cat (display file contents) in Linux CLI - Mini Project: Build & Apply

Display File Contents Using cat Command

📖 Scenario: You are working on a Linux system and want to quickly see what is inside a text file. The cat command helps you display the contents of files right in the terminal.

🎯 Goal: Learn how to use the cat command to display the contents of a file named example.txt.

📋 What You'll Learn

Create a file named example.txt with specific content

Use the cat command to display the file contents

💡 Why This Matters

🌍 Real World

Viewing file contents quickly in the terminal is common when checking logs, configuration files, or any text data.

💼 Career

System administrators, developers, and anyone working with Linux servers use cat daily to inspect files.

1

Create the file example.txt

Create a file named example.txt with the exact content: Hello, this is a test file.

Linux CLI

# Use the echo command to create example.txt with the text
# Your code here

Hint

You can use echo "text" > filename to create a file with text.

2

Check the file exists

Use the ls command to list files and confirm example.txt exists.

Linux CLI

echo "Hello, this is a test file." > example.txt
# Use ls to check example.txt is present
# Your code here

Hint

Use ls example.txt to check the file.

3

Display the contents of example.txt

Use the cat command with example.txt to display its contents.

Linux CLI

echo "Hello, this is a test file." > example.txt
ls example.txt
# Use cat to show the contents of example.txt
# Your code here

Hint

Type cat example.txt to see the file content.

4

View the output of the cat command

Run the script and observe the output. It should display exactly: Hello, this is a test file.

Linux CLI

echo "Hello, this is a test file." > example.txt
ls example.txt
cat example.txt
# Run the commands and see the output

Hint

The last line printed should be the file content.

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