os

package
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 Go to latest Published: Apr 28, 2022 License: BSD-3-Clause Imports: 8 Imported by: 0

Documentation

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

View Source 
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 OpenFile wrapping those of the underlying system. Not all flags may be implemented on a given system.

View Source 
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.

Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.

View Source 
const (
	PathSeparator     = '/' // OS-specific path separator
	PathListSeparator = ':' // OS-specific path list separator
)
View Source 
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

View Source 
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")
)

Portable analogs of some common system call errors.

View Source 
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.

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.

View Source 
var Args []string

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

Functions

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. The program terminates immediately; deferred functions are not run.

func Expand 

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 

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() (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 

func Hostname() (name string, err error)

Hostname returns the host name reported by the kernel.

func IsExist 

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 

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.

func IsPathSeparator 

func IsPathSeparator(c uint8) bool

IsPathSeparator reports whether c is a directory separator character.

func IsPermission 

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 

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 LookupEnv 

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.

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 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 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(oldpath, newpath string) error

Rename renames (moves) oldpath to newpath. If newpath already exists, 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 

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.

func Unsetenv 

func Unsetenv(key string) error

Unsetenv unsets a single environment variable.

Types

type File 

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

File represents an open file descriptor.

func Create 

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 

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, 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, 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 (*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. The file descriptor is valid only until f.Close is called or f is garbage collected.

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) ([]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 (*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. The behavior of Seek on a file opened with O_APPEND is not specified.

func (*File) Stat 

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 (*File) Sync 

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 (*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) (n int, err error)

WriteString is like Write, but writes the contents of string s rather than a slice 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) (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 

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.

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                                     // 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
)

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) IsRegular 

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 (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) (*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 

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. Sending Interrupt on Windows is not implemented.

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. On most operating systems, the Process must be a child of the current process or an error will be returned.

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 reports 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. (On Unix, *syscall.Rusage matches struct rusage as defined in the getrusage(2) manual page.)

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

Source Files

View all Source files

Directories

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

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