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package main
import (
"fmt"
"os"
"strconv"
"github.com/01-edu/z01"
)
func numberOfBytes(args []string) (int, []string) {
n := len(args)
nbytes := 0
var files []string
for i, v := range args {
var err error
_, err = strconv.Atoi(v)
if v == "-c" {
if i >= n-1 {
fmt.Printf("tail: option requires an argument -- 'c'\nTry 'tail --help' for more information.")
os.Exit(1)
}
arg := args[i+1]
nbytes, err = strconv.Atoi(arg)
if err != nil {
fmt.Printf("tail: invalid number of bytes: `%s`\n", arg)
os.Exit(1)
}
continue
}
if err != nil {
files = append(files, v)
}
}
return nbytes, files
}
func fileSize(fi *os.File) int64 {
fil, err := fi.Stat()
if err != nil {
fmt.Println(err.Error())
return 0
}
return fil.Size()
}
func main() {
n := len(os.Args)
if n < 4 {
fmt.Println("Not enough arguments")
os.Exit(1)
}
nbytes, files := numberOfBytes(os.Args[1:])
printName := len(files) > 1
//open files for reading only
for j, f := range files {
fi, err := os.Open(f)
if err != nil {
fmt.Printf("tail: cannot open '%s' for reading: No such file or directory\n", f)
os.Exit(1)
}
if printName {
fmt.Printf("==> %s <==\n", f)
}
read := make([]byte, int(nbytes))
_, er := fi.ReadAt(read, fileSize(fi)-int64(nbytes))
if er != nil {
fmt.Println(er.Error())
}
for _, c := range read {
z01.PrintRune(rune(c))
}
if j < len(files)-1 {
z01.PrintRune('\n')
}
fi.Close()
}
}