Small Go program to do a binary diff between two files

binarydiff.go

package main

import (
	"fmt"
	"io/ioutil"
	"os"
)

func unwrapPathError(err error) error {
	if e, ok := err.(*os.PathError); ok {
		return e.Err
	}
	return err
}

func main() {
	if len(os.Args) != 3 {
		fmt.Fprintf(os.Stderr, "usage: %v FILE FILE\n", os.Args[0])
		os.Exit(1)
	}
	f1, f2 := os.Args[1], os.Args[2]

	d1, err := ioutil.ReadFile(f1)
	if err != nil {
		fmt.Fprintf(os.Stderr, "cannot read file '%v': %v\n", f1, unwrapPathError(err))
		os.Exit(1)
	}
	d2, err := ioutil.ReadFile(f2)
	if err != nil {
		fmt.Fprintf(os.Stderr, "cannot read file '%v': %v\n", f2, unwrapPathError(err))
		os.Exit(1)
	}
	minLen := len(d1)
	if l := len(d2); l < minLen {
		minLen = l
	}
	for i := 0; i < minLen; i++ {
		b1, b2 := d1[i], d2[i]
		if b1 != b2 {
			fmt.Printf("%d: %x != %x\n", i, b1, b2)
		}
	}
	fmt.Printf("extra bytes in %s: %d\n", f1, len(d1)-minLen)
	fmt.Printf("extra bytes in %s: %d\n", f2, len(d2)-minLen)
}