golang如何覆盖输出console，实现进度条

内容简介：golang如何覆盖输出console，实现进度条

在研究K6源代码的时候，发现有一个进度条，觉得不错，就研究了一下怎么实现的，很简单，不说话，直接上代码

package main

import (
	"fmt"
	"os"
	"time"
)

func main() {
	for i := 0; i != 10; i = i + 1 {
		fmt.Fprintf(os.Stdout, "result is %d\r", i)
		time.Sleep(time.Second * 1)
	}
	fmt.Println("over")
}

最后输出的时候，添加\r，原理可以查看 https://stackoverflow.com/questions/15442292/golang-how-to-have-an-inplace-string-that-updates-at-stdout

stdout is a stream (io.Writer). You cannot modify what was already written to it. What can be changed is how is that stream represented in case it is printed to a terminal. Note that there’s no good reason to assume this scenario. An user can e.g. redirect stdout to a pipe or to a file at will. So the proper approach is to first check

if the stdout is going to a terminal

what is that terminal procedure to overwrite a line/a screen

Both of the above is out of this question scope, but let’s assume a terminal realy is our device. Then usually printing

fmt.Printf(“\rOn %d/10″, i)

will overwrite the previous line in the terminal. \r stands for a carriage return, implemented by many terminals as moving the cursor to the beginning of the current line, hence providing the “overwrite line” facility.

As an example of an “other” terminal with a differently supported ‘overwriting’, here is an example at the playground.

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