rw

What is rw?

The 'rw' npm package is a utility library for reading and writing files in Node.js. It provides simple and efficient methods for handling both synchronous and asynchronous file operations, making it easier to work with the file system in Node.js applications.

What are rw's main functionalities?

Reading files synchronously

This feature allows you to read files synchronously. The method 'readFileSync' reads the entire content of the file at the specified path and returns it. This is useful when you need to load file data immediately before proceeding with the rest of your code.

const rw = require('rw');
const data = rw.readFileSync('/path/to/file.txt', 'utf8');
console.log(data);

Writing files synchronously

This feature enables you to write data to a file synchronously. The method 'writeFileSync' writes the specified content to the file at the given path. This is useful for saving data immediately and ensuring that the file write operation completes before moving on in your code.

const rw = require('rw');
rw.writeFileSync('/path/to/file.txt', 'Hello, world!', 'utf8');

Reading files asynchronously

This feature allows you to read files asynchronously. The method 'readFile' reads the file content at the specified path and then executes a callback function with the read data. This is beneficial for non-blocking file operations in Node.js applications.

const rw = require('rw');
rw.readFile('/path/to/file.txt', 'utf8', function(err, data) {
  if (err) throw err;
  console.log(data);
});

Writing files asynchronously

This feature enables you to write data to a file asynchronously. The method 'writeFile' writes the specified content to the file at the given path and then executes a callback function once the write operation is complete. This helps in performing non-blocking file writes.

const rw = require('rw');
rw.writeFile('/path/to/file.txt', 'Hello, async world!', 'utf8', function(err) {
  if (err) throw err;
  console.log('File has been written');
});

Other packages similar to rw

fs-extra

fs-extra is a package that builds on the native 'fs' module in Node.js, providing additional file system methods not found in the standard library. It offers similar functionalities to 'rw' but includes extra features like copying directories and files, removing directories, and ensuring file paths exist.

graceful-fs

graceful-fs is a drop-in replacement for the 'fs' module that makes file system operations more robust by queuing them and avoiding EMFILE errors. It provides similar basic file reading and writing functionalities as 'rw', but with enhancements for handling large numbers of concurrent file system operations.

README

rw - Now stdin and stdout are files.

How do you read a file from stdin? If you thought,

var contents = fs.readFileSync("/dev/stdin", "utf8");

you’d be wrong, because Node only reads up to the size of the file reported by fs.stat rather than reading until it receives an EOF. So, if you redirect a file to your program (cat file | program), you’ll only read the first 65,536 bytes of your file. Oops.

What about writing a file to stdout? If you thought,

fs.writeFileSync("/dev/stdout", contents, "utf8");

you’d also be wrong, because this tries to close stdout, so you get this error:

Error: UNKNOWN, unknown error
    at Object.fs.writeSync (fs.js:528:18)
    at Object.fs.writeFileSync (fs.js:975:21)

(Also, this doesn’t work on Windows, because Windows doesn’t support /dev/stdout, /dev/stdin and /dev/stderr!)

Shucks. So what should you do?

You could use a different pattern for reading from stdin:

var chunks = [];

process.stdin
    .on("data", function(chunk) { chunks.push(chunk); })
    .on("end", function() { console.log(chunks.join("").length); })
    .setEncoding("utf8");

But that’s a pain, since now your code has two different code paths for reading inputs depending on whether you’re reading a real file or stdin. And the code gets even more complex if you want to read that file synchronously.

You could also try a different pattern for writing to stdout:

process.stdout.write(contents);

Or even:

console.log(contents);

But if you try to pipe your output to head, you’ll get this error:

Error: write EPIPE
    at errnoException (net.js:904:11)
    at Object.afterWrite (net.js:720:19)

Huh.

The rw module fixes these problems. It provides an interface just like readFile, readFileSync, writeFile and writeFileSync, but with implementations that work the way you expect on stdin and stdout. If you use these methods on files other than /dev/stdin or /dev/stdout, they simply delegate to the fs methods, so you can trust that they behave identically to the methods you’re used to.

For example, now you can read stdin synchronously like so:

var contents = rw.readFileSync("/dev/stdin", "utf8");

Or to write to stdout:

rw.writeFileSync("/dev/stdout", contents, "utf8");

And rw automatically squashes EPIPE errors, so you can pipe the output of your program to head and you won’t get a spurious stack trace.

To install, npm install rw.

Note

If you want to read synchronously from stdin using readFileSync, you cannot also use process.stdin in the same program. Likewise, if you want to write synchronously to stdout or stderr using writeFileSync, you cannot use process.stdout or process.stderr, respectively. (This includes using console.log and the like!) Failure to heed this warning may result in error: EAGAIN, resource temporarily unavailable. Unfortunately, it does not appear possible for this library to fix this issue automatically, so please use caution.

Only the asynchronous methods readFile and writeFile are supported on Windows. Node has no synchronous API for reading from process.stdin or writing to process.stdout or process.stderr, so you’re out of luck!

API Reference

# rw.readFile(path[, options], callback)

Reads the file at the specified path completely into memory, invoking the specified callback once the data is available and the file is closed. The callback is invoked with two arguments: the error that occurred during read (hopefully null), and the read data. If options is a string, it specifies the encoding to use, in which case the read data will be a string; otherwise options is an object, and may specify encoding and flag properties. This method is a drop-in replacement for fs.readFile and fixes the behavior of special files such as /dev/stdin.

# rw.readFileSync(path[, options])

Reads the file at the specified path completely into memory, synchronously, returning the data. If an error occurred during read, this function throws an error instead. If options is a string, it specifies the encoding to use, in which case the read data will be a string; otherwise options is an object, and may specify encoding and flag properties. This method is a drop-in replacement for fs.readFileSync and fixes the behavior of special files such as /dev/stdin.

# rw.writeFile(path, data[, options], callback)

Writes the specified data (completely in memory) to a file at the specified path, invoking the specified callback once the data is completely written and the file is closed. The callback is invoked with a single argument: the error that occurred during write (hopefully null). If options is a string, it specifies the encoding to use, in which case the data must be a string; otherwise options is an object, and may specify encoding, mode and flag properties. This method is a drop-in replacement for fs.writeFile and fixes the behavior of special files such as /dev/stdout.

# rw.writeFileSync(path, data[, options])

Writes the specified data (completely in memory) to a file at the specified path, synchronously, returning once the data is completely written and the file is closed. Throws an error if one occurs during write. If options is a string, it specifies the encoding to use, in which case the data must be a string; otherwise options is an object, and may specify encoding, mode and flag properties. This method is a drop-in replacement for fs.writeFileSync and fixes the behavior of special files such as /dev/stdout.

# rw.dash.readFile(path[, options], callback)

Equivalent to rw.readFile, except treats a path of - as /dev/stdin. Useful for command-line arguments.

# rw.dash.readFileSync(path[, options])

Equivalent to rw.readFileSync, except treats a path of - as /dev/stdin. Useful for command-line arguments.

# rw.dash.writeFile(path, data[, options], callback)

Equivalent to rw.writeFile, except treats a path of - as /dev/stdout. Useful for command-line arguments.

# rw.dash.writeFileSync(path, data[, options])

Equivalent to rw.writeFileSync, except treats a path of - as /dev/stdout. Useful for command-line arguments.