byteReplacer

package main

import (
	"bufio"
	"os"
	"io"
	"log"
	"fmt"
	"flag"
	"os/signal"
	"syscall"
)

var nthByte int
var replacement int
var buffLines int

func main() {
	initFlags()
	interrupt()
	r := bufio.NewReaderSize(os.Stdin, buffLines*nthByte)
	buf := make([]byte, 0, nthByte)
	replacementByte := byte(replacement)
	for {
		n, err := r.Read(buf[:cap(buf)])
		buf = buf[:n]
		if n < nthByte {
			m, err2 := r.Read(buf[n:cap(buf)])
			err = err2
			buf = buf[:m+n]
		}
		if n == 0 {
			if err == nil {
				continue
			}
			if err == io.EOF {
				break
			}
			log.Fatal(err)
		}
		buf[nthByte-1] = replacementByte
		fmt.Print(string(buf))
	}
}
func interrupt() {
	c := make(chan os.Signal, 2)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	go func() {
		<-c
		os.Exit(1)
	}()
}
func initFlags() {
	flag.IntVar(&nthByte, "n", 136, "Each nth byte will be replaced in stream")
	flag.IntVar(&replacement, "r", 10, "Replacement decimal")
	flag.IntVar(&buffLines, "b", 100, "Number of lines read to buffer")
	flag.Parse()
}