Preview: example_test.go
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/proc/thread-self/root/opt/golang/1.22.0/src/os/example_test.go
// 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:
}
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