src/os/example_test.go - go - Git at Google

 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package os_test

 import (
 	"bytes"
 	"errors"
 	"fmt"
 	"io/fs"
 	"log"
 	"os"
 	"path/filepath"
 	"sync"
 	"time"
 )

 func ExampleOpenFile() {
 	f, err := os.OpenFile("notes.txt", os.O_RDWR|os.O_CREATE, 0644)
 	if err != nil {
 		log.Fatal(err)
 	}
 	if err := f.Close(); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleOpenFile_append() {
 	// If the file doesn't exist, create it, or append to the file
 	f, err := os.OpenFile("access.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 	if err != nil {
 		log.Fatal(err)
 	}
 	if _, err := f.Write([]byte("appended some data\n")); err != nil {
 		f.Close() // ignore error; Write error takes precedence
 		log.Fatal(err)
 	}
 	if err := f.Close(); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleChmod() {
 	if err := os.Chmod("some-filename", 0644); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleChtimes() {
 	mtime := time.Date(2006, time.February, 1, 3, 4, 5, 0, time.UTC)
 	atime := time.Date(2007, time.March, 2, 4, 5, 6, 0, time.UTC)
 	if err := os.Chtimes("some-filename", atime, mtime); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleFileMode() {
 	fi, err := os.Lstat("some-filename")
 	if err != nil {
 		log.Fatal(err)
 	}

 	fmt.Printf("permissions: %#o\n", fi.Mode().Perm()) // 0400, 0777, etc.
 	switch mode := fi.Mode(); {
 	case mode.IsRegular():
 		fmt.Println("regular file")
 	case mode.IsDir():
 		fmt.Println("directory")
 	case mode&fs.ModeSymlink != 0:
 		fmt.Println("symbolic link")
 	case mode&fs.ModeNamedPipe != 0:
 		fmt.Println("named pipe")
 	}
 }

 func ExampleErrNotExist() {
 	filename := "a-nonexistent-file"
 	if _, err := os.Stat(filename); errors.Is(err, fs.ErrNotExist) {
 		fmt.Println("file does not exist")
 	}
 	// Output:
 	// file does not exist
 }

 func ExampleExpand() {
 	mapper := func(placeholderName string) string {
 		switch placeholderName {
 		case "DAY_PART":
 			return "morning"
 		case "NAME":
 			return "Gopher"
 		}

 		return ""
 	}

 	fmt.Println(os.Expand("Good ${DAY_PART}, $NAME!", mapper))

 	// Output:
 	// Good morning, Gopher!
 }

 func ExampleExpandEnv() {
 	os.Setenv("NAME", "gopher")
 	os.Setenv("BURROW", "/usr/gopher")

 	fmt.Println(os.ExpandEnv("$NAME lives in ${BURROW}."))

 	// Output:
 	// gopher lives in /usr/gopher.
 }

 func ExampleLookupEnv() {
 	show := func(key string) {
 		val, ok := os.LookupEnv(key)
 		if !ok {
 			fmt.Printf("%s not set\n", key)
 		} else {
 			fmt.Printf("%s=%s\n", key, val)
 		}
 	}

 	os.Setenv("SOME_KEY", "value")
 	os.Setenv("EMPTY_KEY", "")

 	show("SOME_KEY")
 	show("EMPTY_KEY")
 	show("MISSING_KEY")

 	// Output:
 	// SOME_KEY=value
 	// EMPTY_KEY=
 	// MISSING_KEY not set
 }

 func ExampleGetenv() {
 	os.Setenv("NAME", "gopher")
 	os.Setenv("BURROW", "/usr/gopher")

 	fmt.Printf("%s lives in %s.\n", os.Getenv("NAME"), os.Getenv("BURROW"))

 	// Output:
 	// gopher lives in /usr/gopher.
 }

 func ExampleUnsetenv() {
 	os.Setenv("TMPDIR", "/my/tmp")
 	defer os.Unsetenv("TMPDIR")
 }

 func ExampleReadDir() {
 	files, err := os.ReadDir(".")
 	if err != nil {
 		log.Fatal(err)
 	}

 	for _, file := range files {
 		fmt.Println(file.Name())
 	}
 }

 func ExampleMkdirTemp() {
 	dir, err := os.MkdirTemp("", "example")
 	if err != nil {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(dir) // clean up

 	file := filepath.Join(dir, "tmpfile")
 	if err := os.WriteFile(file, []byte("content"), 0666); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleMkdirTemp_suffix() {
 	logsDir, err := os.MkdirTemp("", "*-logs")
 	if err != nil {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(logsDir) // clean up

