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])
dir.go dir_unix.go env.go error.go error_posix.go error_unix.go exec.go exec_posix.go exec_unix.go executable.go executable_procfs.go file.go file_posix.go file_unix.go getwd.go path.go path_unix.go pipe_linux.go proc.go stat_linux.go stat_unix.go sticky_notbsd.go str.go sys.go sys_linux.go sys_unix.go types.go types_unix.go wait_waitid.go
Flags to OpenFile wrapping those of the underlying system. Not all flags may be implemented on a given system.
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.
) 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
) const (
PathSeparator = '/' // OS-specific path separator
PathListSeparator = ':' // OS-specific path list separator
) DevNull is the name of the operating system's “null device.” On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
const DevNull = "/dev/null"
Portable analogs of some common system call errors.
var (
ErrInvalid = errors.New("invalid argument") // methods on File will return this error when the receiver is nil
ErrPermission = errors.New("permission denied")
ErrExist = errors.New("file already exists")
ErrNotExist = errors.New("file does not exist")
ErrClosed = errors.New("file already closed")
) 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")
) Args hold the command-line arguments, starting with the program name.
var Args []string
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(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.
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, the mode must be non-zero but otherwise only the 0200 bit (owner writable) of mode is used; it controls whether the file's read-only attribute is set or cleared. attribute. The other bits are currently unused. 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.
package main
import (
"log"
"os"
)
func main() {
if err := os.Chmod("some-filename", 0644); err != nil {
log.Fatal(err)
}
}
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.
On Windows, it always returns the syscall.EWINDOWS error, wrapped in *PathError.
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.
package main
import (
"log"
"os"
"time"
)
func main() {
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 Clearenv()
Clearenv deletes all environment variables.
func Environ() []string
Environ returns a copy of strings representing the environment, in the form "key=value".
func Executable() (string, error)
Executable returns the path name for the executable that started the current process. There is no guarantee that the path is still pointing to the correct executable. If a symlink was used to start the process, depending on the operating system, the result might be the symlink or the path it pointed to. If a stable result is needed, path/filepath.EvalSymlinks might help.
Executable returns an absolute path unless an error occurred.
The main use case is finding resources located relative to an executable.
Executable is not supported on nacl.
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. The program terminates immediately; deferred functions are not run.
func Expand(s string, mapping func(string) string) string
Expand replaces ${var} or $var in the string based on the mapping function. For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
func ExpandEnv(s string) string
ExpandEnv replaces ${var} or $var in the string according to the values of the current environment variables. References to undefined variables are replaced by the empty string.
package main
import (
"fmt"
"os"
)
func main() {
fmt.Println(os.ExpandEnv("$USER lives in ${HOME}."))
}
func Getegid() int
Getegid returns the numeric effective group id of the caller.
On Windows, it returns -1.
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. To distinguish between an empty value and an unset value, use LookupEnv.
package main
import (
"fmt"
"os"
)
func main() {
fmt.Printf("%s lives in %s.\n", os.Getenv("USER"), os.Getenv("HOME"))
}
func Geteuid() int
Geteuid returns the numeric effective user id of the caller.
On Windows, it returns -1.
func Getgid() int
Getgid returns the numeric group id of the caller.
On Windows, it returns -1.
func Getgroups() ([]int, error)
Getgroups returns a list of the numeric ids of groups that the caller belongs to.
On Windows, it returns syscall.EWINDOWS. See the os/user package for a possible alternative.
func Getpagesize() int
Getpagesize returns the underlying system's memory page size.
func Getpid() int
Getpid returns the process id of the caller.
func Getppid() int
Getppid returns the process id of the caller's parent.
func Getuid() int
Getuid returns the numeric user id of the caller.
On Windows, it returns -1.
func Getwd() (dir 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() (name string, err error)
Hostname returns the host name reported by the kernel.
func IsExist(err error) bool
IsExist returns a boolean indicating 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(err error) bool
IsNotExist returns a boolean indicating 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.
package main
import (
"fmt"
"os"
)
func main() {
filename := "a-nonexistent-file"
if _, err := os.Stat(filename); os.IsNotExist(err) {
fmt.Printf("file does not exist")
}
}
func IsPathSeparator(c uint8) bool
IsPathSeparator reports whether c is a directory separator character.
func IsPermission(err error) bool
IsPermission returns a boolean indicating whether the error is known to report that permission is denied. It is satisfied by ErrPermission as well as some syscall errors.
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.
On Windows, it always returns the syscall.EWINDOWS error, wrapped in *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 LookupEnv(key string) (string, bool)
LookupEnv retrieves the value of the environment variable named by the key. If the variable is present in the environment the value (which may be empty) is returned and the boolean is true. Otherwise the returned value will be empty and the boolean will be false.
package main
import (
"fmt"
"os"
)
func main() {
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)
}
}
show("USER")
show("GOPATH")
}
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(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(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(name string) error
Remove removes the named file or directory. If there is an error, it will be of type *PathError.
