img.go

package main

import (
	"flag"
	"fmt"
	"image/png"
	"os"
)

func main() {
	flag.Parse()
	inputFilename := flag.Arg(0)
	outputFilename := flag.Arg(1)

	if file, err := os.Open(inputFilename); err == nil {
		defer file.Close()

		image, _ := png.Decode(file)

		if out, err := os.OpenFile(outputFilename, os.O_WRONLY|os.O_CREATE, 0644); err == nil {
			defer out.Close()
			png.Encode(out, image)
		}
	}

	fmt.Println("I guess I saved the file", outputFilename)
}