package main

import (
    "io"
    "log"
    "os"
)

func main() {
    if len(os.Args) > 1 && os.Args[1] != "-" {
        output(os.ReadFile(os.Args[1]))
    } else {
        output(io.ReadAll(os.Stdin))
    }
}

func output(b []byte, err error) {
    if err != nil {
        log.Fatalf("unable to read file %s: %v", os.Args[0], err)
    }
    println(string(b))
}