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Node.js v8.0.0 Documentation
Table of Contents
- File System
- WHATWG URL object support
- Buffer API
- Class: fs.FSWatcher
- Class: fs.ReadStream
- Class: fs.Stats
- Class: fs.WriteStream
- fs.access(path[, mode], callback)
- fs.accessSync(path[, mode])
- fs.appendFile(file, data[, options], callback)
- fs.appendFileSync(file, data[, options])
- fs.chmod(path, mode, callback)
- fs.chmodSync(path, mode)
- fs.chown(path, uid, gid, callback)
- fs.chownSync(path, uid, gid)
- fs.close(fd, callback)
- fs.closeSync(fd)
- fs.constants
- fs.createReadStream(path[, options])
- fs.createWriteStream(path[, options])
- fs.exists(path, callback)
- fs.existsSync(path)
- fs.fchmod(fd, mode, callback)
- fs.fchmodSync(fd, mode)
- fs.fchown(fd, uid, gid, callback)
- fs.fchownSync(fd, uid, gid)
- fs.fdatasync(fd, callback)
- fs.fdatasyncSync(fd)
- fs.fstat(fd, callback)
- fs.fstatSync(fd)
- fs.fsync(fd, callback)
- fs.fsyncSync(fd)
- fs.ftruncate(fd, len, callback)
- fs.ftruncateSync(fd, len)
- fs.futimes(fd, atime, mtime, callback)
- fs.futimesSync(fd, atime, mtime)
- fs.lchmod(path, mode, callback)
- fs.lchmodSync(path, mode)
- fs.lchown(path, uid, gid, callback)
- fs.lchownSync(path, uid, gid)
- fs.link(existingPath, newPath, callback)
- fs.linkSync(existingPath, newPath)
- fs.lstat(path, callback)
- fs.lstatSync(path)
- fs.mkdir(path[, mode], callback)
- fs.mkdirSync(path[, mode])
- fs.mkdtemp(prefix[, options], callback)
- fs.mkdtempSync(prefix[, options])
- fs.open(path, flags[, mode], callback)
- fs.openSync(path, flags[, mode])
- fs.read(fd, buffer, offset, length, position, callback)
- fs.readdir(path[, options], callback)
- fs.readdirSync(path[, options])
- fs.readFile(path[, options], callback)
- fs.readFileSync(path[, options])
- fs.readlink(path[, options], callback)
- fs.readlinkSync(path[, options])
- fs.readSync(fd, buffer, offset, length, position)
- fs.realpath(path[, options], callback)
- fs.realpathSync(path[, options])
- fs.rename(oldPath, newPath, callback)
- fs.renameSync(oldPath, newPath)
- fs.rmdir(path, callback)
- fs.rmdirSync(path)
- fs.stat(path, callback)
- fs.statSync(path)
- fs.symlink(target, path[, type], callback)
- fs.symlinkSync(target, path[, type])
- fs.truncate(path, len, callback)
- fs.truncateSync(path, len)
- fs.unlink(path, callback)
- fs.unlinkSync(path)
- fs.unwatchFile(filename[, listener])
- fs.utimes(path, atime, mtime, callback)
- fs.utimesSync(path, atime, mtime)
- fs.watch(filename[, options][, listener])
- fs.watchFile(filename[, options], listener)
- fs.write(fd, buffer[, offset[, length[, position]]], callback)
- fs.write(fd, string[, position[, encoding]], callback)
- fs.writeFile(file, data[, options], callback)
- fs.writeFileSync(file, data[, options])
- fs.writeSync(fd, buffer[, offset[, length[, position]]])
- fs.writeSync(fd, string[, position[, encoding]])
- FS Constants
File System#
Stability: 2 - Stable
File I/O is provided by simple wrappers around standard POSIX functions. To
use this module do require('fs')
. All the methods have asynchronous and
synchronous forms.
The asynchronous form always takes a completion callback as its last argument.
The arguments passed to the completion callback depend on the method, but the
first argument is always reserved for an exception. If the operation was
completed successfully, then the first argument will be null
or undefined
.
When using the synchronous form any exceptions are immediately thrown.
Exceptions may be handled using try
/catch
, or they may be allowed to
bubble up.
Here is an example of the asynchronous version:
const fs = require('fs');
fs.unlink('/tmp/hello', (err) => {
if (err) throw err;
console.log('successfully deleted /tmp/hello');
});
Here is the synchronous version:
const fs = require('fs');
fs.unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');
With the asynchronous methods there is no guaranteed ordering. So the following is prone to error:
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
It could be that fs.stat
is executed before fs.rename
.
The correct way to do this is to chain the callbacks.
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
});
In busy processes, the programmer is strongly encouraged to use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete--halting all connections.
The relative path to a filename can be used. Remember, however, that this path
will be relative to process.cwd()
.
While it is not recommended, most fs functions allow the callback argument to
be omitted, in which case a default callback is used that rethrows errors. To
get a trace to the original call site, set the NODE_DEBUG
environment
variable:
Note: Omitting the callback function on asynchronous fs functions is deprecated and may result in an error being thrown in the future.
$ cat script.js
function bad() {
require('fs').readFile('/');
}
bad();
$ env NODE_DEBUG=fs node script.js
fs.js:88
throw backtrace;
^
Error: EISDIR: illegal operation on a directory, read
<stack trace.>
WHATWG URL object support#
Stability: 1 - Experimental
For most fs
module functions, the path
or filename
argument may be passed
as a WHATWG URL
object. Only URL
objects using the file:
protocol
are supported.
const fs = require('fs');
const { URL } = require('url');
const fileUrl = new URL('file:///tmp/hello');
fs.readFileSync(fileUrl);
Note: file:
URLs are always absolute paths.
Using WHATWG URL
objects might introduce platform-specific behaviors.
