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# File system <!--introduced_in=v0.10.0--> > Stability: 2 - Stable <!--name=fs--> <!-- source_link=lib/fs.js --> The `node:fs` module enables interacting with the file system in a way modeled on standard POSIX functions. To use the promise-based APIs: ```mjs import * as fs from 'node:fs/promises'; ``` ```cjs const fs = require('node:fs/promises'); ``` To use the callback and sync APIs: ```mjs import * as fs from 'node:fs'; ``` ```cjs const fs = require('node:fs'); ``` All file system operations have synchronous, callback, and promise-based forms, and are accessible using both CommonJS syntax and ES6 Modules (ESM). ## Promise example Promise-based operations return a promise that is fulfilled when the asynchronous operation is complete. ```mjs import { unlink } from 'node:fs/promises'; try { await unlink('/tmp/hello'); console.log('successfully deleted /tmp/hello'); } catch (error) { console.error('there was an error:', error.message); } ``` ```cjs const { unlink } = require('node:fs/promises'); (async function(path) { try { await unlink(path); console.log(`successfully deleted ${path}`); } catch (error) { console.error('there was an error:', error.message); } })('/tmp/hello'); ``` ## Callback example The callback form takes a completion callback function as its last argument and invokes the operation asynchronously. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation is completed successfully, then the first argument is `null` or `undefined`. ```mjs import { unlink } from 'node:fs'; unlink('/tmp/hello', (err) => { if (err) throw err; console.log('successfully deleted /tmp/hello'); }); ``` ```cjs const { unlink } = require('node:fs'); unlink('/tmp/hello', (err) => { if (err) throw err; console.log('successfully deleted /tmp/hello'); }); ``` The callback-based versions of the `node:fs` module APIs are preferable over the use of the promise APIs when maximal performance (both in terms of execution time and memory allocation) is required. ## Synchronous example The synchronous APIs block the Node.js event loop and further JavaScript execution until the operation is complete. Exceptions are thrown immediately and can be handled using `try…catch`, or can be allowed to bubble up. ```mjs import { unlinkSync } from 'node:fs'; try { unlinkSync('/tmp/hello'); console.log('successfully deleted /tmp/hello'); } catch (err) { // handle the error } ``` ```cjs const { unlinkSync } = require('node:fs'); try { unlinkSync('/tmp/hello'); console.log('successfully deleted /tmp/hello'); } catch (err) { // handle the error } ``` ## Promises API <!-- YAML added: v10.0.0 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31553 description: Exposed as `require('fs/promises')`. - version: - v11.14.0 - v10.17.0 pr-url: https://github.com/nodejs/node/pull/26581 description: This API is no longer experimental. - version: v10.1.0 pr-url: https://github.com/nodejs/node/pull/20504 description: The API is accessible via `require('fs').promises` only. --> The `fs/promises` API provides asynchronous file system methods that return promises. The promise APIs use the underlying Node.js threadpool to perform file system operations off the event loop thread. These operations are not synchronized or threadsafe. Care must be taken when performing multiple concurrent modifications on the same file or data corruption may occur. ### Class: `FileHandle` <!-- YAML added: v10.0.0 --> A {FileHandle} object is an object wrapper for a numeric file descriptor. Instances of the {FileHandle} object are created by the `fsPromises.open()` method. All {FileHandle} objects are {EventEmitter}s. If a {FileHandle} is not closed using the `filehandle.close()` method, it will try to automatically close the file descriptor and emit a process warning, helping to prevent memory leaks. Please do not rely on this behavior because it can be unreliable and the file may not be closed. Instead, always explicitly close {FileHandle}s. Node.js may change this behavior in the future. #### Event: `'close'` <!-- YAML added: v15.4.0 --> The `'close'` event is emitted when the {FileHandle} has been closed and can no longer be used. #### `filehandle.appendFile(data[, options])` <!-- YAML added: v10.0.0 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50095 description: The `flush` option is now supported. - version: - v15.14.0 - v14.18.0 pr-url: https://github.com/nodejs/node/pull/37490 description: The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `data` parameter won't coerce unsupported input to strings anymore. --> * `data` {string|Buffer|TypedArray|DataView|AsyncIterable|Iterable|Stream} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `flush` {boolean} If `true`, the underlying file descriptor is flushed prior to closing it. **Default:** `false`. * Returns: {Promise} Fulfills with `undefined` upon success. Alias of [`filehandle.writeFile()`][]. When operating on file handles, the mode cannot be changed from what it was set to with [`fsPromises.open()`][]. Therefore, this is equivalent to [`filehandle.writeFile()`][]. #### `filehandle.chmod(mode)` <!-- YAML added: v10.0.0 --> * `mode` {integer} the file mode bit mask. * Returns: {Promise} Fulfills with `undefined` upon success. Modifies the permissions on the file. See chmod(2). #### `filehandle.chown(uid, gid)` <!-- YAML added: v10.0.0 --> * `uid` {integer} The file's new owner's user id. * `gid` {integer} The file's new group's group id. * Returns: {Promise} Fulfills with `undefined` upon success. Changes the ownership of the file. A wrapper for chown(2). #### `filehandle.close()` <!-- YAML added: v10.0.0 --> * Returns: {Promise} Fulfills with `undefined` upon success. Closes the file handle after waiting for any pending operation on the handle to complete. ```mjs import { open } from 'node:fs/promises'; let filehandle; try { filehandle = await open('thefile.txt', 'r'); } finally { await filehandle?.close(); } ``` #### `filehandle.createReadStream([options])` <!-- YAML added: v16.11.0 --> * `options` {Object} * `encoding` {string} **Default:** `null` * `autoClose` {boolean} **Default:** `true` * `emitClose` {boolean} **Default:** `true` * `start` {integer} * `end` {integer} **Default:** `Infinity` * `highWaterMark` {integer} **Default:** `64 * 1024` * Returns: {fs.ReadStream} Unlike the 16 KiB default `highWaterMark` for a {stream.Readable}, the stream returned by this method has a default `highWaterMark` of 64 KiB. `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, allowed values are in the \[0, [`Number.MAX_SAFE_INTEGER`][]] range. If `start` is omitted or `undefined`, `filehandle.createReadStream()` reads sequentially from the current file position. The `encoding` can be any one of those accepted by {Buffer}. If the `FileHandle` points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. ```mjs import { open } from 'node:fs/promises'; const fd = await open('/dev/input/event0'); // Create a stream from some character device. const stream = fd.createReadStream(); setTimeout(() => { stream.close(); // This may not close the stream. // Artificially marking end-of-stream, as if the underlying resource had // indicated end-of-file by itself, allows the stream to close. // This does not cancel pending read operations, and if there is such an // operation, the process may still not be able to exit successfully // until it finishes. stream.push(null); stream.read(0); }, 100); ``` 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. An example to read the last 10 bytes of a file which is 100 bytes long: ```mjs import { open } from 'node:fs/promises'; const fd = await open('sample.txt'); fd.createReadStream({ start: 90, end: 99 }); ``` #### `filehandle.createWriteStream([options])` <!-- YAML added: v16.11.0 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50093 description: The `flush` option is now supported. --> * `options` {Object} * `encoding` {string} **Default:** `'utf8'` * `autoClose` {boolean} **Default:** `true` * `emitClose` {boolean} **Default:** `true` * `start` {integer} * `highWaterMark` {number} **Default:** `16384` * `flush` {boolean} If `true`, the underlying file descriptor is flushed prior to closing it. **Default:** `false`. * Returns: {fs.WriteStream} `options` may also include a `start` option to allow writing data at some position past the beginning of the file, allowed values are in the \[0, [`Number.MAX_SAFE_INTEGER`][]] range. Modifying a file rather than replacing it may require the `flags` `open` option to be set to `r+` rather than the default `r`. The `encoding` can be any one of those accepted by {Buffer}. If `autoClose` is set to true (default behavior) on `'error'` or `'finish'` 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. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. #### `filehandle.datasync()` <!-- YAML added: v10.0.0 --> * Returns: {Promise} Fulfills with `undefined` upon success. Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX fdatasync(2) documentation for details. Unlike `filehandle.sync` this method does not flush modified metadata. #### `filehandle.fd` <!-- YAML added: v10.0.0 --> * {number} The numeric file descriptor managed by the {FileHandle} object. #### `filehandle.read(buffer, offset, length, position)` <!-- YAML added: v10.0.0 --> * `buffer` {Buffer|TypedArray|DataView} A buffer that will be filled with the file data read. * `offset` {integer} The location in the buffer at which to start filling. **Default:** `0` * `length` {integer} The number of bytes to read. **Default:** `buffer.byteLength - offset` * `position` {integer|bigint|null} The location where to begin reading data from the file. If `null` or `-1`, data will be read from the current file position, and the position will be updated. If `position` is a non-negative integer, the current file position will remain unchanged. **Default:**: `null` * Returns: {Promise} Fulfills upon success with an object with two properties: * `bytesRead` {integer} The number of bytes read * `buffer` {Buffer|TypedArray|DataView} A reference to the passed in `buffer` argument. Reads data from the file and stores that in the given buffer. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. #### `filehandle.read([options])` <!-- YAML added: - v13.11.0 - v12.17.0 --> * `options` {Object} * `buffer` {Buffer|TypedArray|DataView} A buffer that will be filled with the file data read. **Default:** `Buffer.alloc(16384)` * `offset` {integer} The location in the buffer at which to start filling. **Default:** `0` * `length` {integer} The number of bytes to read. **Default:** `buffer.byteLength - offset` * `position` {integer|null} The location where to begin reading data from the file. If `null`, data will be read from the current file position, and the position will be updated. If `position` is an integer, the current file position will remain unchanged. **Default:**: `null` * Returns: {Promise} Fulfills upon success with an object with two properties: * `bytesRead` {integer} The number of bytes read * `buffer` {Buffer|TypedArray|DataView} A reference to the passed in `buffer` argument. Reads data from the file and stores that in the given buffer. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. #### `filehandle.read(buffer[, options])` <!-- YAML added: - v18.2.0 - v16.17.0 --> * `buffer` {Buffer|TypedArray|DataView} A buffer that will be filled with the file data read. * `options` {Object} * `offset` {integer} The location in the buffer at which to start filling. **Default:** `0` * `length` {integer} The number of bytes to read. **Default:** `buffer.byteLength - offset` * `position` {integer} The location where to begin reading data from the file. If `null`, data will be read from the current file position, and the position will be updated. If `position` is an integer, the current file position will remain unchanged. **Default:**: `null` * Returns: {Promise} Fulfills upon success with an object with two properties: * `bytesRead` {integer} The number of bytes read * `buffer` {Buffer|TypedArray|DataView} A reference to the passed in `buffer` argument. Reads data from the file and stores that in the given buffer. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. #### `filehandle.readableWebStream([options])` <!-- YAML added: v17.0.0 changes: - version: v20.0.0 pr-url: https://github.com/nodejs/node/pull/46933 description: Added option to create a 'bytes' stream. --> > Stability: 1 - Experimental * `options` {Object} * `type` {string|undefined} Whether to open a normal or a `'bytes'` stream. **Default:** `undefined` * Returns: {ReadableStream} Returns a `ReadableStream` that may be used to read the files data. An error will be thrown if this method is called more than once or is called after the `FileHandle` is closed or closing. ```mjs import { open, } from 'node:fs/promises'; const file = await open('./some/file/to/read'); for await (const chunk of file.readableWebStream()) console.log(chunk); await file.close(); ``` ```cjs const { open, } = require('node:fs/promises'); (async () => { const file = await open('./some/file/to/read'); for await (const chunk of file.readableWebStream()) console.log(chunk); await file.close(); })(); ``` While the `ReadableStream` will read the file to completion, it will not close the `FileHandle` automatically. User code must still call the `fileHandle.close()` method. #### `filehandle.readFile(options)` <!-- YAML added: v10.0.0 --> * `options` {Object|string} * `encoding` {string|null} **Default:** `null` * `signal` {AbortSignal} allows aborting an in-progress readFile * Returns: {Promise} Fulfills upon a successful read with the contents of the file. If no encoding is specified (using `options.encoding`), the data is returned as a {Buffer} object. Otherwise, the data will be a string. Asynchronously reads the entire contents of a file. If `options` is a string, then it specifies the `encoding`. The {FileHandle} has to support reading. If one or more `filehandle.read()` calls are made on a file handle and then a `filehandle.readFile()` call is made, the data will be read from the current position till the end of the file. It doesn't always read from the beginning of the file. #### `filehandle.readLines([options])` <!-- YAML added: v18.11.0 --> * `options` {Object} * `encoding` {string} **Default:** `null` * `autoClose` {boolean} **Default:** `true` * `emitClose` {boolean} **Default:** `true` * `start` {integer} * `end` {integer} **Default:** `Infinity` * `highWaterMark` {integer} **Default:** `64 * 1024` * Returns: {readline.InterfaceConstructor} Convenience method to create a `readline` interface and stream over the file. See [`filehandle.createReadStream()`][] for the options. ```mjs import { open } from 'node:fs/promises'; const file = await open('./some/file/to/read'); for await (const line of file.readLines()) { console.log(line); } ``` ```cjs const { open } = require('node:fs/promises'); (async () => { const file = await open('./some/file/to/read'); for await (const line of file.readLines()) { console.log(line); } })(); ``` #### `filehandle.readv(buffers[, position])` <!-- YAML added: - v13.13.0 - v12.17.0 --> * `buffers` {Buffer\[]|TypedArray\[]|DataView\[]} * `position` {integer|null} The offset from the beginning of the file where the data should be read from. If `position` is not a `number`, the data will be read from the current position. **Default:** `null` * Returns: {Promise} Fulfills upon success an object containing two properties: * `bytesRead` {integer} the number of bytes read * `buffers` {Buffer\[]|TypedArray\[]|DataView\[]} property containing a reference to the `buffers` input. Read from a file and write to an array of {ArrayBufferView}s #### `filehandle.stat([options])` <!-- YAML added: v10.0.0 changes: - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. --> * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * Returns: {Promise} Fulfills with an {fs.Stats} for the file. #### `filehandle.sync()` <!-- YAML added: v10.0.0 --> * Returns: {Promise} Fulfills with `undefined` upon success. Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX fsync(2) documentation for more detail. #### `filehandle.truncate(len)` <!-- YAML added: v10.0.0 --> * `len` {integer} **Default:** `0` * Returns: {Promise} Fulfills with `undefined` upon success. Truncates the file. If the file was larger than `len` bytes, only the first `len` bytes will be retained in the file. The following example retains only the first four bytes of the file: ```mjs import { open } from 'node:fs/promises'; let filehandle = null; try { filehandle = await open('temp.txt', 'r+'); await filehandle.truncate(4); } finally { await filehandle?.close(); } ``` If the file previously was shorter than `len` bytes, it is extended, and the extended part is filled with null bytes (`'\0'`): If `len` is negative then `0` will be used. #### `filehandle.utimes(atime, mtime)` <!-- YAML added: v10.0.0 --> * `atime` {number|string|Date} * `mtime` {number|string|Date} * Returns: {Promise} Change the file system timestamps of the object referenced by the {FileHandle} then fulfills the promise with no arguments upon success. #### `filehandle.write(buffer, offset[, length[, position]])` <!-- YAML added: v10.0.0 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `buffer` parameter won't coerce unsupported input to buffers anymore. --> * `buffer` {Buffer|TypedArray|DataView} * `offset` {integer} The start position from within `buffer` where the data to write begins. * `length` {integer} The number of bytes from `buffer` to write. **Default:** `buffer.byteLength - offset` * `position` {integer|null} The offset from the beginning of the file where the data from `buffer` should be written. If `position` is not a `number`, the data will be written at the current position. See the POSIX pwrite(2) documentation for more detail. **Default:** `null` * Returns: {Promise} Write `buffer` to the file. The promise is fulfilled with an object containing two properties: * `bytesWritten` {integer} the number of bytes written * `buffer` {Buffer|TypedArray|DataView} a reference to the `buffer` written. It is unsafe to use `filehandle.write()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). For this scenario, use [`filehandle.createWriteStream()`][]. On Linux, positional writes do not 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. #### `filehandle.write(buffer[, options])` <!-- YAML added: - v18.3.0 - v16.17.0 --> * `buffer` {Buffer|TypedArray|DataView} * `options` {Object} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer} **Default:** `null` * Returns: {Promise} Write `buffer` to the file. Similar to the above `filehandle.write` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. #### `filehandle.write(string[, position[, encoding]])` <!-- YAML added: v10.0.0 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `string` parameter won't coerce unsupported input to strings anymore. --> * `string` {string} * `position` {integer|null} The offset from the beginning of the file where the data from `string` should be written. If `position` is not a `number` the data will be written at the current position. See the POSIX pwrite(2) documentation for more detail. **Default:** `null` * `encoding` {string} The expected string encoding. **Default:** `'utf8'` * Returns: {Promise} Write `string` to the file. If `string` is not a string, the promise is rejected with an error. The promise is fulfilled with an object containing two properties: * `bytesWritten` {integer} the number of bytes written * `buffer` {string} a reference to the `string` written. It is unsafe to use `filehandle.write()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). For this scenario, use [`filehandle.createWriteStream()`][]. On Linux, positional writes do not 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. #### `filehandle.writeFile(data, options)` <!-- YAML added: v10.0.0 changes: - version: - v15.14.0 - v14.18.0 pr-url: https://github.com/nodejs/node/pull/37490 description: The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `data` parameter won't coerce unsupported input to strings anymore. --> * `data` {string|Buffer|TypedArray|DataView|AsyncIterable|Iterable|Stream} * `options` {Object|string} * `encoding` {string|null} The expected character encoding when `data` is a string. **Default:** `'utf8'` * Returns: {Promise} Asynchronously writes data to a file, replacing the file if it already exists. `data` can be a string, a buffer, an {AsyncIterable}, or an {Iterable} object. The promise is fulfilled with no arguments upon success. If `options` is a string, then it specifies the `encoding`. The {FileHandle} has to support writing. It is unsafe to use `filehandle.writeFile()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). If one or more `filehandle.write()` calls are made on a file handle and then a `filehandle.writeFile()` call is made, the data will be written from the current position till the end of the file. It doesn't always write from the beginning of the file. #### `filehandle.writev(buffers[, position])` <!-- YAML added: v12.9.0 --> * `buffers` {Buffer\[]|TypedArray\[]|DataView\[]} * `position` {integer|null} The offset from the beginning of the file where the data from `buffers` should be written. If `position` is not a `number`, the data will be written at the current position. **Default:** `null` * Returns: {Promise} Write an array of {ArrayBufferView}s to the file. The promise is fulfilled with an object containing a two properties: * `bytesWritten` {integer} the number of bytes written * `buffers` {Buffer\[]|TypedArray\[]|DataView\[]} a reference to the `buffers` input. It is unsafe to call `writev()` multiple times on the same file without waiting for the promise to be fulfilled (or rejected). 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. #### `filehandle[Symbol.asyncDispose]()` <!-- YAML added: v20.4.0 --> > Stability: 1 - Experimental An alias for `filehandle.close()`. ### `fsPromises.access(path[, mode])` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `mode` {integer} **Default:** `fs.constants.F_OK` * Returns: {Promise} Fulfills with `undefined` upon success. 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. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check [File access constants][] for possible values of `mode`. If the accessibility check is successful, the promise is fulfilled with no value. If any of the accessibility checks fail, the promise is rejected with an {Error} object. The following example checks if the file `/etc/passwd` can be read and written by the current process. ```mjs import { access, constants } from 'node:fs/promises'; try { await access('/etc/passwd', constants.R_OK | constants.W_OK); console.log('can access'); } catch { console.error('cannot access'); } ``` Using `fsPromises.access()` to check for the accessibility of a file before calling `fsPromises.open()` 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. ### `fsPromises.appendFile(path, data[, options])` <!