Reading log files as they're updated in Go

Question

I\'m trying to parse some log files as they\'re being written in Go but I\'m not sure how I would accomplish this without rereading the file again and again while checking f

Answer 1

A simple example:

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
    "time"
)

func tail(filename string, out io.Writer) {
    f, err := os.Open(filename)
    if err != nil {
        panic(err)
    }
    defer f.Close()
    r := bufio.NewReader(f)
    info, err := f.Stat()
    if err != nil {
        panic(err)
    }
    oldSize := info.Size()
    for {
        for line, prefix, err := r.ReadLine(); err != io.EOF; line, prefix, err = r.ReadLine() {
            if prefix {
                fmt.Fprint(out, string(line))
            } else {
                fmt.Fprintln(out, string(line))
            }
        }
        pos, err := f.Seek(0, io.SeekCurrent)
        if err != nil {
            panic(err)
        }
        for {
            time.Sleep(time.Second)
            newinfo, err := f.Stat()
            if err != nil {
                panic(err)
            }
            newSize := newinfo.Size()
            if newSize != oldSize {
                if newSize < oldSize {
                    f.Seek(0, 0)
                } else {
                    f.Seek(pos, io.SeekStart)
                }
                r = bufio.NewReader(f)
                oldSize = newSize
                break
            }
        }
    }
}

func main() {
    tail("x.txt", os.Stdout)
}