 	// Logs can be cleaned out earlier if needed by searching
 	// for all directories whose suffix ends in *-logs.
 	globPattern := filepath.Join(os.TempDir(), "*-logs")
 	matches, err := filepath.Glob(globPattern)
 	if err != nil {
 		log.Fatalf("Failed to match %q: %v", globPattern, err)
 	}

 	for _, match := range matches {
 		if err := os.RemoveAll(match); err != nil {
 			log.Printf("Failed to remove %q: %v", match, err)
 		}
 	}
 }

 func ExampleCreateTemp() {
 	f, err := os.CreateTemp("", "example")
 	if err != nil {
 		log.Fatal(err)
 	}
 	defer os.Remove(f.Name()) // clean up

 	if _, err := f.Write([]byte("content")); err != nil {
 		log.Fatal(err)
 	}
 	if err := f.Close(); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleCreateTemp_suffix() {
 	f, err := os.CreateTemp("", "example.*.txt")
 	if err != nil {
 		log.Fatal(err)
 	}
 	defer os.Remove(f.Name()) // clean up

 	if _, err := f.Write([]byte("content")); err != nil {
 		f.Close()
 		log.Fatal(err)
 	}
 	if err := f.Close(); err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleReadFile() {
 	data, err := os.ReadFile("testdata/hello")
 	if err != nil {
 		log.Fatal(err)
 	}
 	os.Stdout.Write(data)

 	// Output:
 	// Hello, Gophers!
 }

 func ExampleWriteFile() {
 	err := os.WriteFile("testdata/hello", []byte("Hello, Gophers!"), 0666)
 	if err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleMkdir() {
 	err := os.Mkdir("testdir", 0750)
 	if err != nil && !os.IsExist(err) {
 		log.Fatal(err)
 	}
 	err = os.WriteFile("testdir/testfile.txt", []byte("Hello, Gophers!"), 0660)
 	if err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleMkdirAll() {
 	err := os.MkdirAll("test/subdir", 0750)
 	if err != nil {
 		log.Fatal(err)
 	}
 	err = os.WriteFile("test/subdir/testfile.txt", []byte("Hello, Gophers!"), 0660)
 	if err != nil {
 		log.Fatal(err)
 	}
 }

 func ExampleReadlink() {
 	// First, we create a relative symlink to a file.
 	d, err := os.MkdirTemp("", "")
 	if err != nil {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(d)
 	targetPath := filepath.Join(d, "hello.txt")
 	if err := os.WriteFile(targetPath, []byte("Hello, Gophers!"), 0644); err != nil {
 		log.Fatal(err)
 	}
 	linkPath := filepath.Join(d, "hello.link")
 	if err := os.Symlink("hello.txt", filepath.Join(d, "hello.link")); err != nil {
 		if errors.Is(err, errors.ErrUnsupported) {
 			// Allow the example to run on platforms that do not support symbolic links.
 			fmt.Printf("%s links to %s\n", filepath.Base(linkPath), "hello.txt")
 			return
 		}
 		log.Fatal(err)
 	}

 	// Readlink returns the relative path as passed to os.Symlink.
 	dst, err := os.Readlink(linkPath)
 	if err != nil {
 		log.Fatal(err)
 	}
 	fmt.Printf("%s links to %s\n", filepath.Base(linkPath), dst)

 	var dstAbs string
 	if filepath.IsAbs(dst) {
 		dstAbs = dst
 	} else {
 		// Symlink targets are relative to the directory containing the link.
 		dstAbs = filepath.Join(filepath.Dir(linkPath), dst)
 	}

 	// Check that the target is correct by comparing it with os.Stat
 	// on the original target path.
 	dstInfo, err := os.Stat(dstAbs)
 	if err != nil {
 		log.Fatal(err)
 	}
 	targetInfo, err := os.Stat(targetPath)
 	if err != nil {
 		log.Fatal(err)
 	}
 	if !os.SameFile(dstInfo, targetInfo) {
 		log.Fatalf("link destination (%s) is not the same file as %s", dstAbs, targetPath)
 	}