-- YAML added: v10.0.0 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50095 description: The `flush` option is now supported. --> * `path` {string|Buffer|URL|FileHandle} filename or {FileHandle} * `data` {string|Buffer} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `mode` {integer} **Default:** `0o666` * `flag` {string} See [support of file system `flags`][]. **Default:** `'a'`. * `flush` {boolean} If `true`, the underlying file descriptor is flushed prior to closing it. **Default:** `false`. * Returns: {Promise} Fulfills with `undefined` upon success. Asynchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a {Buffer}. If `options` is a string, then it specifies the `encoding`. The `mode` option only affects the newly created file. See [`fs.open()`][] for more details. The `path` may be specified as a {FileHandle} that has been opened for appending (using `fsPromises.open()`). ### `fsPromises.chmod(path, mode)` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `mode` {string|integer} * Returns: {Promise} Fulfills with `undefined` upon success. Changes the permissions of a file. ### `fsPromises.chown(path, uid, gid)` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `uid` {integer} * `gid` {integer} * Returns: {Promise} Fulfills with `undefined` upon success. Changes the ownership of a file. ### `fsPromises.copyFile(src, dest[, mode])` <!-- YAML added: v10.0.0 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/27044 description: Changed `flags` argument to `mode` and imposed stricter type validation. --> * `src` {string|Buffer|URL} source filename to copy * `dest` {string|Buffer|URL} destination filename of the copy operation * `mode` {integer} Optional modifiers that specify the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`) **Default:** `0`. * `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists. * `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. * `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail. * Returns: {Promise} Fulfills with `undefined` upon success. Asynchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. No guarantees are made about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, an attempt will be made to remove the destination. ```mjs import { copyFile, constants } from 'node:fs/promises'; try { await copyFile('source.txt', 'destination.txt'); console.log('source.txt was copied to destination.txt'); } catch { console.error('The file could not be copied'); } // By using COPYFILE_EXCL, the operation will fail if destination.txt exists. try { await copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL); console.log('source.txt was copied to destination.txt'); } catch { console.error('The file could not be copied'); } ``` ### `fsPromises.cp(src, dest[, options])` <!-- YAML added: v16.7.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/47084 description: Accept an additional `mode` option to specify the copy behavior as the `mode` argument of `fs.copyFile()`. - version: - v17.6.0 - v16.15.0 pr-url: https://github.com/nodejs/node/pull/41819 description: Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. --> > Stability: 1 - Experimental * `src` {string|URL} source path to copy. * `dest` {string|URL} destination path to copy to. * `options` {Object} * `dereference` {boolean} dereference symlinks. **Default:** `false`. * `errorOnExist` {boolean} when `force` is `false`, and the destination exists, throw an error. **Default:** `false`. * `filter` {Function} Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. When ignoring a directory, all of its contents will be skipped as well. Can also return a `Promise` that resolves to `true` or `false` **Default:** `undefined`. * `src` {string} source path to copy. * `dest` {string} destination path to copy to. * Returns: {boolean|Promise} A value that is coercible to `boolean` or a `Promise` that fulfils with such value. * `force` {boolean} overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. **Default:** `true`. * `mode` {integer} modifiers for copy operation. **Default:** `0`. See `mode` flag of [`fsPromises.copyFile()`][]. * `preserveTimestamps` {boolean} When `true` timestamps from `src` will be preserved. **Default:** `false`. * `recursive` {boolean} copy directories recursively **Default:** `false` * `verbatimSymlinks` {boolean} When `true`, path resolution for symlinks will be skipped. **Default:** `false` * Returns: {Promise} Fulfills with `undefined` upon success. Asynchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files. When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`. ### `fsPromises.lchmod(path, mode)` <!-- YAML deprecated: v10.0.0 --> * `path` {string|Buffer|URL} * `mode` {integer} * Returns: {Promise} Fulfills with `undefined` upon success. Changes the permissions on a symbolic link. This method is only implemented on macOS. ### `fsPromises.lchown(path, uid, gid)` <!-- YAML added: v10.0.0 changes: - version: v10.6.0 pr-url: https://github.com/nodejs/node/pull/21498 description: This API is no longer deprecated. --> * `path` {string|Buffer|URL} * `uid` {integer} * `gid` {integer} * Returns: {Promise} Fulfills with `undefined` upon success. Changes the ownership on a symbolic link. ### `fsPromises.lutimes(path, atime, mtime)` <!-- YAML added: - v14.5.0 - v12.19.0 --> * `path` {string|Buffer|URL} * `atime` {number|string|Date} * `mtime` {number|string|Date} * Returns: {Promise} Fulfills with `undefined` upon success. Changes the access and modification times of a file in the same way as [`fsPromises.utimes()`][], with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed. ### `fsPromises.link(existingPath, newPath)` <!-- YAML added: v10.0.0 --> * `existingPath` {string|Buffer|URL} * `newPath` {string|Buffer|URL} * Returns: {Promise} Fulfills with `undefined` upon success. Creates a new link from the `existingPath` to the `newPath`. See the POSIX link(2) documentation for more detail. ### `fsPromises.lstat(path[, options])` <!-- YAML added: v10.0.0 changes: - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * Returns: {Promise} Fulfills with the {fs.Stats} object for the given symbolic link `path`. Equivalent to [`fsPromises.stat()`][] unless `path` refers to a symbolic link, in which case the link itself is stat-ed, not the file that it refers to. Refer to the POSIX lstat(2) document for more detail. ### `fsPromises.mkdir(path[, options])` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `options` {Object|integer} * `recursive` {boolean} **Default:** `false` * `mode` {string|integer} Not supported on Windows. **Default:** `0o777`. * Returns: {Promise} Upon success, fulfills with `undefined` if `recursive` is `false`, or the first directory path created if `recursive` is `true`. Asynchronously creates a directory. The optional `options` argument can be an integer specifying `mode` (permission and sticky bits), or an object with a `mode` property and a `recursive` property indicating whether parent directories should be created. Calling `fsPromises.mkdir()` when `path` is a directory that exists results in a rejection only when `recursive` is false. ```mjs import { mkdir } from 'node:fs/promises'; try { const projectFolder = new URL('./test/project/', import.meta.url); const createDir = await mkdir(projectFolder, { recursive: true }); console.log(`created ${createDir}`); } catch (err) { console.error(err.message); } ``` ```cjs const { mkdir } = require('node:fs/promises'); const { join } = require('node:path'); async function makeDirectory() { const projectFolder = join(__dirname, 'test', 'project'); const dirCreation = await mkdir(projectFolder, { recursive: true }); console.log(dirCreation); return dirCreation; } makeDirectory().catch(console.error); ``` ### `fsPromises.mkdtemp(prefix[, options])` <!-- YAML added: v10.0.0 changes: - version: v20.6.0 pr-url: https://github.com/nodejs/node/pull/48828 description: The `prefix` parameter now accepts buffers and URL. - version: - v16.5.0 - v14.18.0 pr-url: https://github.com/nodejs/node/pull/39028 description: The `prefix` parameter now accepts an empty string. --> * `prefix` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {Promise} Fulfills with a string containing the file system path of the newly created temporary directory. Creates a unique temporary directory. A unique directory name is generated by appending six random characters to the end of the provided `prefix`. Due to platform inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing `X` characters in `prefix` with random characters. The optional `options` argument can be a string specifying an encoding, or an object with an `encoding` property specifying the character encoding to use. ```mjs import { mkdtemp } from 'node:fs/promises'; import { join } from 'node:path'; import { tmpdir } from 'node:os'; try { await mkdtemp(join(tmpdir(), 'foo-')); } catch (err) { console.error(err); } ``` The `fsPromises.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('node:path').sep`). ### `fsPromises.open(path, flags[, mode])` <!-- YAML added: v10.0.0 changes: - version: v11.1.0 pr-url: https://github.com/nodejs/node/pull/23767 description: The `flags` argument is now optional and defaults to `'r'`. --> * `path` {string|Buffer|URL} * `flags` {string|number} See [support of file system `flags`][]. **Default:** `'r'`. * `mode` {string|integer} Sets the file mode (permission and sticky bits) if the file is created. **Default:** `0o666` (readable and writable) * Returns: {Promise} Fulfills with a {FileHandle} object. Opens a {FileHandle}. Refer to the POSIX open(2) documentation for more detail. Some characters (`< > : " / \ | ? *`) are reserved under Windows as documented by [Naming Files, Paths, and Namespaces][]. Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by [this MSDN page][MSDN-Using-Streams]. ### `fsPromises.opendir(path[, options])` <!-- YAML added: v12.12.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/41439 description: Added `recursive` option. - version: - v13.1.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30114 description: The `bufferSize` option was introduced. --> * `path` {string|Buffer|URL} * `options` {Object} * `encoding` {string|null} **Default:** `'utf8'` * `bufferSize` {number} Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. **Default:** `32` * `recursive` {boolean} Resolved `Dir` will be an {AsyncIterable} containing all sub files and directories. **Default:** `false` * Returns: {Promise} Fulfills with an {fs.Dir}. Asynchronously open a directory for iterative scanning. See the POSIX opendir(3) documentation for more detail. Creates an {fs.Dir}, which contains all further functions for reading from and cleaning up the directory. The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations. Example using async iteration: ```mjs import { opendir } from 'node:fs/promises'; try { const dir = await opendir('./'); for await (const dirent of dir) console.log(dirent.name); } catch (err) { console.error(err); } ``` When using the async iterator, the {fs.Dir} object will be automatically closed after the iterator exits. ### `fsPromises.readdir(path[, options])` <!-- YAML added: v10.0.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/41439 description: Added `recursive` option. - version: v10.11.0 pr-url: https://github.com/nodejs/node/pull/22020 description: New option `withFileTypes` was added. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `withFileTypes` {boolean} **Default:** `false` * `recursive` {boolean} If `true`, reads the contents of a directory recursively. In recursive mode, it will list all files, sub files, and directories. **Default:** `false`. * Returns: {Promise} Fulfills with an array of the names of the files in the directory excluding `'.'` and `'..'`. Reads the contents of a directory. 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. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as {Buffer} objects. If `options.withFileTypes` is set to `true`, the returned array will contain {fs.Dirent} objects. ```mjs import { readdir } from 'node:fs/promises'; try { const files = await readdir(path); for (const file of files) console.log(file); } catch (err) { console.error(err); } ``` ### `fsPromises.readFile(path[, options])` <!-- YAML added: v10.0.0 changes: - version: - v15.2.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/35911 description: The options argument may include an AbortSignal to abort an ongoing readFile request. --> * `path` {string|Buffer|URL|FileHandle} filename or `FileHandle` * `options` {Object|string} * `encoding` {string|null} **Default:** `null` * `flag` {string} See [support of file system `flags`][]. **Default:** `'r'`. * `signal` {AbortSignal} allows aborting an in-progress readFile * Returns: {Promise} Fulfills with the contents of the file. Asynchronously reads the entire contents of a file. If no encoding is specified (using `options.encoding`), the data is returned as a {Buffer} object. Otherwise, the data will be a string. If `options` is a string, then it specifies the encoding. When the `path` is a directory, the behavior of `fsPromises.readFile()` is platform-specific. On macOS, Linux, and Windows, the promise will be rejected with an error. On FreeBSD, a representation of the directory's contents will be returned. An example of reading a `package.json` file located in the same directory of the running code: ```mjs import { readFile } from 'node:fs/promises'; try { const filePath = new URL('./package.json', import.meta.url); const contents = await readFile(filePath, { encoding: 'utf8' }); console.log(contents); } catch (err) { console.error(err.message); } ``` ```cjs const { readFile } = require('node:fs/promises'); const { resolve } = require('node:path'); async function logFile() { try { const filePath = resolve('./package.json'); const contents = await readFile(filePath, { encoding: 'utf8' }); console.log(contents); } catch (err) { console.error(err.message); } } logFile(); ``` It is possible to abort an ongoing `readFile` using an {AbortSignal}. If a request is aborted the promise returned is rejected with an `AbortError`: ```mjs import { readFile } from 'node:fs/promises'; try { const controller = new AbortController(); const { signal } = controller; const promise = readFile(fileName, { signal }); // Abort the request before the promise settles. controller.abort(); await promise; } catch (err) { // When a request is aborted - err is an AbortError console.error(err); } ``` Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.readFile` performs. Any specified {FileHandle} has to support reading. ### `fsPromises.readlink(path[, options])` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {Promise} Fulfills with the `linkString` upon success. Reads the contents of the symbolic link referred to by `path`. See the POSIX readlink(2) documentation for more detail. The promise is fulfilled with the `linkString` upon success. 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 returned. If the `encoding` is set to `'buffer'`, the link path returned will be passed as a {Buffer} object. ### `fsPromises.realpath(path[, options])` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {Promise} Fulfills with the resolved path upon success. Determines the actual location of `path` using the same semantics as the `fs.realpath.native()` function. 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. If the `encoding` is set to `'buffer'`, the path returned will be passed as a {Buffer} object. On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction. ### `fsPromises.rename(oldPath, newPath)` <!-- YAML added: v10.0.0 --> * `oldPath` {string|Buffer|URL} * `newPath` {string|Buffer|URL} * Returns: {Promise} Fulfills with `undefined` upon success. Renames `oldPath` to `newPath`. ### `fsPromises.rmdir(path[, options])` <!-- YAML added: v10.0.0 changes: - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37216 description: "Using `fsPromises.rmdir(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX." - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37216 description: "Using `fsPromises.rmdir(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error." - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37302 description: The `recursive` option is deprecated, using it triggers a deprecation warning. - version: v14.14.0 pr-url: https://github.com/nodejs/node/pull/35579 description: The `recursive` option is deprecated, use `fsPromises.rm` instead. - version: - v13.3.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30644 description: The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. - version: v12.10.0 pr-url: https://github.com/nodejs/node/pull/29168 description: The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. --> * `path` {string|Buffer|URL} * `options` {Object} * `maxRetries` {integer} If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`. * `recursive` {boolean} If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. **Default:** `false`. **Deprecated.** * `retryDelay` {integer} The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`. * Returns: {Promise} Fulfills with `undefined` upon success. Removes the directory identified by `path`. Using `fsPromises.rmdir()` on a file (not a directory) results in the promise being rejected with an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. To get a behavior similar to the `rm -rf` Unix command, use [`fsPromises.rm()`][] with options `{ recursive: true, force: true }`. ### `fsPromises.rm(path[, options])` <!-- YAML added: v14.14.0 --> * `path` {string|Buffer|URL} * `options` {Object} * `force` {boolean} When `true`, exceptions will be ignored if `path` does not exist. **Default:** `false`. * `maxRetries` {integer} If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`. * `recursive` {boolean} If `true`, perform a recursive directory removal. In recursive mode operations are retried on failure. **Default:** `false`. * `retryDelay` {integer} The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`. * Returns: {Promise} Fulfills with `undefined` upon success. Removes files and directories (modeled on the standard POSIX `rm` utility). ### `fsPromises.stat(path[, options])` <!-- YAML added: v10.0.0 changes: - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * Returns: {Promise} Fulfills with the {fs.Stats} object for the given `path`. ### `fsPromises.statfs(path[, options])` <!-- YAML added: - v19.6.0 - v18.15.0 --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.StatFs} object should be `bigint`. **Default:** `false`. * Returns: {Promise} Fulfills with the {fs.StatFs} object for the given `path`. ### `fsPromises.symlink(target, path[, type])` <!-- YAML added: v10.0.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/42894 description: If the `type` argument is `null` or omitted, Node.js will autodetect `target` type and automatically select `dir` or `file`. --> * `target` {string|Buffer|URL} * `path` {string|Buffer|URL} * `type` {string|null} **Default:** `null` * Returns: {Promise} Fulfills with `undefined` upon success. Creates a symbolic link. The `type` argument is only used on Windows platforms and can be one of `'dir'`, `'file'`, or `'junction'`. If the `type` argument is not a string, Node.js will autodetect `target` type and use `'file'` or `'dir'`. If the `target` does not exist, `'file'` will be used. Windows junction points require the destination path to be absolute. When using `'junction'`, the `target` argument will automatically be normalized to absolute path. Junction points on NTFS volumes can only point to directories. ### `fsPromises.truncate(path[, len])` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `len` {integer} **Default:** `0` * Returns: {Promise} Fulfills with `undefined` upon success. Truncates (shortens or extends the length) of the content at `path` to `len` bytes. ### `fsPromises.unlink(path)` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * Returns: {Promise} Fulfills with `undefined` upon success. If `path` refers to a symbolic link, then the link is removed without affecting the file or directory to which that link refers. If the `path` refers to a file path that is not a symbolic link, the file is deleted. See the POSIX unlink(2) documentation for more detail. ### `fsPromises.utimes(path, atime, mtime)` <!-- YAML added: v10.0.0 --> * `path` {string|Buffer|URL} * `atime` {number|string|Date} * `mtime` {number|string|Date} * Returns: {Promise} Fulfills with `undefined` upon success. Change the file system timestamps of the object referenced by `path`. The `atime` and `mtime` arguments follow these rules: * Values can be either numbers representing Unix epoch time, `Date`s, or a numeric string like `'123456789.0'`. * If the value can not be converted to a number, or is `NaN`, `Infinity`, or `-Infinity`, an `Error` will be thrown. ### `fsPromises.watch(filename[, options])` <!-- YAML added: - v15.9.0 - v14.18.0 --> * `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'`. * `signal` {AbortSignal} An {AbortSignal} used to signal when the watcher should stop. * Returns: {AsyncIterator} of objects with the properties: * `eventType` {string} The type of change * `filename` {string|Buffer|null} The name of the file changed. Returns an async iterator that watches for changes on `filename`, where `filename` is either a file or a directory. ```js const { watch } = require('node:fs/promises'); const ac = new AbortController(); const { signal } = ac; setTimeout(() => ac.abort(), 10000); (async () => { try { const watcher = watch(__filename, { signal }); for await (const event of watcher) console.log(event); } catch (err) { if (err.name === 'AbortError') return; throw err; } })(); ``` On most platforms, `'rename'` is emitted whenever a filename appears or disappears in the directory. All the [caveats][] for `fs.watch()` also apply to `fsPromises.watch()`. ### `fsPromises.writeFile(file, data[, options])` <!-- YAML added: v10.0.0 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50009 description: The `flush` option is now supported. - version: - v15.14.0 - v14.18.0 pr-url: https://github.com/nodejs/node/pull/37490 description: The `data` argument supports `AsyncIterable`, `Iterable`, and `Stream`. - version: - v15.2.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/35993 description: The options argument may include an AbortSignal to abort an ongoing writeFile request. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `data` parameter won't coerce unsupported input to strings anymore. --> * `file` {string|Buffer|URL|FileHandle} filename or `FileHandle` * `data` {string|Buffer|TypedArray|DataView|AsyncIterable|Iterable|Stream} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `mode` {integer} **Default:** `0o666` * `flag` {string} See [support of file system `flags`][]. **Default:** `'w'`. * `flush` {boolean} If all data is successfully written to the file, and `flush` is `true`, `filehandle.sync()` is used to flush the data. **Default:** `false`. * `signal` {AbortSignal} allows aborting an in-progress writeFile * Returns: {Promise} Fulfills with `undefined` upon success. Asynchronously writes data to a file, replacing the file if it already exists. `data` can be a string, a buffer, an {AsyncIterable}, or an {Iterable} object. The `encoding` option is ignored if `data` is a buffer. If `options` is a string, then it specifies the encoding. The `mode` option only affects the newly created file. See [`fs.open()`][] for more details. Any specified {FileHandle} has to support writing. It is unsafe to use `fsPromises.writeFile()` multiple times on the same file without waiting for the promise to be settled. Similarly to `fsPromises.readFile` - `fsPromises.writeFile` is a convenience method that performs multiple `write` calls internally to write the buffer passed to it. For performance sensitive code consider using [`fs.createWriteStream()`][] or [`filehandle.createWriteStream()`][]. It is possible to use an {AbortSignal} to cancel an `fsPromises.writeFile()`. Cancelation is "best effort", and some amount of data is likely still to be written. ```mjs import { writeFile } from 'node:fs/promises'; import { Buffer } from 'node:buffer'; try { const controller = new AbortController(); const { signal } = controller; const data = new Uint8Array(Buffer.from('Hello Node.js')); const promise = writeFile('message.txt', data, { signal }); // Abort the request before the promise settles. controller.abort(); await promise; } catch (err) { // When a request is aborted - err is an AbortError console.error(err); } ``` Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.writeFile` performs. ### `fsPromises.constants` <!