Go Tips連載3: ファイルを扱うちょっとしたスクリプトをGoで書くときのTips5選

func hasCopyright(r io.Reader) (bool, error) {
	b, err := ioutil.ReadAll(r)
	if err != nil {
		return false, err
	}
	return bytes.Contains(b, []byte("Copyright")), nil
}

// 非推奨: 具象の構造体を引数に取る関数
func hasCopyright(f *os.File) (bool, error) {
	b, err := ioutil.ReadAll(f)
	if err != nil {
		return false, err
	}
	return bytes.Contains(b, []byte("Copyright")), nil
}

package main

import (
	"io"
	"strings"
	"testing"
)

func Test_hasCopyright(t *testing.T) {
	type args struct {
		reader io.Reader
	}
	tests := []struct {
		name    string
		args    args
		want    bool
		wantErr bool
	}{
		{"正常", args{strings.NewReader(`Copyright`)}, true, false},
		{"MITライセンス", args{strings.NewReader(`MIT License

Copyright (c) 2020, Future Corporation

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.`)}, true, false},
		{"空文字", args{strings.NewReader(``)}, false, false},
		{"cが小文字", args{strings.NewReader(`copyright`)}, false, false},
		{"スペース有り", args{strings.NewReader(`Copy right`)}, false, false},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got, err := hasCopyright(tt.args.reader)
			if (err != nil) != tt.wantErr {
				t.Errorf("hasCopyright() error = %v, wantErr %v", err, tt.wantErr)
				return
			}
			if got != tt.want {
				t.Errorf("hasCopyright() got = %v, want %v", got, tt.want)
			}
		})
	}
}

package main

import (
	"bytes"
	"testing"
)

func Test_writeHello(t *testing.T) {
	tests := []struct {
		name  string
		wantW string
		diff  bool
	}{
		{"正常", "\nHello World.\n", false},
		{"終端の改行がない", "\nHello World.", true},
		{"先頭の改行がない", "Hello World.\n", true},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			w := &bytes.Buffer{}
			writeHello(w)
			if gotW := w.String(); gotW != tt.wantW {
				if !tt.diff {
					t.Errorf("writeHello() = %v, want %v", gotW, tt.wantW)
				}
			}
		})
	}
}

package main

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

func main() {
	f, err := os.Open("list.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	for sc.Scan() {
		// list.txt にかかれている行の文字列を用いて処理をする
		line := sc.Text()
		fmt.Println(line)
	}
	if err := sc.Err(); err != nil {
		log.Fatal(err)
	}
}
// 出力結果:
// future-architect/vuls
// future-architect/gcp-instance-scheduler
// future-architect/cheetah-grid
// future-architect/uroborosql
// future-architect/icons

func main() {
	f, err := os.Open("list.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	r := bufio.NewReader(f)
	for {
		// list.txt にかかれている行の文字列を用いて処理をする
		line, _, err := r.ReadLine()
		if err != nil {
			if err == io.EOF {
				break
			}
			log.Fatal(err)
		}
		fmt.Printf("%s\n", string(line))
	}
}

package main

import (
	"fmt"
	"log"
	"os/exec"
)

func main() {
	cmd := exec.Command("git", "clone", "-b", "delelop", "https://...")
	if err := cmd.Run(); err != nil {
		log.Fatal(err)
	}
	fmt.Println(cmd.ProcessState.Pid())
	fmt.Println(cmd.ProcessState.String())
}
// 実行結果:
// 1234
// exit status 0

b, err := exec.Command("/bin/sh", "-c", "ls", "*.go").Output()

package main

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
)

func main() {
	tempDir, err := ioutil.TempDir(".", "temp")
	if err != nil {
		log.Fatal(err)
	}
	// defer os.RemoveAll(tempDir) とすればスクリプト終了時に一時ディレクトリを削除することも可能

	testFilePath := filepath.Join(tempDir, "test.txt")
	f, err := os.Create(testFilePath)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	writeHello(f)
}