os - The Go Programming Language

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Package os

Overview ?

Overview ?

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])

Index

Constants
Variables
func Chdir(dir string) error
func Chmod(name string, mode FileMode) error
func Chown(name string, uid, gid int) error
func Chtimes(name string, atime time.Time, mtime time.Time) error
func Clearenv()
func Environ() []string
func Exit(code int)
func Expand(s string, mapping func(string) string) string
func ExpandEnv(s string) string
func Getegid() int
func Getenv(key string) string
func Geteuid() int
func Getgid() int
func Getgroups() ([]int, error)
func Getpagesize() int
func Getpid() int
func Getppid() int
func Getuid() int
func Getwd() (pwd string, err error)
func Hostname() (name string, err error)
func IsExist(err error) bool
func IsNotExist(err error) bool
func IsPathSeparator(c uint8) bool
func IsPermission(err error) bool
func Lchown(name string, uid, gid int) error
func Link(oldname, newname string) error
func Mkdir(name string, perm FileMode) error
func MkdirAll(path string, perm FileMode) error
func NewSyscallError(syscall string, err error) error
func Readlink(name string) (string, error)
func Remove(name string) error
func RemoveAll(path string) error
func Rename(oldname, newname string) error
func SameFile(fi1, fi2 FileInfo) bool
func Setenv(key, value string) error
func Symlink(oldname, newname string) error
func TempDir() string
func Truncate(name string, size int64) error
type File
    func Create(name string) (file *File, err error)
    func NewFile(fd uintptr, name string) *File
    func Open(name string) (file *File, err error)
    func OpenFile(name string, flag int, perm FileMode) (file *File, err error)
    func Pipe() (r *File, w *File, err error)
    func (f *File) Chdir() error
    func (f *File) Chmod(mode FileMode) error
    func (f *File) Chown(uid, gid int) error
    func (f *File) Close() error
    func (f *File) Fd() uintptr
    func (f *File) Name() string
    func (f *File) Read(b []byte) (n int, err error)
    func (f *File) ReadAt(b []byte, off int64) (n int, err error)
    func (f *File) Readdir(n int) (fi []FileInfo, err error)
    func (f *File) Readdirnames(n int) (names []string, err error)
    func (f *File) Seek(offset int64, whence int) (ret int64, err error)
    func (f *File) Stat() (fi FileInfo, err error)
    func (f *File) Sync() (err error)
    func (f *File) Truncate(size int64) error
    func (f *File) Write(b []byte) (n int, err error)
    func (f *File) WriteAt(b []byte, off int64) (n int, err error)
    func (f *File) WriteString(s string) (ret int, err error)
type FileInfo
    func Lstat(name string) (fi FileInfo, err error)
    func Stat(name string) (fi FileInfo, err error)
type FileMode
    func (m FileMode) IsDir() bool
    func (m FileMode) Perm() FileMode
    func (m FileMode) String() string
type LinkError
    func (e *LinkError) Error() string
type PathError
    func (e *PathError) Error() string
type ProcAttr
type Process
    func FindProcess(pid int) (p *Process, err error)
    func StartProcess(name string, argv []string, attr *ProcAttr) (*Process, error)
    func (p *Process) Kill() error
    func (p *Process) Release() error
    func (p *Process) Signal(sig Signal) error
    func (p *Process) Wait() (*ProcessState, error)
type ProcessState
    func (p *ProcessState) Exited() bool
    func (p *ProcessState) Pid() int
    func (p *ProcessState) String() string
    func (p *ProcessState) Success() bool
    func (p *ProcessState) Sys() interface{}
    func (p *ProcessState) SysUsage() interface{}
    func (p *ProcessState) SystemTime() time.Duration
    func (p *ProcessState) UserTime() time.Duration
type Signal
type SyscallError
    func (e *SyscallError) Error() string

Package files

dir_unix.go doc.go env.go error.go error_posix.go exec.go exec_posix.go exec_unix.go file.go file_posix.go file_unix.go getwd.go path.go path_unix.go proc.go stat_linux.go sys_linux.go types.go

Constants

const (
    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.
    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  // if possible, truncate file when opened.
)

Flags to Open wrapping those of the underlying system. Not all flags may be implemented on a given system. 

