Unix "cat" command in Go

cat.go

package main

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

//
// This script implements the unix cat.
//
func cat(r io.Reader) ([]byte, error) {
    data, err := ioutil.ReadAll(r);

    if (err != nil) {
        return nil, err
    }

    return data, nil
}

func main() {
    var output []byte
    var err error

    args := os.Args[1:]

    if len(args) > 0 {
        for _, file := range args {
            data, err := os.Open(file)
            defer data.Close()

            if err != nil {
                log.Panic(err)
            }

            output, err = cat(data)

            if err != nil {
                log.Panic(err)
            }


            fmt.Print(string(output))
        }
    } else {
        output, err = cat(os.Stdin)

        if err != nil {
            log.Panic(err)
        }

        fmt.Print(string(output))
    }
}