-- YAML added: - v18.4.0 - v16.17.0 --> * {Object} Returns an object containing commonly used constants for file system operations. The object is the same as `fs.constants`. See [FS constants][] for more details. ## Callback API The callback APIs perform all operations asynchronously, without blocking the event loop, then invoke a callback function upon completion or error. The callback APIs use the underlying Node.js threadpool to perform file system operations off the event loop thread. These operations are not synchronized or threadsafe. Care must be taken when performing multiple concurrent modifications on the same file or data corruption may occur. ### `fs.access(path[, mode], callback)` <!-- YAML added: v0.11.15 changes: - version: v20.8.0 pr-url: https://github.com/nodejs/node/pull/49683 description: The constants `fs.F_OK`, `fs.R_OK`, `fs.W_OK` and `fs.X_OK` which were present directly on `fs` are deprecated. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v6.3.0 pr-url: https://github.com/nodejs/node/pull/6534 description: The constants like `fs.R_OK`, etc which were present directly on `fs` were moved into `fs.constants` as a soft deprecation. Thus for Node.js `< v6.3.0` use `fs` to access those constants, or do something like `(fs.constants || fs).R_OK` to work with all versions. --> * `path` {string|Buffer|URL} * `mode` {integer} **Default:** `fs.constants.F_OK` * `callback` {Function} * `err` {Error} 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. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check [File access constants][] for possible values of `mode`. 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 an `Error` object. The following examples check if `package.json` exists, and if it is readable or writable. ```mjs import { access, constants } from 'node:fs'; const file = 'package.json'; // Check if the file exists in the current directory. access(file, constants.F_OK, (err) => { console.log(`${file} ${err ? 'does not exist' : 'exists'}`); }); // Check if the file is readable. access(file, constants.R_OK, (err) => { console.log(`${file} ${err ? 'is not readable' : 'is readable'}`); }); // Check if the file is writable. access(file, constants.W_OK, (err) => { console.log(`${file} ${err ? 'is not writable' : 'is writable'}`); }); // Check if the file is readable and writable. access(file, constants.R_OK | constants.W_OK, (err) => { console.log(`${file} ${err ? 'is not' : 'is'} readable and writable`); }); ``` Do not use `fs.access()` to check for the accessibility of a file before calling `fs.open()`, `fs.readFile()`, or `fs.writeFile()`. 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. **write (NOT RECOMMENDED)** ```mjs import { access, open, close } from 'node:fs'; access('myfile', (err) => { if (!err) { console.error('myfile already exists'); return; } open('myfile', 'wx', (err, fd) => { if (err) throw err; try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); }); ``` **write (RECOMMENDED)** ```mjs import { open, close } from 'node:fs'; open('myfile', 'wx', (err, fd) => { if (err) { if (err.code === 'EEXIST') { console.error('myfile already exists'); return; } throw err; } try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); ``` **read (NOT RECOMMENDED)** ```mjs import { access, open, close } from 'node:fs'; access('myfile', (err) => { if (err) { if (err.code === 'ENOENT') { console.error('myfile does not exist'); return; } throw err; } open('myfile', 'r', (err, fd) => { if (err) throw err; try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); }); ``` **read (RECOMMENDED)** ```mjs import { open, close } from 'node:fs'; open('myfile', 'r', (err, fd) => { if (err) { if (err.code === 'ENOENT') { console.error('myfile does not exist'); return; } throw err; } try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); ``` 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 will not be used directly, for example when its accessibility is a signal from another process. On Windows, access-control policies (ACLs) on a directory may limit access to a file or directory. The `fs.access()` function, however, does not check the ACL and therefore may report that a path is accessible even if the ACL restricts the user from reading or writing to it. ### `fs.appendFile(path, data[, options], callback)` <!-- YAML added: v0.6.7 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50095 description: The `flush` option is now supported. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7831 description: The passed `options` object will never be modified. - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3163 description: The `file` parameter can be a file descriptor now. --> * `path` {string|Buffer|URL|number} filename or file descriptor * `data` {string|Buffer} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `mode` {integer} **Default:** `0o666` * `flag` {string} See [support of file system `flags`][]. **Default:** `'a'`. * `flush` {boolean} If `true`, the underlying file descriptor is flushed prior to closing it. **Default:** `false`. * `callback` {Function} * `err` {Error} Asynchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a {Buffer}. The `mode` option only affects the newly created file. See [`fs.open()`][] for more details. ```mjs import { appendFile } from 'node: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: ```mjs import { appendFile } from 'node:fs'; appendFile('message.txt', 'data to append', 'utf8', callback); ``` The `path` may be specified as a numeric file descriptor that has been opened for appending (using `fs.open()` or `fs.openSync()`). The file descriptor will not be closed automatically. ```mjs import { open, close, appendFile } from 'node:fs'; function closeFd(fd) { close(fd, (err) => { if (err) throw err; }); } open('message.txt', 'a', (err, fd) => { if (err) throw err; try { appendFile(fd, 'data to append', 'utf8', (err) => { closeFd(fd); if (err) throw err; }); } catch (err) { closeFd(fd); throw err; } }); ``` ### `fs.chmod(path, mode, callback)` <!-- YAML added: v0.1.30 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `mode` {string|integer} * `callback` {Function} * `err` {Error} Asynchronously changes the permissions of a file. No arguments other than a possible exception are given to the completion callback. See the POSIX chmod(2) documentation for more detail. ```mjs import { chmod } from 'node:fs'; chmod('my_file.txt', 0o775, (err) => { if (err) throw err; console.log('The permissions for file "my_file.txt" have been changed!'); }); ``` #### File modes The `mode` argument used in both the `fs.chmod()` and `fs.chmodSync()` methods is a numeric bitmask created using a logical OR of the following constants: | Constant | Octal | Description | | ---------------------- | ------- | ------------------------ | | `fs.constants.S_IRUSR` | `0o400` | read by owner | | `fs.constants.S_IWUSR` | `0o200` | write by owner | | `fs.constants.S_IXUSR` | `0o100` | execute/search by owner | | `fs.constants.S_IRGRP` | `0o40` | read by group | | `fs.constants.S_IWGRP` | `0o20` | write by group | | `fs.constants.S_IXGRP` | `0o10` | execute/search by group | | `fs.constants.S_IROTH` | `0o4` | read by others | | `fs.constants.S_IWOTH` | `0o2` | write by others | | `fs.constants.S_IXOTH` | `0o1` | execute/search by others | An easier method of constructing the `mode` is to use a sequence of three octal digits (e.g. `765`). The left-most digit (`7` in the example), specifies the permissions for the file owner. The middle digit (`6` in the example), specifies permissions for the group. The right-most digit (`5` in the example), specifies the permissions for others. | Number | Description | | ------ | ------------------------ | | `7` | read, write, and execute | | `6` | read and write | | `5` | read and execute | | `4` | read only | | `3` | write and execute | | `2` | write only | | `1` | execute only | | `0` | no permission | For example, the octal value `0o765` means: * The owner may read, write, and execute the file. * The group may read and write the file. * Others may read and execute the file. When using raw numbers where file modes are expected, any value larger than `0o777` may result in platform-specific behaviors that are not supported to work consistently. Therefore constants like `S_ISVTX`, `S_ISGID`, or `S_ISUID` are not exposed in `fs.constants`. Caveats: on Windows only the write permission can be changed, and the distinction among the permissions of group, owner, or others is not implemented. ### `fs.chown(path, uid, gid, callback)` <!-- YAML added: v0.1.97 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `uid` {integer} * `gid` {integer} * `callback` {Function} * `err` {Error} Asynchronously changes owner and group of a file. No arguments other than a possible exception are given to the completion callback. See the POSIX chown(2) documentation for more detail. ### `fs.close(fd[, callback])` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: - v15.9.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/37174 description: A default callback is now used if one is not provided. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `callback` {Function} * `err` {Error} Closes the file descriptor. No arguments other than a possible exception are given to the completion callback. Calling `fs.close()` on any file descriptor (`fd`) that is currently in use through any other `fs` operation may lead to undefined behavior. See the POSIX close(2) documentation for more detail. ### `fs.copyFile(src, dest[, mode], callback)` <!-- YAML added: v8.5.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/27044 description: Changed `flags` argument to `mode` and imposed stricter type validation. --> * `src` {string|Buffer|URL} source filename to copy * `dest` {string|Buffer|URL} destination filename of the copy operation * `mode` {integer} modifiers for copy operation. **Default:** `0`. * `callback` {Function} * `err` {Error} Asynchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. No arguments other than a possible exception are given to the callback function. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination. `mode` is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`). * `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists. * `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. * `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail. ```mjs import { copyFile, constants } from 'node:fs'; function callback(err) { if (err) throw err; console.log('source.txt was copied to destination.txt'); } // destination.txt will be created or overwritten by default. copyFile('source.txt', 'destination.txt', callback); // By using COPYFILE_EXCL, the operation will fail if destination.txt exists. copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL, callback); ``` ### `fs.cp(src, dest[, options], callback)` <!-- YAML added: v16.7.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/47084 description: Accept an additional `mode` option to specify the copy behavior as the `mode` argument of `fs.copyFile()`. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: - v17.6.0 - v16.15.0 pr-url: https://github.com/nodejs/node/pull/41819 description: Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. --> > Stability: 1 - Experimental * `src` {string|URL} source path to copy. * `dest` {string|URL} destination path to copy to. * `options` {Object} * `dereference` {boolean} dereference symlinks. **Default:** `false`. * `errorOnExist` {boolean} when `force` is `false`, and the destination exists, throw an error. **Default:** `false`. * `filter` {Function} Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. When ignoring a directory, all of its contents will be skipped as well. Can also return a `Promise` that resolves to `true` or `false` **Default:** `undefined`. * `src` {string} source path to copy. * `dest` {string} destination path to copy to. * Returns: {boolean|Promise} A value that is coercible to `boolean` or a `Promise` that fulfils with such value. * `force` {boolean} overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. **Default:** `true`. * `mode` {integer} modifiers for copy operation. **Default:** `0`. See `mode` flag of [`fs.copyFile()`][]. * `preserveTimestamps` {boolean} When `true` timestamps from `src` will be preserved. **Default:** `false`. * `recursive` {boolean} copy directories recursively **Default:** `false` * `verbatimSymlinks` {boolean} When `true`, path resolution for symlinks will be skipped. **Default:** `false` * `callback` {Function} * `err` {Error} Asynchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files. When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`. ### `fs.createReadStream(path[, options])` <!-- YAML added: v0.1.31 changes: - version: v16.10.0 pr-url: https://github.com/nodejs/node/pull/40013 description: The `fs` option does not need `open` method if an `fd` was provided. - version: v16.10.0 pr-url: https://github.com/nodejs/node/pull/40013 description: The `fs` option does not need `close` method if `autoClose` is `false`. - version: v15.5.0 pr-url: https://github.com/nodejs/node/pull/36431 description: Add support for `AbortSignal`. - version: - v15.4.0 pr-url: https://github.com/nodejs/node/pull/35922 description: The `fd` option accepts FileHandle arguments. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31408 description: Change `emitClose` default to `true`. - version: - v13.6.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/29083 description: The `fs` options allow overriding the used `fs` implementation. - version: v12.10.0 pr-url: https://github.com/nodejs/node/pull/29212 description: Enable `emitClose` option. - version: v11.0.0 pr-url: https://github.com/nodejs/node/pull/19898 description: Impose new restrictions on `start` and `end`, throwing more appropriate errors in cases when we cannot reasonably handle the input values. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7831 description: The passed `options` object will never be modified. - version: v2.3.0 pr-url: https://github.com/nodejs/node/pull/1845 description: The passed `options` object can be a string now. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `flags` {string} See [support of file system `flags`][]. **Default:** `'r'`. * `encoding` {string} **Default:** `null` * `fd` {integer|FileHandle} **Default:** `null` * `mode` {integer} **Default:** `0o666` * `autoClose` {boolean} **Default:** `true` * `emitClose` {boolean} **Default:** `true` * `start` {integer} * `end` {integer} **Default:** `Infinity` * `highWaterMark` {integer} **Default:** `64 * 1024` * `fs` {Object|null} **Default:** `null` * `signal` {AbortSignal|null} **Default:** `null` * Returns: {fs.ReadStream} Unlike the 16 KiB default `highWaterMark` for a {stream.Readable}, the stream returned by this method has a default `highWaterMark` of 64 KiB. `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, allowed values are in the \[0, [`Number.MAX_SAFE_INTEGER`][]] range. 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. `fd` should be blocking; non-blocking `fd`s should be passed to {net.Socket}. If `fd` points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. By providing the `fs` option, it is possible to override the corresponding `fs` implementations for `open`, `read`, and `close`. When providing the `fs` option, an override for `read` is required. If no `fd` is provided, an override for `open` is also required. If `autoClose` is `true`, an override for `close` is also required. ```mjs import { createReadStream } from 'node:fs'; // Create a stream from some character device. const stream = createReadStream('/dev/input/event0'); setTimeout(() => { stream.close(); // This may not close the stream. // Artificially marking end-of-stream, as if the underlying resource had // indicated end-of-file by itself, allows the stream to close. // This does not cancel pending read operations, and if there is such an // operation, the process may still not be able to exit successfully // until it finishes. stream.push(null); stream.read(0); }, 100); ``` 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: ```mjs import { createReadStream } from 'node:fs'; createReadStream('sample.txt', { start: 90, end: 99 }); ``` If `options` is a string, then it specifies the encoding. ### `fs.createWriteStream(path[, options])` <!-- YAML added: v0.1.31 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50093 description: The `flush` option is now supported. - version: v16.10.0 pr-url: https://github.com/nodejs/node/pull/40013 description: The `fs` option does not need `open` method if an `fd` was provided. - version: v16.10.0 pr-url: https://github.com/nodejs/node/pull/40013 description: The `fs` option does not need `close` method if `autoClose` is `false`. - version: v15.5.0 pr-url: https://github.com/nodejs/node/pull/36431 description: Add support for `AbortSignal`. - version: - v15.4.0 pr-url: https://github.com/nodejs/node/pull/35922 description: The `fd` option accepts FileHandle arguments. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31408 description: Change `emitClose` default to `true`. - version: - v13.6.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/29083 description: The `fs` options allow overriding the used `fs` implementation. - version: v12.10.0 pr-url: https://github.com/nodejs/node/pull/29212 description: Enable `emitClose` option. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7831 description: The passed `options` object will never be modified. - version: v5.5.0 pr-url: https://github.com/nodejs/node/pull/3679 description: The `autoClose` option is supported now. - version: v2.3.0 pr-url: https://github.com/nodejs/node/pull/1845 description: The passed `options` object can be a string now. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `flags` {string} See [support of file system `flags`][]. **Default:** `'w'`. * `encoding` {string} **Default:** `'utf8'` * `fd` {integer|FileHandle} **Default:** `null` * `mode` {integer} **Default:** `0o666` * `autoClose` {boolean} **Default:** `true` * `emitClose` {boolean} **Default:** `true` * `start` {integer} * `fs` {Object|null} **Default:** `null` * `signal` {AbortSignal|null} **Default:** `null` * `highWaterMark` {number} **Default:** `16384` * `flush` {boolean} If `true`, the underlying file descriptor is flushed prior to closing it. **Default:** `false`. * Returns: {fs.WriteStream} `options` may also include a `start` option to allow writing data at some position past the beginning of the file, allowed values are in the \[0, [`Number.MAX_SAFE_INTEGER`][]] range. Modifying a file rather than replacing it may require the `flags` option to be set to `r+` rather than the default `w`. The `encoding` can be any one of those accepted by {Buffer}. If `autoClose` is set to true (default behavior) on `'error'` or `'finish'` 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. By default, the stream will emit a `'close'` event after it has been destroyed. Set the `emitClose` option to `false` to change this behavior. By providing the `fs` option it is possible to override the corresponding `fs` implementations for `open`, `write`, `writev`, and `close`. Overriding `write()` without `writev()` can reduce performance as some optimizations (`_writev()`) will be disabled. When providing the `fs` option, overrides for at least one of `write` and `writev` are required. If no `fd` option is supplied, an override for `open` is also required. If `autoClose` is `true`, an override for `close` is also required. Like {fs.ReadStream}, if `fd` is specified, {fs.WriteStream} will ignore the `path` argument and will use the specified file descriptor. This means that no `'open'` event will be emitted. `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)` <!-- YAML added: v0.0.2 deprecated: v1.0.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> > Stability: 0 - Deprecated: Use [`fs.stat()`][] or [`fs.access()`][] instead. * `path` {string|Buffer|URL} * `callback` {Function} * `exists` {boolean} Test whether or not the element at the given `path` exists by checking with the file system. Then call the `callback` argument with either true or false: ```mjs import { exists } from 'node:fs'; exists('/etc/passwd', (e) => { console.log(e ? 'it exists' : 'no passwd!'); }); ``` **The parameters for this callback are 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()`. If `path` is a symbolic link, it is followed. Thus, if `path` exists but points to a non-existent element, the callback will receive the value `false`. 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. **write (NOT RECOMMENDED)** ```mjs import { exists, open, close } from 'node:fs'; exists('myfile', (e) => { if (e) { console.error('myfile already exists'); } else { open('myfile', 'wx', (err, fd) => { if (err) throw err; try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); } }); ``` **write (RECOMMENDED)** ```mjs import { open, close } from 'node:fs'; open('myfile', 'wx', (err, fd) => { if (err) { if (err.code === 'EEXIST') { console.error('myfile already exists'); return; } throw err; } try { writeMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); ``` **read (NOT RECOMMENDED)** ```mjs import { open, close, exists } from 'node:fs'; exists('myfile', (e) => { if (e) { open('myfile', 'r', (err, fd) => { if (err) throw err; try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); } else { console.error('myfile does not exist'); } }); ``` **read (RECOMMENDED)** ```mjs import { open, close } from 'node:fs'; open('myfile', 'r', (err, fd) => { if (err) { if (err.code === 'ENOENT') { console.error('myfile does not exist'); return; } throw err; } try { readMyData(fd); } finally { close(fd, (err) => { if (err) throw err; }); } }); ``` 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.fchmod(fd, mode, callback)` <!-- YAML added: v0.4.7 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `mode` {string|integer} * `callback` {Function} * `err` {Error} Sets the permissions on the file. No arguments other than a possible exception are given to the completion callback. See the POSIX fchmod(2) documentation for more detail. ### `fs.fchown(fd, uid, gid, callback)` <!-- YAML added: v0.4.7 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `uid` {integer} * `gid` {integer} * `callback` {Function} * `err` {Error} Sets the owner of the file. No arguments other than a possible exception are given to the completion callback. See the POSIX fchown(2) documentation for more detail. ### `fs.fdatasync(fd, callback)` <!-- YAML added: v0.1.96 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `callback` {Function} * `err` {Error} Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX fdatasync(2) documentation for details. No arguments other than a possible exception are given to the completion callback. ### `fs.fstat(fd[, options], callback)` <!