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
)

Seek whence values. 

const (
    PathSeparator     = '/' // OS-specific path separator
    PathListSeparator = ':' // OS-specific path list separator
)
const DevNull = "/dev/null"

DevNull is the name of the operating system's “null device.” On Unix-like systems, it is "/dev/null"; on Windows, "NUL".

Variables

var (
    ErrInvalid    = errors.New("invalid argument")
    ErrPermission = errors.New("permission denied")
    ErrExist      = errors.New("file already exists")
    ErrNotExist   = errors.New("file does not exist")
)

Portable analogs of some common system call errors. 

var (
    Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
    Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
    Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
)

Stdin, Stdout, and Stderr are open Files pointing to the standard input, standard output, and standard error file descriptors. 

var Args []string

Args hold the command-line arguments, starting with the program name.

func Chdir

func Chdir(dir string) error

Chdir changes the current working directory to the named directory. If there is an error, it will be of type *PathError.

func Chmod

func Chmod(name string, mode FileMode) error

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.

func Chown

func Chown(name string, uid, gid int) error

Chown changes the numeric uid and gid of the named file. If the file is a symbolic link, it changes the uid and gid of the link's target. If there is an error, it will be of type *PathError.

func Chtimes

func Chtimes(name string, atime time.Time, mtime time.Time) error

Chtimes changes the access and modification times of the named file, similar to the Unix utime() or utimes() functions.

The underlying filesystem may truncate or round the values to a less precise time unit. If there is an error, it will be of type *PathError.

func Clearenv

func Clearenv()

Clearenv deletes all environment variables.

func Environ

func Environ() []string

Environ returns a copy of strings representing the environment, in the form "key=value".

func Exit

func Exit(code int)

Exit causes the current program to exit with the given status code. Conventionally, code zero indicates success, non-zero an error.

func Expand

func Expand(s string, mapping func(string) string) string

Expand replaces ${var} or $var in the string based on the mapping function. Invocations of undefined variables are replaced with the empty string.

func ExpandEnv

func ExpandEnv(s string) string

ExpandEnv replaces ${var} or $var in the string according to the values of the current environment variables. References to undefined variables are replaced by the empty string.

func Getegid

func Getegid() int

Getegid returns the numeric effective group id of the caller.

func Getenv

func Getenv(key string) string

Getenv retrieves the value of the environment variable named by the key. It returns the value, which will be empty if the variable is not present.

func Geteuid

func Geteuid() int

Geteuid returns the numeric effective user id of the caller.

func Getgid

func Getgid() int

Getgid returns the numeric group id of the caller.

func Getgroups

func Getgroups() ([]int, error)

Getgroups returns a list of the numeric ids of groups that the caller belongs to.

func Getpagesize

func Getpagesize() int

Getpagesize returns the underlying system's memory page size.

func Getpid

func Getpid() int

Getpid returns the process id of the caller.

func Getppid

func Getppid() int

Getppid returns the process id of the caller's parent.

func Getuid

func Getuid() int

Getuid returns the numeric user id of the caller.

func Getwd

func Getwd() (pwd string, err error)

Getwd returns a rooted path name corresponding to the current directory. If the current directory can be reached via multiple paths (due to symbolic links), Getwd may return any one of them.

func Hostname

func Hostname() (name string, err error)

Hostname returns the host name reported by the kernel.

func IsExist

func IsExist(err error) bool

IsExist returns whether the error is known to report that a file or directory already exists. It is satisfied by ErrExist as well as some syscall errors.

func IsNotExist

func IsNotExist(err error) bool

IsNotExist returns whether the error is known to report that a file or directory does not exist. It is satisfied by ErrNotExist as well as some syscall errors.

func IsPathSeparator

func IsPathSeparator(c uint8) bool

IsPathSeparator returns true if c is a directory separator character.

func IsPermission

func IsPermission(err error) bool

IsPermission returns whether the error is known to report that permission is denied. It is satisfied by ErrPermission as well as some syscall errors.

func Lchown

func Lchown(name string, uid, gid int) error

Lchown changes the numeric uid and gid of the named file. If the file is a symbolic link, it changes the uid and gid of the link itself. If there is an error, it will be of type *PathError. 

func Link(oldname, newname string) error

Link creates newname as a hard link to the oldname file. If there is an error, it will be of type *LinkError.