 	// Output:
 	// hello.link links to hello.txt
 }

 func ExampleUserCacheDir() {
 	dir, dirErr := os.UserCacheDir()
 	if dirErr == nil {
 		dir = filepath.Join(dir, "ExampleUserCacheDir")
 	}

 	getCache := func(name string) ([]byte, error) {
 		if dirErr != nil {
 			return nil, &os.PathError{Op: "getCache", Path: name, Err: os.ErrNotExist}
 		}
 		return os.ReadFile(filepath.Join(dir, name))
 	}

 	var mkdirOnce sync.Once
 	putCache := func(name string, b []byte) error {
 		if dirErr != nil {
 			return &os.PathError{Op: "putCache", Path: name, Err: dirErr}
 		}
 		mkdirOnce.Do(func() {
 			if err := os.MkdirAll(dir, 0700); err != nil {
 				log.Printf("can't create user cache dir: %v", err)
 			}
 		})
 		return os.WriteFile(filepath.Join(dir, name), b, 0600)
 	}

 	// Read and store cached data.
 	// …
 	_ = getCache
 	_ = putCache

 	// Output:
 }

 func ExampleUserConfigDir() {
 	dir, dirErr := os.UserConfigDir()

 	var (
 		configPath string
 		origConfig []byte
 	)
 	if dirErr == nil {
 		configPath = filepath.Join(dir, "ExampleUserConfigDir", "example.conf")
 		var err error
 		origConfig, err = os.ReadFile(configPath)
 		if err != nil && !os.IsNotExist(err) {
 			// The user has a config file but we couldn't read it.
 			// Report the error instead of ignoring their configuration.
 			log.Fatal(err)
 		}
 	}

 	// Use and perhaps make changes to the config.
 	config := bytes.Clone(origConfig)
 	// …

 	// Save changes.
 	if !bytes.Equal(config, origConfig) {
 		if configPath == "" {
 			log.Printf("not saving config changes: %v", dirErr)
 		} else {
 			err := os.MkdirAll(filepath.Dir(configPath), 0700)
 			if err == nil {
 				err = os.WriteFile(configPath, config, 0600)
 			}
 			if err != nil {
 				log.Printf("error saving config changes: %v", err)
 			}
 		}
 	}

 	// Output:
 }
	// Copyright 2016 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package os_test

	import (
	"bytes"
	"errors"
	"fmt"
	"io/fs"
	"log"
	"os"
	"path/filepath"
	"sync"
	"time"
	)

	func ExampleOpenFile() {
	f, err := os.OpenFile("notes.txt", os.O_RDWR\|os.O_CREATE, 0644)
	if err != nil {
	log.Fatal(err)
	}
	if err := f.Close(); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleOpenFile_append() {
	// If the file doesn't exist, create it, or append to the file
	f, err := os.OpenFile("access.log", os.O_APPEND\|os.O_CREATE\|os.O_WRONLY, 0644)
	if err != nil {
	log.Fatal(err)
	}
	if _, err := f.Write([]byte("appended some data\n")); err != nil {
	f.Close() // ignore error; Write error takes precedence
	log.Fatal(err)
	}
	if err := f.Close(); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleChmod() {
	if err := os.Chmod("some-filename", 0644); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleChtimes() {
	mtime := time.Date(2006, time.February, 1, 3, 4, 5, 0, time.UTC)
	atime := time.Date(2007, time.March, 2, 4, 5, 6, 0, time.UTC)
	if err := os.Chtimes("some-filename", atime, mtime); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleFileMode() {
	fi, err := os.Lstat("some-filename")
	if err != nil {
	log.Fatal(err)
	}

	fmt.Printf("permissions: %#o\n", fi.Mode().Perm()) // 0400, 0777, etc.
	switch mode := fi.Mode(); {
	case mode.IsRegular():
	fmt.Println("regular file")
	case mode.IsDir():
	fmt.Println("directory")
	case mode&fs.ModeSymlink != 0:
	fmt.Println("symbolic link")
	case mode&fs.ModeNamedPipe != 0:
	fmt.Println("named pipe")
	}
	}

	func ExampleErrNotExist() {
	filename := "a-nonexistent-file"
	if _, err := os.Stat(filename); errors.Is(err, fs.ErrNotExist) {
	fmt.Println("file does not exist")
	}
	// Output:
	// file does not exist
	}

	func ExampleExpand() {
	mapper := func(placeholderName string) string {
	switch placeholderName {
	case "DAY_PART":
	return "morning"
	case "NAME":
	return "Gopher"
	}

	return ""
	}

	fmt.Println(os.Expand("Good ${DAY_PART}, $NAME!", mapper))

	// Output:
	// Good morning, Gopher!
	}

	func ExampleExpandEnv() {
	os.Setenv("NAME", "gopher")
	os.Setenv("BURROW", "/usr/gopher")

	fmt.Println(os.ExpandEnv("$NAME lives in ${BURROW}."))

