Make a bunch of files

main.go

package main

import (
        "flag"
        "fmt"
        "io"
        "log"
        "os"
        "path/filepath"
)

var (
        n    = flag.Int("n", 1, "number of files to create")
        size = flag.Int64("size", 1*1024*1024*1024, "total size of output files to create in bytes")
)

type charReader struct{}

func (_ charReader) Read(b []byte) (int, error) {
        var n int
        for i := range b {
                b[i] = 'A'
                n++
        }
        return n, nil
}

func main() {
        flag.Parse()
        if err := os.MkdirAll("out", 0775); err != nil {
                log.Fatal(err)
        }

        each := *size / int64(*n)
        for i := 0; i < *n; i++ {
                name := filepath.Join("out", fmt.Sprintf("data-%d", i))
                fd, err := os.OpenFile(name, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0600)
                if err != nil {
                        log.Fatal(err)
                }
                n, err := io.Copy(fd, io.LimitReader(charReader{}, each))
                log.Printf("%s: wrote %v bytes\n", name, n)
                if err != nil {
                        log.Fatal(err)
                }
                if err := fd.Close(); err != nil {
                        log.Fatal(err)
                }
        }
        fmt.Printf("wrote %d files of %d bytes each totalling %d bytes\n", *n, each, *size)
}