func Mkdir

func Mkdir(name string, perm FileMode) error

Mkdir creates a new directory with the specified name and permission bits. If there is an error, it will be of type *PathError.

func MkdirAll

func MkdirAll(path string, perm FileMode) error

MkdirAll creates a directory named path, along with any necessary parents, and returns nil, or else returns an error. The permission bits perm are used for all directories that MkdirAll creates. If path is already a directory, MkdirAll does nothing and returns nil.

func NewSyscallError

func NewSyscallError(syscall string, err error) error

NewSyscallError returns, as an error, a new SyscallError with the given system call name and error details. As a convenience, if err is nil, NewSyscallError returns nil. 

func Readlink(name string) (string, error)

Readlink returns the destination of the named symbolic link. If there is an error, it will be of type *PathError.

func Remove

func Remove(name string) error

Remove removes the named file or directory. If there is an error, it will be of type *PathError.

func RemoveAll

func RemoveAll(path string) error

RemoveAll removes path and any children it contains. It removes everything it can but returns the first error it encounters. If the path does not exist, RemoveAll returns nil (no error).

func Rename

func Rename(oldname, newname string) error

Rename renames a file.

func SameFile

func SameFile(fi1, fi2 FileInfo) bool

SameFile reports whether fi1 and fi2 describe the same file. For example, on Unix this means that the device and inode fields of the two underlying structures are identical; on other systems the decision may be based on the path names. SameFile only applies to results returned by this package's Stat. It returns false in other cases.

func Setenv

func Setenv(key, value string) error

Setenv sets the value of the environment variable named by the key. It returns an error, if any. 

func Symlink(oldname, newname string) error

Symlink creates newname as a symbolic link to oldname. If there is an error, it will be of type *LinkError.

func TempDir

func TempDir() string

TempDir returns the default directory to use for temporary files.

func Truncate

func Truncate(name string, size int64) error

Truncate changes the size of the named file. If the file is a symbolic link, it changes the size of the link's target. If there is an error, it will be of type *PathError.

type File

type File struct {
    // contains filtered or unexported fields
}

File represents an open file descriptor.

func Create

func Create(name string) (file *File, err error)

Create creates the named file mode 0666 (before umask), truncating it if it already exists. 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 NewFile

func NewFile(fd uintptr, name string) *File

NewFile returns a new File with the given file descriptor and name.

func Open

func Open(name string) (file *File, err error)

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 OpenFile

func OpenFile(name string, flag int, perm FileMode) (file *File, err error)

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.) and perm, (0666 etc.) if applicable. 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 Pipe

func Pipe() (r *File, w *File, err error)

Pipe returns a connected pair of Files; reads from r return bytes written to w. It returns the files and an error, if any.

func (*File) Chdir

func (f *File) Chdir() error

Chdir changes the current working directory to the file, which must be a directory. If there is an error, it will be of type *PathError.

func (*File) Chmod

func (f *File) Chmod(mode FileMode) error

Chmod changes the mode of the file to mode. If there is an error, it will be of type *PathError.

func (*File) Chown

func (f *File) Chown(uid, gid int) error

Chown changes the numeric uid and gid of the named file. If there is an error, it will be of type *PathError.

func (*File) Close

func (f *File) Close() error

Close closes the File, rendering it unusable for I/O. It returns an error, if any.

func (*File) Fd

func (f *File) Fd() uintptr

Fd returns the integer Unix file descriptor referencing the open file.

func (*File) Name

func (f *File) Name() string

Name returns the name of the file as presented to Open.

func (*File) Read

func (f *File) Read(b []byte) (n int, err error)

Read reads up to len(b) bytes from the File. It returns the number of bytes read and an error, if any. EOF is signaled by a zero count with err set to io.EOF.

func (*File) ReadAt

func (f *File) ReadAt(b []byte, off int64) (n int, err error)

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) Readdir

func (f *File) Readdir(n int) (fi []FileInfo, err error)

Readdir reads the contents of the directory associated with file and returns an array of up to n FileInfo values, as would be returned by Lstat, in directory order. Subsequent calls on the same file will yield further FileInfos.

If n > 0, Readdir returns at most n FileInfo structures. In this case, if Readdir returns an empty slice, it will return a non-nil error explaining why. At the end of a directory, the error is io.EOF.