	// Output:
	// gopher lives in /usr/gopher.
	}

	func ExampleLookupEnv() {
	show := func(key string) {
	val, ok := os.LookupEnv(key)
	if !ok {
	fmt.Printf("%s not set\n", key)
	} else {
	fmt.Printf("%s=%s\n", key, val)
	}
	}

	os.Setenv("SOME_KEY", "value")
	os.Setenv("EMPTY_KEY", "")

	show("SOME_KEY")
	show("EMPTY_KEY")
	show("MISSING_KEY")

	// Output:
	// SOME_KEY=value
	// EMPTY_KEY=
	// MISSING_KEY not set
	}

	func ExampleGetenv() {
	os.Setenv("NAME", "gopher")
	os.Setenv("BURROW", "/usr/gopher")

	fmt.Printf("%s lives in %s.\n", os.Getenv("NAME"), os.Getenv("BURROW"))

	// Output:
	// gopher lives in /usr/gopher.
	}

	func ExampleUnsetenv() {
	os.Setenv("TMPDIR", "/my/tmp")
	defer os.Unsetenv("TMPDIR")
	}

	func ExampleReadDir() {
	files, err := os.ReadDir(".")
	if err != nil {
	log.Fatal(err)
	}

	for _, file := range files {
	fmt.Println(file.Name())
	}
	}

	func ExampleMkdirTemp() {
	dir, err := os.MkdirTemp("", "example")
	if err != nil {
	log.Fatal(err)
	}
	defer os.RemoveAll(dir) // clean up

	file := filepath.Join(dir, "tmpfile")
	if err := os.WriteFile(file, []byte("content"), 0666); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleMkdirTemp_suffix() {
	logsDir, err := os.MkdirTemp("", "*-logs")
	if err != nil {
	log.Fatal(err)
	}
	defer os.RemoveAll(logsDir) // clean up

	// Logs can be cleaned out earlier if needed by searching
	// for all directories whose suffix ends in *-logs.
	globPattern := filepath.Join(os.TempDir(), "*-logs")
	matches, err := filepath.Glob(globPattern)
	if err != nil {
	log.Fatalf("Failed to match %q: %v", globPattern, err)
	}

	for _, match := range matches {
	if err := os.RemoveAll(match); err != nil {
	log.Printf("Failed to remove %q: %v", match, err)
	}
	}
	}

	func ExampleCreateTemp() {
	f, err := os.CreateTemp("", "example")
	if err != nil {
	log.Fatal(err)
	}
	defer os.Remove(f.Name()) // clean up

	if _, err := f.Write([]byte("content")); err != nil {
	log.Fatal(err)
	}
	if err := f.Close(); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleCreateTemp_suffix() {
	f, err := os.CreateTemp("", "example.*.txt")
	if err != nil {
	log.Fatal(err)
	}
	defer os.Remove(f.Name()) // clean up

	if _, err := f.Write([]byte("content")); err != nil {
	f.Close()
	log.Fatal(err)
	}
	if err := f.Close(); err != nil {
	log.Fatal(err)
	}
	}

	func ExampleReadFile() {
	data, err := os.ReadFile("testdata/hello")
	if err != nil {
	log.Fatal(err)
	}
	os.Stdout.Write(data)

