如何从每个10秒的Go文件中读取最后一行 [英] How to Read last lines from a big file with Go every 10 secs

问题描述

如何从大日志文件中读取最后两行而不将其完全加载到内存中？

how can I read the last two lines from a big log file without load it into memory completely?

我需要每10秒读一遍（在Win机器上）...我被卡住，试图读最后一行。

I need read it every 10 secs(On a Win machine)...and I'm stuck trying to read the last lines..

package main

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

const MYFILE = "logfile.log"

func main() {
    c := time.Tick(10 * time.Second)
    for now := range c {
        readFile(MYFILE)
    }
}

func readFile(fname string){
    file, err:=os.Open(fname)
    if err!=nil{
        panic(err)
    }
    buf:=make([]byte, 32)
    c, err:=file.ReadAt(32, ????)
    fmt.Printf("%s\n", c)


}

日志文件类似于：

07/25/2013 11:55:42.400, 0.559
07/25/2013 11:55:52.200, 0.477
07/25/2013 11:56:02.000, 0.463
07/25/2013 11:56:11.800, 0.454
07/25/2013 11:56:21.600, 0.424
07/25/2013 11:56:31.400, 0.382
07/25/2013 11:56:41.200, 0.353
07/25/2013 11:56:51.000, 0.384
07/25/2013 11:57:00.800, 0.393
07/25/2013 11:57:10.600, 0.456

谢谢！

Thanks!

推荐答案

您可以使用 file.Seek（）或 file.ReadAt（）几乎结束然后向前读取。你只能估计从哪里开始寻找，除非你知道2行= x字节。

You can use file.Seek() or file.ReadAt() to almost the end and then Reading forward. You can only estimate where to start seeking unless you can know that 2 lines = x bytes.

你可以通过使用 os.Stat（name）

以下是一个基于ReadAt，Stat和您的样本日志文件：

Here is an example based on ReadAt, Stat, and your sample log file:

package main

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

const MYFILE = "logfile.log"

func main() {
    c := time.Tick(10 * time.Second)
    for _ = range c {
        readFile(MYFILE)
    }
}

func readFile(fname string) {
    file, err := os.Open(fname)
    if err != nil {
        panic(err)
    }
    defer file.Close()

    buf := make([]byte, 62)
    stat, err := os.Stat(fname)
    start := stat.Size() - 62
    _, err = file.ReadAt(buf, start)
    if err == nil {
        fmt.Printf("%s\n", buf)
    }

}

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