-- YAML added: v0.1.95 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * `callback` {Function} * `err` {Error} * `stats` {fs.Stats} Invokes the callback with the {fs.Stats} for the file descriptor. See the POSIX fstat(2) documentation for more detail. ### `fs.fsync(fd, callback)` <!-- YAML added: v0.1.96 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `callback` {Function} * `err` {Error} Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX fsync(2) documentation for more detail. No arguments other than a possible exception are given to the completion callback. ### `fs.ftruncate(fd[, len], callback)` <!-- YAML added: v0.8.6 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `len` {integer} **Default:** `0` * `callback` {Function} * `err` {Error} Truncates the file descriptor. No arguments other than a possible exception are given to the completion callback. See the POSIX ftruncate(2) documentation for more detail. 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: ```mjs import { open, close, ftruncate } from 'node:fs'; function closeFd(fd) { close(fd, (err) => { if (err) throw err; }); } open('temp.txt', 'r+', (err, fd) => { if (err) throw err; try { ftruncate(fd, 4, (err) => { closeFd(fd); if (err) throw err; }); } catch (err) { closeFd(fd); if (err) throw err; } }); ``` If the file previously was shorter than `len` bytes, it is extended, and the extended part is filled with null bytes (`'\0'`): If `len` is negative then `0` will be used. ### `fs.futimes(fd, atime, mtime, callback)` <!-- YAML added: v0.4.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v4.1.0 pr-url: https://github.com/nodejs/node/pull/2387 description: Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. --> * `fd` {integer} * `atime` {number|string|Date} * `mtime` {number|string|Date} * `callback` {Function} * `err` {Error} Change the file system timestamps of the object referenced by the supplied file descriptor. See [`fs.utimes()`][]. ### `fs.lchmod(path, mode, callback)` <!-- YAML deprecated: v0.4.7 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37460 description: The error returned may be an `AggregateError` if more than one error is returned. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `mode` {integer} * `callback` {Function} * `err` {Error|AggregateError} Changes the permissions on a symbolic link. No arguments other than a possible exception are given to the completion callback. This method is only implemented on macOS. See the POSIX lchmod(2) documentation for more detail. ### `fs.lchown(path, uid, gid, callback)` <!-- YAML changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.6.0 pr-url: https://github.com/nodejs/node/pull/21498 description: This API is no longer deprecated. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v0.4.7 description: Documentation-only deprecation. --> * `path` {string|Buffer|URL} * `uid` {integer} * `gid` {integer} * `callback` {Function} * `err` {Error} Set the owner of the symbolic link. No arguments other than a possible exception are given to the completion callback. See the POSIX lchown(2) documentation for more detail. ### `fs.lutimes(path, atime, mtime, callback)` <!-- YAML added: - v14.5.0 - v12.19.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. --> * `path` {string|Buffer|URL} * `atime` {number|string|Date} * `mtime` {number|string|Date} * `callback` {Function} * `err` {Error} Changes the access and modification times of a file in the same way as [`fs.utimes()`][], with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed. No arguments other than a possible exception are given to the completion callback. ### `fs.link(existingPath, newPath, callback)` <!-- YAML added: v0.1.31 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `existingPath` {string|Buffer|URL} * `newPath` {string|Buffer|URL} * `callback` {Function} * `err` {Error} Creates a new link from the `existingPath` to the `newPath`. See the POSIX link(2) documentation for more detail. No arguments other than a possible exception are given to the completion callback. ### `fs.lstat(path[, options], callback)` <!-- YAML added: v0.1.30 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * `callback` {Function} * `err` {Error} * `stats` {fs.Stats} Retrieves the {fs.Stats} for the symbolic link referred to by the path. 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. See the POSIX lstat(2) documentation for more details. ### `fs.mkdir(path[, options], callback)` <!-- YAML added: v0.1.8 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: - v13.11.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/31530 description: In `recursive` mode, the callback now receives the first created path as an argument. - version: v10.12.0 pr-url: https://github.com/nodejs/node/pull/21875 description: The second argument can now be an `options` object with `recursive` and `mode` properties. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `options` {Object|integer} * `recursive` {boolean} **Default:** `false` * `mode` {string|integer} Not supported on Windows. **Default:** `0o777`. * `callback` {Function} * `err` {Error} * `path` {string|undefined} Present only if a directory is created with `recursive` set to `true`. Asynchronously creates a directory. The callback is given a possible exception and, if `recursive` is `true`, the first directory path created, `(err[, path])`. `path` can still be `undefined` when `recursive` is `true`, if no directory was created (for instance, if it was previously created). The optional `options` argument can be an integer specifying `mode` (permission and sticky bits), or an object with a `mode` property and a `recursive` property indicating whether parent directories should be created. Calling `fs.mkdir()` when `path` is a directory that exists results in an error only when `recursive` is false. If `recursive` is false and the directory exists, an `EEXIST` error occurs. ```mjs import { mkdir } from 'node:fs'; // Create ./tmp/a/apple, regardless of whether ./tmp and ./tmp/a exist. mkdir('./tmp/a/apple', { recursive: true }, (err) => { if (err) throw err; }); ``` On Windows, using `fs.mkdir()` on the root directory even with recursion will result in an error: ```mjs import { mkdir } from 'node:fs'; mkdir('/', { recursive: true }, (err) => { // => [Error: EPERM: operation not permitted, mkdir 'C:\'] }); ``` See the POSIX mkdir(2) documentation for more details. ### `fs.mkdtemp(prefix[, options], callback)` <!-- YAML added: v5.10.0 changes: - version: v20.6.0 pr-url: https://github.com/nodejs/node/pull/48828 description: The `prefix` parameter now accepts buffers and URL. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: - v16.5.0 - v14.18.0 pr-url: https://github.com/nodejs/node/pull/39028 description: The `prefix` parameter now accepts an empty string. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v6.2.1 pr-url: https://github.com/nodejs/node/pull/6828 description: The `callback` parameter is optional now. --> * `prefix` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `callback` {Function} * `err` {Error} * `directory` {string} Creates a unique temporary directory. Generates six random characters to be appended behind a required `prefix` to create a unique temporary directory. Due to platform inconsistencies, avoid trailing `X` characters in `prefix`. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing `X` characters in `prefix` with random characters. The created directory 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. ```mjs import { mkdtemp } from 'node:fs'; import { join } from 'node:path'; import { tmpdir } from 'node:os'; mkdtemp(join(tmpdir(), 'foo-'), (err, directory) => { if (err) throw err; console.log(directory); // Prints: /tmp/foo-itXde2 or C:\Users\...\AppData\Local\Temp\foo-itXde2 }); ``` 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('node:path').sep`). ```mjs import { tmpdir } from 'node:os'; import { mkdtemp } from 'node:fs'; // The parent directory for the new temporary directory const tmpDir = tmpdir(); // This method is *INCORRECT*: mkdtemp(tmpDir, (err, directory) => { if (err) throw err; console.log(directory); // Will print something similar to `/tmpabc123`. // A new temporary directory is created at the file system root // rather than *within* the /tmp directory. }); // This method is *CORRECT*: import { sep } from 'node:path'; mkdtemp(`${tmpDir}${sep}`, (err, directory) => { if (err) throw err; console.log(directory); // Will print something similar to `/tmp/abc123`. // A new temporary directory is created within // the /tmp directory. }); ``` ### `fs.open(path[, flags[, mode]], callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v11.1.0 pr-url: https://github.com/nodejs/node/pull/23767 description: The `flags` argument is now optional and defaults to `'r'`. - version: v9.9.0 pr-url: https://github.com/nodejs/node/pull/18801 description: The `as` and `as+` flags are supported now. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `flags` {string|number} See [support of file system `flags`][]. **Default:** `'r'`. * `mode` {string|integer} **Default:** `0o666` (readable and writable) * `callback` {Function} * `err` {Error} * `fd` {integer} Asynchronous file open. See the POSIX open(2) documentation for more details. `mode` sets the file mode (permission and sticky bits), but only if the file was created. On Windows, only the write permission can be manipulated; see [`fs.chmod()`][]. The callback gets two arguments `(err, fd)`. Some characters (`< > : " / \ | ? *`) are reserved under Windows as documented by [Naming Files, Paths, and Namespaces][]. Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by [this MSDN page][MSDN-Using-Streams]. Functions based on `fs.open()` exhibit this behavior as well: `fs.writeFile()`, `fs.readFile()`, etc. ### `fs.openAsBlob(path[, options])` <!-- YAML added: v19.8.0 --> > Stability: 1 - Experimental * `path` {string|Buffer|URL} * `options` {Object} * `type` {string} An optional mime type for the blob. * Returns: {Promise} Fulfills with a {Blob} upon success. Returns a {Blob} whose data is backed by the given file. The file must not be modified after the {Blob} is created. Any modifications will cause reading the {Blob} data to fail with a `DOMException` error. Synchronous stat operations on the file when the `Blob` is created, and before each read in order to detect whether the file data has been modified on disk. ```mjs import { openAsBlob } from 'node:fs'; const blob = await openAsBlob('the.file.txt'); const ab = await blob.arrayBuffer(); blob.stream(); ``` ```cjs const { openAsBlob } = require('node:fs'); (async () => { const blob = await openAsBlob('the.file.txt'); const ab = await blob.arrayBuffer(); blob.stream(); })(); ``` ### `fs.opendir(path[, options], callback)` <!-- YAML added: v12.12.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/41439 description: Added `recursive` option. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: - v13.1.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30114 description: The `bufferSize` option was introduced. --> * `path` {string|Buffer|URL} * `options` {Object} * `encoding` {string|null} **Default:** `'utf8'` * `bufferSize` {number} Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. **Default:** `32` * `recursive` {boolean} **Default:** `false` * `callback` {Function} * `err` {Error} * `dir` {fs.Dir} Asynchronously open a directory. See the POSIX opendir(3) documentation for more details. Creates an {fs.Dir}, which contains all further functions for reading from and cleaning up the directory. The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations. ### `fs.read(fd, buffer, offset, length, position, callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22150 description: The `buffer` parameter can now be any `TypedArray`, or a `DataView`. - version: v7.4.0 pr-url: https://github.com/nodejs/node/pull/10382 description: The `buffer` parameter can now be a `Uint8Array`. - version: v6.0.0 pr-url: https://github.com/nodejs/node/pull/4518 description: The `length` parameter can now be `0`. --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} The buffer that the data will be written to. * `offset` {integer} The position in `buffer` to write the data to. * `length` {integer} The number of bytes to read. * `position` {integer|bigint|null} Specifies where to begin reading from in the file. If `position` is `null` or `-1 `, data will be read from the current file position, and the file position will be updated. If `position` is an integer, the file position will be unchanged. * `callback` {Function} * `err` {Error} * `bytesRead` {integer} * `buffer` {Buffer} Read data from the file specified by `fd`. The callback is given the three arguments, `(err, bytesRead, buffer)`. If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero. If this method is invoked as its [`util.promisify()`][]ed version, it returns a promise for an `Object` with `bytesRead` and `buffer` properties. The `fs.read()` method reads data from the file specified by the file descriptor (`fd`). The `length` argument indicates the maximum number of bytes that Node.js will attempt to read from the kernel. However, the actual number of bytes read (`bytesRead`) can be lower than the specified `length` for various reasons. For example: * If the file is shorter than the specified `length`, `bytesRead` will be set to the actual number of bytes read. * If the file encounters EOF (End of File) before the buffer could be filled, Node.js will read all available bytes until EOF is encountered, and the `bytesRead` parameter in the callback will indicate the actual number of bytes read, which may be less than the specified `length`. * If the file is on a slow network `filesystem` or encounters any other issue during reading, `bytesRead` can be lower than the specified `length`. Therefore, when using `fs.read()`, it's important to check the `bytesRead` value to determine how many bytes were actually read from the file. Depending on your application logic, you may need to handle cases where `bytesRead` is lower than the specified `length`, such as by wrapping the read call in a loop if you require a minimum amount of bytes. This behavior is similar to the POSIX `preadv2` function. ### `fs.read(fd[, options], callback)` <!-- YAML added: - v13.11.0 - v12.17.0 changes: - version: - v13.11.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/31402 description: Options object can be passed in to make buffer, offset, length, and position optional. --> * `fd` {integer} * `options` {Object} * `buffer` {Buffer|TypedArray|DataView} **Default:** `Buffer.alloc(16384)` * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer|bigint|null} **Default:** `null` * `callback` {Function} * `err` {Error} * `bytesRead` {integer} * `buffer` {Buffer} Similar to the [`fs.read()`][] function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. ### `fs.read(fd, buffer[, options], callback)` <!-- YAML added: - v18.2.0 - v16.17.0 --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} The buffer that the data will be written to. * `options` {Object} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer|bigint} **Default:** `null` * `callback` {Function} * `err` {Error} * `bytesRead` {integer} * `buffer` {Buffer} Similar to the [`fs.read()`][] function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. ### `fs.readdir(path[, options], callback)` <!-- YAML added: v0.1.8 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/41439 description: Added `recursive` option. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22020 description: New option `withFileTypes` was added. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v6.0.0 pr-url: https://github.com/nodejs/node/pull/5616 description: The `options` parameter was added. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `withFileTypes` {boolean} **Default:** `false` * `recursive` {boolean} If `true`, reads the contents of a directory recursively. In recursive mode, it will list all files, sub files and directories. **Default:** `false`. * `callback` {Function} * `err` {Error} * `files` {string\[]|Buffer\[]|fs.Dirent\[]} 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 `'..'`. See the POSIX readdir(3) documentation for more details. 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. If `options.withFileTypes` is set to `true`, the `files` array will contain {fs.Dirent} objects. ### `fs.readFile(path[, options], callback)` <!-- YAML added: v0.1.29 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37460 description: The error returned may be an `AggregateError` if more than one error is returned. - version: - v15.2.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/35911 description: The options argument may include an AbortSignal to abort an ongoing readFile request. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v5.1.0 pr-url: https://github.com/nodejs/node/pull/3740 description: The `callback` will always be called with `null` as the `error` parameter in case of success. - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3163 description: The `path` parameter can be a file descriptor now. --> * `path` {string|Buffer|URL|integer} filename or file descriptor * `options` {Object|string} * `encoding` {string|null} **Default:** `null` * `flag` {string} See [support of file system `flags`][]. **Default:** `'r'`. * `signal` {AbortSignal} allows aborting an in-progress readFile * `callback` {Function} * `err` {Error|AggregateError} * `data` {string|Buffer} Asynchronously reads the entire contents of a file. ```mjs import { readFile } from 'node: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: ```mjs import { readFile } from 'node:fs'; readFile('/etc/passwd', 'utf8', callback); ``` 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. ```mjs import { readFile } from 'node:fs'; // macOS, Linux, and Windows readFile('<directory>', (err, data) => { // => [Error: EISDIR: illegal operation on a directory, read <directory>] }); // FreeBSD readFile('<directory>', (err, data) => { // => null, <data> }); ``` It is possible to abort an ongoing request using an `AbortSignal`. If a request is aborted the callback is called with an `AbortError`: ```mjs import { readFile } from 'node:fs'; const controller = new AbortController(); const signal = controller.signal; readFile(fileInfo[0].name, { signal }, (err, buf) => { // ... }); // When you want to abort the request controller.abort(); ``` The `fs.readFile()` function buffers the entire file. To minimize memory costs, when possible prefer streaming via `fs.createReadStream()`. Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.readFile` performs. #### File descriptors 1. Any specified file descriptor has to support reading. 2. If a file descriptor is specified as the `path`, it will not be closed automatically. 3. The reading will begin at the current position. For example, if the file already had `'Hello World'` and six bytes are read with the file descriptor, the call to `fs.readFile()` with the same file descriptor, would give `'World'`, rather than `'Hello World'`. #### Performance Considerations The `fs.readFile()` method asynchronously reads the contents of a file into memory one chunk at a time, allowing the event loop to turn between each chunk. This allows the read operation to have less impact on other activity that may be using the underlying libuv thread pool but means that it will take longer to read a complete file into memory. The additional read overhead can vary broadly on different systems and depends on the type of file being read. If the file type is not a regular file (a pipe for instance) and Node.js is unable to determine an actual file size, each read operation will load on 64 KiB of data. For regular files, each read will process 512 KiB of data. For applications that require as-fast-as-possible reading of file contents, it is better to use `fs.read()` directly and for application code to manage reading the full contents of the file itself. The Node.js GitHub issue [#25741][] provides more information and a detailed analysis on the performance of `fs.readFile()` for multiple file sizes in different Node.js versions. ### `fs.readlink(path[, options], callback)` <!-- YAML added: v0.1.31 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `callback` {Function} * `err` {Error} * `linkString` {string|Buffer} Reads the contents of the symbolic link referred to by `path`. The callback gets two arguments `(err, linkString)`. See the POSIX readlink(2) documentation for more details. 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.readv(fd, buffers[, position], callback)` <!-- YAML added: - v13.13.0 - v12.17.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. --> * `fd` {integer} * `buffers` {ArrayBufferView\[]} * `position` {integer|null} **Default:** `null` * `callback` {Function} * `err` {Error} * `bytesRead` {integer} * `buffers` {ArrayBufferView\[]} Read from a file specified by `fd` and write to an array of `ArrayBufferView`s using `readv()`. `position` is the offset from the beginning of the file from where data should be read. If `typeof position !== 'number'`, the data will be read from the current position. The callback will be given three arguments: `err`, `bytesRead`, and `buffers`. `bytesRead` is how many bytes were read from the file. If this method is invoked as its [`util.promisify()`][]ed version, it returns a promise for an `Object` with `bytesRead` and `buffers` properties. ### `fs.realpath(path[, options], callback)` <!-- YAML added: v0.1.31 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v8.0.0 pr-url: https://github.com/nodejs/node/pull/13028 description: Pipe/Socket resolve support was added. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v6.4.0 pr-url: https://github.com/nodejs/node/pull/7899 description: Calling `realpath` now works again for various edge cases on Windows. - version: v6.0.0 pr-url: https://github.com/nodejs/node/pull/3594 description: The `cache` parameter was removed. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `callback` {Function} * `err` {Error} * `resolvedPath` {string|Buffer} Asynchronously computes the canonical pathname by resolving `.`, `..`, and symbolic links. A canonical pathname is not necessarily unique. Hard links and bind mounts can expose a file system entity through many pathnames. This function behaves like realpath(3), with some exceptions: 1. No case conversion is performed on case-insensitive file systems. 2. The maximum number of symbolic links is platform-independent and generally (much) higher than what the native realpath(3) implementation supports. 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. If `path` resolves to a socket or a pipe, the function will return a system dependent name for that object. A path that does not exist results in an ENOENT error. `error.path` is the absolute file path. ### `fs.realpath.native(path[, options], callback)` <!-- YAML added: v9.2.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `callback` {Function} * `err` {Error} * `resolvedPath` {string|Buffer} Asynchronous realpath(3). The `callback` gets two arguments `(err, resolvedPath)`. 