Master the command line tools and scripting of Go language

As a rapidly developing programming language, one of the characteristics of the Go language is its support and dependence on command line tools. Command line tools are a type of program that deal directly with users. They can implement rich functions through simple command line instructions. Go language provides a simple and powerful API to help developers easily build efficient and easy-to-maintain command line tools and script programs. This article will introduce how to use Go language to write streamlined and efficient command line tools and scripts.

1. Command line parameter parsing

The most important part of the command line tool is the command line parameter parsing. The flag package is provided in the Go language to handle the parsing of command line parameters. An example is as follows:

package main

import (
    "flag"
    "fmt"
)

var nFlag = flag.Bool("n", false, "print line numbers")
var sFlag = flag.String("s", " ", "separator")

func main() {
    flag.Parse()
    fmt.Println("nFlag:", *nFlag)
    fmt.Println("sFlag:", *sFlag)
    args := flag.Args()
    for i, arg := range args {
        fmt.Printf("arg[%d]: %s
", i, arg)
    }
}

In the above code, we define two command line flag variables, nFlag and sFlag. The first parameter is the flag name, the second parameter is the default value, and the third parameter is the explanation. In the main function, first run the flag.Parse() function, and obtain the value of the flag through nFlag and sFlag, and obtain all non-flag parameters through flag.Args().

2. Building command line tools

There are many ways to build command line tools in the Go language, among which the cobra package is more commonly used. Cobra is a powerful library that can help us quickly build efficient and useful command line tools.

Let’s illustrate with a simple example:

package main

import (
    "fmt"

    "github.com/spf13/cobra"
)

func main() {
    var rootCmd = &cobra.Command{
        Use:   "app",
        Short: "Brief description of your application",
        Long:  "A longer description that spans multiple lines and likely contains examples and usage of using your application.",
        Run: func(cmd *cobra.Command, args []string) {
            fmt.Println("Hello, World!")
        },
    }

    if err := rootCmd.Execute(); err != nil {
        fmt.Println(err)
    }
}

In the above code, we first define a rootCmd variable, the variable type is &cobra.Command, and then set Use, Short, Long and Run and other attributes. Among them, the Use attribute specifies the command name, the Short attribute is a short description of the command line tool, the Long attribute is a detailed description of the command line tool, and the Run attribute is the specific operation performed by the command line.

3. Script writing

In addition to command line tools, we can also write simple script programs through Go language for specific task processing. Compared with command line tools, script programs can run more freely. Generally, there is no need to generate a separate program file. You only need to save the code as a .go file. The following is a simple script example for counting the number of occurrences of each word in a piece of text:

package main

import (
    "bufio"
    "fmt"
    "os"
    "strings"
)

func main() {
    freq := make(map[string]int)

    scanner := bufio.NewScanner(os.Stdin)
    scanner.Split(bufio.ScanWords)

    for scanner.Scan() {
        word := strings.ToLower(scanner.Text())
        freq[word]++
    }

    if err := scanner.Err(); err != nil {
        fmt.Fprintln(os.Stderr, "reading standard input:", err)
    }

    for w, c := range freq {
        fmt.Printf("%s:    %d
", w, c)
    }
}

In the above code, we first created an empty map variable freq to count the number of occurrences of each word. . Then a scanner is created through bufio.NewScanner(os.Stdin) for scanning the standard input stream (ie keyboard input) line by line. Use freq[word] to increment the number of occurrences of a word, and print out the number of occurrences of each word at the end.

Summary

This article introduces the implementation of command line tools and scripting in Go language. Through the flag package and cobra package, you can easily parse command line parameters and build an efficient and useful command line. tool. Through the above examples, we can find that the Go language makes command line tools and scripting extremely easy with its simple and powerful API. For developers who need to frequently use command line tools, mastering the command line tools and scripting methods of the Go language will help them get twice the result with half the effort.

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