On Windows, file:
URLs with a hostname convert to UNC paths, while file:
URLs with drive letters convert to local absolute paths. file:
URLs without a
hostname nor a drive letter will result in a throw :
// On Windows :
// - WHATWG file URLs with hostname convert to UNC path
// file://hostname/p/a/t/h/file => \\hostname\p\a\t\h\file
fs.readFileSync(new URL('file://hostname/p/a/t/h/file'));
// - WHATWG file URLs with drive letters convert to absolute path
// file:///C:/tmp/hello => C:\tmp\hello
fs.readFileSync(new URL('file:///C:/tmp/hello'));
// - WHATWG file URLs without hostname must have a drive letters
fs.readFileSync(new URL('file:///notdriveletter/p/a/t/h/file'));
fs.readFileSync(new URL('file:///c/p/a/t/h/file'));
// TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must be absolute
Note: file:
URLs with drive letters must use :
as a separator just after
the drive letter. Using another separator will result in a throw.
On all other platforms, file:
URLs with a hostname are unsupported and will
result in a throw:
// On other platforms:
// - WHATWG file URLs with hostname are unsupported
// file://hostname/p/a/t/h/file => throw!
fs.readFileSync(new URL('file://hostname/p/a/t/h/file'));
// TypeError [ERR_INVALID_FILE_URL_PATH]: must be absolute
// - WHATWG file URLs convert to absolute path
// file:///tmp/hello => /tmp/hello
fs.readFileSync(new URL('file:///tmp/hello'));
A file:
URL having encoded slash characters will result in a throw on all
platforms:
// On Windows
fs.readFileSync(new URL('file:///C:/p/a/t/h/%2F'));
fs.readFileSync(new URL('file:///C:/p/a/t/h/%2f'));
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
\ or / characters */
// On POSIX
fs.readFileSync(new URL('file:///p/a/t/h/%2F'));
fs.readFileSync(new URL('file:///p/a/t/h/%2f'));
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
/ characters */
On Windows, file:
URLs having encoded backslash will result in a throw:
// On Windows
fs.readFileSync(new URL('file:///C:/path/%5C'));
fs.readFileSync(new URL('file:///C:/path/%5c'));
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
\ or / characters */
Buffer API#
fs
functions support passing and receiving paths as both strings
and Buffers. The latter is intended to make it possible to work with
filesystems that allow for non-UTF-8 filenames. For most typical
uses, working with paths as Buffers will be unnecessary, as the string
API converts to and from UTF-8 automatically.
Note: On certain file systems (such as NTFS and HFS+) filenames
will always be encoded as UTF-8. On such file systems, passing
non-UTF-8 encoded Buffers to fs
functions will not work as expected.
Class: fs.FSWatcher#
Objects returned from fs.watch()
are of this type.
The listener
callback provided to fs.watch()
receives the returned FSWatcher's
change
events.
The object itself emits these events:
Event: 'change'#
eventType
<string> The type of fs changefilename
<string> | <Buffer> The filename that changed (if relevant/available)
Emitted when something changes in a watched directory or file.
See more details in fs.watch()
.
The filename
argument may not be provided depending on operating system
support. If filename
is provided, it will be provided as a Buffer
if
fs.watch()
is called with its encoding
option set to 'buffer'
, otherwise
filename
will be a string.
// Example when handled through fs.watch listener
fs.watch('./tmp', {encoding: 'buffer'}, (eventType, filename) => {
if (filename)
console.log(filename);
// Prints: <Buffer ...>
});
Event: 'error'#
error
<Error>
Emitted when an error occurs.
watcher.close()#
Stop watching for changes on the given fs.FSWatcher
.
Class: fs.ReadStream#
ReadStream
is a Readable Stream.
Event: 'close'#
Emitted when the ReadStream
's underlying file descriptor has been closed
using the fs.close()
method.
Event: 'open'#
fd
<integer> Integer file descriptor used by the ReadStream.
Emitted when the ReadStream's file is opened.
readStream.bytesRead#
The number of bytes read so far.
readStream.path#
The path to the file the stream is reading from as specified in the first
argument to fs.createReadStream()
. If path
is passed as a string, then
readStream.path
will be a string. If path
is passed as a Buffer
, then
readStream.path
will be a Buffer
.
Class: fs.Stats#
Objects returned from fs.stat()
, fs.lstat()
and fs.fstat()
and their
synchronous counterparts are of this type.
stats.isFile()
stats.isDirectory()
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isSymbolicLink()
(only valid withfs.lstat()
)stats.isFIFO()
stats.isSocket()
For a regular file util.inspect(stats)
would return a string very
similar to this:
Stats {
dev: 2114,
ino: 48064969,
mode: 33188,
nlink: 1,
uid: 85,
gid: 100,
rdev: 0,
size: 527,
blksize: 4096,
blocks: 8,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT }
Please note that atime
, mtime
, birthtime
, and ctime
are
instances of Date
object and appropriate methods should be used
to compare the values of these objects. For most general uses
getTime()
will return the number of milliseconds elapsed
since 1 January 1970 00:00:00 UTC and this integer should be sufficient for
any comparison, however there are additional methods which can be used for
displaying fuzzy information. More details can be found in the
MDN JavaScript Reference page.
Stat Time Values#
The times in the stat object have the following semantics:
atime
"Access Time" - Time when file data last accessed. Changed by the mknod(2), utimes(2), and read(2) system calls.mtime
"Modified Time" - Time when file data last modified. Changed by the mknod(2), utimes(2), and write(2) system calls.ctime
"Change Time" - Time when file status was last changed (inode data modification). Changed by the chmod(2), chown(2), link(2), mknod(2), rename(2), unlink(2), utimes(2), read(2), and write(2) system calls.birthtime
"Birth Time" - Time of file creation. Set once when the file is created. On filesystems where birthtime is not available, this field may instead hold either thectime
or1970-01-01T00:00Z
(ie, unix epoch timestamp0
). Note that this value may be greater thanatime
ormtime
in this case. On Darwin and other FreeBSD variants, also set if theatime
is explicitly set to an earlier value than the currentbirthtime
using the utimes(2) system call.
Prior to Node v0.12, the ctime
held the birthtime
on Windows
systems. Note that as of v0.12, ctime
is not "creation time", and
on Unix systems, it never was.
Class: fs.WriteStream#
WriteStream
is a Writable Stream.
Event: 'close'#
Emitted when the WriteStream
's underlying file descriptor has been closed
using the fs.close()
method.
Event: 'open'#
fd
<integer> Integer file descriptor used by the WriteStream.
