Use the flag.StringVar function to define command line parameters and get their values

Use the flag.StringVar function to define command line parameters and obtain their values

Command line parameters are a very common method of passing parameters, which can be conveniently specified in the terminal or command line when the program is running. some settings or configurations. In Go language, you can use the flag package to handle command line parameters. The flag package provides FlagSet, BoolVar, IntVar, StringVar and other functions to define and parse command line parameters. This article will focus on the flag.StringVar function and give a usage example.

flag.StringVar function is defined as follows:

func StringVar(p *string, name string, value string, usage string)

Among them, p is a string type Pointer, used to store the value of the command line parameter; name is the name of the command line parameter, usually starting with a dash, such as "-name"; value is the default value of the command line parameter; usage is the command line parameter description information.

The following is a simple sample code:

package main

import (
    "flag"
    "fmt"
)

func main() {
    // 定义一个名称为name的命令行参数，默认值为"default"，描述信息为"This is a name parameter"
    var name string
    flag.StringVar(&name, "name", "default", "This is a name parameter")

    // 解析命令行参数
    flag.Parse()

    // 输出参数值
    fmt.Println("Name:", name)
}

In the above code, we first use the flag.StringVar function to define a command line parameter named name, whose default value is "default ", the description information is "This is a name parameter". Then, use the flag.Parse() function to parse the command line arguments. Finally, the value of the parameter is output through the fmt.Println function.

When we run the program in the terminal or command line, we can specify the value of the command line parameter in the following way:

$ go run main.go -name Jack

The output result is as follows:

Name: Jack

Note, When running a program, there needs to be a space between the command line argument and the program name. The command line parameters defined by the program through the flag.StringVar function can be specified by adding the parameter name and corresponding value after the program name. In the above example, we used the "-name" parameter name to specify the value of the name parameter as "Jack".

To summarize, use the flag.StringVar function to easily define command line parameters and store their values ​​in specified variables. By parsing command line parameters, we can flexibly control the behavior of the program. Using the flag package to process command line parameters can improve the ease of use and scalability of the program.

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