fs

The fs module provides synchronous, Node.js-compatible file system APIs for JSH applications.

readFileSync()

Reads a file and returns its content as a string (default: utf8) or as bytes.

Syntax

readFileSync(path[, options])

Usage example

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const fs = require('fs');
const content = fs.readFileSync('/lib/fs/index.js', 'utf8');
console.println(content.length);

writeFileSync()

Writes data to a file. Creates the file or overwrites existing content.

Syntax

writeFileSync(path, data[, options])

Usage example

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const fs = require('fs');
fs.writeFileSync('/work/test.txt', 'Hello', 'utf8');

appendFileSync()

Appends data to a file. Creates the file when it does not exist.

Syntax

appendFileSync(path, data[, options])

Usage example

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const fs = require('fs');
fs.writeFileSync('/work/append.txt', 'Line 1\n', 'utf8');
fs.appendFileSync('/work/append.txt', 'Line 2\n', 'utf8');

countLinesSync()

Counts newline-separated lines in a file.

Syntax

countLinesSync(path)

Usage example

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const fs = require('fs');
console.println(fs.countLinesSync('/work/append.txt'));

existsSync()

Returns true if a file or directory exists.

Syntax

existsSync(path)

Usage example

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const fs = require('fs');
console.println(fs.existsSync('/work/test.txt'));
console.println(fs.existsSync('/work/not-found.txt'));

statSync()

Returns file or directory metadata.

Syntax

statSync(path)

Returned fields

• name, size, mode, mtime, atime, ctime, birthtime
• isFile(), isDirectory(), isSymbolicLink()
• isBlockDevice(), isCharacterDevice(), isFIFO(), isSocket()

Usage example

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const fs = require('fs');
const st = fs.statSync('/work/test.txt');
console.println(st.isFile(), st.size);
console.println(st.name);

lstatSync()

Returns file metadata. Current implementation behaves the same as statSync().

Syntax

lstatSync(path)

readdirSync()

Reads directory entries.

• Default: returns string[]
• withFileTypes: true: returns entry objects with name and type methods
• recursive: true: returns recursive entries

The current runtime directory listing includes . and .. entries.

Syntax

readdirSync(path[, options])

Usage example

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const fs = require('fs');
const names = fs.readdirSync('/lib');
const entries = fs.readdirSync('/lib', { withFileTypes: true });
console.println(names.length, entries.length);

mkdirSync()

Creates a directory. Supports recursive creation.

Syntax

mkdirSync(path[, options])

Usage example

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const fs = require('fs');
fs.mkdirSync('/work/a/b/c', { recursive: true });

rmdirSync()

Removes a directory. With { recursive: true }, removes children first.

Syntax

rmdirSync(path[, options])

rmSync()

Removes a file or directory.

• Directory removal uses rmdirSync() internally
• force: true suppresses errors

Syntax

rmSync(path[, options])

unlinkSync()

Removes a file.

Syntax

unlinkSync(path)

renameSync()

Renames or moves a file/directory in the same mounted filesystem.

Syntax

renameSync(oldPath, newPath)

copyFileSync()

Copies a single file.

COPYFILE_EXCL fails when destination exists.

Syntax

copyFileSync(src, dest[, flags])

cpSync()

Copies a file or directory.

Directory copy requires { recursive: true }.

Syntax

cpSync(src, dest[, options])

symlinkSync()

Creates a symbolic link.

Syntax

symlinkSync(target, path)

readlinkSync()

Reads a symbolic link target.

Syntax

readlinkSync(path)

realpathSync()

Returns a resolved path with symlink resolution behavior.

Syntax

realpathSync(path)

accessSync()

Checks path accessibility.

• Throws ENOENT when path does not exist
• Supports mode constants: F_OK, R_OK, W_OK, X_OK

Syntax

accessSync(path[, mode])

truncateSync()

Truncates file content.

• No length: truncates to 0
• With length: keeps first len bytes

Syntax

truncateSync(path[, len])

openSync()

Opens a file and returns a numeric file descriptor.

Supports string flags such as r, r+, w, w+, a, a+, wx, wx+, ax, ax+.

Syntax

openSync(path, flags[, mode])

closeSync()

Closes a file descriptor.

Syntax

closeSync(fd)

readSync()

Reads from a file descriptor into a buffer.

Syntax

readSync(fd, buffer, offset, length[, position])

writeSync()

Writes string or buffer data to a file descriptor.

Syntax

writeSync(fd, buffer, offset, length[, position])

fstatSync()

Returns metadata from a file descriptor.

Syntax

fstatSync(fd)

fchmodSync(), fchownSync()

Changes mode/owner via file descriptor.

Syntax

fchmodSync(fd, mode)
fchownSync(fd, uid, gid)

fsyncSync(), fdatasyncSync()

Flushes pending file data to storage.

fdatasyncSync() currently uses the same behavior as fsyncSync().

Syntax

fsyncSync(fd)
fdatasyncSync(fd)

chmodSync(), chownSync()

Changes mode/owner by path.

On Windows, chmod/chown are no-op compatible behaviors in the current runtime implementation.

Syntax

chmodSync(path, mode)
chownSync(path, uid, gid)

createReadStream(), createWriteStream()

Creates stream objects compatible with EventEmitter-based usage.

Syntax

createReadStream(path[, options])
createWriteStream(path[, options])

Usage example

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const fs = require('fs');
const rs = fs.createReadStream('/work/in.txt', { encoding: 'utf8' });
const ws = fs.createWriteStream('/work/out.txt', { encoding: 'utf8' });
rs.pipe(ws);

platform(), arch()

Returns runtime platform and architecture strings.

Syntax

platform()
arch()

Usage example

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const fs = require('fs');
console.println(fs.platform());
console.println(fs.arch());

constants

Constant object for access, copy, and open flags.

Main fields

• Access: F_OK, R_OK, W_OK, X_OK
• Copy: COPYFILE_EXCL, COPYFILE_FICLONE, COPYFILE_FICLONE_FORCE
• Open: O_RDONLY, O_WRONLY, O_RDWR, O_CREAT, O_EXCL, O_TRUNC, O_APPEND

Usage example

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const fs = require('fs');
fs.accessSync('/work/test.txt', fs.constants.F_OK);

Aliases

For Node.js compatibility, the module also exports non-Sync aliases.

Examples: readFile, writeFile, appendFile, readdir, mkdir, rm, stat, open, close, read, write, fstat, fsync, fdatasync.