Emitted when the WriteStream's file is opened.
writeStream.bytesWritten#
The number of bytes written so far. Does not include data that is still queued for writing.
writeStream.path#
The path to the file the stream is writing to as specified in the first
argument to fs.createWriteStream()
. If path
is passed as a string, then
writeStream.path
will be a string. If path
is passed as a Buffer
, then
writeStream.path
will be a Buffer
.
fs.access(path[, mode], callback)#
path
<string> | <Buffer> | <URL>mode
<integer>callback
<Function>
Tests a user's permissions for the file or directory specified by path
.
The mode
argument is an optional integer that specifies the accessibility
checks to be performed. The following constants define the possible values of
mode
. It is possible to create a mask consisting of the bitwise OR of two or
more values.
fs.constants.F_OK
-path
is visible to the calling process. This is useful for determining if a file exists, but says nothing aboutrwx
permissions. Default if nomode
is specified.fs.constants.R_OK
-path
can be read by the calling process.fs.constants.W_OK
-path
can be written by the calling process.fs.constants.X_OK
-path
can be executed by the calling process. This has no effect on Windows (will behave likefs.constants.F_OK
).
The final argument, callback
, is a callback function that is invoked with
a possible error argument. If any of the accessibility checks fail, the error
argument will be populated. The following example checks if the file
/etc/passwd
can be read and written by the current process.
fs.access('/etc/passwd', fs.constants.R_OK | fs.constants.W_OK, (err) => {
console.log(err ? 'no access!' : 'can read/write');
});
Using fs.access()
to check for the accessibility of a file before calling
fs.open()
, fs.readFile()
or fs.writeFile()
is not recommended. Doing
so introduces a race condition, since other processes may change the file's
state between the two calls. Instead, user code should open/read/write the
file directly and handle the error raised if the file is not accessible.
For example:
write (NOT RECOMMENDED)
fs.access('myfile', (err) => {
if (!err) {
console.error('myfile already exists');
return;
}
fs.open('myfile', 'wx', (err, fd) => {
if (err) throw err;
writeMyData(fd);
});
});
write (RECOMMENDED)
fs.open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === 'EEXIST') {
console.error('myfile already exists');
return;
}
throw err;
}
writeMyData(fd);
});
read (NOT RECOMMENDED)
fs.access('myfile', (err) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
fs.open('myfile', 'r', (err, fd) => {
if (err) throw err;
readMyData(fd);
});
});
read (RECOMMENDED)
fs.open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
readMyData(fd);
});
The "not recommended" examples above check for accessibility and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.
In general, check for the accessibility of a file only if the file won’t be used directly, for example when its accessibility is a signal from another process.
fs.accessSync(path[, mode])#
Synchronous version of fs.access()
. This throws if any accessibility
checks fail, and does nothing otherwise.
fs.appendFile(file, data[, options], callback)#
file
<string> | <Buffer> | <number> filename or file descriptordata
<string> | <Buffer>options
<Object> | <string>callback
<Function>
Asynchronously append data to a file, creating the file if it does not yet exist.
data
can be a string or a buffer.
Example:
fs.appendFile('message.txt', 'data to append', (err) => {
if (err) throw err;
console.log('The "data to append" was appended to file!');
});
If options
is a string, then it specifies the encoding. Example:
fs.appendFile('message.txt', 'data to append', 'utf8', callback);
Any specified file descriptor has to have been opened for appending.
Note: If a file descriptor is specified as the file
, it will not be closed
automatically.
fs.appendFileSync(file, data[, options])#
file
<string> | <Buffer> | <number> filename or file descriptordata
<string> | <Buffer>options
<Object> | <string>
The synchronous version of fs.appendFile()
. Returns undefined
.
fs.chmod(path, mode, callback)#
path
<string> | <Buffer> | <URL>mode
<integer>callback
<Function>
Asynchronous chmod(2). No arguments other than a possible exception are given to the completion callback.
fs.chmodSync(path, mode)#
Synchronous chmod(2). Returns undefined
.
fs.chown(path, uid, gid, callback)#
Asynchronous chown(2). No arguments other than a possible exception are given to the completion callback.
fs.chownSync(path, uid, gid)#
Synchronous chown(2). Returns undefined
.
fs.close(fd, callback)#
fd
<integer>callback
<Function>
Asynchronous close(2). No arguments other than a possible exception are given to the completion callback.
fs.closeSync(fd)#
fd
<integer>
Synchronous close(2). Returns undefined
.
fs.constants#
Returns an object containing commonly used constants for file system operations. The specific constants currently defined are described in FS Constants.
fs.createReadStream(path[, options])#
Returns a new ReadStream
object. (See Readable Stream).
Be aware that, unlike the default value set for highWaterMark
on a
readable stream (16 kb), the stream returned by this method has a
default value of 64 kb for the same parameter.
options
is an object or string with the following defaults:
const defaults = {
flags: 'r',
encoding: null,
fd: null,
mode: 0o666,
autoClose: true
};
options
can include start
and end
values to read a range of bytes from
the file instead of the entire file. Both start
and end
are inclusive and
start counting at 0. If fd
is specified and start
is omitted or undefined
,
fs.createReadStream()
reads sequentially from the current file position.
The encoding
can be any one of those accepted by Buffer
.
If fd
is specified, ReadStream
will ignore the path
argument and will use
the specified file descriptor. This means that no 'open'
event will be
emitted. Note that fd
should be blocking; non-blocking fd
s should be passed
to net.Socket
.
If autoClose
is false, then the file descriptor won't be closed, even if
there's an error. It is the application's responsibility to close it and make
sure there's no file descriptor leak. If autoClose
is set to true (default
behavior), on error
or end
the file descriptor will be closed
automatically.
mode
sets the file mode (permission and sticky bits), but only if the
file was created.
An example to read the last 10 bytes of a file which is 100 bytes long:
fs.createReadStream('sample.txt', {start: 90, end: 99});
If options
is a string, then it specifies the encoding.
fs.createWriteStream(path[, options])#
Returns a new WriteStream
object. (See Writable Stream).
options
is an object or string with the following defaults:
const defaults = {
flags: 'w',
defaultEncoding: 'utf8',
fd: null,
mode: 0o666,
autoClose: true
};
options
may also include a start
option to allow writing data at
some position past the beginning of the file. Modifying a file rather
than replacing it may require a flags
mode of r+
rather than the
default mode w
. The defaultEncoding
can be any one of those accepted by
Buffer
.
