golang flag usage

The flag package in golang provides a simple way to handle command line parameters. By using the flag package, we can easily pass and process various instructions when running Go programs. This article will introduce the usage of flag package and its implementation.

Golang flag package overview

flag package provides the function of processing command line parameters. The purpose of this package is to provide a simple and elegant way for the Go language so that you can easily support command line parameters in your Go applications. By using this package, you will not have to hand-write complex parsing logic to process command line parameters, you only need to customize the flag according to a fixed format.

Introduction to commonly used functions in the flag package

There are four commonly used functions in the flag package, which are:

1. flag.String(): This function defines a Flag of string type, and its name, default value, and usage prompt information are used as parameters. For example, we can define a flag of string type named "name" in the following way:

name := flag.String("name", "default", "Input String")

The first parameter in the above code is the name of the flag, and the second parameter is Default value, the third parameter is usage information. We can also use "flag.Parse()" for usage parsing.

2. flag.Bool(): This function defines a Boolean flag and takes its name, default value, and usage prompt information as parameters. For example, we can define a Boolean flag named "is_config" in the following way:

isConfig := flag.Bool("is_config", false, "Is Config Set")

The first parameter in the above code is the name of the flag, and the second parameter is the default value, the third parameter is usage information. We can also parse through "flag.Parse()".

3. flag.Int(): This function defines an integer type flag and takes its name, default value, and usage prompt information as parameters. For example, we can define a flag of integer type named "count" in the following way:

count := flag.Int("count", 1, "input count")

The first parameter in the above code is the name of the flag, and the second parameter is Default value, the third parameter is usage information. We can also parse through "flag.Parse()".

4. flag.Parse(): This function is used to read all parameters saved in flag, parse the command line parameters into corresponding types and values, and assign them to variables corresponding to flag. For example, we can parse the above flag through the following code:

flag.Parse()

flag package usage example

We assume that we now want to use the flag package to implement the following command line parameters:

./example -c config.yml -t 20 -v

The specific code implementation is as follows:

package main

import (
    "flag"
    "fmt"
)

func main() {
    config := flag.String("c", "default.yml", "Input config file name")
    timeout := flag.Int("t", 10, "Maximum waiting time (seconds)")
    verbose := flag.Bool("v", false, "Print verbose log")
    flag.Parse()

    fmt.Println("config file:", *config)
    fmt.Println("timeout:", *timeout)
    fmt.Println("verbose log:", *verbose)
}

The above code uses three flags to represent "c", "t" and "v", which respectively represent the config file name, the maximum waiting time and whether to output detailed information. log information. We can parse the command line parameters by calling "flag.Parse()". When executed, the output result is as follows:

config file: config.yml
timeout: 20
verbose log: true

We can see that the flag package has successfully parsed the parameters we specified on the command line. Parameters are assigned to corresponding variables. It should be noted that we can map a flag to multiple variables at the same time. These variables must be of the same type. An example is as follows:

package main

import (
    "flag"
    "fmt"
)

func main() {
  var name string
  flag.StringVar(&name, "name", "default", "input name")
  flag.Parse()
  fmt.Println(name)
}

Running the program and passing the command line parameters will output the passed parameters, otherwise the default value "default" will be output.

Advantages and disadvantages of golang flag package

Advantages:

1. When processing command line parameters, the flag package is easy to use and only requires simple code to complete the analysis. operate.
2. When a command line program is provided, users can quickly master how to use the program, and because the program interface provided by the standard library is used, the user experience is better.
3. Using the flag package to develop programs can make the code more readable and cleaner.

Disadvantages:

1. When using the flag package for command line parameter processing, you should try to use export flags (that is, the name of the flag should be capitalized), Otherwise these flags will not be accessible from the outside.
2. The flag package does not support complex data structures, such as maps and structures.

Summary

This article introduces the usage of the flag package in golang in detail by introducing the overview, common functions, implementation methods, advantages and disadvantages of the flag package. By using the flag package, we can quickly and easily parse and manage command line parameters, making our code more concise and easier to maintain. In practical applications, we need to choose whether to use this package based on the actual situation.

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