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. On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction. ### `fs.rename(oldPath, newPath, callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `oldPath` {string|Buffer|URL} * `newPath` {string|Buffer|URL} * `callback` {Function} * `err` {Error} Asynchronously rename file at `oldPath` to the pathname provided as `newPath`. In the case that `newPath` already exists, it will be overwritten. If there is a directory at `newPath`, an error will be raised instead. No arguments other than a possible exception are given to the completion callback. See also: rename(2). ```mjs import { rename } from 'node:fs'; rename('oldFile.txt', 'newFile.txt', (err) => { if (err) throw err; console.log('Rename complete!'); }); ``` ### `fs.rmdir(path[, options], callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37216 description: "Using `fs.rmdir(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX." - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37216 description: "Using `fs.rmdir(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error." - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37302 description: The `recursive` option is deprecated, using it triggers a deprecation warning. - version: v14.14.0 pr-url: https://github.com/nodejs/node/pull/35579 description: The `recursive` option is deprecated, use `fs.rm` instead. - version: - v13.3.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30644 description: The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. - version: v12.10.0 pr-url: https://github.com/nodejs/node/pull/29168 description: The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameters can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `options` {Object} * `maxRetries` {integer} If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`. * `recursive` {boolean} If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. **Default:** `false`. **Deprecated.** * `retryDelay` {integer} The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`. * `callback` {Function} * `err` {Error} Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback. Using `fs.rmdir()` on a file (not a directory) results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. To get a behavior similar to the `rm -rf` Unix command, use [`fs.rm()`][] with options `{ recursive: true, force: true }`. ### `fs.rm(path[, options], callback)` <!-- YAML added: v14.14.0 changes: - version: - v17.3.0 - v16.14.0 pr-url: https://github.com/nodejs/node/pull/41132 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {Object} * `force` {boolean} When `true`, exceptions will be ignored if `path` does not exist. **Default:** `false`. * `maxRetries` {integer} If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`. * `recursive` {boolean} If `true`, perform a recursive removal. In recursive mode operations are retried on failure. **Default:** `false`. * `retryDelay` {integer} The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`. * `callback` {Function} * `err` {Error} Asynchronously removes files and directories (modeled on the standard POSIX `rm` utility). No arguments other than a possible exception are given to the completion callback. ### `fs.stat(path[, options], callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * `callback` {Function} * `err` {Error} * `stats` {fs.Stats} 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][]. [`fs.stat()`][] follows symbolic links. Use [`fs.lstat()`][] to look at the links themselves. 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. For example, given the following directory structure: ```text - txtDir -- file.txt - app.js ``` The next program will check for the stats of the given paths: ```mjs import { stat } from 'node:fs'; const pathsToCheck = ['./txtDir', './txtDir/file.txt']; for (let i = 0; i < pathsToCheck.length; i++) { stat(pathsToCheck[i], (err, stats) => { console.log(stats.isDirectory()); console.log(stats); }); } ``` The resulting output will resemble: ```console true Stats { dev: 16777220, mode: 16877, nlink: 3, uid: 501, gid: 20, rdev: 0, blksize: 4096, ino: 14214262, size: 96, blocks: 0, atimeMs: 1561174653071.963, mtimeMs: 1561174614583.3518, ctimeMs: 1561174626623.5366, birthtimeMs: 1561174126937.2893, atime: 2019-06-22T03:37:33.072Z, mtime: 2019-06-22T03:36:54.583Z, ctime: 2019-06-22T03:37:06.624Z, birthtime: 2019-06-22T03:28:46.937Z } false Stats { dev: 16777220, mode: 33188, nlink: 1, uid: 501, gid: 20, rdev: 0, blksize: 4096, ino: 14214074, size: 8, blocks: 8, atimeMs: 1561174616618.8555, mtimeMs: 1561174614584, ctimeMs: 1561174614583.8145, birthtimeMs: 1561174007710.7478, atime: 2019-06-22T03:36:56.619Z, mtime: 2019-06-22T03:36:54.584Z, ctime: 2019-06-22T03:36:54.584Z, birthtime: 2019-06-22T03:26:47.711Z } ``` ### `fs.statfs(path[, options], callback)` <!-- YAML added: - v19.6.0 - v18.15.0 --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.StatFs} object should be `bigint`. **Default:** `false`. * `callback` {Function} * `err` {Error} * `stats` {fs.StatFs} Asynchronous statfs(2). Returns information about the mounted file system which contains `path`. The callback gets two arguments `(err, stats)` where `stats` is an {fs.StatFs} object. In case of an error, the `err.code` will be one of [Common System Errors][]. ### `fs.symlink(target, path[, type], callback)` <!-- YAML added: v0.1.31 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v12.0.0 pr-url: https://github.com/nodejs/node/pull/23724 description: If the `type` argument is left undefined, Node will autodetect `target` type and automatically select `dir` or `file`. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. --> * `target` {string|Buffer|URL} * `path` {string|Buffer|URL} * `type` {string|null} **Default:** `null` * `callback` {Function} * `err` {Error} Creates the link called `path` pointing to `target`. No arguments other than a possible exception are given to the completion callback. See the POSIX symlink(2) documentation for more details. The `type` argument is only available on Windows and ignored on other platforms. It can be set to `'dir'`, `'file'`, or `'junction'`. If the `type` argument is not a string, Node.js will autodetect `target` type and use `'file'` or `'dir'`. If the `target` does not exist, `'file'` will be used. Windows junction points require the destination path to be absolute. When using `'junction'`, the `target` argument will automatically be normalized to absolute path. Junction points on NTFS volumes can only point to directories. Relative targets are relative to the link's parent directory. ```mjs import { symlink } from 'node:fs'; symlink('./mew', './mewtwo', callback); ``` The above example creates a symbolic link `mewtwo` which points to `mew` in the same directory: ```bash $ tree . . ├── mew └── mewtwo -> ./mew ``` ### `fs.truncate(path[, len], callback)` <!-- YAML added: v0.8.6 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37460 description: The error returned may be an `AggregateError` if more than one error is returned. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `len` {integer} **Default:** `0` * `callback` {Function} * `err` {Error|AggregateError} Truncates the file. 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. ```mjs import { truncate } from 'node:fs'; // Assuming that 'path/file.txt' is a regular file. truncate('path/file.txt', (err) => { if (err) throw err; console.log('path/file.txt was truncated'); }); ``` ```cjs const { truncate } = require('node:fs'); // Assuming that 'path/file.txt' is a regular file. truncate('path/file.txt', (err) => { if (err) throw err; console.log('path/file.txt was truncated'); }); ``` Passing a file descriptor is deprecated and may result in an error being thrown in the future. See the POSIX truncate(2) documentation for more details. ### `fs.unlink(path, callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `path` {string|Buffer|URL} * `callback` {Function} * `err` {Error} Asynchronously removes a file or symbolic link. No arguments other than a possible exception are given to the completion callback. ```mjs import { unlink } from 'node:fs'; // Assuming that 'path/file.txt' is a regular file. unlink('path/file.txt', (err) => { if (err) throw err; console.log('path/file.txt was deleted'); }); ``` `fs.unlink()` will not work on a directory, empty or otherwise. To remove a directory, use [`fs.rmdir()`][]. See the POSIX unlink(2) documentation for more details. ### `fs.unwatchFile(filename[, listener])` <!-- YAML added: v0.1.31 --> * `filename` {string|Buffer|URL} * `listener` {Function} Optional, a listener previously attached using `fs.watchFile()` 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. Using [`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)` <!-- YAML added: v0.4.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v8.0.0 pr-url: https://github.com/nodejs/node/pull/11919 description: "`NaN`, `Infinity`, and `-Infinity` are no longer valid time specifiers." - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v4.1.0 pr-url: https://github.com/nodejs/node/pull/2387 description: Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. --> * `path` {string|Buffer|URL} * `atime` {number|string|Date} * `mtime` {number|string|Date} * `callback` {Function} * `err` {Error} Change the file system timestamps of the object referenced by `path`. The `atime` and `mtime` arguments follow these rules: * Values can be either numbers representing Unix epoch time in seconds, `Date`s, or a numeric string like `'123456789.0'`. * If the value can not be converted to a number, or is `NaN`, `Infinity`, or `-Infinity`, an `Error` will be thrown. ### `fs.watch(filename[, options][, listener])` <!-- YAML added: v0.5.10 changes: - version: v19.1.0 pr-url: https://github.com/nodejs/node/pull/45098 description: Added recursive support for Linux, AIX and IBMi. - version: - v15.9.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/37190 description: Added support for closing the watcher with an AbortSignal. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7831 description: The passed `options` object will never be modified. --> * `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'`. * `signal` {AbortSignal} allows closing the watcher with an AbortSignal. * `listener` {Function|undefined} **Default:** `undefined` * `eventType` {string} * `filename` {string|Buffer|null} * Returns: {fs.FSWatcher} Watch for changes on `filename`, where `filename` is either a file or a directory. 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. On most platforms, `'rename'` is emitted whenever a filename appears or disappears in the directory. 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`. If a `signal` is passed, aborting the corresponding AbortController will close the returned {fs.FSWatcher}. #### Caveats <!--type=misc--> The `fs.watch` API is not 100% consistent across platforms, and is unavailable in some situations. On Windows, no events will be emitted if the watched directory is moved or renamed. An `EPERM` error is reported when the watched directory is deleted. ##### Availability <!--type=misc--> This feature depends on the underlying operating system providing a way to be notified of file system changes. * On Linux systems, this uses [`inotify(7)`][]. * On BSD systems, this uses [`kqueue(2)`][]. * On macOS, this uses [`kqueue(2)`][] for files and [`FSEvents`][] 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. * On IBM i systems, this feature is not supported. If the underlying functionality is not available for some reason, then `fs.watch()` will not be able to function and may throw an exception. 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 or Docker. It is still possible to use `fs.watchFile()`, which uses stat polling, but this method is slower and less reliable. ##### Inodes <!--type=misc--> 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. AIX files retain the same inode for the lifetime of a file. Saving and closing a watched file on AIX will result in two notifications (one for adding new content, and one for truncation). ##### Filename argument <!--type=misc--> 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`. ```mjs import { watch } from 'node: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)` <!-- YAML added: v0.1.31 changes: - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: The `bigint` option is now supported. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `filename` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `filename` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} **Default:** `false` * `persistent` {boolean} **Default:** `true` * `interval` {integer} **Default:** `5007` * `listener` {Function} * `current` {fs.Stats} * `previous` {fs.Stats} * Returns: {fs.StatWatcher} 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 `listener` gets two arguments the current stat object and the previous stat object: ```mjs import { watchFile } from 'node: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`. If the `bigint` option is `true`, the numeric values in these objects are specified as `BigInt`s. To be notified when the file was modified, not just accessed, it is necessary to compare `curr.mtimeMs` and `prev.mtimeMs`. 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). 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. Using [`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. When a file being watched by `fs.watchFile()` disappears and reappears, then the contents of `previous` in the second callback event (the file's reappearance) will be the same as the contents of `previous` in the first callback event (its disappearance). This happens when: * the file is deleted, followed by a restore * the file is renamed and then renamed a second time back to its original name ### `fs.write(fd, buffer, offset[, length[, position]], callback)` <!-- YAML added: v0.0.2 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `buffer` parameter won't coerce unsupported input to strings anymore. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22150 description: The `buffer` parameter can now be any `TypedArray` or a `DataView`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.4.0 pr-url: https://github.com/nodejs/node/pull/10382 description: The `buffer` parameter can now be a `Uint8Array`. - version: v7.2.0 pr-url: https://github.com/nodejs/node/pull/7856 description: The `offset` and `length` parameters are optional now. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer|null} **Default:** `null` * `callback` {Function} * `err` {Error} * `bytesWritten` {integer} * `buffer` {Buffer|TypedArray|DataView} 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. It is unsafe to use `fs.write()` multiple times on the same file without waiting for the callback. For this scenario, [`fs.createWriteStream()`][] is 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, buffer[, options], callback)` <!-- YAML added: - v18.3.0 - v16.17.0 --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} * `options` {Object} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer} **Default:** `null` * `callback` {Function} * `err` {Error} * `bytesWritten` {integer} * `buffer` {Buffer|TypedArray|DataView} Write `buffer` to the file specified by `fd`. Similar to the above `fs.write` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. ### `fs.write(fd, string[, position[, encoding]], callback)` <!-- YAML added: v0.11.5 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/42796 description: Passing to the `string` parameter an object with an own `toString` function is no longer supported. - version: v17.8.0 pr-url: https://github.com/nodejs/node/pull/42149 description: Passing to the `string` parameter an object with an own `toString` function is deprecated. - version: v14.12.0 pr-url: https://github.com/nodejs/node/pull/34993 description: The `string` parameter will stringify an object with an explicit `toString` function. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `string` parameter won't coerce unsupported input to strings anymore. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.2.0 pr-url: https://github.com/nodejs/node/pull/7856 description: The `position` parameter is optional now. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. --> * `fd` {integer} * `string` {string} * `position` {integer|null} **Default:** `null` * `encoding` {string} **Default:** `'utf8'` * `callback` {Function} * `err` {Error} * `written` {integer} * `string` {string} Write `string` to the file specified by `fd`. If `string` is not a string, an exception is thrown. `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. Bytes written is not necessarily the same as string characters written. See [`Buffer.byteLength`][]. It is unsafe to use `fs.write()` multiple times on the same file without waiting for the callback. For this scenario, [`fs.createWriteStream()`][] is 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. On Windows, if the file descriptor is connected to the console (e.g. `fd == 1` or `stdout`) a string containing non-ASCII characters will not be rendered properly by default, regardless of the encoding used. It is possible to configure the console to render UTF-8 properly by changing the active codepage with the `chcp 65001` command. See the [chcp][] docs for more details. ### `fs.writeFile(file, data[, options], callback)` <!-- YAML added: v0.1.29 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50009 description: The `flush` option is now supported. - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/42796 description: Passing to the `string` parameter an object with an own `toString` function is no longer supported. - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. - version: v17.8.0 pr-url: https://github.com/nodejs/node/pull/42149 description: Passing to the `string` parameter an object with an own `toString` function is deprecated. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37460 description: The error returned may be an `AggregateError` if more than one error is returned. - version: - v15.2.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/35993 description: The options argument may include an AbortSignal to abort an ongoing writeFile request. - version: v14.12.0 pr-url: https://github.com/nodejs/node/pull/34993 description: The `data` parameter will stringify an object with an explicit `toString` function. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `data` parameter won't coerce unsupported input to strings anymore. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22150 description: The `data` parameter can now be any `TypedArray` or a `DataView`. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/12562 description: The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime. - version: v7.4.0 pr-url: https://github.com/nodejs/node/pull/10382 description: The `data` parameter can now be a `Uint8Array`. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7897 description: The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013. - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3163 description: The `file` parameter can be a file descriptor now. --> * `file` {string|Buffer|URL|integer} filename or file descriptor * `data` {string|Buffer|TypedArray|DataView} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `mode` {integer} **Default:** `0o666` * `flag` {string} See [support of file system `flags`][]. **Default:** `'w'`. * `flush` {boolean} If all data is successfully written to the file, and `flush` is `true`, `fs.fsync()` is used to flush the data. **Default:** `false`. * `signal` {AbortSignal} allows aborting an in-progress writeFile * `callback` {Function} * `err` {Error|AggregateError} When `file` is a filename, asynchronously writes data to the file, replacing the file if it already exists. `data` can be a string or a buffer. When `file` is a file descriptor, the behavior is similar to calling `fs.write()` directly (which is recommended). See the notes below on using a file descriptor. The `encoding` option is ignored if `data` is a buffer. The `mode` option only affects the newly created file. See [`fs.open()`][] for more details. ```mjs import { writeFile } from 'node:fs'; import { Buffer } from 'node:buffer'; const data = new Uint8Array(Buffer.from('Hello Node.js')); writeFile('message.txt', data, (err) => { if (err) throw err; console.log('The file has been saved!'); }); ``` If `options` is a string, then it specifies the encoding: ```mjs import { writeFile } from 'node:fs'; writeFile('message.txt', 'Hello Node.js', 'utf8', callback); ``` It is unsafe to use `fs.writeFile()` multiple times on the same file without waiting for the callback. For this scenario, [`fs.createWriteStream()`][] is recommended. Similarly to `fs.readFile` - `fs.writeFile` is a convenience method that performs multiple `write` calls internally to write the buffer passed to it. For performance sensitive code consider using [`fs.createWriteStream()`][]. It is possible to use an {AbortSignal} to cancel an `fs.writeFile()`. Cancelation is "best effort", and some amount of data is likely still to be written. ```mjs import { writeFile } from 'node:fs'; import { Buffer } from 'node:buffer'; const controller = new AbortController(); const { signal } = controller; const data = new Uint8Array(Buffer.from('Hello Node.js')); writeFile('message.txt', data, { signal }, (err) => { // When a request is aborted - the callback is called with an AbortError }); // When the request should be aborted controller.abort(); ``` Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering `fs.writeFile` performs. #### Using `fs.writeFile()` with file descriptors When `file` is a file descriptor, the behavior is almost identical to directly calling `fs.write()` like: ```mjs import { write } from 'node:fs'; import { Buffer } from 'node:buffer'; write(fd, Buffer.from(data, options.encoding), callback); ``` The difference from directly calling `fs.write()` is that under some unusual conditions, `fs.write()` might write only part of the buffer and need to be retried to write the remaining data, whereas `fs.writeFile()` retries until the data is entirely written (or an error occurs). The implications of this are a common source of confusion. In the file descriptor case, the file is not replaced! The data is not necessarily written to the beginning of the file, and the file's original data may remain before and/or after the newly written data. For example, if `fs.writeFile()` is called twice in a row, first to write the string `'Hello'`, then to write the string `', World'`, the file would contain `'Hello, World'`, and might contain some of the file's original data (depending on the size of the original file, and the position of the file descriptor). If a file name had been used instead of a descriptor, the file would be guaranteed to contain only `', World'`. ### `fs.writev(fd, buffers[, position], callback)` <!-- YAML added: v12.9.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. --> * `fd` {integer} * `buffers` {ArrayBufferView\[]} * `position` {integer|null} **Default:** `null` * `callback` {Function} * `err` {Error} * `bytesWritten` {integer} * `buffers` {ArrayBufferView\[]} Write an array of `ArrayBufferView`s to the file specified by `fd` using `writev()`. `position` is 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. The callback will be given three arguments: `err`, `bytesWritten`, and `buffers`. `bytesWritten` is how many bytes were written from `buffers`. If this method is [`util.promisify()`][]ed, it returns a promise for an `Object` with `bytesWritten` and `buffers` properties. It is unsafe to use `fs.writev()` multiple times on the same file without waiting for the callback. For this scenario, use [`fs.createWriteStream()`][]. 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. ## Synchronous API The synchronous APIs perform all operations synchronously, blocking the event loop until the operation completes or fails. ### `fs.accessSync(path[, mode])` <!