If n <= 0, Readdir returns all the FileInfo from the directory in a single slice. In this case, if Readdir succeeds (reads all the way to the end of the directory), it returns the slice and a nil error. If it encounters an error before the end of the directory, Readdir returns the FileInfo read until that point and a non-nil error.

func (*File) Readdirnames

func (f *File) Readdirnames(n int) (names []string, err error)

Readdirnames reads and returns a slice of names from the directory f.

If n > 0, Readdirnames returns at most n names. In this case, if Readdirnames returns an empty slice, it will return a non-nil error explaining why. At the end of a directory, the error is io.EOF.

If n <= 0, Readdirnames returns all the names from the directory in a single slice. In this case, if Readdirnames succeeds (reads all the way to the end of the directory), it returns the slice and a nil error. If it encounters an error before the end of the directory, Readdirnames returns the names read until that point and a non-nil error.

func (*File) Seek

func (f *File) Seek(offset int64, whence int) (ret int64, err error)

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.

func (*File) Stat

func (f *File) Stat() (fi FileInfo, err error)

Stat returns the FileInfo structure describing file. If there is an error, it will be of type *PathError.

func (*File) Sync

func (f *File) Sync() (err error)

Sync commits the current contents of the file to stable storage. Typically, this means flushing the file system's in-memory copy of recently written data to disk.

func (*File) Truncate

func (f *File) Truncate(size int64) error

Truncate changes the size of the file. It does not change the I/O offset. If there is an error, it will be of type *PathError.

func (*File) Write

func (f *File) Write(b []byte) (n int, err error)

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) WriteAt

func (f *File) WriteAt(b []byte, off int64) (n int, err error)

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).

func (*File) WriteString

func (f *File) WriteString(s string) (ret int, err error)

WriteString is like Write, but writes the contents of string s rather than an array of bytes.

type FileInfo

type FileInfo interface {
    Name() string       // base name of the file
    Size() int64        // length in bytes for regular files; system-dependent for others
    Mode() FileMode     // file mode bits
    ModTime() time.Time // modification time
    IsDir() bool        // abbreviation for Mode().IsDir()
    Sys() interface{}   // underlying data source (can return nil)
}

A FileInfo describes a file and is returned by Stat and Lstat

func Lstat

func Lstat(name string) (fi FileInfo, err error)

Lstat returns a FileInfo describing the named file. If the file is a symbolic link, the returned FileInfo describes the symbolic link. Lstat makes no attempt to follow the link. If there is an error, it will be of type *PathError.

func Stat

func Stat(name string) (fi FileInfo, err error)

Stat returns a FileInfo describing the named file. If there is an error, it will be of type *PathError.

type FileMode

type FileMode uint32

A FileMode represents a file's mode and permission bits. The bits have the same definition on all systems, so that information about files can be moved from one system to another portably. Not all bits apply to all systems. The only required bit is ModeDir for directories. 

const (
    // The single letters are the abbreviations
    // used by the String method's formatting.
    ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
    ModeAppend                                     // a: append-only
    ModeExclusive                                  // l: exclusive use
    ModeTemporary                                  // T: temporary file (not backed up)
    ModeSymlink                                    // L: symbolic link
    ModeDevice                                     // D: device file
    ModeNamedPipe                                  // p: named pipe (FIFO)
    ModeSocket                                     // S: Unix domain socket
    ModeSetuid                                     // u: setuid
    ModeSetgid                                     // g: setgid
    ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
    ModeSticky

    // Mask for the type bits. For regular files, none will be set.
    ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice

    ModePerm FileMode = 0777 // permission bits
)

The defined file mode bits are the most significant bits of the FileMode. The nine least-significant bits are the standard Unix rwxrwxrwx permissions. The values of these bits should be considered part of the public API and may be used in wire protocols or disk representations: they must not be changed, although new bits might be added.

func (FileMode) IsDir

func (m FileMode) IsDir() bool

IsDir reports whether m describes a directory. That is, it tests for the ModeDir bit being set in m.

func (FileMode) Perm

func (m FileMode) Perm() FileMode

Perm returns the Unix permission bits in m.

func (FileMode) String

func (m FileMode) String() string

type LinkError

type LinkError struct {
    Op  string
    Old string
    New string
    Err error
}

LinkError records an error during a link or symlink or rename system call and the paths that caused it.

