ls (list files and directories) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of ls -l in a directory with one file named file.txt?

You run the command ls -l in a directory containing a single file named file.txt. What will the output look like?

Linux CLI

ls -l

A

total 0
-rw-r--r-- 1 user user 0 Apr 27 12:00 file.txt

B -rw-r--r-- 1 user user 0 Apr 27 12:00 file.txt

C

total 1
-rw-r--r-- 1 user user 0 Apr 27 12:00 file.txt

D file.txt

💡 Hint

The -l option shows detailed info including permissions, owner, size, and date.

The ls -l command lists files with detailed info. It starts with a line showing total blocks (usually 0 or more), then one line per file with permissions, links, owner, group, size, date, and name.

💻 Command Output

intermediate

What does ls -a show in a directory with files file1, .hidden?

You run ls -a in a directory containing two files: file1 and .hidden. What will the output be?

Linux CLI

ls -a

A file1

B file1 .hidden

C .hidden

D . .. file1 .hidden

💡 Hint

The -a option shows all files, including hidden and special entries.

The ls -a command lists all files including hidden files (those starting with a dot) and the special entries . (current directory) and .. (parent directory).

📝 Syntax

advanced

Which ls command lists files sorted by modification time, newest first?

You want to list files sorted by modification time, newest first. Which command is correct?

A ls -ltr

B ls -lt

C ls -ltu

D ls -lS

💡 Hint

The -t option sorts by modification time, -r reverses order.

ls -lt lists files in long format sorted by modification time, newest first. Adding -r reverses order (oldest first). -lS sorts by size, -ltu sorts by access time.

🔧 Debug

advanced

Why does ls -l /nonexistent produce an error?

You run ls -l /nonexistent but get an error message. What is the reason?

A The -l option is invalid with absolute paths

B You need root permissions to list /nonexistent

C The directory /nonexistent does not exist

D The command requires a trailing slash on directories

💡 Hint

Check if the directory exists before listing.

The error occurs because the directory /nonexistent does not exist. ls cannot list files in a directory that is missing.

🚀 Application

expert

How to list only directories in current folder using ls and shell features?

You want to list only directories (not files) in the current folder using ls combined with shell commands. Which command achieves this?

A ls -d */

B ls -l | grep '^d'

C ls -a | grep -v '^-'

D ls -F | grep '/'

💡 Hint

The -d option lists directories themselves, and */ matches directories.

ls -d */ lists only directories in the current folder by matching names ending with a slash. Other options may list files or rely on parsing output which can be unreliable.

Practice

1. What does the ls command do in Linux?

easy

A. Creates a new directory

B. Deletes files from the current folder

C. Lists files and directories in the current folder

D. Moves files to another folder

Solution

1. Step 1: Understand the purpose of ls

   The ls command is used to show what files and folders are inside a directory.

2. Step 2: Identify the correct description

   Among the options, only listing files and directories matches what ls does.

3. Final Answer:

   Lists files and directories in the current folder -> Option C

4. Quick Check:

   ls = list files [OK]

Hint: Remember: ls = list files and folders [OK]

Common Mistakes:

• Confusing ls with commands like rm or mkdir
• Thinking ls deletes or moves files
• Assuming ls creates directories

2. Which of these is the correct syntax to list all files including hidden ones in a directory?

easy

A. ls -l

B. ls -r

C. ls -h

D. ls -a

Solution

1. Step 1: Recall option meanings for ls

   -a shows all files including hidden (those starting with a dot).

2. Step 2: Match option to requirement

   Only ls -a lists hidden files; others do different things like long format or reverse order.

3. Final Answer:

   ls -a -> Option D

4. Quick Check:

   -a means all files [OK]

Hint: Use -a to see hidden files starting with . [OK]

Common Mistakes:

• Using -l instead of -a to see hidden files
• Confusing -r (reverse) with -a
• Thinking -h shows hidden files

3. What will be the output of the command ls -l /tmp if the /tmp directory contains two files named file1.txt and file2.log?

medium

A. file1.txt file2.log

B. Detailed list showing permissions, owner, size, and date for file1.txt and file2.log

C. Only hidden files in /tmp

D. An error saying /tmp does not exist

Solution

1. Step 1: Understand -l option with ls

   The -l option shows a detailed list including permissions, owner, size, and modification date.

2. Step 2: Apply to /tmp directory contents

   Since /tmp has two files, the command will show detailed info lines for both files.

3. Final Answer:

   Detailed list showing permissions, owner, size, and date for file1.txt and file2.log -> Option B

4. Quick Check:

   ls -l = detailed list [OK]

Hint: -l means long detailed listing [OK]

Common Mistakes:

• Expecting just filenames without details
• Thinking it lists only hidden files
• Assuming it shows an error if directory exists

4. You run ls -la /home/user but get an error: ls: cannot access '/home/user': No such file or directory. What is the most likely cause?

medium

A. /home/user directory does not exist

B. You forgot to add the -a option

C. You need to run the command as root

D. The ls command is misspelled

Solution

1. Step 1: Analyze the error message

   The error says the directory '/home/user' cannot be accessed because it does not exist.

2. Step 2: Check other options

   Options -a and running as root do not cause this error; misspelling ls would cause a different error.

3. Final Answer:

   /home/user directory does not exist -> Option A

4. Quick Check:

   Directory missing = cannot access error [OK]

Hint: Check if directory exists before blaming options [OK]

Common Mistakes:

• Assuming missing -a causes error
• Thinking root is always needed
• Confusing command misspelling with directory missing

5. You want to list all files in the directory /var/log sorted by modification time, newest first, including hidden files. Which command should you use?

hard

A. ls -lat /var/log

B. ls -ltr /var/log

C. ls -al /var/log

D. ls -lh /var/log

Solution

1. Step 1: Identify options needed

   -a shows hidden files, -t sorts by modification time, newest first, and -l gives detailed listing.

2. Step 2: Match options to command

   Only ls -lat /var/log combines all needed options correctly.

3. Final Answer:

   ls -lat /var/log -> Option A

4. Quick Check:

   -lat = list all, sort by time [OK]

Hint: Use -lat to list all files sorted by time [OK]

Common Mistakes:

• Using -ltr which sorts oldest first
• Forgetting -a to show hidden files
• Using -lh which shows size but not sorting