-- YAML added: v0.11.15 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `mode` {integer} **Default:** `fs.constants.F_OK` Synchronously 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. `mode` should be either the value `fs.constants.F_OK` or a mask consisting of the bitwise OR of any of `fs.constants.R_OK`, `fs.constants.W_OK`, and `fs.constants.X_OK` (e.g. `fs.constants.W_OK | fs.constants.R_OK`). Check [File access constants][] for possible values of `mode`. If any of the accessibility checks fail, an `Error` will be thrown. Otherwise, the method will return `undefined`. ```mjs import { accessSync, constants } from 'node:fs'; try { accessSync('etc/passwd', constants.R_OK | constants.W_OK); console.log('can read/write'); } catch (err) { console.error('no access!'); } ``` ### `fs.appendFileSync(path, data[, options])` <!-- YAML added: v0.6.7 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50095 description: The `flush` option is now supported. - version: v7.0.0 pr-url: https://github.com/nodejs/node/pull/7831 description: The passed `options` object will never be modified. - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3163 description: The `file` parameter can be a file descriptor now. --> * `path` {string|Buffer|URL|number} filename or file descriptor * `data` {string|Buffer} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `mode` {integer} **Default:** `0o666` * `flag` {string} See [support of file system `flags`][]. **Default:** `'a'`. * `flush` {boolean} If `true`, the underlying file descriptor is flushed prior to closing it. **Default:** `false`. Synchronously append data to a file, creating the file if it does not yet exist. `data` can be a string or a {Buffer}. The `mode` option only affects the newly created file. See [`fs.open()`][] for more details. ```mjs import { appendFileSync } from 'node:fs'; try { appendFileSync('message.txt', 'data to append'); console.log('The "data to append" was appended to file!'); } catch (err) { /* Handle the error */ } ``` If `options` is a string, then it specifies the encoding: ```mjs import { appendFileSync } from 'node:fs'; appendFileSync('message.txt', 'data to append', 'utf8'); ``` The `path` may be specified as a numeric file descriptor that has been opened for appending (using `fs.open()` or `fs.openSync()`). The file descriptor will not be closed automatically. ```mjs import { openSync, closeSync, appendFileSync } from 'node:fs'; let fd; try { fd = openSync('message.txt', 'a'); appendFileSync(fd, 'data to append', 'utf8'); } catch (err) { /* Handle the error */ } finally { if (fd !== undefined) closeSync(fd); } ``` ### `fs.chmodSync(path, mode)` <!-- YAML added: v0.6.7 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `mode` {string|integer} For detailed information, see the documentation of the asynchronous version of this API: [`fs.chmod()`][]. See the POSIX chmod(2) documentation for more detail. ### `fs.chownSync(path, uid, gid)` <!-- YAML added: v0.1.97 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `uid` {integer} * `gid` {integer} Synchronously changes owner and group of a file. Returns `undefined`. This is the synchronous version of [`fs.chown()`][]. See the POSIX chown(2) documentation for more detail. ### `fs.closeSync(fd)` <!-- YAML added: v0.1.21 --> * `fd` {integer} Closes the file descriptor. Returns `undefined`. Calling `fs.closeSync()` on any file descriptor (`fd`) that is currently in use through any other `fs` operation may lead to undefined behavior. See the POSIX close(2) documentation for more detail. ### `fs.copyFileSync(src, dest[, mode])` <!-- YAML added: v8.5.0 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/27044 description: Changed `flags` argument to `mode` and imposed stricter type validation. --> * `src` {string|Buffer|URL} source filename to copy * `dest` {string|Buffer|URL} destination filename of the copy operation * `mode` {integer} modifiers for copy operation. **Default:** `0`. Synchronously copies `src` to `dest`. By default, `dest` is overwritten if it already exists. Returns `undefined`. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination. `mode` is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. `fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE`). * `fs.constants.COPYFILE_EXCL`: The copy operation will fail if `dest` already exists. * `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. * `fs.constants.COPYFILE_FICLONE_FORCE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail. ```mjs import { copyFileSync, constants } from 'node:fs'; // destination.txt will be created or overwritten by default. copyFileSync('source.txt', 'destination.txt'); console.log('source.txt was copied to destination.txt'); // By using COPYFILE_EXCL, the operation will fail if destination.txt exists. copyFileSync('source.txt', 'destination.txt', constants.COPYFILE_EXCL); ``` ### `fs.cpSync(src, dest[, options])` <!-- YAML added: v16.7.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/47084 description: Accept an additional `mode` option to specify the copy behavior as the `mode` argument of `fs.copyFile()`. - version: - v17.6.0 - v16.15.0 pr-url: https://github.com/nodejs/node/pull/41819 description: Accepts an additional `verbatimSymlinks` option to specify whether to perform path resolution for symlinks. --> > Stability: 1 - Experimental * `src` {string|URL} source path to copy. * `dest` {string|URL} destination path to copy to. * `options` {Object} * `dereference` {boolean} dereference symlinks. **Default:** `false`. * `errorOnExist` {boolean} when `force` is `false`, and the destination exists, throw an error. **Default:** `false`. * `filter` {Function} Function to filter copied files/directories. Return `true` to copy the item, `false` to ignore it. When ignoring a directory, all of its contents will be skipped as well. **Default:** `undefined` * `src` {string} source path to copy. * `dest` {string} destination path to copy to. * Returns: {boolean} Any non-`Promise` value that is coercible to `boolean`. * `force` {boolean} overwrite existing file or directory. The copy operation will ignore errors if you set this to false and the destination exists. Use the `errorOnExist` option to change this behavior. **Default:** `true`. * `mode` {integer} modifiers for copy operation. **Default:** `0`. See `mode` flag of [`fs.copyFileSync()`][]. * `preserveTimestamps` {boolean} When `true` timestamps from `src` will be preserved. **Default:** `false`. * `recursive` {boolean} copy directories recursively **Default:** `false` * `verbatimSymlinks` {boolean} When `true`, path resolution for symlinks will be skipped. **Default:** `false` Synchronously copies the entire directory structure from `src` to `dest`, including subdirectories and files. When copying a directory to another directory, globs are not supported and behavior is similar to `cp dir1/ dir2/`. ### `fs.existsSync(path)` <!-- YAML added: v0.1.21 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * Returns: {boolean} Returns `true` if the path exists, `false` otherwise. For detailed information, see the documentation of the asynchronous version of this API: [`fs.exists()`][]. `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. ```mjs import { existsSync } from 'node:fs'; if (existsSync('/etc/passwd')) console.log('The path exists.'); ``` ### `fs.fchmodSync(fd, mode)` <!-- YAML added: v0.4.7 --> * `fd` {integer} * `mode` {string|integer} Sets the permissions on the file. Returns `undefined`. See the POSIX fchmod(2) documentation for more detail. ### `fs.fchownSync(fd, uid, gid)` <!-- YAML added: v0.4.7 --> * `fd` {integer} * `uid` {integer} The file's new owner's user id. * `gid` {integer} The file's new group's group id. Sets the owner of the file. Returns `undefined`. See the POSIX fchown(2) documentation for more detail. ### `fs.fdatasyncSync(fd)` <!-- YAML added: v0.1.96 --> * `fd` {integer} Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX fdatasync(2) documentation for details. Returns `undefined`. ### `fs.fstatSync(fd[, options])` <!-- YAML added: v0.1.95 changes: - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. --> * `fd` {integer} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * Returns: {fs.Stats} Retrieves the {fs.Stats} for the file descriptor. See the POSIX fstat(2) documentation for more detail. ### `fs.fsyncSync(fd)` <!-- YAML added: v0.1.96 --> * `fd` {integer} Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX fsync(2) documentation for more detail. Returns `undefined`. ### `fs.ftruncateSync(fd[, len])` <!-- YAML added: v0.8.6 --> * `fd` {integer} * `len` {integer} **Default:** `0` Truncates the file descriptor. Returns `undefined`. For detailed information, see the documentation of the asynchronous version of this API: [`fs.ftruncate()`][]. ### `fs.futimesSync(fd, atime, mtime)` <!-- YAML added: v0.4.2 changes: - version: v4.1.0 pr-url: https://github.com/nodejs/node/pull/2387 description: Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. --> * `fd` {integer} * `atime` {number|string|Date} * `mtime` {number|string|Date} Synchronous version of [`fs.futimes()`][]. Returns `undefined`. ### `fs.lchmodSync(path, mode)` <!-- YAML deprecated: v0.4.7 --> * `path` {string|Buffer|URL} * `mode` {integer} Changes the permissions on a symbolic link. Returns `undefined`. This method is only implemented on macOS. See the POSIX lchmod(2) documentation for more detail. ### `fs.lchownSync(path, uid, gid)` <!-- YAML changes: - version: v10.6.0 pr-url: https://github.com/nodejs/node/pull/21498 description: This API is no longer deprecated. - version: v0.4.7 description: Documentation-only deprecation. --> * `path` {string|Buffer|URL} * `uid` {integer} The file's new owner's user id. * `gid` {integer} The file's new group's group id. Set the owner for the path. Returns `undefined`. See the POSIX lchown(2) documentation for more details. ### `fs.lutimesSync(path, atime, mtime)` <!-- YAML added: - v14.5.0 - v12.19.0 --> * `path` {string|Buffer|URL} * `atime` {number|string|Date} * `mtime` {number|string|Date} Change the file system timestamps of the symbolic link referenced by `path`. Returns `undefined`, or throws an exception when parameters are incorrect or the operation fails. This is the synchronous version of [`fs.lutimes()`][]. ### `fs.linkSync(existingPath, newPath)` <!-- YAML added: v0.1.31 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. --> * `existingPath` {string|Buffer|URL} * `newPath` {string|Buffer|URL} Creates a new link from the `existingPath` to the `newPath`. See the POSIX link(2) documentation for more detail. Returns `undefined`. ### `fs.lstatSync(path[, options])` <!-- YAML added: v0.1.30 changes: - version: - v15.3.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/33716 description: Accepts a `throwIfNoEntry` option to specify whether an exception should be thrown if the entry does not exist. - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * `throwIfNoEntry` {boolean} Whether an exception will be thrown if no file system entry exists, rather than returning `undefined`. **Default:** `true`. * Returns: {fs.Stats} Retrieves the {fs.Stats} for the symbolic link referred to by `path`. See the POSIX lstat(2) documentation for more details. ### `fs.mkdirSync(path[, options])` <!-- YAML added: v0.1.21 changes: - version: - v13.11.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/31530 description: In `recursive` mode, the first created path is returned now. - version: v10.12.0 pr-url: https://github.com/nodejs/node/pull/21875 description: The second argument can now be an `options` object with `recursive` and `mode` properties. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {Object|integer} * `recursive` {boolean} **Default:** `false` * `mode` {string|integer} Not supported on Windows. **Default:** `0o777`. * Returns: {string|undefined} Synchronously creates a directory. Returns `undefined`, or if `recursive` is `true`, the first directory path created. This is the synchronous version of [`fs.mkdir()`][]. See the POSIX mkdir(2) documentation for more details. ### `fs.mkdtempSync(prefix[, options])` <!-- YAML added: v5.10.0 changes: - version: v20.6.0 pr-url: https://github.com/nodejs/node/pull/48828 description: The `prefix` parameter now accepts buffers and URL. - version: - v16.5.0 - v14.18.0 pr-url: https://github.com/nodejs/node/pull/39028 description: The `prefix` parameter now accepts an empty string. --> * `prefix` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {string} Returns the created directory path. For detailed information, see the documentation of the asynchronous version of this API: [`fs.mkdtemp()`][]. 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.opendirSync(path[, options])` <!-- YAML added: v12.12.0 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/41439 description: Added `recursive` option. - version: - v13.1.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30114 description: The `bufferSize` option was introduced. --> * `path` {string|Buffer|URL} * `options` {Object} * `encoding` {string|null} **Default:** `'utf8'` * `bufferSize` {number} Number of directory entries that are buffered internally when reading from the directory. Higher values lead to better performance but higher memory usage. **Default:** `32` * `recursive` {boolean} **Default:** `false` * Returns: {fs.Dir} Synchronously open a directory. See opendir(3). Creates an {fs.Dir}, which contains all further functions for reading from and cleaning up the directory. The `encoding` option sets the encoding for the `path` while opening the directory and subsequent read operations. ### `fs.openSync(path[, flags[, mode]])` <!-- YAML added: v0.1.21 changes: - version: v11.1.0 pr-url: https://github.com/nodejs/node/pull/23767 description: The `flags` argument is now optional and defaults to `'r'`. - version: v9.9.0 pr-url: https://github.com/nodejs/node/pull/18801 description: The `as` and `as+` flags are supported now. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `flags` {string|number} **Default:** `'r'`. See [support of file system `flags`][]. * `mode` {string|integer} **Default:** `0o666` * Returns: {number} Returns an integer representing the file descriptor. For detailed information, see the documentation of the asynchronous version of this API: [`fs.open()`][]. ### `fs.readdirSync(path[, options])` <!-- YAML added: v0.1.21 changes: - version: v20.1.0 pr-url: https://github.com/nodejs/node/pull/41439 description: Added `recursive` option. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22020 description: New option `withFileTypes` was added. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * `withFileTypes` {boolean} **Default:** `false` * `recursive` {boolean} If `true`, reads the contents of a directory recursively. In recursive mode, it will list all files, sub files, and directories. **Default:** `false`. * Returns: {string\[]|Buffer\[]|fs.Dirent\[]} Reads the contents of the directory. See the POSIX readdir(3) documentation for more details. 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 returned. If the `encoding` is set to `'buffer'`, the filenames returned will be passed as {Buffer} objects. If `options.withFileTypes` is set to `true`, the result will contain {fs.Dirent} objects. ### `fs.readFileSync(path[, options])` <!-- YAML added: v0.1.8 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3163 description: The `path` parameter can be a file descriptor now. --> * `path` {string|Buffer|URL|integer} filename or file descriptor * `options` {Object|string} * `encoding` {string|null} **Default:** `null` * `flag` {string} See [support of file system `flags`][]. **Default:** `'r'`. * Returns: {string|Buffer} Returns the contents of the `path`. For detailed information, see the documentation of the asynchronous version of this API: [`fs.readFile()`][]. If the `encoding` option is specified then this function returns a string. Otherwise it returns a buffer. Similar to [`fs.readFile()`][], when the path is a directory, the behavior of `fs.readFileSync()` is platform-specific. ```mjs import { readFileSync } from 'node:fs'; // macOS, Linux, and Windows readFileSync('<directory>'); // => [Error: EISDIR: illegal operation on a directory, read <directory>] // FreeBSD readFileSync('<directory>'); // => <data> ``` ### `fs.readlinkSync(path[, options])` <!-- YAML added: v0.1.31 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {string|Buffer} Returns the symbolic link's string value. See the POSIX readlink(2) documentation for more details. 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 returned. 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])` <!-- YAML added: v0.1.21 changes: - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22150 description: The `buffer` parameter can now be any `TypedArray` or a `DataView`. - version: v6.0.0 pr-url: https://github.com/nodejs/node/pull/4518 description: The `length` parameter can now be `0`. --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} * `offset` {integer} * `length` {integer} * `position` {integer|bigint|null} **Default:** `null` * Returns: {number} Returns the number of `bytesRead`. For detailed information, see the documentation of the asynchronous version of this API: [`fs.read()`][]. ### `fs.readSync(fd, buffer[, options])` <!-- YAML added: - v13.13.0 - v12.17.0 changes: - version: - v13.13.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/32460 description: Options object can be passed in to make offset, length, and position optional. --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} * `options` {Object} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer|bigint|null} **Default:** `null` * Returns: {number} Returns the number of `bytesRead`. Similar to the above `fs.readSync` function, this version takes an optional `options` object. If no `options` object is specified, it will default with the above values. For detailed information, see the documentation of the asynchronous version of this API: [`fs.read()`][]. ### `fs.readvSync(fd, buffers[, position])` <!-- YAML added: - v13.13.0 - v12.17.0 --> * `fd` {integer} * `buffers` {ArrayBufferView\[]} * `position` {integer|null} **Default:** `null` * Returns: {number} The number of bytes read. For detailed information, see the documentation of the asynchronous version of this API: [`fs.readv()`][]. ### `fs.realpathSync(path[, options])` <!-- YAML added: v0.1.31 changes: - version: v8.0.0 pr-url: https://github.com/nodejs/node/pull/13028 description: Pipe/Socket resolve support was added. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v6.4.0 pr-url: https://github.com/nodejs/node/pull/7899 description: Calling `realpathSync` now works again for various edge cases on Windows. - version: v6.0.0 pr-url: https://github.com/nodejs/node/pull/3594 description: The `cache` parameter was removed. --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {string|Buffer} Returns the resolved pathname. For detailed information, see the documentation of the asynchronous version of this API: [`fs.realpath()`][]. ### `fs.realpathSync.native(path[, options])` <!-- YAML added: v9.2.0 --> * `path` {string|Buffer|URL} * `options` {string|Object} * `encoding` {string} **Default:** `'utf8'` * Returns: {string|Buffer} Synchronous realpath(3). 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 returned. If the `encoding` is set to `'buffer'`, the path returned will be passed as a {Buffer} object. On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on `/proc` in order for this function to work. Glibc does not have this restriction. ### `fs.renameSync(oldPath, newPath)` <!-- YAML added: v0.1.21 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. --> * `oldPath` {string|Buffer|URL} * `newPath` {string|Buffer|URL} Renames the file from `oldPath` to `newPath`. Returns `undefined`. See the POSIX rename(2) documentation for more details. ### `fs.rmdirSync(path[, options])` <!-- YAML added: v0.1.21 changes: - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37216 description: "Using `fs.rmdirSync(path, { recursive: true })` on a `path` that is a file is no longer permitted and results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX." - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37216 description: "Using `fs.rmdirSync(path, { recursive: true })` on a `path` that does not exist is no longer permitted and results in a `ENOENT` error." - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37302 description: The `recursive` option is deprecated, using it triggers a deprecation warning. - version: v14.14.0 pr-url: https://github.com/nodejs/node/pull/35579 description: The `recursive` option is deprecated, use `fs.rmSync` instead. - version: - v13.3.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30644 description: The `maxBusyTries` option is renamed to `maxRetries`, and its default is 0. The `emfileWait` option has been removed, and `EMFILE` errors use the same retry logic as other errors. The `retryDelay` option is now supported. `ENFILE` errors are now retried. - version: v12.10.0 pr-url: https://github.com/nodejs/node/pull/29168 description: The `recursive`, `maxBusyTries`, and `emfileWait` options are now supported. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameters can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {Object} * `maxRetries` {integer} If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js retries the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`. * `recursive` {boolean} If `true`, perform a recursive directory removal. In recursive mode, operations are retried on failure. **Default:** `false`. **Deprecated.** * `retryDelay` {integer} The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`. Synchronous rmdir(2). Returns `undefined`. Using `fs.rmdirSync()` on a file (not a directory) results in an `ENOENT` error on Windows and an `ENOTDIR` error on POSIX. To get a behavior similar to the `rm -rf` Unix command, use [`fs.rmSync()`][] with options `{ recursive: true, force: true }`. ### `fs.rmSync(path[, options])` <!-- YAML added: v14.14.0 changes: - version: - v17.3.0 - v16.14.0 pr-url: https://github.com/nodejs/node/pull/41132 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {Object} * `force` {boolean} When `true`, exceptions will be ignored if `path` does not exist. **Default:** `false`. * `maxRetries` {integer} If an `EBUSY`, `EMFILE`, `ENFILE`, `ENOTEMPTY`, or `EPERM` error is encountered, Node.js will retry the operation with a linear backoff wait of `retryDelay` milliseconds longer on each try. This option represents the number of retries. This option is ignored if the `recursive` option is not `true`. **Default:** `0`. * `recursive` {boolean} If `true`, perform a recursive directory removal. In recursive mode operations are retried on failure. **Default:** `false`. * `retryDelay` {integer} The amount of time in milliseconds to wait between retries. This option is ignored if the `recursive` option is not `true`. **Default:** `100`. Synchronously removes files and directories (modeled on the standard POSIX `rm` utility). Returns `undefined`. ### `fs.statSync(path[, options])` <!-- YAML added: v0.1.21 changes: - version: - v15.3.0 - v14.17.0 pr-url: https://github.com/nodejs/node/pull/33716 description: Accepts a `throwIfNoEntry` option to specify whether an exception should be thrown if the entry does not exist. - version: v10.5.0 pr-url: https://github.com/nodejs/node/pull/20220 description: Accepts an additional `options` object to specify whether the numeric values returned should be bigint. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.Stats} object should be `bigint`. **Default:** `false`. * `throwIfNoEntry` {boolean} Whether an exception will be thrown if no file system entry exists, rather than returning `undefined`. **Default:** `true`. * Returns: {fs.Stats} Retrieves the {fs.Stats} for the path. ### `fs.statfsSync(path[, options])` <!-- YAML added: - v19.6.0 - v18.15.0 --> * `path` {string|Buffer|URL} * `options` {Object} * `bigint` {boolean} Whether the numeric values in the returned {fs.StatFs} object should be `bigint`. **Default:** `false`. * Returns: {fs.StatFs} Synchronous statfs(2). Returns information about the mounted file system which contains `path`. In case of an error, the `err.code` will be one of [Common System Errors][]. ### `fs.symlinkSync(target, path[, type])` <!-- YAML added: v0.1.31 changes: - version: v12.0.0 pr-url: https://github.com/nodejs/node/pull/23724 description: If the `type` argument is left undefined, Node will autodetect `target` type and automatically select `dir` or `file`. - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*. --> * `target` {string|Buffer|URL} * `path` {string|Buffer|URL} * `type` {string|null} **Default:** `null` Returns `undefined`. For detailed information, see the documentation of the asynchronous version of this API: [`fs.symlink()`][]. ### `fs.truncateSync(path[, len])` <!-- YAML added: v0.8.6 --> * `path` {string|Buffer|URL} * `len` {integer} **Default:** `0` Truncates the file. Returns `undefined`. A file descriptor can also be passed as the first argument. In this case, `fs.ftruncateSync()` is called. Passing a file descriptor is deprecated and may result in an error being thrown in the future. ### `fs.unlinkSync(path)` <!-- YAML added: v0.1.21 changes: - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. --> * `path` {string|Buffer|URL} Synchronous unlink(2). Returns `undefined`. ### `fs.utimesSync(path, atime, mtime)` <!-- YAML added: v0.4.2 changes: - version: v8.0.0 pr-url: https://github.com/nodejs/node/pull/11919 description: "`NaN`, `Infinity`, and `-Infinity` are no longer valid time specifiers." - version: v7.6.0 pr-url: https://github.com/nodejs/node/pull/10739 description: The `path` parameter can be a WHATWG `URL` object using `file:` protocol. - version: v4.1.0 pr-url: https://github.com/nodejs/node/pull/2387 description: Numeric strings, `NaN`, and `Infinity` are now allowed time specifiers. --> * `path` {string|Buffer|URL} * `atime` {number|string|Date} * `mtime` {number|string|Date} Returns `undefined`. For detailed information, see the documentation of the asynchronous version of this API: [`fs.utimes()`][]. ### `fs.writeFileSync(file, data[, options])` <!-- YAML added: v0.1.29 changes: - version: v20.10.0 pr-url: https://github.com/nodejs/node/pull/50009 description: The `flush` option is now supported. - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/42796 description: Passing to the `data` parameter an object with an own `toString` function is no longer supported. - version: v17.8.0 pr-url: https://github.com/nodejs/node/pull/42149 description: Passing to the `data` parameter an object with an own `toString` function is deprecated. - version: v14.12.0 pr-url: https://github.com/nodejs/node/pull/34993 description: The `data` parameter will stringify an object with an explicit `toString` function. - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `data` parameter won't coerce unsupported input to strings anymore. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22150 description: The `data` parameter can now be any `TypedArray` or a `DataView`. - version: v7.4.0 pr-url: https://github.com/nodejs/node/pull/10382 description: The `data` parameter can now be a `Uint8Array`. - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3163 description: The `file` parameter can be a file descriptor now. --> * `file` {string|Buffer|URL|integer} filename or file descriptor * `data` {string|Buffer|TypedArray|DataView} * `options` {Object|string} * `encoding` {string|null} **Default:** `'utf8'` * `mode` {integer} **Default:** `0o666` * `flag` {string} See [support of file system `flags`][]. **Default:** `'w'`. * `flush` {boolean} If all data is successfully written to the file, and `flush` is `true`, `fs.fsyncSync()` is used to flush the data. Returns `undefined`. The `mode` option only affects the newly created file. See [`fs.open()`][] for more details. For detailed information, see the documentation of the asynchronous version of this API: [`fs.writeFile()`][]. ### `fs.writeSync(fd, buffer, offset[, length[, position]])` <!-- YAML added: v0.1.21 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `buffer` parameter won't coerce unsupported input to strings anymore. - version: v10.10.0 pr-url: https://github.com/nodejs/node/pull/22150 description: The `buffer` parameter can now be any `TypedArray` or a `DataView`. - version: v7.4.0 pr-url: https://github.com/nodejs/node/pull/10382 description: The `buffer` parameter can now be a `Uint8Array`. - version: v7.2.0 pr-url: https://github.com/nodejs/node/pull/7856 description: The `offset` and `length` parameters are optional now. --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer|null} **Default:** `null` * Returns: {number} The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: [`fs.write(fd, buffer...)`][]. ### `fs.writeSync(fd, buffer[, options])` <!-- YAML added: - v18.3.0 - v16.17.0 --> * `fd` {integer} * `buffer` {Buffer|TypedArray|DataView} * `options` {Object} * `offset` {integer} **Default:** `0` * `length` {integer} **Default:** `buffer.byteLength - offset` * `position` {integer} **Default:** `null` * Returns: {number} The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: [`fs.write(fd, buffer...)`][]. ### `fs.writeSync(fd, string[, position[, encoding]])` <!-- YAML added: v0.11.5 changes: - version: v14.0.0 pr-url: https://github.com/nodejs/node/pull/31030 description: The `string` parameter won't coerce unsupported input to strings anymore. - version: v7.2.0 pr-url: https://github.com/nodejs/node/pull/7856 description: The `position` parameter is optional now. --> * `fd` {integer} * `string` {string} * `position` {integer|null} **Default:** `null` * `encoding` {string} **Default:** `'utf8'` * Returns: {number} The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: [`fs.write(fd, string...)`][]. ### `fs.writevSync(fd, buffers[, position])` <!-- YAML added: v12.9.0 --> * `fd` {integer} * `buffers` {ArrayBufferView\[]} * `position` {integer|null} **Default:** `null` * Returns: {number} The number of bytes written. For detailed information, see the documentation of the asynchronous version of this API: [`fs.writev()`][]. ## Common Objects The common objects are shared by all of the file system API variants (promise, callback, and synchronous). ### Class: `fs.Dir` <!-- YAML added: v12.12.0 --> A class representing a directory stream. Created by [`fs.opendir()`][], [`fs.opendirSync()`][], or [`fsPromises.opendir()`][]. ```mjs import { opendir } from 'node:fs/promises'; try { const dir = await opendir('./'); for await (const dirent of dir) console.log(dirent.name); } catch (err) { console.error(err); } ``` When using the async iterator, the {fs.Dir} object will be automatically closed after the iterator exits. #### `dir.close()` <!-- YAML added: v12.12.0 --> * Returns: {Promise} Asynchronously close the directory's underlying resource handle. Subsequent reads will result in errors. A promise is returned that will be fulfilled after the resource has been closed. #### `dir.close(callback)` <!-- YAML added: v12.12.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. --> * `callback` {Function} * `err` {Error} Asynchronously close the directory's underlying resource handle. Subsequent reads will result in errors. The `callback` will be called after the resource handle has been closed. #### `dir.closeSync()` <!-- YAML added: v12.12.0 --> Synchronously close the directory's underlying resource handle. Subsequent reads will result in errors. #### `dir.path` <!-- YAML added: v12.12.0 --> * {string} The read-only path of this directory as was provided to [`fs.opendir()`][], [`fs.opendirSync()`][], or [`fsPromises.opendir()`][]. #### `dir.read()` <!-- YAML added: v12.12.0 --> * Returns: {Promise} Fulfills with a {fs.Dirent|null} Asynchronously read the next directory entry via readdir(3) as an {fs.Dirent}. A promise is returned that will be fulfilled with an {fs.Dirent}, or `null` if there are no more directory entries to read. Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. #### `dir.read(callback)` <!-- YAML added: v12.12.0 --> * `callback` {Function} * `err` {Error} * `dirent` {fs.Dirent|null} Asynchronously read the next directory entry via readdir(3) as an {fs.Dirent}. After the read is completed, the `callback` will be called with an {fs.Dirent}, or `null` if there are no more directory entries to read. Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. #### `dir.readSync()` <!-- YAML added: v12.12.0 --> * Returns: {fs.Dirent|null} Synchronously read the next directory entry as an {fs.Dirent}. See the POSIX readdir(3) documentation for more detail. If there are no more directory entries to read, `null` will be returned. Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. #### `dir[Symbol.asyncIterator]()` <!-- YAML added: v12.12.0 --> * Returns: {AsyncIterator} An AsyncIterator of {fs.Dirent} Asynchronously iterates over the directory until all entries have been read. Refer to the POSIX readdir(3) documentation for more detail. Entries returned by the async iterator are always an {fs.Dirent}. The `null` case from `dir.read()` is handled internally. See {fs.Dir} for an example. Directory entries returned by this iterator are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results. ### Class: `fs.Dirent` <!-- YAML added: v10.10.0 --> A representation of a directory entry, which can be a file or a subdirectory within the directory, as returned by reading from an {fs.Dir}. The directory entry is a combination of the file name and file type pairs. Additionally, when [`fs.readdir()`][] or [`fs.readdirSync()`][] is called with the `withFileTypes` option set to `true`, the resulting array is filled with {fs.Dirent} objects, rather than strings or {Buffer}s. #### `dirent.isBlockDevice()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a block device. #### `dirent.isCharacterDevice()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a character device. #### `dirent.isDirectory()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a file system directory. #### `dirent.isFIFO()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a first-in-first-out (FIFO) pipe. #### `dirent.isFile()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a regular file. #### `dirent.isSocket()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a socket. #### `dirent.isSymbolicLink()` <!-- YAML added: v10.10.0 --> * Returns: {boolean} Returns `true` if the {fs.Dirent} object describes a symbolic link. #### `dirent.name` <!-- YAML added: v10.10.0 --> * {string|Buffer} The file name that this {fs.Dirent} object refers to. The type of this value is determined by the `options.encoding` passed to [`fs.readdir()`][] or [`fs.readdirSync()`][]. #### `dirent.parentPath` <!-- YAML added: - v20.12.0 --> > Stability: 1 – Experimental * {string} The path to the parent directory of the file this {fs.Dirent} object refers to. #### `dirent.path` <!-- YAML added: - v20.1.0 - v18.17.0 deprecated: v20.12.0 --> > Stability: 0 - Deprecated: Use [`dirent.parentPath`][] instead. * {string} Alias for `dirent.parentPath`. ### Class: `fs.FSWatcher` <!-- YAML added: v0.5.8 --> * Extends {EventEmitter} A successful call to [`fs.watch()`][] method will return a new {fs.FSWatcher} object. All {fs.FSWatcher} objects emit a `'change'` event whenever a specific watched file is modified. #### Event: `'change'` <!-- YAML added: v0.5.8 --> * `eventType` {string} The type of change event that has occurred * `filename` {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 UTF-8 string. ```mjs import { watch } from 'node:fs'; // Example when handled through fs.watch() listener watch('./tmp', { encoding: 'buffer' }, (eventType, filename) => { if (filename) { console.log(filename); // Prints: <Buffer ...> } }); ``` #### Event: `'close'` <!-- YAML added: v10.0.0 --> Emitted when the watcher stops watching for changes. The closed {fs.FSWatcher} object is no longer usable in the event handler. #### Event: `'error'` <!-- YAML added: v0.5.8 --> * `error` {Error} Emitted when an error occurs while watching the file. The errored {fs.FSWatcher} object is no longer usable in the event handler. #### `watcher.close()` <!-- YAML added: v0.5.8 --> Stop watching for changes on the given {fs.FSWatcher}. Once stopped, the {fs.FSWatcher} object is no longer usable. #### `watcher.ref()` <!-- YAML added: - v14.3.0 - v12.20.0 --> * Returns: {fs.FSWatcher} When called, requests that the Node.js event loop _not_ exit so long as the {fs.FSWatcher} is active. Calling `watcher.ref()` multiple times will have no effect. By default, all {fs.FSWatcher} objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously. #### `watcher.unref()` <!-- YAML added: - v14.3.0 - v12.20.0 --> * Returns: {fs.FSWatcher} When called, the active {fs.FSWatcher} object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the {fs.FSWatcher} object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect. ### Class: `fs.StatWatcher` <!-- YAML added: - v14.3.0 - v12.20.0 --> * Extends {EventEmitter} A successful call to `fs.watchFile()` method will return a new {fs.StatWatcher} object. #### `watcher.ref()` <!-- YAML added: - v14.3.0 - v12.20.0 --> * Returns: {fs.StatWatcher} When called, requests that the Node.js event loop _not_ exit so long as the {fs.StatWatcher} is active. Calling `watcher.ref()` multiple times will have no effect. By default, all {fs.StatWatcher} objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously. #### `watcher.unref()` <!-- YAML added: - v14.3.0 - v12.20.0 --> * Returns: {fs.StatWatcher} When called, the active {fs.StatWatcher} object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the {fs.StatWatcher} object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect. ### Class: `fs.ReadStream` <!-- YAML added: v0.1.93 --> * Extends: {stream.Readable} Instances of {fs.ReadStream} are created and returned using the [`fs.createReadStream()`][] function. #### Event: `'close'` <!-- YAML added: v0.1.93 --> Emitted when the {fs.ReadStream}'s underlying file descriptor has been closed. #### Event: `'open'` <!-- YAML added: v0.1.93 --> * `fd` {integer} Integer file descriptor used by the {fs.ReadStream}. Emitted when the {fs.ReadStream}'s file descriptor has been opened. #### Event: `'ready'` <!-- YAML added: v9.11.0 --> Emitted when the {fs.ReadStream} is ready to be used. Fires immediately after `'open'`. #### `readStream.bytesRead` <!-- YAML added: v6.4.0 --> * {number} The number of bytes that have been read so far. #### `readStream.path` <!-- YAML added: v0.1.93 --> * {string|Buffer} 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}. If `fd` is specified, then `readStream.path` will be `undefined`. #### `readStream.pending` <!-- YAML added: - v11.2.0 - v10.16.0 --> * {boolean} This property is `true` if the underlying file has not been opened yet, i.e. before the `'ready'` event is emitted. ### Class: `fs.Stats` <!-- YAML added: v0.1.21 changes: - version: v20.13.0 pr-url: https://github.com/nodejs/node/pull/51879 description: Public constructor is deprecated. - version: v8.1.0 pr-url: https://github.com/nodejs/node/pull/13173 description: Added times as numbers. --> A {fs.Stats} object provides information about a file. Objects returned from [`fs.stat()`][], [`fs.lstat()`][], [`fs.fstat()`][], and their synchronous counterparts are of this type. If `bigint` in the `options` passed to those methods is true, the numeric values will be `bigint` instead of `number`, and the object will contain additional nanosecond-precision properties suffixed with `Ns`. `Stat` objects are not to be created directly using the `new` keyword. ```console Stats { dev: 2114, ino: 48064969, mode: 33188, nlink: 1, uid: 85, gid: 100, rdev: 0, size: 527, blksize: 4096, blocks: 8, atimeMs: 1318289051000.1, mtimeMs: 1318289051000.1, ctimeMs: 1318289051000.1, birthtimeMs: 1318289051000.1, 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 } ``` `bigint` version: ```console BigIntStats { dev: 2114n, ino: 48064969n, mode: 33188n, nlink: 1n, uid: 85n, gid: 100n, rdev: 0n, size: 527n, blksize: 4096n, blocks: 8n, atimeMs: 1318289051000n, mtimeMs: 1318289051000n, ctimeMs: 1318289051000n, birthtimeMs: 1318289051000n, atimeNs: 1318289051000000000n, mtimeNs: 1318289051000000000n, ctimeNs: 1318289051000000000n, birthtimeNs: 1318289051000000000n, 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 } ``` #### `stats.isBlockDevice()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a block device. #### `stats.isCharacterDevice()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a character device. #### `stats.isDirectory()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a file system directory. If the {fs.Stats} object was obtained from calling [`fs.lstat()`][] on a symbolic link which resolves to a directory, this method will return `false`. This is because [`fs.lstat()`][] returns information about a symbolic link itself and not the path it resolves to. #### `stats.isFIFO()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a first-in-first-out (FIFO) pipe. #### `stats.isFile()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a regular file. #### `stats.isSocket()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a socket. #### `stats.isSymbolicLink()` <!-- YAML added: v0.1.10 --> * Returns: {boolean} Returns `true` if the {fs.Stats} object describes a symbolic link. This method is only valid when using [`fs.lstat()`][]. #### `stats.dev` * {number|bigint} The numeric identifier of the device containing the file. #### `stats.ino` * {number|bigint} The file system specific "Inode" number for the file. #### `stats.mode` * {number|bigint} A bit-field describing the file type and mode. #### `stats.nlink` * {number|bigint} The number of hard-links that exist for the file. #### `stats.uid` * {number|bigint} The numeric user identifier of the user that owns the file (POSIX). #### `stats.gid` * {number|bigint} The numeric group identifier of the group that owns the file (POSIX). #### `stats.rdev` * {number|bigint} A numeric device identifier if the file represents a device. #### `stats.size` * {number|bigint} The size of the file in bytes. If the underlying file system does not support getting the size of the file, this will be `0`. #### `stats.blksize` * {number|bigint} The file system block size for i/o operations. #### `stats.blocks` * {number|bigint} The number of blocks allocated for this file. #### `stats.atimeMs` <!-- YAML added: v8.1.0 --> * {number|bigint} The timestamp indicating the last time this file was accessed expressed in milliseconds since the POSIX Epoch. #### `stats.mtimeMs` <!-- YAML added: v8.1.0 --> * {number|bigint} The timestamp indicating the last time this file was modified expressed in milliseconds since the POSIX Epoch. #### `stats.ctimeMs` <!-- YAML added: v8.1.0 --> * {number|bigint} The timestamp indicating the last time the file status was changed expressed in milliseconds since the POSIX Epoch. #### `stats.birthtimeMs` <!-- YAML added: v8.1.0 --> * {number|bigint} The timestamp indicating the creation time of this file expressed in milliseconds since the POSIX Epoch. #### `stats.atimeNs` <!-- YAML added: v12.10.0 --> * {bigint} Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time this file was accessed expressed in nanoseconds since the POSIX Epoch. #### `stats.mtimeNs` <!-- YAML added: v12.10.0 --> * {bigint} Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time this file was modified expressed in nanoseconds since the POSIX Epoch. #### `stats.ctimeNs` <!-- YAML added: v12.10.0 --> * {bigint} Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the last time the file status was changed expressed in nanoseconds since the POSIX Epoch. #### `stats.birthtimeNs` <!-- YAML added: v12.10.0 --> * {bigint} Only present when `bigint: true` is passed into the method that generates the object. The timestamp indicating the creation time of this file expressed in nanoseconds since the POSIX Epoch. #### `stats.atime` <!-- YAML added: v0.11.13 --> * {Date} The timestamp indicating the last time this file was accessed. #### `stats.mtime` <!-- YAML added: v0.11.13 --> * {Date} The timestamp indicating the last time this file was modified. #### `stats.ctime` <!-- YAML added: v0.11.13 --> * {Date} The timestamp indicating the last time the file status was changed. #### `stats.birthtime` <!-- YAML added: v0.11.13 --> * {Date} The timestamp indicating the creation time of this file. #### Stat time values The `atimeMs`, `mtimeMs`, `ctimeMs`, `birthtimeMs` properties are numeric values that hold the corresponding times in milliseconds. Their precision is platform specific. When `bigint: true` is passed into the method that generates the object, the properties will be [bigints][], otherwise they will be [numbers][MDN-Number]. The `atimeNs`, `mtimeNs`, `ctimeNs`, `birthtimeNs` properties are [bigints][] that hold the corresponding times in nanoseconds. They are only present when `bigint: true` is passed into the method that generates the object. Their precision is platform specific. `atime`, `mtime`, `ctime`, and `birthtime` are [`Date`][MDN-Date] object alternate representations of the various times. The `Date` and number values are not connected. Assigning a new number value, or mutating the `Date` value, will not be reflected in the corresponding alternate representation. 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 file systems where birthtime is not available, this field may instead hold either the `ctime` or `1970-01-01T00:00Z` (ie, Unix epoch timestamp `0`). This value may be greater than `atime` or `mtime` in this case. On Darwin and other FreeBSD variants, also set if the `atime` is explicitly set to an earlier value than the current `birthtime` using the utimes(2) system call. Prior to Node.js 0.12, the `ctime` held the `birthtime` on Windows systems. As of 0.12, `ctime` is not "creation time", and on Unix systems, it never was. ### Class: `fs.StatFs` <!-- YAML added: - v19.6.0 - v18.15.0 --> Provides information about a mounted file system. Objects returned from [`fs.statfs()`][] and its synchronous counterpart are of this type. If `bigint` in the `options` passed to those methods is `true`, the numeric values will be `bigint` instead of `number`. ```console StatFs { type: 1397114950, bsize: 4096, blocks: 121938943, bfree: 61058895, bavail: 61058895, files: 999, ffree: 1000000 } ``` `bigint` version: ```console StatFs { type: 1397114950n, bsize: 4096n, blocks: 121938943n, bfree: 61058895n, bavail: 61058895n, files: 999n, ffree: 1000000n } ``` #### `statfs.bavail` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Free blocks available to unprivileged users. #### `statfs.bfree` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Free blocks in file system. #### `statfs.blocks` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Total data blocks in file system. #### `statfs.bsize` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Optimal transfer block size. #### `statfs.ffree` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Free file nodes in file system. #### `statfs.files` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Total file nodes in file system. #### `statfs.type` <!