cat_command.go

//【TRY】catコマンドを作ろう
package main

import (
	"bufio"
	"flag"
	"fmt"
	"log"
	"os"
)

var (
	isShowLineNo *bool = flag.Bool("n", false, "show line number")
	lineNo       int
)

func main() {
	flag.Parse()
	args := flag.Args()

	for _, b := range args {
		if err := readFile(b, &lineNo); err != nil {
			log.Fatal(err)
		}
	}
}

func readFile(b string, lineNo *int) error {
	f, err := os.Open(b)
	if err != nil {
		return err
	}
	defer f.Close()

	scanner := bufio.NewScanner(f)

	for scanner.Scan() {
		if *isShowLineNo {
			*lineNo++
			print(*lineNo, ": ")
		}
		fmt.Println(scanner.Text())
	}

	if err := scanner.Err(); err != nil {
		fmt.Fprintln(os.Stderr, "fail to read", err)
	}
	return nil
}