exec for running shell commands in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the exec function in Node.js?

The exec function runs shell commands from a Node.js script, letting you execute system commands and get their output.

beginner

Which Node.js module provides the exec function?

The child_process module provides the exec function to run shell commands.

intermediate

What are the three main arguments of exec(command, options, callback)?

1. command: The shell command string to run.<br>2. options: Optional settings like environment variables.<br>3. callback: Function called with error, stdout, and stderr after command finishes.

intermediate

How do you handle errors when using exec?

Check if the error argument in the callback is set. If yes, the command failed or had issues. You can then handle or log the error.

beginner

What is a simple example of using exec to list files in the current directory?

const { exec } = require('child_process');
exec('ls', (error, stdout, stderr) => {
  if (error) {
    console.error(`Error: ${error.message}`);
    return;
  }
  if (stderr) {
    console.error(`Stderr: ${stderr}`);
    return;
  }
  console.log(`Files:\n${stdout}`);
});

Which module must you import to use exec in Node.js?

A http

B fs

C os

D child_process

The exec function is part of the child_process module.

What does the exec callback receive as arguments?

A error, stdout, stderr

B stdout, stderr, error

C command, options, callback

D input, output, error

The callback receives error, stdout, and stderr in that order.

If a shell command run by exec fails, where will the error info appear?

A In the <code>error</code> argument of the callback

B In the <code>stdout</code> argument

C In the <code>options</code> argument

D In the <code>command</code> string

Errors are passed as the first argument error in the callback.

Which of these is a correct way to run the pwd command using exec?

A exec('pwd', (stdout, stderr) => { console.log(stdout); });

B exec('pwd', (err) => { console.log(err); });

C exec('pwd', (err, stdout) => { console.log(stdout); });

D exec('pwd', (error, output) => { console.log(output); });

The callback receives error first, then stdout. Option C uses correct argument order.

What is a common use case for exec in Node.js?

A Manipulating arrays

B Running system shell commands and getting their output

C Creating HTTP servers

D Reading files from disk

exec is used to run shell commands and capture their output.

Explain how to use exec to run a shell command and handle its output and errors.

Think about the three arguments in the callback and how to safely use them.

Describe a simple example where exec is used to list files in a directory and print them.

Remember the common 'ls' command and how to handle callback arguments.