如何读取多个文本文件并通过重复间隔5秒通过电子邮件发送每个文件的最后一行

package main
import (
    "fmt"
    "os"
    "time"
    //"log"
    //"net/smtp"
)
const myfile1 = "data1.txt"
const myfile2 = "data2.txt"
const myfile3 = "data3.txt"
const myfile4 = "data4.txt"
func main() {
    c := time.Tick(5 * time.Second)
    for _ = range c {
        readLastLine(myfile1)
        readLastLine(myfile2)
        readLastLine(myfile3)
        readLastLine(myfile4)
    }
}
func readLastLine(fname string) {
    file, err := os.Open(fname)
    if err != nil {
        panic(err)
    }
    defer file.Close()
    fi, err := file.Stat()
    if err != nil {
        fmt.Println(err)
    }
    buf := make([]byte, 85)
    n, err := file.ReadAt(buf, fi.Size()-int64(len(buf)))
    if err != nil {
        fmt.Println(err)
    }
    buf = buf[:n]
    //fmt.Printf("%s", buf)

        mkey := fmt.Sprintf("%s %s
","From: Server
" + "To: customermail@yahoo.in
" + "Subject: Last Saved on
"+"
",buf)
        auth := smtp.PlainAuth("","","","",)
        err = smtp.SendMail("",auth, "",[]string{""}, []byte(mkey),)
        if err != nil {log.Printf("smtp error: %s", err)
        return}
        log.Print("Mail Sent.")

}

am trying to send 4 text files last line by email every 5 sec but result like this email sending 4 times. each file data separately :
last saved data from datafiles
sys1 last scan 2018-02-08 15:30:00
Mail Sent.
last saved data from datafiles
sys2 last scan 2018-02-08 15:35:00
Mail Sent.
last saved data from datafiles
sys3 last scan 2018-02-08 15:56:00
Mail Sent.
last saved data from datafiles
sys4 last scan 2018-02-08 15:30:00
Mail Sent.

but i want send email for 4 files last lines at once in one mail like this:
last saved data from datafiles
sys1 last scan 2018-02-08 15:30:00
sys2 last scan 2018-02-08 15:35:00
sys3 last scan 2018-02-08 15:56:00
sys4 last scan 2018-02-08 15:30:00
Mail Sent.

any suggestions plz.

You should separate the reading part from the sending logic, here you have a working example of what I mean:

package main

import (
    "bytes"
    "log"
    "os"
    "time"
)

var files = [2]string{
    "file1.txt",
    "file2.txt",
}

func main() {
    c := time.Tick(1 * time.Second)
    for range c {
        str, err := readFiles()
        if err != nil {
            panic(err)
        }

        err = sendEmail(str)
        if err != nil {
            panic(err)
        }
    }
}

func readFile(fname string) ([]byte, error) {
    file, err := os.Open(fname)
    if err != nil {
        return nil, err
    }
    defer file.Close()

    fi, err := file.Stat()
    if err != nil {
        return nil, err
    }

    buf := make([]byte, 34)
    n, err := file.ReadAt(buf, fi.Size()-int64(len(buf)))
    if err != nil {
        return nil, err
    }

    return buf[:n], nil
}

func readFiles() (string, error) {
    buff := new(bytes.Buffer)

    for _, fname := range files {
        l, err := readFile(fname)
        if err != nil {
            return "", err
        }
        buff.Write(l)
        // This prevents all logs to be in the same line.
        buff.WriteString("
")
    }

    return buff.String(), nil
}

func sendEmail(str string) error {
    log.Printf("
Mail Sent with:
---
%v
---

", str)
    return nil
}

One big caveat: Last line of all files should be the same length.