// Copyright 2009 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 provides a platform-independent interface to operating system // functionality. The design is Unix-like, although the error handling is // Go-like; failing calls return values of type error rather than error numbers. // Often, more information is available within the error. For example, // if a call that takes a file name fails, such as Open or Stat, the error // will include the failing file name when printed and will be of type // *PathError, which may be unpacked for more information. // // The os interface is intended to be uniform across all operating systems. // Features not generally available appear in the system-specific package syscall. // // Here is a simple example, opening a file and reading some of it. // // file, err := os.Open("file.go") // For read access. // if err != nil { // log.Fatal(err) // } // // If the open fails, the error string will be self-explanatory, like // // open file.go: no such file or directory // // The file's data can then be read into a slice of bytes. Read and // Write take their byte counts from the length of the argument slice. // // data := make([]byte, 100) // count, err := file.Read(data) // if err != nil { // log.Fatal(err) // } // fmt.Printf("read %d bytes: %q\n", count, data[:count]) // // Note: The maximum number of concurrent operations on a File may be limited by // the OS or the system. The number should be high, but exceeding it may degrade // performance or cause other issues. //
package os import ( ) // Name returns the name of the file as presented to Open. func ( *File) () string { return .name } // Stdin, Stdout, and Stderr are open Files pointing to the standard input, // standard output, and standard error file descriptors. // // Note that the Go runtime writes to standard error for panics and crashes; // closing Stderr may cause those messages to go elsewhere, perhaps // to a file opened later. var ( Stdin = NewFile(uintptr(syscall.Stdin), "/dev/stdin") Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout") Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr") ) // Flags to OpenFile wrapping those of the underlying system. Not all // flags may be implemented on a given system. const ( // Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified. O_RDONLY int = syscall.O_RDONLY // open the file read-only. O_WRONLY int = syscall.O_WRONLY // open the file write-only. O_RDWR int = syscall.O_RDWR // open the file read-write. // The remaining values may be or'ed in to control behavior. O_APPEND int = syscall.O_APPEND // append data to the file when writing. O_CREATE int = syscall.O_CREAT // create a new file if none exists. O_EXCL int = syscall.O_EXCL // used with O_CREATE, file must not exist. O_SYNC int = syscall.O_SYNC // open for synchronous I/O. O_TRUNC int = syscall.O_TRUNC // truncate regular writable file when opened. ) // Seek whence values. // // Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd. const ( SEEK_SET int = 0 // seek relative to the origin of the file SEEK_CUR int = 1 // seek relative to the current offset SEEK_END int = 2 // seek relative to the end ) // LinkError records an error during a link or symlink or rename // system call and the paths that caused it. type LinkError struct { Op string Old string New string Err error } func ( *LinkError) () string { return .Op + " " + .Old + " " + .New + ": " + .Err.Error() } func ( *LinkError) () error { return .Err } // Read reads up to len(b) bytes from the File. // It returns the number of bytes read and any error encountered. // At end of file, Read returns 0, io.EOF. func ( *File) ( []byte) ( int, error) { if := .checkValid("read"); != nil { return 0, } , := .read() return , .wrapErr("read", ) } // ReadAt reads len(b) bytes from the File starting at byte offset off. // It returns the number of bytes read and the error, if any. // ReadAt always returns a non-nil error when n < len(b). // At end of file, that error is io.EOF. func ( *File) ( []byte, int64) ( int, error) { if := .checkValid("read"); != nil { return 0, } if < 0 { return 0, &PathError{Op: "readat", Path: .name, Err: errors.New("negative offset")} } for len() > 0 { , := .pread(, ) if != nil { = .wrapErr("read", ) break } += = [:] += int64() } return } // ReadFrom implements io.ReaderFrom. func ( *File) ( io.Reader) ( int64, error) { if := .checkValid("write"); != nil { return 0, } , , := .readFrom() if ! { return genericReadFrom(, ) // without wrapping } return , .wrapErr("write", ) } func genericReadFrom( *File, io.Reader) (int64, error) { return io.Copy(onlyWriter{}, ) } type onlyWriter struct { io.Writer } // Write writes len(b) bytes to the File. // It returns the number of bytes written and an error, if any. // Write returns a non-nil error when n != len(b). func ( *File) ( []byte) ( int, error) { if := .checkValid("write"); != nil { return 0, } , := .write() if < 0 { = 0 } if != len() { = io.ErrShortWrite } epipecheck(, ) if != nil { = .wrapErr("write", ) } return , } var errWriteAtInAppendMode = errors.New("os: invalid use of WriteAt on file opened with O_APPEND") // WriteAt writes len(b) bytes to the File starting at byte offset off. // It returns the number of bytes written and an error, if any. // WriteAt returns a non-nil error when n != len(b). // // If file was opened with the O_APPEND flag, WriteAt returns an error. func ( *File) ( []byte, int64) ( int, error) { if := .checkValid("write"); != nil { return 0, } if .appendMode { return 0, errWriteAtInAppendMode } if < 0 { return 0, &PathError{Op: "writeat", Path: .name, Err: errors.New("negative offset")} } for len() > 0 { , := .pwrite(, ) if != nil { = .wrapErr("write", ) break } += = [:] += int64() } return } // Seek sets the offset for the next Read or Write on file to offset, interpreted // according to whence: 0 means relative to the origin of the file, 1 means // relative to the current offset, and 2 means relative to the end. // It returns the new offset and an error, if any. // The behavior of Seek on a file opened with O_APPEND is not specified. // // If f is a directory, the behavior of Seek varies by operating // system; you can seek to the beginning of the directory on Unix-like // operating systems, but not on Windows. func ( *File) ( int64, int) ( int64, error) { if := .checkValid("seek"); != nil { return 0, } , := .seek(, ) if == nil && .dirinfo != nil && != 0 { = syscall.EISDIR } if != nil { return 0, .wrapErr("seek", ) } return , nil } // WriteString is like Write, but writes the contents of string s rather than // a slice of bytes. func ( *File) ( string) ( int, error) { return .Write([]byte()) } // Mkdir creates a new directory with the specified name and permission // bits (before umask). // If there is an error, it will be of type *PathError. func ( string, FileMode) error { if runtime.GOOS == "windows" && isWindowsNulName() { return &PathError{Op: "mkdir", Path: , Err: syscall.ENOTDIR} } := fixLongPath() := ignoringEINTR(func() error { return syscall.Mkdir(, syscallMode()) }) if != nil { return &PathError{Op: "mkdir", Path: , Err: } } // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris if !supportsCreateWithStickyBit && &ModeSticky != 0 { = setStickyBit() if != nil { Remove() return } } return nil } // setStickyBit adds ModeSticky to the permission bits of path, non atomic. func setStickyBit( string) error { , := Stat() if != nil { return } return Chmod(, .Mode()|ModeSticky) } // Chdir changes the current working directory to the named directory. // If there is an error, it will be of type *PathError. func ( string) error { if := syscall.Chdir(); != nil { testlog.Open() // observe likely non-existent directory return &PathError{Op: "chdir", Path: , Err: } } if := testlog.Logger(); != nil { , := Getwd() if == nil { .Chdir() } } return nil } // Open opens the named file for reading. If successful, methods on // the returned file can be used for reading; the associated file // descriptor has mode O_RDONLY. // If there is an error, it will be of type *PathError. func ( string) (*File, error) { return OpenFile(, O_RDONLY, 0) } // Create creates or truncates the named file. If the file already exists, // it is truncated. If the file does not exist, it is created with mode 0666 // (before umask). If successful, methods on the returned File can // be used for I/O; the associated file descriptor has mode O_RDWR. // If there is an error, it will be of type *PathError. func ( string) (*File, error) { return OpenFile(, O_RDWR|O_CREATE|O_TRUNC, 0666) } // OpenFile is the generalized open call; most users will use Open // or Create instead. It opens the named file with specified flag // (O_RDONLY etc.). If the file does not exist, and the O_CREATE flag // is passed, it is created with mode perm (before umask). If successful, // methods on the returned File can be used for I/O. // If there is an error, it will be of type *PathError. func ( string, int, FileMode) (*File, error) { testlog.Open() , := openFileNolog(, , ) if != nil { return nil, } .appendMode = &O_APPEND != 0 return , nil } // lstat is overridden in tests. var lstat = Lstat // Rename renames (moves) oldpath to newpath. // If newpath already exists and is not a directory, Rename replaces it. // OS-specific restrictions may apply when oldpath and newpath are in different directories. // If there is an error, it will be of type *LinkError. func (, string) error { return rename(, ) } // Many functions in package syscall return a count of -1 instead of 0. // Using fixCount(call()) instead of call() corrects the count. func fixCount( int, error) (int, error) { if < 0 { = 0 } return , } // wrapErr wraps an error that occurred during an operation on an open file. // It passes io.EOF through unchanged, otherwise converts // poll.ErrFileClosing to ErrClosed and wraps the error in a PathError. func ( *File) ( string, error) error { if == nil || == io.EOF { return } if == poll.ErrFileClosing { = ErrClosed } return &PathError{Op: , Path: .name, Err: } } // TempDir returns the default directory to use for temporary files. // // On Unix systems, it returns $TMPDIR if non-empty, else /tmp. // On Windows, it uses GetTempPath, returning the first non-empty // value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory. // On Plan 9, it returns /tmp. // // The directory is neither guaranteed to exist nor have accessible // permissions. func () string { return tempDir() } // UserCacheDir returns the default root directory to use for user-specific // cached data. Users should create their own application-specific subdirectory // within this one and use that. // // On Unix systems, it returns $XDG_CACHE_HOME as specified by // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if // non-empty, else $HOME/.cache. // On Darwin, it returns $HOME/Library/Caches. // On Windows, it returns %LocalAppData%. // On Plan 9, it returns $home/lib/cache. // // If the location cannot be determined (for example, $HOME is not defined), // then it will return an error. func () (string, error) { var string switch runtime.GOOS { case "windows": = Getenv("LocalAppData") if == "" { return "", errors.New("%LocalAppData% is not defined") } case "darwin", "ios": = Getenv("HOME") if == "" { return "", errors.New("$HOME is not defined") } += "/Library/Caches" case "plan9": = Getenv("home") if == "" { return "", errors.New("$home is not defined") } += "/lib/cache" default: // Unix = Getenv("XDG_CACHE_HOME") if == "" { = Getenv("HOME") if == "" { return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined") } += "/.cache" } } return , nil } // UserConfigDir returns the default root directory to use for user-specific // configuration data. Users should create their own application-specific // subdirectory within this one and use that. // // On Unix systems, it returns $XDG_CONFIG_HOME as specified by // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if // non-empty, else $HOME/.config. // On Darwin, it returns $HOME/Library/Application Support. // On Windows, it returns %AppData%. // On Plan 9, it returns $home/lib. // // If the location cannot be determined (for example, $HOME is not defined), // then it will return an error. func () (string, error) { var string switch runtime.GOOS { case "windows": = Getenv("AppData") if == "" { return "", errors.New("%AppData% is not defined") } case "darwin", "ios": = Getenv("HOME") if == "" { return "", errors.New("$HOME is not defined") } += "/Library/Application Support" case "plan9": = Getenv("home") if == "" { return "", errors.New("$home is not defined") } += "/lib" default: // Unix = Getenv("XDG_CONFIG_HOME") if == "" { = Getenv("HOME") if == "" { return "", errors.New("neither $XDG_CONFIG_HOME nor $HOME are defined") } += "/.config" } } return , nil } // UserHomeDir returns the current user's home directory. // // On Unix, including macOS, it returns the $HOME environment variable. // On Windows, it returns %USERPROFILE%. // On Plan 9, it returns the $home environment variable. func () (string, error) { , := "HOME", "$HOME" switch runtime.GOOS { case "windows": , = "USERPROFILE", "%userprofile%" case "plan9": , = "home", "$home" } if := Getenv(); != "" { return , nil } // On some geese the home directory is not always defined. switch runtime.GOOS { case "android": return "/sdcard", nil case "ios": return "/", nil } return "", errors.New( + " is not defined") } // Chmod changes the mode of the named file to mode. // If the file is a symbolic link, it changes the mode of the link's target. // If there is an error, it will be of type *PathError. // // A different subset of the mode bits are used, depending on the // operating system. // // On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and // ModeSticky are used. // // On Windows, only the 0200 bit (owner writable) of mode is used; it // controls whether the file's read-only attribute is set or cleared. // The other bits are currently unused. For compatibility with Go 1.12 // and earlier, use a non-zero mode. Use mode 0400 for a read-only // file and 0600 for a readable+writable file. // // On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive, // and ModeTemporary are used. func ( string, FileMode) error { return chmod(, ) } // Chmod changes the mode of the file to mode. // If there is an error, it will be of type *PathError. func ( *File) ( FileMode) error { return .chmod() } // SetDeadline sets the read and write deadlines