Simple parallel md5sum compatible to GNU md5sum

md5sum.go

package main

// go build md5sum.go
// ./md5sum ~/*.log
// # or
// ./md5sum << EOF

import (
        "crypto/md5"
        "fmt"
        "io"
        "os"
        "sync"
)

func main() {
        tarList := make([]*os.File, notLessThan(len(os.Args)-1, 1))

        if len(os.Args) == 1 {
                tarList[0] = os.Stdin
        } else {
                for i, fN := range os.Args[1:] {

                        fi, err := os.Lstat(fN)
                        if err != nil {
                                fmt.Printf("md5sum: %s\n", err)
                                continue
                        }
                        if fi.Mode().IsDir() {
                                fmt.Printf("md5sum: %s is a directory\n", fN)
                                continue
                        }

                        f, err := os.Open(fN)
                        if err != nil {
                                fmt.Printf("md5sum: %s\n", err)
                                continue
                        }
                        }
                        tarList[i] = f
                }
        }
        wg := &sync.WaitGroup{}
        for _, f := range tarList {
                if f == nil {
                        continue
                }
                wg.Add(1)
                go doSum(f, wg)
        }
        wg.Wait()
}

func doSum(f *os.File, wg *sync.WaitGroup) {
        defer wg.Done()
        defer f.Close()

        h := md5.New()
        if _, err := io.Copy(h, f); err != nil {
                fmt.Printf("md5sum:%s\n", err)
                return
        }
        ret := h.Sum(nil)
        fmt.Printf("%x  %s\n", ret, f.Name())
        return
}

func notLessThan(a, b int) int {
        if a < b {
                return b
        }
        return a
}