Code to merge striped files into the "actual" file

merge.go

package main

import (
	"fmt"
	"os"
	"strconv"
	"syscall"
	"time"

	"github.com/dustin/go-humanize"
)

var numread, numout, outSize uint64

func main() {
	var err error

	if len(os.Args) < 4 {
		fmt.Println("Parameters: stripesize output file1...")
		os.Exit(0)
	}
	stripeSizeStr := os.Args[1]
	outSizeStr := os.Args[2]
	outfile := os.Args[3]
	s := len(os.Args) - 4
	stripeSize, err := strconv.Atoi(stripeSizeStr)
	if err != nil {
		panic(err)
	}

	outSize, err = strconv.ParseUint(outSizeStr, 10, 64)
	if err != nil {
		panic(err)
	}

	fdOut, err := syscall.Open(outfile, syscall.O_CREAT|syscall.O_EXCL|syscall.O_RDWR, 0600)

	if err != nil {
		panic(err)
		return
	}

	defer syscall.Close(fdOut)

	fd := make([]int, s, s)
	for i := 0; i < s; i++ {
		fd[i], err = syscall.Open(os.Args[i+4], syscall.O_RDONLY, 0777)

		if err != nil {
			fmt.Print(err.Error(), "\n")
			return
		}

		defer syscall.Close(fd[i])
	}

	var bytesread, bytesout int
	buffer := make([]byte, stripeSize)
	loop := true

	go func() {
		for {
			showProgress()
			time.Sleep(5 * time.Second)
		}
	}()

	for {
		for _, file := range fd {
			bytesread, err = syscall.Read(file, buffer)

			if err != nil {
				panic(err)
			}

			if bytesread < stripeSize {
				loop = false
				break
			}
			numread += uint64(bytesread)

			bytesout, err = syscall.Write(fdOut, buffer)
			if err != nil {
				panic(err)
			}
			numout += uint64(bytesout)
		}
		if numout > outSize {
			loop = false
		}

		if !loop {
			break
		}
	}

	showProgress()
}

func showProgress() {
	fmt.Printf("Read: %s; written: %s/%s\n", humanize.Bytes(numread), humanize.Bytes(numout), humanize.Bytes(outSize))
}