CODEWITHSUNDEEP
node.jsfs
Shuai Li
Shuai Li

Reputation: 2776

How does fs.readFile(<Buffer> | <integer) work?

We can give a string arg to fs.readFile to represent a file path

fs.readFile('/etc/passwd', (err, data) => {
  if (err) throw err;
  console.log(data);
});

But I notice the offical documentation said:

fs.readFile(path[, options], callback)

path can be a Buffer or an integer. Then I try 

const fs = require('fs')

fs.readFile(1, (err, data) => {
  if (err) throw err;
  console.log(data);
});

Then it throw an error.

I am really confused, how this arg can be a integer? Can anybody gives a example?

Upvotes: 2

Views: 1428

Answers (2)

Amit Beckenstein
Amit Beckenstein

Reputation: 1332

According to the official documentation: path is either string or Buffer or URL or integer, and the description of the parameter is: "filename or file descriptor".

  • string | Buffer | URL - path is treated as a filename (something like "/path/to/your/file")

  • integer - path is treated as a file descriptor.

So if you pass an integer, NodeJS accesses the file by the file descriptor.

Read more about how NodeJS handles file descriptors.

Upvotes: 1

robertklep
robertklep

Reputation: 203514

The integer argument that you can pass should represent a valid file descriptor. For example, stdin typically has file descriptor 0, so to read a "file" from stdin you can use this:

fs.readFile(0, (err, data) => {
  if (err) throw err;
  console.log(data);
});

Instead of 0, you can also use process.stdin.fd.

Another way to get a file descriptor is to use fs.open().

Upvotes: 3

Related Questions