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(oldpath, newpath string) error
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 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(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() string
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 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.
func Unsetenv(key string) error
Unsetenv unsets a single environment variable.
package main
import (
"os"
)
func main() {
os.Setenv("TMPDIR", "/my/tmp")
defer os.Unsetenv("TMPDIR")
}
File represents an open file descriptor.
type File struct {
// contains filtered or unexported fields
} func Create(name string) (*File, error)
Create creates the named file with 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(fd uintptr, name string) *File
NewFile returns a new File with the given file descriptor and name. The returned value will be nil if fd is not a valid file descriptor.
func Open(name string) (*File, 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(name string, flag int, perm FileMode) (*File, 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.
package main
import (
"log"
"os"
)
func main() {
f, err := os.OpenFile("notes.txt", os.O_RDWR|os.O_CREATE, 0755)
if err != nil {
log.Fatal(err)
}
if err := f.Close(); err != nil {
log.Fatal(err)
}
}
package main
import (
"log"
"os"
)
func main() {
// 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 {
log.Fatal(err)
}
if err := f.Close(); err != nil {
log.Fatal(err)
}
}
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 (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 (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 (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.
On Windows, it always returns the syscall.EWINDOWS error, wrapped in *PathError.
func (f *File) Close() error
Close closes the File, rendering it unusable for I/O. It returns an error, if any.
func (f *File) Fd() uintptr
Fd returns the integer Unix file descriptor referencing the open file. The file descriptor is valid only until f.Close is called or f is garbage collected.
func (f *File) Name() string
Name returns the name of the file as presented to Open.
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 any error encountered. At end of file, Read returns 0, io.EOF.
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 (f *File) Readdir(n int) ([]FileInfo, error)
Readdir reads the contents of the directory associated with file and returns a slice 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 (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 (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. The behavior of Seek on a file opened with O_APPEND is not specified.
func (f *File) Stat() (FileInfo, error)
Stat returns the FileInfo structure describing file. If there is an error, it will be of type *PathError.
func (f *File) Sync() 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 (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 (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 (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 (f *File) WriteString(s string) (n int, err error)
WriteString is like Write, but writes the contents of string s rather than a slice of bytes.
A FileInfo describes a file and is returned by Stat and Lstat.
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)
} func Lstat(name string) (FileInfo, 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(name string) (FileInfo, error)
Stat returns a FileInfo describing the named file. If there is an error, it will be of type *PathError.
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.
type FileMode uint32
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.
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; Plan 9 only
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 // t: sticky
// Mask for the type bits. For regular files, none will be set.
ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice
ModePerm FileMode = 0777 // Unix permission bits
) package main
import (
"fmt"
"log"
"os"
)
func main() {
fi, err := os.Lstat("some-filename")
if err != nil {
log.Fatal(err)
}
switch mode := fi.Mode(); {
case mode.IsRegular():
fmt.Println("regular file")
case mode.IsDir():
fmt.Println("directory")
case mode&os.ModeSymlink != 0:
fmt.Println("symbolic link")
case mode&os.ModeNamedPipe != 0:
fmt.Println("named pipe")
}
}
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 (m FileMode) IsRegular() bool
IsRegular reports whether m describes a regular file. That is, it tests that no mode type bits are set.
func (m FileMode) Perm() FileMode
Perm returns the Unix permission bits in m.
func (m FileMode) String() string
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 (e *LinkError) Error() string
PathError records an error and the operation and file path that caused it.
type PathError struct {
Op string
Path string
Err error
} func (e *PathError) Error() string
ProcAttr holds the attributes that will be applied to a new process started by StartProcess.
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
} Process stores the information about a process created by StartProcess.
type Process struct {
Pid int
// contains filtered or unexported fields
} func FindProcess(pid int) (*Process, 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.
On Unix systems, FindProcess always succeeds and returns a Process for the given pid, regardless of whether the process exists.
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 (p *Process) Kill() error
Kill causes the Process to exit immediately.
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 (p *Process) Signal(sig Signal) error
Signal sends a signal to the Process. Sending Interrupt on Windows is not implemented.
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. On most operating systems, the Process must be a child of the current process or an error will be returned.
ProcessState stores information about a process, as reported by Wait.
type ProcessState struct {
// contains filtered or unexported fields
} func (p *ProcessState) Exited() bool
Exited reports whether the program has exited.
func (p *ProcessState) Pid() int
Pid returns the process id of the exited process.
func (p *ProcessState) String() string
func (p *ProcessState) Success() bool
Success reports whether the program exited successfully, such as with exit status 0 on Unix.
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 (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. (On Unix, *syscall.Rusage matches struct rusage as defined in the getrusage(2) manual page.)
func (p *ProcessState) SystemTime() time.Duration
SystemTime returns the system CPU time of the exited process and its children.
func (p *ProcessState) UserTime() time.Duration
UserTime returns the user CPU time of the exited process and its children.
A Signal represents an operating system signal. The usual underlying implementation is operating system-dependent: on Unix it is syscall.Signal.
type Signal interface {
String() string
Signal() // to distinguish from other Stringers
} 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).
var (
Interrupt Signal = syscall.SIGINT
Kill Signal = syscall.SIGKILL
) SyscallError records an error from a specific system call.
type SyscallError struct {
Syscall string
Err error
} func (e *SyscallError) Error() string
| 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. |
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/os/