If autoClose
is set to true (default behavior) on error
or end
the file descriptor will be closed automatically. If autoClose
is false,
then the file descriptor won't be closed, even if there's an error.
It is the application's responsibility to close it and make sure there's no
file descriptor leak.
Like ReadStream
, if fd
is specified, WriteStream
will ignore the
path
argument and will use the specified file descriptor. This means that no
'open'
event will be emitted. Note that fd
should be blocking; non-blocking
fd
s should be passed to net.Socket
.
If options
is a string, then it specifies the encoding.
fs.exists(path, callback)#
Stability: 0 - Deprecated: Usefs.stat()
orfs.access()
instead.
path
<string> | <Buffer> | <URL>callback
<Function>
Test whether or not the given path exists by checking with the file system.
Then call the callback
argument with either true or false. Example:
fs.exists('/etc/passwd', (exists) => {
console.log(exists ? 'it\'s there' : 'no passwd!');
});
Note that the parameter to this callback is not consistent with other
Node.js callbacks. Normally, the first parameter to a Node.js callback is
an err
parameter, optionally followed by other parameters. The
fs.exists()
callback has only one boolean parameter. This is one reason
fs.access()
is recommended instead of fs.exists()
.
Using fs.exists()
to check for the existence of a file before calling
fs.open()
, fs.readFile()
or fs.writeFile()
is not recommended. Doing
so introduces a race condition, since other processes may change the file's
state between the two calls. Instead, user code should open/read/write the
file directly and handle the error raised if the file does not exist.
For example:
write (NOT RECOMMENDED)
fs.exists('myfile', (exists) => {
if (exists) {
console.error('myfile already exists');
} else {
fs.open('myfile', 'wx', (err, fd) => {
if (err) throw err;
writeMyData(fd);
});
}
});
write (RECOMMENDED)
fs.open('myfile', 'wx', (err, fd) => {
if (err) {
if (err.code === 'EEXIST') {
console.error('myfile already exists');
return;
}
throw err;
}
writeMyData(fd);
});
read (NOT RECOMMENDED)
fs.exists('myfile', (exists) => {
if (exists) {
fs.open('myfile', 'r', (err, fd) => {
readMyData(fd);
});
} else {
console.error('myfile does not exist');
}
});
read (RECOMMENDED)
fs.open('myfile', 'r', (err, fd) => {
if (err) {
if (err.code === 'ENOENT') {
console.error('myfile does not exist');
return;
}
throw err;
}
readMyData(fd);
});
The "not recommended" examples above check for existence and then use the file; the "recommended" examples are better because they use the file directly and handle the error, if any.
In general, check for the existence of a file only if the file won’t be used directly, for example when its existence is a signal from another process.
fs.existsSync(path)#
Synchronous version of fs.exists()
.
Returns true
if the file exists, false
otherwise.
Note that fs.exists()
is deprecated, but fs.existsSync()
is not.
(The callback
parameter to fs.exists()
accepts parameters that are
inconsistent with other Node.js callbacks. fs.existsSync()
does not use
a callback.)
fs.fchmod(fd, mode, callback)#
fd
<integer>mode
<integer>callback
<Function>
Asynchronous fchmod(2). No arguments other than a possible exception are given to the completion callback.
fs.fchmodSync(fd, mode)#
Synchronous fchmod(2). Returns undefined
.
fs.fchown(fd, uid, gid, callback)#
fd
<integer>uid
<integer>gid
<integer>callback
<Function>
Asynchronous fchown(2). No arguments other than a possible exception are given to the completion callback.
fs.fchownSync(fd, uid, gid)#
Synchronous fchown(2). Returns undefined
.
fs.fdatasync(fd, callback)#
fd
<integer>callback
<Function>
Asynchronous fdatasync(2). No arguments other than a possible exception are given to the completion callback.
fs.fdatasyncSync(fd)#
fd
<integer>
Synchronous fdatasync(2). Returns undefined
.
fs.fstat(fd, callback)#
fd
<integer>callback
<Function>
Asynchronous fstat(2). The callback gets two arguments (err, stats)
where
stats
is an fs.Stats
object. fstat()
is identical to stat()
,
except that the file to be stat-ed is specified by the file descriptor fd
.
fs.fstatSync(fd)#
fd
<integer>
Synchronous fstat(2). Returns an instance of fs.Stats
.
fs.fsync(fd, callback)#
fd
<integer>callback
<Function>
Asynchronous fsync(2). No arguments other than a possible exception are given to the completion callback.
fs.fsyncSync(fd)#
fd
<integer>
Synchronous fsync(2). Returns undefined
.
fs.ftruncate(fd, len, callback)#
fd
<integer>len
<integer> default =0
callback
<Function>
Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.
If the file referred to by the file descriptor was larger than len
bytes, only
the first len
bytes will be retained in the file.
For example, the following program retains only the first four bytes of the file
console.log(fs.readFileSync('temp.txt', 'utf8'));
// Prints: Node.js
// get the file descriptor of the file to be truncated
const fd = fs.openSync('temp.txt', 'r+');
// truncate the file to first four bytes
fs.ftruncate(fd, 4, (err) => {
assert.ifError(err);
console.log(fs.readFileSync('temp.txt', 'utf8'));
});
// Prints: Node
If the file previously was shorter than len
bytes, it is extended, and the
extended part is filled with null bytes ('\0'). For example,
console.log(fs.readFileSync('temp.txt', 'utf-8'));
// Prints: Node.js
// get the file descriptor of the file to be truncated
const fd = fs.openSync('temp.txt', 'r+');
// truncate the file to 10 bytes, whereas the actual size is 7 bytes
fs.ftruncate(fd, 10, (err) => {
assert.ifError(err);
console.log(fs.readFileSync('temp.txt'));
});
// Prints: <Buffer 4e 6f 64 65 2e 6a 73 00 00 00>
// ('Node.js\0\0\0' in UTF8)
The last three bytes are null bytes ('\0'), to compensate the over-truncation.
fs.ftruncateSync(fd, len)#
Synchronous ftruncate(2). Returns undefined
.
fs.futimes(fd, atime, mtime, callback)#
fd
<integer>atime
<integer>mtime
<integer>callback
<Function>
Change the file timestamps of a file referenced by the supplied file descriptor.
fs.futimesSync(fd, atime, mtime)#
Synchronous version of fs.futimes()
. Returns undefined
.
fs.lchmod(path, mode, callback)#
path
<string> | <Buffer>mode
<integer>callback
<Function>
Asynchronous lchmod(2). No arguments other than a possible exception are given to the completion callback.