func (*LinkError) Error

func (e *LinkError) Error() string

type PathError

type PathError struct {
    Op   string
    Path string
    Err  error
}

PathError records an error and the operation and file path that caused it.

func (*PathError) Error

func (e *PathError) Error() string

type ProcAttr

type ProcAttr struct {
    // If Dir is non-empty, the child changes into the directory before
    // creating the process.
    Dir string
    // If Env is non-nil, it gives the environment variables for the
    // new process in the form returned by Environ.
    // If it is nil, the result of Environ will be used.
    Env []string
    // Files specifies the open files inherited by the new process.  The
    // first three entries correspond to standard input, standard output, and
    // standard error.  An implementation may support additional entries,
    // depending on the underlying operating system.  A nil entry corresponds
    // to that file being closed when the process starts.
    Files []*File

    // Operating system-specific process creation attributes.
    // Note that setting this field means that your program
    // may not execute properly or even compile on some
    // operating systems.
    Sys *syscall.SysProcAttr
}

ProcAttr holds the attributes that will be applied to a new process started by StartProcess.

type Process

type Process struct {
    Pid int
    // contains filtered or unexported fields
}

Process stores the information about a process created by StartProcess.

func FindProcess

func FindProcess(pid int) (p *Process, err error)

FindProcess looks for a running process by its pid. The Process it returns can be used to obtain information about the underlying operating system process.

func StartProcess

func StartProcess(name string, argv []string, attr *ProcAttr) (*Process, error)

StartProcess starts a new process with the program, arguments and attributes specified by name, argv and attr.

StartProcess is a low-level interface. The os/exec package provides higher-level interfaces.

If there is an error, it will be of type *PathError.

func (*Process) Kill

func (p *Process) Kill() error

Kill causes the Process to exit immediately.

func (*Process) Release

func (p *Process) Release() error

Release releases any resources associated with the Process p, rendering it unusable in the future. Release only needs to be called if Wait is not.

func (*Process) Signal

func (p *Process) Signal(sig Signal) error

Signal sends a signal to the Process.

func (*Process) Wait

func (p *Process) Wait() (*ProcessState, error)

Wait waits for the Process to exit, and then returns a ProcessState describing its status and an error, if any. Wait releases any resources associated with the Process.

type ProcessState

type ProcessState struct {
    // contains filtered or unexported fields
}

ProcessState stores information about a process, as reported by Wait.

func (*ProcessState) Exited

func (p *ProcessState) Exited() bool

Exited returns whether the program has exited.

func (*ProcessState) Pid

func (p *ProcessState) Pid() int

Pid returns the process id of the exited process.

func (*ProcessState) String

func (p *ProcessState) String() string

func (*ProcessState) Success

func (p *ProcessState) Success() bool

Success reports whether the program exited successfully, such as with exit status 0 on Unix.

func (*ProcessState) Sys

func (p *ProcessState) Sys() interface{}

Sys returns system-dependent exit information about the process. Convert it to the appropriate underlying type, such as syscall.WaitStatus on Unix, to access its contents.

func (*ProcessState) SysUsage

func (p *ProcessState) SysUsage() interface{}

SysUsage returns system-dependent resource usage information about the exited process. Convert it to the appropriate underlying type, such as *syscall.Rusage on Unix, to access its contents.

func (*ProcessState) SystemTime

func (p *ProcessState) SystemTime() time.Duration

SystemTime returns the system CPU time of the exited process and its children.

func (*ProcessState) UserTime

func (p *ProcessState) UserTime() time.Duration

UserTime returns the user CPU time of the exited process and its children.

type Signal

type Signal interface {
    String() string
    Signal() // to distinguish from other Stringers
}

A Signal represents an operating system signal. The usual underlying implementation is operating system-dependent: on Unix it is syscall.Signal. 

var (
    Interrupt Signal = syscall.SIGINT
    Kill      Signal = syscall.SIGKILL
)

The only signal values guaranteed to be present on all systems are Interrupt (send the process an interrupt) and Kill (force the process to exit).

type SyscallError

type SyscallError struct {
    Syscall string
    Err     error
}

SyscallError records an error from a specific system call.

func (*SyscallError) Error

func (e *SyscallError) Error() string

Subdirectories

Name      Synopsis
exec      Package exec runs external commands.
signal      Package signal implements access to incoming signals.
user      Package user allows user account lookups by name or id.
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