey.AskOne(prompt, &color)

    // 输出命令行参数
    fmt.Printf("color=%s
", color)
}

In the above example, we use a third-party librarygithub.com/AlecAivazis/survey/v2Defines a drop-down box option. Then, use the survey.AskOne() function to display the drop-down box and let the user select.

Run the program:

$ go run main.go

Output result:

? Pick a color: 
  ▸ red
    blue
    green
  Answer: red
color=red

We can see that the user can select a color from several options and store the selected value in color variable.

Summary

This article introduces how to use command line parameters in Go. We can use os.Args to get all command line parameters, or we can use the flag package or a custom method to parse command line parameters. Using command line parameters can make our programs more flexible and easier to use, and is also a necessary skill for writing high-quality command line tools.

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