Only available on macOS.
fs.lchmodSync(path, mode)#
Synchronous lchmod(2). Returns undefined
.
fs.lchown(path, uid, gid, callback)#
path
<string> | <Buffer>uid
<integer>gid
<integer>callback
<Function>
Asynchronous lchown(2). No arguments other than a possible exception are given to the completion callback.
fs.lchownSync(path, uid, gid)#
Synchronous lchown(2). Returns undefined
.
fs.link(existingPath, newPath, callback)#
Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.
fs.linkSync(existingPath, newPath)#
Synchronous link(2). Returns undefined
.
fs.lstat(path, callback)#
path
<string> | <Buffer> | <URL>callback
<Function>
Asynchronous lstat(2). The callback gets two arguments (err, stats)
where
stats
is a fs.Stats
object. lstat()
is identical to stat()
,
except that if path
is a symbolic link, then the link itself is stat-ed,
not the file that it refers to.
fs.lstatSync(path)#
Synchronous lstat(2). Returns an instance of fs.Stats
.
fs.mkdir(path[, mode], callback)#
path
<string> | <Buffer> | <URL>mode
<integer>callback
<Function>
Asynchronous mkdir(2). No arguments other than a possible exception are given
to the completion callback. mode
defaults to 0o777
.
fs.mkdirSync(path[, mode])#
Synchronous mkdir(2). Returns undefined
.
fs.mkdtemp(prefix[, options], callback)#
prefix
<string>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Creates a unique temporary directory.
Generates six random characters to be appended behind a required
prefix
to create a unique temporary directory.
The created folder path is passed as a string to the callback's second parameter.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use.
Example:
fs.mkdtemp('/tmp/foo-', (err, folder) => {
if (err) throw err;
console.log(folder);
// Prints: /tmp/foo-itXde2
});
Note: The fs.mkdtemp()
method will append the six randomly selected
characters directly to the prefix
string. For instance, given a directory
/tmp
, if the intention is to create a temporary directory within /tmp
,
the prefix
must end with a trailing platform-specific path separator
(require('path').sep
).
// The parent directory for the new temporary directory
const tmpDir = '/tmp';
// This method is *INCORRECT*:
fs.mkdtemp(tmpDir, (err, folder) => {
if (err) throw err;
console.log(folder);
// Will print something similar to `/tmpabc123`.
// Note that a new temporary directory is created
// at the file system root rather than *within*
// the /tmp directory.
});
// This method is *CORRECT*:
const { sep } = require('path');
fs.mkdtemp(`${tmpDir}${sep}`, (err, folder) => {
if (err) throw err;
console.log(folder);
// Will print something similar to `/tmp/abc123`.
// A new temporary directory is created within
// the /tmp directory.
});
fs.mkdtempSync(prefix[, options])#
The synchronous version of fs.mkdtemp()
. Returns the created
folder path.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use.
fs.open(path, flags[, mode], callback)#
Asynchronous file open. See open(2). flags
can be:
'r'
- Open file for reading. An exception occurs if the file does not exist.'r+'
- Open file for reading and writing. An exception occurs if the file does not exist.'rs+'
- Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache.This is primarily useful for opening files on NFS mounts as it allows skipping the potentially stale local cache. It has a very real impact on I/O performance so using this flag is not recommended unless it is needed.
Note that this doesn't turn
fs.open()
into a synchronous blocking call. If synchronous operation is desiredfs.openSync()
should be used.'w'
- Open file for writing. The file is created (if it does not exist) or truncated (if it exists).'wx'
- Like'w'
but fails ifpath
exists.'w+'
- Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).'wx+'
- Like'w+'
but fails ifpath
exists.'a'
- Open file for appending. The file is created if it does not exist.'ax'
- Like'a'
but fails ifpath
exists.'a+'
- Open file for reading and appending. The file is created if it does not exist.'ax+'
- Like'a+'
but fails ifpath
exists.
mode
sets the file mode (permission and sticky bits), but only if the file was
created. It defaults to 0666
, readable and writable.
The callback gets two arguments (err, fd)
.
The exclusive flag 'x'
(O_EXCL
flag in open(2)) ensures that path
is newly
created. On POSIX systems, path
is considered to exist even if it is a symlink
to a non-existent file. The exclusive flag may or may not work with network file
systems.
flags
can also be a number as documented by open(2); commonly used constants
are available from fs.constants
. On Windows, flags are translated to
their equivalent ones where applicable, e.g. O_WRONLY
to FILE_GENERIC_WRITE
,
or O_EXCL|O_CREAT
to CREATE_NEW
, as accepted by CreateFileW.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
Note: The behavior of fs.open()
is platform-specific for some flags. As
such, opening a directory on macOS and Linux with the 'a+'
flag - see example
below - will return an error. In contrast, on Windows and FreeBSD, a file
descriptor will be returned.
// macOS and Linux
fs.open('<directory>', 'a+', (err, fd) => {
// => [Error: EISDIR: illegal operation on a directory, open <directory>]
});
// Windows and FreeBSD
fs.open('<directory>', 'a+', (err, fd) => {
// => null, <fd>
});
fs.openSync(path, flags[, mode])#
Synchronous version of fs.open()
. Returns an integer representing the file
descriptor.
fs.read(fd, buffer, offset, length, position, callback)#
fd
<integer>buffer
<Buffer> | <Uint8Array>offset
<integer>length
<integer>position
<integer>callback
<Function>
Read data from the file specified by fd
.
buffer
is the buffer that the data will be written to.
offset
is the offset in the buffer to start writing at.
length
is an integer specifying the number of bytes to read.
position
is an integer specifying where to begin reading from in the file.