for a File. // It is equivalent to calling both SetReadDeadline and SetWriteDeadline. // // Only some kinds of files support setting a deadline. Calls to SetDeadline // for files that do not support deadlines will return ErrNoDeadline. // On most systems ordinary files do not support deadlines, but pipes do. // // A deadline is an absolute time after which I/O operations fail with an // error instead of blocking. The deadline applies to all future and pending // I/O, not just the immediately following call to Read or Write. // After a deadline has been exceeded, the connection can be refreshed // by setting a deadline in the future. // // If the deadline is exceeded a call to Read or Write or to other I/O // methods will return an error that wraps ErrDeadlineExceeded. // This can be tested using errors.Is(err, os.ErrDeadlineExceeded). // That error implements the Timeout method, and calling the Timeout // method will return true, but there are other possible errors for which // the Timeout will return true even if the deadline has not been exceeded. // // An idle timeout can be implemented by repeatedly extending // the deadline after successful Read or Write calls. // // A zero value for t means I/O operations will not time out. func ( *File) ( time.Time) error { return .setDeadline() } // SetReadDeadline sets the deadline for future Read calls and any // currently-blocked Read call. // A zero value for t means Read will not time out. // Not all files support setting deadlines; see SetDeadline. func ( *File) ( time.Time) error { return .setReadDeadline() } // SetWriteDeadline sets the deadline for any future Write calls and any // currently-blocked Write call. // Even if Write times out, it may return n > 0, indicating that // some of the data was successfully written. // A zero value for t means Write will not time out. // Not all files support setting deadlines; see SetDeadline. func ( *File) ( time.Time) error { return .setWriteDeadline() } // SyscallConn returns a raw file. // This implements the syscall.Conn interface. func ( *File) () (syscall.RawConn, error) { if := .checkValid("SyscallConn"); != nil { return nil, } return newRawConn() } // isWindowsNulName reports whether name is os.DevNull ('NUL') on Windows. // True is returned if name is 'NUL' whatever the case. func isWindowsNulName( string) bool { if len() != 3 { return false } if [0] != 'n' && [0] != 'N' { return false } if [1] != 'u' && [1] != 'U' { return false } if [2] != 'l' && [2] != 'L' { return false } return true } // DirFS returns a file system (an fs.FS) for the tree of files rooted at the directory dir. // // Note that DirFS("/prefix") only guarantees that the Open calls it makes to the // operating system will begin with "/prefix": DirFS("/prefix").Open("file") is the // same as os.Open("/prefix/file"). So if /prefix/file is a symbolic link pointing outside // the /prefix tree, then using DirFS does not stop the access any more than using // os.Open does. DirFS is therefore not a general substitute for a chroot-style security // mechanism when the directory tree contains arbitrary content. func ( string) fs.FS { return dirFS() } func containsAny(, string) bool { for := 0; < len(); ++ { for := 0; < len(); ++ { if [] == [] { return true } } } return false } type dirFS string func ( dirFS) ( string) (fs.File, error) { if !fs.ValidPath() || runtime.GOOS == "windows" && containsAny(, `\:`) { return nil, &PathError{Op: "open", Path: , Err: ErrInvalid} } , := Open(string() + "/" + ) if != nil { return nil, // nil fs.File } return , nil } // ReadFile reads the named file and returns the contents. // A successful call returns err == nil, not err == EOF. // Because ReadFile reads the whole file, it does not treat an EOF from Read // as an error to be reported. func ( string) ([]byte, error) { , := Open() if != nil { return nil, } defer .Close() var int if , := .Stat(); == nil { := .Size() if int64(int()) == { = int() } } ++ // one byte for final read at EOF // If a file claims a small size, read at least 512 bytes. // In particular, files in Linux's /proc claim size 0 but // then do not work right if read in small pieces, // so an initial read of 1 byte would not work correctly. if < 512 { = 512 } := make([]byte, 0, ) for { if len() >= cap() { := append([:cap()], 0) = [:len()] } , := .Read([len():cap()]) = [:len()+] if != nil { if == io.EOF { = nil } return , } } } // WriteFile writes data to the named file, creating it if necessary. // If the file does not exist, WriteFile creates it with permissions perm (before umask); // otherwise WriteFile truncates it before writing, without changing permissions. func ( string, []byte, FileMode) error { , := OpenFile(, O_WRONLY|O_CREATE|O_TRUNC, ) if != nil { return } _, = .Write() if := .Close(); != nil && == nil { = } return }