exec for running shell commands in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the exec function from the child_process module.

Node.js

const { [1] } = require('child_process');

Drag options to blanks, or click blank then click option'

Afork

Bspawn

Cexec

DexecFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using spawn instead of exec

Trying to import the whole module without destructuring

Using execFile which is different

The exec function is imported from the child_process module to run shell commands.

2fill in blank

medium

Complete the code to run the shell command 'ls -l' using exec.

Node.js

exec('[1]', (error, stdout, stderr) => {
  if (error) {
    console.error(`Error: ${error.message}`);
    return;
  }
  console.log(stdout);
});

Drag options to blanks, or click blank then click option'

Aecho Hello

Bls -l

Cpwd

Ddir

Attempts:

3 left

💡 Hint

Common Mistakes

Using Windows command 'dir' on Unix

Using 'pwd' which shows current directory only

Using 'echo Hello' which just prints text

The command ls -l lists files in long format on Unix-like systems.

3fill in blank

hard

Fix the error in the callback parameters to correctly handle exec output.

Node.js

exec('node -v', ([1]) => {
  if (error) {
    console.error(error);
    return;
  }
  console.log(stdout);
});

Drag options to blanks, or click blank then click option'

Aerror, stdout, stderr

Berr, output

Cerror

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using only one parameter and missing stdout

Using wrong parameter names

Not handling stderr

The callback for exec receives three parameters: error, stdout, and stderr.

4fill in blank

hard

Fill both blanks to run 'echo Hello' and print the output or error.

Node.js

exec('[1]', (error, [2], stderr) => {
  if (error) {
    console.error(`Error: ${error.message}`);
    return;
  }
  console.log([2]);
});

Drag options to blanks, or click blank then click option'

Aecho Hello

Bstdout

Coutput

Dls

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong command

Using wrong variable name for output

Ignoring error handling

The command is echo Hello and the output is in stdout.

5fill in blank

hard

Fill all three blanks to run 'cat file.txt', handle errors, and print output.

Node.js

exec('[1]', ([2], [3], stderr) => {
  if ([2]) {
    console.error(`Error: $[2].message}`);
    return;
  }
  console.log([3]);
});

Drag options to blanks, or click blank then click option'

Acat file.txt

Berror

Cstdout

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong command like 'ls' instead of 'cat'

Mixing up error and output parameters

Not checking for error before printing output

The command cat file.txt reads the file content. The callback parameters are error and stdout for output.

Practice

1. What does the exec function in Node.js primarily do?

easy

A. Runs shell commands from within a Node.js program

B. Creates a new HTTP server

C. Reads files from the filesystem

D. Starts a database connection

Solution

1. Step 1: Understand the purpose of exec

   The exec function is designed to run shell commands from Node.js code.

2. Step 2: Compare with other options

   Creating servers, reading files, or database connections are unrelated to exec.

3. Final Answer:

   Runs shell commands from within a Node.js program -> Option A

4. Quick Check:

   exec runs shell commands = B [OK]

Hint: Remember exec runs shell commands, not servers or files [OK]

Common Mistakes:

• Confusing exec with file reading functions
• Thinking exec creates servers
• Assuming exec manages databases

2. Which is the correct way to import and use exec from the child_process module in Node.js?

easy

A. import exec from 'child_process';

B. const exec = require('child_process').exec;

C. const exec = require('exec');

D. import { exec } from 'child_process';

Solution

1. Step 1: Recall Node.js import syntax for exec

   In Node.js CommonJS, exec is imported as const exec = require('child_process').exec;.

2. Step 2: Check other options for correctness

   import exec from 'child_process'; uses ES module default import incorrectly; const exec = require('exec'); tries to require a non-existent module; import { exec } from 'child_process'; is ES module named import but Node.js needs special config.

3. Final Answer:

   const exec = require('child_process').exec; -> Option B

4. Quick Check:

   CommonJS import for exec = A [OK]

Hint: Use require('child_process').exec for standard Node.js [OK]

Common Mistakes:

• Using import without Node.js ES module setup
• Requiring wrong module name
• Confusing default and named imports

3. What will the following Node.js code output if the current directory contains a file named test.txt?

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(`Output: ${stdout}`);
});

medium

A. Output: test.txt

B. Error: ls command not found

C. Stderr: Permission denied

D. No output

Solution

1. Step 1: Understand exec running 'ls'

   The command ls lists files in the current directory. If test.txt exists, it will appear in the output.

2. Step 2: Analyze callback behavior

   No error or stderr means output is printed with file names, so console logs 'Output: test.txt\n'.

3. Final Answer:

   Output: test.txt -> Option A

4. Quick Check:

   exec runs ls, outputs files = A [OK]

Hint: exec callback logs stdout if no error or stderr [OK]

Common Mistakes:

• Assuming error if command runs successfully
• Ignoring stdout content
• Confusing stderr with stdout

4. Identify the error in this Node.js code using exec:

const { exec } = require('child_process');
exec('node -v', (error, stdout, stderr) => {
  if (error) {
    console.log(error);
  }
  console.log(stdout);
});

medium

A. Callback function has wrong parameters

B. Incorrect command syntax for node version

C. Missing error return causes stdout to print even on error

D. exec is not imported correctly

Solution

1. Step 1: Check error handling logic

   The code logs error but does not return or stop, so stdout logs even if error occurs.

2. Step 2: Understand impact of missing return

   This can cause confusing output mixing error and stdout, which is not ideal.

3. Final Answer:

   Missing error return causes stdout to print even on error -> Option C

4. Quick Check:

   Missing error return causes stdout to print even on error = D [OK]

Hint: Return after error to avoid printing stdout [OK]

Common Mistakes:

• Not returning after error check
• Assuming exec import is wrong
• Thinking command syntax is incorrect

5. You want to run a shell command that lists all files but only print those containing the word 'log'. Which exec usage correctly achieves this in Node.js?

hard

A. exec('ls > grep log', (err, stdout) => { if (!err) console.log(stdout); });

B. exec('ls && grep log', (err, stdout) => { if (!err) console.log(stdout); });

C. exec('ls | find log', (err, stdout) => { if (!err) console.log(stdout); });

D. exec('ls | grep log', (err, stdout) => { if (!err) console.log(stdout); });

Solution

1. Step 1: Understand shell command chaining

   The pipe | sends output of ls to grep log to filter lines containing 'log'.

2. Step 2: Evaluate each option's command

   ls | grep log correctly pipes output to grep for filtering; ls > grep log uses redirection to create a file; ls && grep log runs sequentially without piping; ls | find log pipes to filesystem search tool unsuitable for text filtering.

3. Final Answer:

   exec('ls | grep log', (err, stdout) => { if (!err) console.log(stdout); }); -> Option D

4. Quick Check:

   Pipe output to grep for filtering = C [OK]

Hint: Use pipe (|) to filter command output with grep [OK]

Common Mistakes:

• Using && instead of | for piping output
• Misusing redirection operators
• Confusing grep with find command