If position
is null
, data will be read from the current file position.
The callback is given the three arguments, (err, bytesRead, buffer)
.
If this method is invoked as its util.promisify()
ed version, it returns
a Promise for an object with bytesRead
and buffer
properties.
fs.readdir(path[, options], callback)#
path
<string> | <Buffer> | <URL>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Asynchronous readdir(3). Reads the contents of a directory.
The callback gets two arguments (err, files)
where files
is an array of
the names of the files in the directory excluding '.'
and '..'
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the filenames passed to the callback. If the encoding
is set to 'buffer'
,
the filenames returned will be passed as Buffer
objects.
fs.readdirSync(path[, options])#
Synchronous readdir(3). Returns an array of filenames excluding '.'
and
'..'
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the filenames passed to the callback. If the encoding
is set to 'buffer'
,
the filenames returned will be passed as Buffer
objects.
fs.readFile(path[, options], callback)#
path
<string> | <Buffer> | <URL> | <integer> filename or file descriptoroptions
<Object> | <string>callback
<Function>
Asynchronously reads the entire contents of a file. Example:
fs.readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
The callback is passed two arguments (err, data)
, where data
is the
contents of the file.
If no encoding is specified, then the raw buffer is returned.
If options
is a string, then it specifies the encoding. Example:
fs.readFile('/etc/passwd', 'utf8', callback);
Note: When the path is a directory, the behavior of
fs.readFile()
and [fs.readFileSync()
][] is platform-specific. On macOS,
Linux, and Windows, an error will be returned. On FreeBSD, a representation
of the directory's contents will be returned.
// macOS, Linux and Windows
fs.readFile('<directory>', (err, data) => {
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
});
// FreeBSD
fs.readFile('<directory>', (err, data) => {
// => null, <data>
});
Any specified file descriptor has to support reading.
Note: If a file descriptor is specified as the path
, it will not be closed
automatically.
fs.readFileSync(path[, options])#
path
<string> | <Buffer> | <URL> | <integer> filename or file descriptoroptions
<Object> | <string>
Synchronous version of fs.readFile
. Returns the contents of the file
.
If the encoding
option is specified then this function returns a
string. Otherwise it returns a buffer.
Note: Similar to [fs.readFile()
][], when the path is a directory, the
behavior of fs.readFileSync()
is platform-specific.
// macOS, Linux and Windows
fs.readFileSync('<directory>');
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
// FreeBSD
fs.readFileSync('<directory>'); // => null, <data>
fs.readlink(path[, options], callback)#
path
<string> | <Buffer> | <URL>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Asynchronous readlink(2). The callback gets two arguments (err,
linkString)
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the link path passed to the callback. If the encoding
is set to 'buffer'
,
the link path returned will be passed as a Buffer
object.
fs.readlinkSync(path[, options])#
Synchronous readlink(2). Returns the symbolic link's string value.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the link path passed to the callback. If the encoding
is set to 'buffer'
,
the link path returned will be passed as a Buffer
object.
fs.readSync(fd, buffer, offset, length, position)#
fd
<integer>buffer
<string> | <Buffer> | <Uint8Array>offset
<integer>length
<integer>position
<integer>
Synchronous version of fs.read()
. Returns the number of bytesRead
.
fs.realpath(path[, options], callback)#
path
<string> | <Buffer> | <URL>options
<string> | <Object>encoding
<string> default ='utf8'
callback
<Function>
Asynchronous realpath(3). The callback
gets two arguments (err,
resolvedPath)
. May use process.cwd
to resolve relative paths.
Only paths that can be converted to UTF8 strings are supported.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the path passed to the callback. If the encoding
is set to 'buffer'
,
the path returned will be passed as a Buffer
object.
Note: If path
resolves to a socket or a pipe, the function will return a
system dependent name for that object.
fs.realpathSync(path[, options])#
Synchronous realpath(3). Returns the resolved path.
Only paths that can be converted to UTF8 strings are supported.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the returned value. If the encoding
is set to 'buffer'
, the path returned
will be passed as a Buffer
object.
Note: If path
resolves to a socket or a pipe, the function will return a
system dependent name for that object.
fs.rename(oldPath, newPath, callback)#
Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.
fs.renameSync(oldPath, newPath)#
Synchronous rename(2). Returns undefined
.
fs.rmdir(path, callback)#
path
<string> | <Buffer> | <URL>callback
<Function>
Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.
fs.rmdirSync(path)#
Synchronous rmdir(2). Returns undefined
.
fs.stat(path, callback)#
path
<string> | <Buffer> | <URL>callback
<Function>
Asynchronous stat(2). The callback gets two arguments (err, stats)
where
stats
is an fs.Stats
object.
In case of an error, the err.code
will be one of Common System Errors.
Using fs.stat()
to check for the existence of a file before calling
fs.open()
, fs.readFile()
or fs.writeFile()
is not recommended.
Instead, user code should open/read/write the file directly and handle the
error raised if the file is not available.
To check if a file exists without manipulating it afterwards, fs.access()
is recommended.
fs.statSync(path)#
Synchronous stat(2). Returns an instance of fs.Stats
.
fs.symlink(target, path[, type], callback)#
target
<string> | <Buffer> | <URL>path
<string> | <Buffer> | <URL>type
<string>callback
<Function>
Asynchronous symlink(2). No arguments other than a possible exception are given
to the completion callback. The type
argument can be set to 'dir'
,
'file'
, or 'junction'
(default is 'file'
) and is only available on
Windows (ignored on other platforms). Note that Windows junction points require
the destination path to be absolute. When using 'junction'
, the target
argument will automatically be normalized to absolute path.