-- YAML added: - v19.6.0 - v18.15.0 --> * {number|bigint} Type of file system. ### Class: `fs.WriteStream` <!-- YAML added: v0.1.93 --> * Extends {stream.Writable} Instances of {fs.WriteStream} are created and returned using the [`fs.createWriteStream()`][] function. #### Event: `'close'` <!-- YAML added: v0.1.93 --> Emitted when the {fs.WriteStream}'s underlying file descriptor has been closed. #### Event: `'open'` <!-- YAML added: v0.1.93 --> * `fd` {integer} Integer file descriptor used by the {fs.WriteStream}. Emitted when the {fs.WriteStream}'s file is opened. #### Event: `'ready'` <!-- YAML added: v9.11.0 --> Emitted when the {fs.WriteStream} is ready to be used. Fires immediately after `'open'`. #### `writeStream.bytesWritten` <!-- YAML added: v0.4.7 --> The number of bytes written so far. Does not include data that is still queued for writing. #### `writeStream.close([callback])` <!-- YAML added: v0.9.4 --> * `callback` {Function} * `err` {Error} Closes `writeStream`. Optionally accepts a callback that will be executed once the `writeStream` is closed. #### `writeStream.path` <!-- YAML added: v0.1.93 --> 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}. #### `writeStream.pending` <!-- YAML added: v11.2.0 --> * {boolean} This property is `true` if the underlying file has not been opened yet, i.e. before the `'ready'` event is emitted. ### `fs.constants` * {Object} Returns an object containing commonly used constants for file system operations. #### FS constants The following constants are exported by `fs.constants` and `fsPromises.constants`. Not every constant will be available on every operating system; this is especially important for Windows, where many of the POSIX specific definitions are not available. For portable applications it is recommended to check for their presence before use. To use more than one constant, use the bitwise OR `|` operator. Example: ```mjs import { open, constants } from 'node:fs'; const { O_RDWR, O_CREAT, O_EXCL, } = constants; open('/path/to/my/file', O_RDWR | O_CREAT | O_EXCL, (err, fd) => { // ... }); ``` ##### File access constants The following constants are meant for use as the `mode` parameter passed to [`fsPromises.access()`][], [`fs.access()`][], and [`fs.accessSync()`][]. <table> <tr> <th>Constant</th> <th>Description</th> </tr> <tr> <td><code>F_OK</code></td> <td>Flag indicating that the file is visible to the calling process. This is useful for determining if a file exists, but says nothing about <code>rwx</code> permissions. Default if no mode is specified.</td> </tr> <tr> <td><code>R_OK</code></td> <td>Flag indicating that the file can be read by the calling process.</td> </tr> <tr> <td><code>W_OK</code></td> <td>Flag indicating that the file can be written by the calling process.</td> </tr> <tr> <td><code>X_OK</code></td> <td>Flag indicating that the file can be executed by the calling process. This has no effect on Windows (will behave like <code>fs.constants.F_OK</code>).</td> </tr> </table> The definitions are also available on Windows. ##### File copy constants The following constants are meant for use with [`fs.copyFile()`][]. <table> <tr> <th>Constant</th> <th>Description</th> </tr> <tr> <td><code>COPYFILE_EXCL</code></td> <td>If present, the copy operation will fail with an error if the destination path already exists.</td> </tr> <tr> <td><code>COPYFILE_FICLONE</code></td> <td>If present, the copy operation will attempt to create a copy-on-write reflink. If the underlying platform does not support copy-on-write, then a fallback copy mechanism is used.</td> </tr> <tr> <td><code>COPYFILE_FICLONE_FORCE</code></td> <td>If present, the copy operation will attempt to create a copy-on-write reflink. If the underlying platform does not support copy-on-write, then the operation will fail with an error.</td> </tr> </table> The definitions are also available on Windows. ##### File open constants The following constants are meant for use with `fs.open()`. <table> <tr> <th>Constant</th> <th>Description</th> </tr> <tr> <td><code>O_RDONLY</code></td> <td>Flag indicating to open a file for read-only access.</td> </tr> <tr> <td><code>O_WRONLY</code></td> <td>Flag indicating to open a file for write-only access.</td> </tr> <tr> <td><code>O_RDWR</code></td> <td>Flag indicating to open a file for read-write access.</td> </tr> <tr> <td><code>O_CREAT</code></td> <td>Flag indicating to create the file if it does not already exist.</td> </tr> <tr> <td><code>O_EXCL</code></td> <td>Flag indicating that opening a file should fail if the <code>O_CREAT</code> flag is set and the file already exists.</td> </tr> <tr> <td><code>O_NOCTTY</code></td> <td>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).</td> </tr> <tr> <td><code>O_TRUNC</code></td> <td>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.</td> </tr> <tr> <td><code>O_APPEND</code></td> <td>Flag indicating that data will be appended to the end of the file.</td> </tr> <tr> <td><code>O_DIRECTORY</code></td> <td>Flag indicating that the open should fail if the path is not a directory.</td> </tr> <tr> <td><code>O_NOATIME</code></td> <td>Flag indicating reading accesses to the file system will no longer result in an update to the <code>atime</code> information associated with the file. This flag is available on Linux operating systems only.</td> </tr> <tr> <td><code>O_NOFOLLOW</code></td> <td>Flag indicating that the open should fail if the path is a symbolic link.</td> </tr> <tr> <td><code>O_SYNC</code></td> <td>Flag indicating that the file is opened for synchronized I/O with write operations waiting for file integrity.</td> </tr> <tr> <td><code>O_DSYNC</code></td> <td>Flag indicating that the file is opened for synchronized I/O with write operations waiting for data integrity.</td> </tr> <tr> <td><code>O_SYMLINK</code></td> <td>Flag indicating to open the symbolic link itself rather than the resource it is pointing to.</td> </tr> <tr> <td><code>O_DIRECT</code></td> <td>When set, an attempt will be made to minimize caching effects of file I/O.</td> </tr> <tr> <td><code>O_NONBLOCK</code></td> <td>Flag indicating to open the file in nonblocking mode when possible.</td> </tr> <tr> <td><code>UV_FS_O_FILEMAP</code></td> <td>When set, a memory file mapping is used to access the file. This flag is available on Windows operating systems only. On other operating systems, this flag is ignored.</td> </tr> </table> On Windows, only `O_APPEND`, `O_CREAT`, `O_EXCL`, `O_RDONLY`, `O_RDWR`, `O_TRUNC`, `O_WRONLY`, and `UV_FS_O_FILEMAP` are available. ##### File type constants The following constants are meant for use with the {fs.Stats} object's `mode` property for determining a file's type. <table> <tr> <th>Constant</th> <th>Description</th> </tr> <tr> <td><code>S_IFMT</code></td> <td>Bit mask used to extract the file type code.</td> </tr> <tr> <td><code>S_IFREG</code></td> <td>File type constant for a regular file.</td> </tr> <tr> <td><code>S_IFDIR</code></td> <td>File type constant for a directory.</td> </tr> <tr> <td><code>S_IFCHR</code></td> <td>File type constant for a character-oriented device file.</td> </tr> <tr> <td><code>S_IFBLK</code></td> <td>File type constant for a block-oriented device file.</td> </tr> <tr> <td><code>S_IFIFO</code></td> <td>File type constant for a FIFO/pipe.</td> </tr> <tr> <td><code>S_IFLNK</code></td> <td>File type constant for a symbolic link.</td> </tr> <tr> <td><code>S_IFSOCK</code></td> <td>File type constant for a socket.</td> </tr> </table> On Windows, only `S_IFCHR`, `S_IFDIR`, `S_IFLNK`, `S_IFMT`, and `S_IFREG`, are available. ##### 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. <table> <tr> <th>Constant</th> <th>Description</th> </tr> <tr> <td><code>S_IRWXU</code></td> <td>File mode indicating readable, writable, and executable by owner.</td> </tr> <tr> <td><code>S_IRUSR</code></td> <td>File mode indicating readable by owner.</td> </tr> <tr> <td><code>S_IWUSR</code></td> <td>File mode indicating writable by owner.</td> </tr> <tr> <td><code>S_IXUSR</code></td> <td>File mode indicating executable by owner.</td> </tr> <tr> <td><code>S_IRWXG</code></td> <td>File mode indicating readable, writable, and executable by group.</td> </tr> <tr> <td><code>S_IRGRP</code></td> <td>File mode indicating readable by group.</td> </tr> <tr> <td><code>S_IWGRP</code></td> <td>File mode indicating writable by group.</td> </tr> <tr> <td><code>S_IXGRP</code></td> <td>File mode indicating executable by group.</td> </tr> <tr> <td><code>S_IRWXO</code></td> <td>File mode indicating readable, writable, and executable by others.</td> </tr> <tr> <td><code>S_IROTH</code></td> <td>File mode indicating readable by others.</td> </tr> <tr> <td><code>S_IWOTH</code></td> <td>File mode indicating writable by others.</td> </tr> <tr> <td><code>S_IXOTH</code></td> <td>File mode indicating executable by others.</td> </tr> </table> On Windows, only `S_IRUSR` and `S_IWUSR` are available. ## Notes ### Ordering of callback and promise-based operations Because they are executed asynchronously by the underlying thread pool, there is no guaranteed ordering when using either the callback or promise-based methods. For example, the following is prone to error because the `fs.stat()` operation might complete before the `fs.rename()` operation: ```js const fs = require('node:fs'); 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 is important to correctly order the operations by awaiting the results of one before invoking the other: ```mjs import { rename, stat } from 'node:fs/promises'; const oldPath = '/tmp/hello'; const newPath = '/tmp/world'; try { await rename(oldPath, newPath); const stats = await stat(newPath); console.log(`stats: ${JSON.stringify(stats)}`); } catch (error) { console.error('there was an error:', error.message); } ``` ```cjs const { rename, stat } = require('node:fs/promises'); (async function(oldPath, newPath) { try { await rename(oldPath, newPath); const stats = await stat(newPath); console.log(`stats: ${JSON.stringify(stats)}`); } catch (error) { console.error('there was an error:', error.message); } })('/tmp/hello', '/tmp/world'); ``` Or, when using the callback APIs, move the `fs.stat()` call into the callback of the `fs.rename()` operation: ```mjs import { rename, stat } from 'node:fs'; rename('/tmp/hello', '/tmp/world', (err) => { if (err) throw err; stat('/tmp/world', (err, stats) => { if (err) throw err; console.log(`stats: ${JSON.stringify(stats)}`); }); }); ``` ```cjs const { rename, stat } = require('node:fs/promises'); rename('/tmp/hello', '/tmp/world', (err) => { if (err) throw err; stat('/tmp/world', (err, stats) => { if (err) throw err; console.log(`stats: ${JSON.stringify(stats)}`); }); }); ``` ### File paths Most `fs` operations accept file paths that may be specified in the form of a string, a {Buffer}, or a {URL} object using the `file:` protocol. #### String paths String paths are interpreted as UTF-8 character sequences identifying the absolute or relative filename. Relative paths will be resolved relative to the current working directory as determined by calling `process.cwd()`. Example using an absolute path on POSIX: ```mjs import { open } from 'node:fs/promises'; let fd; try { fd = await open('/open/some/file.txt', 'r'); // Do something with the file } finally { await fd?.close(); } ``` Example using a relative path on POSIX (relative to `process.cwd()`): ```mjs import { open } from 'node:fs/promises'; let fd; try { fd = await open('file.txt', 'r'); // Do something with the file } finally { await fd?.close(); } ``` #### File URL paths <!-- YAML added: v7.6.0 --> For most `node:fs` module functions, the `path` or `filename` argument may be passed as a {URL} object using the `file:` protocol. ```mjs import { readFileSync } from 'node:fs'; readFileSync(new URL('file:///tmp/hello')); ``` `file:` URLs are always absolute paths. ##### Platform-specific considerations On Windows, `file:` {URL}s with a host name convert to UNC paths, while `file:` {URL}s with drive letters convert to local absolute paths. `file:` {URL}s with no host name and no drive letter will result in an error: ```mjs import { readFileSync } from 'node:fs'; // On Windows : // - WHATWG file URLs with hostname convert to UNC path // file://hostname/p/a/t/h/file => \\hostname\p\a\t\h\file 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 readFileSync(new URL('file:///C:/tmp/hello')); // - WHATWG file URLs without hostname must have a drive letters readFileSync(new URL('file:///notdriveletter/p/a/t/h/file')); readFileSync(new URL('file:///c/p/a/t/h/file')); // TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must be absolute ``` `file:` {URL}s with drive letters must use `:` as a separator just after the drive letter. Using another separator will result in an error. On all other platforms, `file:` {URL}s with a host name are unsupported and will result in an error: ```mjs import { readFileSync } from 'node:fs'; // On other platforms: // - WHATWG file URLs with hostname are unsupported // file://hostname/p/a/t/h/file => throw! 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 readFileSync(new URL('file:///tmp/hello')); ``` A `file:` {URL} having encoded slash characters will result in an error on all platforms: ```mjs import { readFileSync } from 'node:fs'; // On Windows readFileSync(new URL('file:///C:/p/a/t/h/%2F')); 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 readFileSync(new URL('file:///p/a/t/h/%2F')); 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:` {URL}s having encoded backslash will result in an error: ```mjs import { readFileSync } from 'node:fs'; // On Windows readFileSync(new URL('file:///C:/path/%5C')); readFileSync(new URL('file:///C:/path/%5c')); /* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded \ or / characters */ ``` #### Buffer paths Paths specified using a {Buffer} are useful primarily on certain POSIX operating systems that treat file paths as opaque byte sequences. On such systems, it is possible for a single file path to contain sub-sequences that use multiple character encodings. As with string paths, {Buffer} paths may be relative or absolute: Example using an absolute path on POSIX: ```mjs import { open } from 'node:fs/promises'; import { Buffer } from 'node:buffer'; let fd; try { fd = await open(Buffer.from('/open/some/file.txt'), 'r'); // Do something with the file } finally { await fd?.close(); } ``` #### Per-drive working directories on Windows On Windows, Node.js follows the concept of per-drive working directory. This behavior can be observed when using a drive path without a backslash. For example `fs.readdirSync('C:\\')` can potentially return a different result than `fs.readdirSync('C:')`. For more information, see [this MSDN page][MSDN-Rel-Path]. ### File descriptors On POSIX systems, for every process, the kernel maintains a table of currently open files and resources. Each open file is assigned a simple numeric identifier called a _file descriptor_. At the system-level, all file system operations use these file descriptors to identify and track each specific file. Windows systems use a different but conceptually similar mechanism for tracking resources. To simplify things for users, Node.js abstracts away the differences between operating systems and assigns all open files a numeric file descriptor. The callback-based `fs.open()`, and synchronous `fs.openSync()` methods open a file and allocate a new file descriptor. Once allocated, the file descriptor may be used to read data from, write data to, or request information about the file. Operating systems limit the number of file descriptors that may be open at any given time so it is critical to close the descriptor when operations are completed. Failure to do so will result in a memory leak that will eventually cause an application to crash. ```mjs import { open, close, fstat } from 'node:fs'; function closeFd(fd) { close(fd, (err) => { if (err) throw err; }); } open('/open/some/file.txt', 'r', (err, fd) => { if (err) throw err; try { fstat(fd, (err, stat) => { if (err) { closeFd(fd); throw err; } // use stat closeFd(fd); }); } catch (err) { closeFd(fd); throw err; } }); ``` The promise-based APIs use a {FileHandle} object in place of the numeric file descriptor. These objects are better managed by the system to ensure that resources are not leaked. However, it is still required that they are closed when operations are completed: ```mjs import { open } from 'node:fs/promises'; let file; try { file = await open('/open/some/file.txt', 'r'); const stat = await file.stat(); // use stat } finally { await file.close(); } ``` ### Threadpool usage All callback and promise-based file system APIs (with the exception of `fs.FSWatcher()`) use libuv's threadpool. This can have surprising and negative performance implications for some applications. See the [`UV_THREADPOOL_SIZE`][] documentation for more information. ### File system flags The following flags are available wherever the `flag` option takes a string. * `'a'`: Open file for appending. The file is created if it does not exist. * `'ax'`: Like `'a'` but fails if the path exists. * `'a+'`: Open file for reading and appending. The file is created if it does not exist. * `'ax+'`: Like `'a+'` but fails if the path exists. * `'as'`: Open file for appending in synchronous mode. The file is created if it does not exist. * `'as+'`: Open file for reading and appending in synchronous mode. The file is created if it does not exist. * `'r'`: Open file for reading. An exception occurs if the file does not exist. * `'rs'`: Open file for reading in synchronous mode. 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. This doesn't turn `fs.open()` or `fsPromises.open()` into a synchronous blocking call. If synchronous operation is desired, something like `fs.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 if the path 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 if the path exists. `flag` 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`. The exclusive flag `'x'` (`O_EXCL` flag in open(2)) causes the operation to return an error if the path already exists. On POSIX, if the path is a symbolic link, using `O_EXCL` returns an error even if the link is to a path that does not exist. The exclusive flag might not work with network file systems. 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. Modifying a file rather than replacing it may require the `flag` option to be set to `'r+'` rather than the default `'w'`. The behavior of some flags are platform-specific. As such, opening a directory on macOS and Linux with the `'a+'` flag, as in the example below, will return an error. In contrast, on Windows and FreeBSD, a file descriptor or a `FileHandle` will be returned. ```js // 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> }); ``` On Windows, opening an existing hidden file using the `'w'` flag (either through `fs.open()`, `fs.writeFile()`, or `fsPromises.open()`) will fail with `EPERM`. Existing hidden files can be opened for writing with the `'r+'` flag. A call to `fs.ftruncate()` or `filehandle.truncate()` can be used to reset the file contents. [#25741]: https://github.com/nodejs/node/issues/25741 [Common System Errors]: errors.md#common-system-errors [FS constants]: #fs-constants [File access constants]: #file-access-constants [MDN-Date]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date [MDN-Number]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type [MSDN-Rel-Path]: https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file#fully-qualified-vs-relative-paths [MSDN-Using-Streams]: https://docs.microsoft.com/en-us/windows/desktop/FileIO/using-streams [Naming Files, Paths, and Namespaces]: https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file [`AHAFS`]: https://developer.ibm.com/articles/au-aix_event_infrastructure/ [`Buffer.byteLength`]: buffer.md#static-method-bufferbytelengthstring-encoding [`FSEvents`]: https://developer.apple.com/documentation/coreservices/file_system_events [`Number.MAX_SAFE_INTEGER`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER [`ReadDirectoryChangesW`]: https://docs.microsoft.com/en-us/windows/desktop/api/winbase/nf-winbase-readdirectorychangesw [`UV_THREADPOOL_SIZE`]: cli.md#uv_threadpool_sizesize [`dirent.parentPath`]: #direntparentpath [`event ports`]: https://illumos.org/man/port_create [`filehandle.createReadStream()`]: #filehandlecreatereadstreamoptions [`filehandle.createWriteStream()`]: #filehandlecreatewritestreamoptions [`filehandle.writeFile()`]: #filehandlewritefiledata-options [`fs.access()`]: #fsaccesspath-mode-callback [`fs.accessSync()`]: #fsaccesssyncpath-mode [`fs.chmod()`]: #fschmodpath-mode-callback [`fs.chown()`]: #fschownpath-uid-gid-callback [`fs.copyFile()`]: #fscopyfilesrc-dest-mode-callback [`fs.copyFileSync()`]: #fscopyfilesyncsrc-dest-mode [`fs.createReadStream()`]: #fscreatereadstreampath-options [`fs.createWriteStream()`]: #fscreatewritestreampath-options [`fs.exists()`]: #fsexistspath-callback [`fs.fstat()`]: #fsfstatfd-options-callback [`fs.ftruncate()`]: #fsftruncatefd-len-callback [`fs.futimes()`]: #fsfutimesfd-atime-mtime-callback [`fs.lstat()`]: #fslstatpath-options-callback [`fs.lutimes()`]: #fslutimespath-atime-mtime-callback [`fs.mkdir()`]: #fsmkdirpath-options-callback [`fs.mkdtemp()`]: #fsmkdtempprefix-options-callback [`fs.open()`]: #fsopenpath-flags-mode-callback [`fs.opendir()`]: #fsopendirpath-options-callback [`fs.opendirSync()`]: #fsopendirsyncpath-options [`fs.read()`]: #fsreadfd-buffer-offset-length-position-callback [`fs.readFile()`]: #fsreadfilepath-options-callback [`fs.readFileSync()`]: #fsreadfilesyncpath-options [`fs.readdir()`]: #fsreaddirpath-options-callback [`fs.readdirSync()`]: #fsreaddirsyncpath-options [`fs.readv()`]: #fsreadvfd-buffers-position-callback [`fs.realpath()`]: #fsrealpathpath-options-callback [`fs.rm()`]: #fsrmpath-options-callback [`fs.rmSync()`]: #fsrmsyncpath-options [`fs.rmdir()`]: #fsrmdirpath-options-callback [`fs.stat()`]: #fsstatpath-options-callback [`fs.statfs()`]: #fsstatfspath-options-callback [`fs.symlink()`]: #fssymlinktarget-path-type-callback [`fs.utimes()`]: #fsutimespath-atime-mtime-callback [`fs.watch()`]: #fswatchfilename-options-listener [`fs.write(fd, buffer...)`]: #fswritefd-buffer-offset-length-position-callback [`fs.write(fd, string...)`]: #fswritefd-string-position-encoding-callback [`fs.writeFile()`]: #fswritefilefile-data-options-callback [`fs.writev()`]: #fswritevfd-buffers-position-callback [`fsPromises.access()`]: #fspromisesaccesspath-mode [`fsPromises.copyFile()`]: #fspromisescopyfilesrc-dest-mode [`fsPromises.open()`]: #fspromisesopenpath-flags-mode [`fsPromises.opendir()`]: #fspromisesopendirpath-options [`fsPromises.rm()`]: #fspromisesrmpath-options [`fsPromises.stat()`]: #fspromisesstatpath-options [`fsPromises.utimes()`]: #fspromisesutimespath-atime-mtime [`inotify(7)`]: https://man7.org/linux/man-pages/man7/inotify.7.html [`kqueue(2)`]: https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2 [`util.promisify()`]: util.md#utilpromisifyoriginal [bigints]: https://tc39.github.io/proposal-bigint [caveats]: #caveats [chcp]: https://ss64.com/nt/chcp.html [inode]: https://en.wikipedia.org/wiki/Inode [support of file system `flags`]: #file-system-flags