Reading data from stdin or a file in Go

iotest.go

/*
If no filename given as argument, read from stdin. Allows use as piped tool.

mashbridge@hex iotest$ go build iotest.go 
mashbridge@hex iotest$ ./iotest x.txt 
file data: foo bar

mashbridge@hex iotest$ ./iotest < x.txt 
stdin data: foo bar

mashbridge@hex iotest$ echo "bingo" | ./iotest 
stdin data: bingo
*/
package main

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

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func main() {
	flag.Parse()
	var data []byte
	var err error
	switch flag.NArg() {
	case 0:
		data, err = ioutil.ReadAll(os.Stdin)
		check(err)
		fmt.Printf("stdin data: %v\n", string(data))
		break
	case 1:
		data, err = ioutil.ReadFile(flag.Arg(0))
		check(err)
		fmt.Printf("file data: %v\n", string(data))
		break
	default:
		fmt.Printf("input must be from stdin or file\n")
		os.Exit(1)
	}
}