Here is an example below:
fs.symlink('./foo', './new-port', callback);
It creates a symbolic link named "new-port" that points to "foo".
fs.symlinkSync(target, path[, type])#
Synchronous symlink(2). Returns undefined
.
fs.truncate(path, len, callback)#
path
<string> | <Buffer>len
<integer> default =0
callback
<Function>
Asynchronous truncate(2). No arguments other than a possible exception are
given to the completion callback. A file descriptor can also be passed as the
first argument. In this case, fs.ftruncate()
is called.
fs.truncateSync(path, len)#
Synchronous truncate(2). Returns undefined
. A file descriptor can also be
passed as the first argument. In this case, fs.ftruncateSync()
is called.
fs.unlink(path, callback)#
path
<string> | <Buffer> | <URL>callback
<Function>
Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.
fs.unlinkSync(path)#
Synchronous unlink(2). Returns undefined
.
fs.unwatchFile(filename[, listener])#
filename
<string> | <Buffer>listener
<Function>
Stop watching for changes on filename
. If listener
is specified, only that
particular listener is removed. Otherwise, all listeners are removed,
effectively stopping watching of filename
.
Calling fs.unwatchFile()
with a filename that is not being watched is a
no-op, not an error.
Note: fs.watch()
is more efficient than fs.watchFile()
and
fs.unwatchFile()
. fs.watch()
should be used instead of fs.watchFile()
and fs.unwatchFile()
when possible.
fs.utimes(path, atime, mtime, callback)#
Change file timestamps of the file referenced by the supplied path.
Note: The arguments atime
and mtime
of the following related functions
follow these rules:
- The value should be a Unix timestamp in seconds. For example,
Date.now()
returns milliseconds, so it should be divided by 1000 before passing it in. - If the value is a numeric string like
'123456789'
, the value will get converted to the corresponding number. - If the value is
NaN
,Infinity
or-Infinity
, an Error will be thrown.
fs.utimesSync(path, atime, mtime)#
Synchronous version of fs.utimes()
. Returns undefined
.
fs.watch(filename[, options][, listener])#
filename
<string> | <Buffer> | <URL>options
<string> | <Object>persistent
<boolean> Indicates whether the process should continue to run as long as files are being watched. default =true
recursive
<boolean> Indicates whether all subdirectories should be watched, or only the current directory. This applies when a directory is specified, and only on supported platforms (See Caveats). default =false
encoding
<string> Specifies the character encoding to be used for the filename passed to the listener. default ='utf8'
listener
<Function>
Watch for changes on filename
, where filename
is either a file or a
directory. The returned object is a fs.FSWatcher
.
The second argument is optional. If options
is provided as a string, it
specifies the encoding
. Otherwise options
should be passed as an object.
The listener callback gets two arguments (eventType, filename)
. eventType
is either
'rename'
or 'change'
, and filename
is the name of the file which triggered
the event.
Note that on most platforms, 'rename'
is emitted whenever a filename appears
or disappears in the directory.
Also note the listener callback is attached to the 'change'
event fired by
fs.FSWatcher
, but it is not the same thing as the 'change'
value of
eventType
.
Caveats#
The fs.watch
API is not 100% consistent across platforms, and is
unavailable in some situations.
The recursive option is only supported on macOS and Windows.
Availability#
This feature depends on the underlying operating system providing a way to be notified of filesystem changes.
- On Linux systems, this uses
inotify
- On BSD systems, this uses
kqueue
- On macOS, this uses
kqueue
for files andFSEvents
for directories. - On SunOS systems (including Solaris and SmartOS), this uses
event ports
. - On Windows systems, this feature depends on
ReadDirectoryChangesW
. - On Aix systems, this feature depends on
AHAFS
, which must be enabled.
If the underlying functionality is not available for some reason, then
fs.watch
will not be able to function. For example, watching files or
directories can be unreliable, and in some cases impossible, on network file
systems (NFS, SMB, etc), or host file systems when using virtualization software
such as Vagrant, Docker, etc.
It is still possible to use fs.watchFile()
, which uses stat polling, but
this method is slower and less reliable.
Inodes#
On Linux and macOS systems, fs.watch()
resolves the path to an inode and
watches the inode. If the watched path is deleted and recreated, it is assigned
a new inode. The watch will emit an event for the delete but will continue
watching the original inode. Events for the new inode will not be emitted.
This is expected behavior.
In AIX, save and close of a file being watched causes two notifications - one for adding new content, and one for truncation. Moreover, save and close operations on some platforms cause inode changes that force watch operations to become invalid and ineffective. AIX retains inode for the lifetime of a file, that way though this is different from Linux / macOS, this improves the usability of file watching. This is expected behavior.
Filename Argument#
Providing filename
argument in the callback is only supported on Linux,
macOS, Windows, and AIX. Even on supported platforms, filename
is not always
guaranteed to be provided. Therefore, don't assume that filename
argument is
always provided in the callback, and have some fallback logic if it is null.
fs.watch('somedir', (eventType, filename) => {
console.log(`event type is: ${eventType}`);
if (filename) {
console.log(`filename provided: ${filename}`);
} else {
console.log('filename not provided');
}
});
fs.watchFile(filename[, options], listener)#
filename
<string> | <Buffer> | <URL>options
<Object>listener
<Function>
Watch for changes on filename
. The callback listener
will be called each
time the file is accessed.
The options
argument may be omitted. If provided, it should be an object. The
options
object may contain a boolean named persistent
that indicates
whether the process should continue to run as long as files are being watched.
The options
object may specify an interval
property indicating how often the
target should be polled in milliseconds. The default is
{ persistent: true, interval: 5007 }
.
The listener
gets two arguments the current stat object and the previous
stat object:
fs.watchFile('message.text', (curr, prev) => {
console.log(`the current mtime is: ${curr.mtime}`);
console.log(`the previous mtime was: ${prev.mtime}`);
});
These stat objects are instances of fs.Stat
.
To be notified when the file was modified, not just accessed, it is necessary
to compare curr.mtime
and prev.mtime
.
Note: When an fs.watchFile
operation results in an ENOENT
error, it
will invoke the listener once, with all the fields zeroed (or, for dates, the
Unix Epoch). In Windows, blksize
and blocks
fields will be undefined
,
instead of zero. If the file is created later on, the listener will be called
again, with the latest stat objects. This is a change in functionality since
v0.10.
