cat (display file contents) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command?

You have a file named example.txt with the following content:

Hello
World

What will be the output of the command cat example.txt?

Linux CLI

cat example.txt

A

Hello
World

B Hello World

C Hello\nWorld

D example.txt

💡 Hint

The cat command prints the file content exactly as it is.

The cat command outputs the content of the file preserving line breaks. So it prints 'Hello' on the first line and 'World' on the second line.

💻 Command Output

intermediate

What happens when you use cat on multiple files?

You have two files:
file1.txt contains:

Apple

file2.txt contains:

Banana

What is the output of cat file1.txt file2.txt?

Linux CLI

cat file1.txt file2.txt

A AppleBanana

B Apple\nBanana

C

Apple
Banana

D file1.txt file2.txt

💡 Hint

The cat command concatenates files and prints their contents in order.

The command prints the content of file1.txt followed by the content of file2.txt, preserving line breaks.

💻 Command Output

advanced

What is the output of this command with a non-existent file?

What happens when you run cat missing.txt if missing.txt does not exist?

Linux CLI

cat missing.txt

A No output, command succeeds silently

B Syntax error

C missing.txt

D cat: missing.txt: No such file or directory

💡 Hint

Try to think what happens when a file is not found.

The cat command prints an error message to standard error if the file does not exist.

💻 Command Output

advanced

What is the output of this command with input redirection?

What will be the output of cat < file.txt if file.txt contains:

Line1
Line2

?

Linux CLI

cat < file.txt

A

Line1
Line2

B Line1\nLine2

C Line1 Line2

D Error: invalid syntax

💡 Hint

Input redirection feeds the file content to the command as standard input.

Using input redirection, cat reads from the file and outputs its content preserving line breaks.

🧠 Conceptual

expert

How many lines will this command output?

You run the command cat fileA.txt fileB.txt | wc -l.

fileA.txt has 3 lines, fileB.txt has 5 lines.

What is the output number?

A 3

B 8

C 5

D 1

💡 Hint

The pipe sends combined output of both files to wc -l which counts lines.

The cat command concatenates both files, so total lines are 3 + 5 = 8. The wc -l counts these lines.

Practice

1. What does the cat command do in Linux?

easy

A. Deletes a file permanently

B. Displays the contents of a file on the terminal

C. Changes file permissions

D. Creates a new directory

Solution

1. Step 1: Understand the purpose of cat

   The cat command is used to read and display the contents of files in the terminal.

2. Step 2: Compare with other options

   Deleting files, changing permissions, or creating directories are done by other commands like rm, chmod, and mkdir.

3. Final Answer:

   Displays the contents of a file on the terminal -> Option B

4. Quick Check:

   cat shows file contents [OK]

Hint: Remember: cat = concatenate and show file content [OK]

Common Mistakes:

• Confusing cat with rm or mkdir
• Thinking cat edits files
• Assuming cat deletes files

2. Which of the following is the correct syntax to display the contents of a file named notes.txt using cat?

easy

A. cat notes.txt

B. cat -f notes.txt

C. cat > notes.txt

D. cat -r notes.txt

Solution

1. Step 1: Identify the basic syntax of cat

   The basic command to display a file is cat filename, so cat notes.txt is correct.

2. Step 2: Understand incorrect options

   -f and -r are not valid options for cat. The cat > filename syntax is used to create or overwrite a file, not display it.

3. Final Answer:

   cat notes.txt -> Option A

4. Quick Check:

   Basic syntax is cat filename [OK]

Hint: Use just 'cat filename' to show file content [OK]

Common Mistakes:

• Adding invalid options like -f or -r
• Using > which overwrites files
• Confusing cat with other commands

3. What will be the output of the command cat -n file.txt if file.txt contains:

Hello
World

medium

A. Hello
World

B. Hello 1
World 2

C. Error: invalid option

D. 1 Hello
2 World

Solution

1. Step 1: Understand the -n option

   The -n option numbers each line of the output when displaying file contents.

2. Step 2: Apply numbering to each line

   Given the file has two lines: "Hello" and "World", the output will prefix each line with its line number: "1 Hello" and "2 World".

3. Final Answer:

   1 Hello 2 World -> Option D

4. Quick Check:

   cat -n adds line numbers [OK]

Hint: Use -n to add line numbers to output [OK]

Common Mistakes:

• Ignoring line numbers
• Placing numbers after text
• Thinking -n is invalid

4. You run cat file1.txt file2.txt but get an error: cat: file2.txt: No such file or directory. What is the most likely cause?

medium

A. You used the wrong command syntax

B. file1.txt is empty

C. file2.txt does not exist in the current directory

D. You do not have permission to read file1.txt

Solution

1. Step 1: Analyze the error message

   The error says file2.txt is missing, so the system cannot find it in the current directory.

2. Step 2: Check other options

   Empty file1.txt or permission issues on file1.txt would not cause this error. The syntax is correct for displaying multiple files.

3. Final Answer:

   file2.txt does not exist in the current directory -> Option C

4. Quick Check:

   Missing file causes 'No such file' error [OK]

Hint: Check file existence if 'No such file' error appears [OK]

Common Mistakes:

• Assuming syntax error
• Ignoring missing file
• Blaming permissions wrongly

5. You want to combine the contents of chapter1.txt and chapter2.txt into a new file book.txt. Which command correctly does this using cat?

hard

A. cat chapter1.txt chapter2.txt > book.txt

B. cat > chapter1.txt chapter2.txt > book.txt

C. cat chapter1.txt > chapter2.txt > book.txt

D. cat book.txt > chapter1.txt chapter2.txt

Solution

1. Step 1: Understand output redirection with cat

   The command cat file1 file2 > newfile concatenates file1 and file2 contents and writes to newfile.

2. Step 2: Analyze each option

   cat chapter1.txt chapter2.txt > book.txt correctly concatenates chapter1.txt and chapter2.txt into book.txt. Options A, C, and D misuse redirection or file order, causing errors or overwrites.

3. Final Answer:

   cat chapter1.txt chapter2.txt > book.txt -> Option A

4. Quick Check:

   Use cat file1 file2 > newfile to combine files [OK]

Hint: Use > after files to save combined output [OK]

Common Mistakes:

• Misplacing > causing overwrite
• Using > multiple times incorrectly
• Confusing input and output files