	// Output:
	// Hello, Gophers!
	}

	func ExampleWriteFile() {
	err := os.WriteFile("testdata/hello", []byte("Hello, Gophers!"), 0666)
	if err != nil {
	log.Fatal(err)
	}
	}

	func ExampleMkdir() {
	err := os.Mkdir("testdir", 0750)
	if err != nil && !os.IsExist(err) {
	log.Fatal(err)
	}
	err = os.WriteFile("testdir/testfile.txt", []byte("Hello, Gophers!"), 0660)
	if err != nil {
	log.Fatal(err)
	}
	}

	func ExampleMkdirAll() {
	err := os.MkdirAll("test/subdir", 0750)
	if err != nil {
	log.Fatal(err)
	}
	err = os.WriteFile("test/subdir/testfile.txt", []byte("Hello, Gophers!"), 0660)
	if err != nil {
	log.Fatal(err)
	}
	}

	func ExampleReadlink() {
	// First, we create a relative symlink to a file.
	d, err := os.MkdirTemp("", "")
	if err != nil {
	log.Fatal(err)
	}
	defer os.RemoveAll(d)
	targetPath := filepath.Join(d, "hello.txt")
	if err := os.WriteFile(targetPath, []byte("Hello, Gophers!"), 0644); err != nil {
	log.Fatal(err)
	}
	linkPath := filepath.Join(d, "hello.link")
	if err := os.Symlink("hello.txt", filepath.Join(d, "hello.link")); err != nil {
	if errors.Is(err, errors.ErrUnsupported) {
	// Allow the example to run on platforms that do not support symbolic links.
	fmt.Printf("%s links to %s\n", filepath.Base(linkPath), "hello.txt")
	return
	}
	log.Fatal(err)
	}

	// Readlink returns the relative path as passed to os.Symlink.
	dst, err := os.Readlink(linkPath)
	if err != nil {
	log.Fatal(err)
	}
	fmt.Printf("%s links to %s\n", filepath.Base(linkPath), dst)

	var dstAbs string
	if filepath.IsAbs(dst) {
	dstAbs = dst
	} else {
	// Symlink targets are relative to the directory containing the link.
	dstAbs = filepath.Join(filepath.Dir(linkPath), dst)
	}

	// Check that the target is correct by comparing it with os.Stat
	// on the original target path.
	dstInfo, err := os.Stat(dstAbs)
	if err != nil {
	log.Fatal(err)
	}
	targetInfo, err := os.Stat(targetPath)
	if err != nil {
	log.Fatal(err)
	}
	if !os.SameFile(dstInfo, targetInfo) {
	log.Fatalf("link destination (%s) is not the same file as %s", dstAbs, targetPath)
	}

	// Output:
	// hello.link links to hello.txt
	}

	func ExampleUserCacheDir() {
	dir, dirErr := os.UserCacheDir()
	if dirErr == nil {
	dir = filepath.Join(dir, "ExampleUserCacheDir")
	}

	getCache := func(name string) ([]byte, error) {
	if dirErr != nil {
	return nil, &os.PathError{Op: "getCache", Path: name, Err: os.ErrNotExist}
	}
	return os.ReadFile(filepath.Join(dir, name))
	}

	var mkdirOnce sync.Once
	putCache := func(name string, b []byte) error {
	if dirErr != nil {
	return &os.PathError{Op: "putCache", Path: name, Err: dirErr}
	}
	mkdirOnce.Do(func() {
	if err := os.MkdirAll(dir, 0700); err != nil {
	log.Printf("can't create user cache dir: %v", err)
	}
	})
	return os.WriteFile(filepath.Join(dir, name), b, 0600)
	}

	// Read and store cached data.
	// …
	_ = getCache
	_ = putCache

	// Output:
	}

	func ExampleUserConfigDir() {
	dir, dirErr := os.UserConfigDir()

	var (
	configPath string
	origConfig []byte
	)
	if dirErr == nil {
	configPath = filepath.Join(dir, "ExampleUserConfigDir", "example.conf")
	var err error
	origConfig, err = os.ReadFile(configPath)
	if err != nil && !os.IsNotExist(err) {
	// The user has a config file but we couldn't read it.
	// Report the error instead of ignoring their configuration.
	log.Fatal(err)
	}
	}

	// Use and perhaps make changes to the config.
	config := bytes.Clone(origConfig)
	// …

	// Save changes.
	if !bytes.Equal(config, origConfig) {
	if configPath == "" {
	log.Printf("not saving config changes: %v", dirErr)
	} else {
	err := os.MkdirAll(filepath.Dir(configPath), 0700)
	if err == nil {
	err = os.WriteFile(configPath, config, 0600)
	}
	if err != nil {
	log.Printf("error saving config changes: %v", err)
	}
	}
	}

	// Output:
	}