Note: fs.watch()
is more efficient than fs.watchFile
and
fs.unwatchFile
. fs.watch
should be used instead of fs.watchFile
and
fs.unwatchFile
when possible.
fs.write(fd, buffer[, offset[, length[, position]]], callback)#
fd
<integer>buffer
<Buffer> | <Uint8Array>offset
<integer>length
<integer>position
<integer>callback
<Function>
Write buffer
to the file specified by fd
.
offset
determines the part of the buffer to be written, and length
is
an integer specifying the number of bytes to write.
position
refers to the offset from the beginning of the file where this data
should be written. If typeof position !== 'number'
, the data will be written
at the current position. See pwrite(2).
The callback will be given three arguments (err, bytesWritten, buffer)
where
bytesWritten
specifies how many bytes were written from buffer
.
If this method is invoked as its util.promisify()
ed version, it returns
a Promise for an object with bytesWritten
and buffer
properties.
Note that it is unsafe to use fs.write
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.write(fd, string[, position[, encoding]], callback)#
fd
<integer>string
<string>position
<integer>encoding
<string>callback
<Function>
Write string
to the file specified by fd
. If string
is not a string, then
the value will be coerced to one.
position
refers to the offset from the beginning of the file where this data
should be written. If typeof position !== 'number'
the data will be written at
the current position. See pwrite(2).
encoding
is the expected string encoding.
The callback will receive the arguments (err, written, string)
where written
specifies how many bytes the passed string required to be written. Note that
bytes written is not the same as string characters. See Buffer.byteLength
.
Unlike when writing buffer
, the entire string must be written. No substring
may be specified. This is because the byte offset of the resulting data may not
be the same as the string offset.
Note that it is unsafe to use fs.write
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.writeFile(file, data[, options], callback)#
file
<string> | <Buffer> | <integer> filename or file descriptordata
<string> | <Buffer> | <Uint8Array>options
<Object> | <string>callback
<Function>
Asynchronously writes data to a file, replacing the file if it already exists.
data
can be a string or a buffer.
The encoding
option is ignored if data
is a buffer. It defaults
to 'utf8'
.
Example:
fs.writeFile('message.txt', 'Hello Node.js', (err) => {
if (err) throw err;
console.log('The file has been saved!');
});
If options
is a string, then it specifies the encoding. Example:
fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);
Any specified file descriptor has to support writing.
Note that it is unsafe to use fs.writeFile
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
Note: If a file descriptor is specified as the file
, it will not be closed
automatically.
fs.writeFileSync(file, data[, options])#
file
<string> | <Buffer> | <integer> filename or file descriptordata
<string> | <Buffer> | <Uint8Array>options
<Object> | <string>
The synchronous version of fs.writeFile()
. Returns undefined
.
fs.writeSync(fd, buffer[, offset[, length[, position]]])#
fs.writeSync(fd, string[, position[, encoding]])#
Synchronous versions of fs.write()
. Returns the number of bytes written.
FS Constants#
The following constants are exported by fs.constants
.
Note: Not every constant will be available on every operating system.
File Access Constants#
The following constants are meant for use with fs.access()
.
Constant | Description |
---|---|
F_OK |
Flag indicating that the file is visible to the calling process. |
R_OK |
Flag indicating that the file can be read by the calling process. |
W_OK |
Flag indicating that the file can be written by the calling process. |
X_OK |
Flag indicating that the file can be executed by the calling process. |
File Open Constants#
The following constants are meant for use with fs.open()
.
Constant | Description |
---|---|
O_RDONLY |
Flag indicating to open a file for read-only access. |
O_WRONLY |
Flag indicating to open a file for write-only access. |
O_RDWR |
Flag indicating to open a file for read-write access. |
O_CREAT |
Flag indicating to create the file if it does not already exist. |
O_EXCL |
Flag indicating that opening a file should fail if the
O_CREAT flag is set and the file already exists. |
O_NOCTTY |
Flag indicating that if path identifies a terminal device, opening the path shall not cause that terminal to become the controlling terminal for the process (if the process does not already have one). |
O_TRUNC |
Flag indicating that if the file exists and is a regular file, and the file is opened successfully for write access, its length shall be truncated to zero. |
O_APPEND |
Flag indicating that data will be appended to the end of the file. |
O_DIRECTORY |
Flag indicating that the open should fail if the path is not a directory. |
O_NOATIME |
Flag indicating reading accesses to the file system will no longer
result in an update to the atime information associated with the file.
This flag is available on Linux operating systems only. |
O_NOFOLLOW |
Flag indicating that the open should fail if the path is a symbolic link. |
O_SYNC |
Flag indicating that the file is opened for synchronous I/O. |
O_SYMLINK |
Flag indicating to open the symbolic link itself rather than the resource it is pointing to. |
O_DIRECT |
When set, an attempt will be made to minimize caching effects of file I/O. |
O_NONBLOCK |
Flag indicating to open the file in nonblocking mode when possible. |
File Type Constants#
The following constants are meant for use with the fs.Stats
object's
mode
property for determining a file's type.
Constant | Description |
---|---|
S_IFMT |
Bit mask used to extract the file type code. |
S_IFREG |
File type constant for a regular file. |
S_IFDIR |
File type constant for a directory. |
S_IFCHR |
File type constant for a character-oriented device file. |
S_IFBLK |
File type constant for a block-oriented device file. |
S_IFIFO |
File type constant for a FIFO/pipe. |
S_IFLNK |
File type constant for a symbolic link. |
S_IFSOCK |
File type constant for a socket. |
File Mode Constants#
The following constants are meant for use with the fs.Stats
object's
mode
property for determining the access permissions for a file.
Constant | Description |
---|---|
S_IRWXU |
File mode indicating readable, writable and executable by owner. |
S_IRUSR |
File mode indicating readable by owner. |
S_IWUSR |
File mode indicating writable by owner. |
S_IXUSR |
File mode indicating executable by owner. |
S_IRWXG |
File mode indicating readable, writable and executable by group. |
S_IRGRP |
File mode indicating readable by group. |
S_IWGRP |
File mode indicating writable by group. |
S_IXGRP |
File mode indicating executable by group. |
S_IRWXO |
File mode indicating readable, writable and executable by others. |
S_IROTH |
File mode indicating readable by others. |
S_IWOTH |
File mode indicating writable by others. |
S_IXOTH |
File mode indicating executable by others. |