tee for splitting output in Linux CLI - Mini Project: Build & Apply

Using tee to Split Command Output

📖 Scenario: You are working on a Linux system and want to save the output of a command to a file while also seeing it on the screen. This is useful when you want to keep a record of what you see without losing the live view.

🎯 Goal: Learn how to use the tee command to split the output of a command so it is both saved to a file and displayed on the terminal.

📋 What You'll Learn

Create a file with some sample text

Use the tee command to save and display output

Understand how to append output to a file using tee

💡 Why This Matters

🌍 Real World

System administrators and developers often need to save logs or command outputs while still monitoring them live on the terminal.

💼 Career

Knowing how to use tee helps in debugging, logging, and monitoring scripts or commands in real time, a common task in IT and DevOps roles.

1

Create a sample text file

Create a file called sample.txt with the exact content: Hello World

Linux CLI

# Create the file sample.txt with the text Hello World
# Your code here

Hint

Use the echo command with redirection > to create the file.

2

Use tee to save and display output

Use the command cat sample.txt | tee output.txt to display the content of sample.txt and save it to output.txt at the same time.

Linux CLI

echo "Hello World" > sample.txt
# Use tee to display and save the content of sample.txt
# Your code here

Hint

The tee command reads from standard input and writes to standard output and files.

3

Append output to the file using tee

Use the command echo "Goodbye" | tee -a output.txt to append the text Goodbye to output.txt and display it on the screen.

Linux CLI

echo "Hello World" > sample.txt
cat sample.txt | tee output.txt
# Append Goodbye to output.txt and display it
# Your code here

Hint

Use the -a option with tee to append instead of overwrite.

4

Display the final content of output.txt

Use the command cat output.txt to display the full content of output.txt.

Linux CLI

echo "Hello World" > sample.txt
cat sample.txt | tee output.txt
echo "Goodbye" | tee -a output.txt
# Display the content of output.txt
# Your code here

Hint

The file output.txt should contain both lines.

Practice

1. What does the tee command do in Linux?

easy

A. It splits the output of a command to both the screen and a file simultaneously.

B. It merges multiple files into one.

C. It deletes files after displaying their content.

D. It changes file permissions.

Solution

1. Step 1: Understand the purpose of tee

   The tee command takes the output of a command and sends it to both the terminal (screen) and a file at the same time.

2. Step 2: Compare options with this behavior

   Only It splits the output of a command to both the screen and a file simultaneously. describes this behavior correctly. Other options describe unrelated actions.

3. Final Answer:

   It splits the output of a command to both the screen and a file simultaneously. -> Option A

4. Quick Check:

   tee splits output = A [OK]

Hint: Remember: tee shows output and saves it simultaneously [OK]

Common Mistakes:

• Thinking tee merges files
• Confusing tee with file deletion
• Assuming tee changes permissions

2. Which of the following is the correct syntax to use tee to save output to a file named log.txt?

easy

A. tee command > log.txt

B. command tee > log.txt

C. command | tee log.txt

D. command > tee log.txt

Solution

1. Step 1: Recall the pipe usage with tee

   The output of a command is piped using | into tee to save it to a file.

2. Step 2: Check each option's syntax

   Only command | tee log.txt uses the correct pipe syntax: command | tee log.txt. Others misuse redirection or order.

3. Final Answer:

   command | tee log.txt -> Option C

4. Quick Check:

   Pipe output to tee = D [OK]

Hint: Use pipe (|) before tee to split output [OK]

Common Mistakes:

• Using > before tee instead of pipe
• Placing tee before command
• Confusing redirection with tee syntax

3. What will be the output on the screen and in the file output.txt after running this command?

echo "Hello World" | tee output.txt

medium

A. Screen: Hello WorldFile output.txt: Hello World

B. Screen: (empty)File output.txt: Hello World

C. Screen: Hello WorldFile output.txt: (empty)

D. Screen: (empty)File output.txt: (empty)

Solution

1. Step 1: Understand echo piped to tee

   The echo command outputs "Hello World" which is piped to tee. Tee writes it to the file and also outputs it to the screen.

2. Step 2: Determine output locations

   Both the screen and the file output.txt will contain "Hello World".

3. Final Answer:

   Screen: Hello World; File output.txt: Hello World -> Option A

4. Quick Check:

   tee duplicates output to screen and file = B [OK]

Hint: tee shows output on screen and saves to file simultaneously [OK]

Common Mistakes:

• Assuming tee only writes to file
• Thinking tee suppresses screen output
• Confusing echo output with tee behavior

4. You want to append output to log.txt instead of overwriting it. Which command fixes the error in this script?

ls -l | tee log.txt

medium

A. ls -l > tee -a log.txt

B. ls -l | tee > log.txt

C. tee -a ls -l log.txt

D. ls -l | tee -a log.txt

Solution

1. Step 1: Identify the need to append output

   The default tee overwrites files. To append, use the -a option.

2. Step 2: Check correct syntax for appending

   ls -l | tee -a log.txt correctly uses tee -a log.txt with pipe from ls -l. Others misuse redirection or order.

3. Final Answer:

   ls -l | tee -a log.txt -> Option D

4. Quick Check:

   Use -a with tee to append = C [OK]

Hint: Add -a option to tee to append instead of overwrite [OK]

Common Mistakes:

• Using > redirection with tee incorrectly
• Placing tee before command
• Forgetting the -a option for append

5. You want to run a script that outputs system info and save it to sysinfo.log while still seeing it live on screen. You also want to keep adding to the log without erasing old data. Which command achieves this?

hard

A. uname -a | tee sysinfo.log

B. uname -a | tee -a sysinfo.log

C. tee -a sysinfo.log | uname -a

D. uname -a > tee -a sysinfo.log

Solution

1. Step 1: Understand the requirement to append and show output

   The command must show output on screen and append to the file without overwriting.

2. Step 2: Identify correct tee usage

   uname -a | tee -a sysinfo.log uses tee -a sysinfo.log with pipe from uname -a, which appends and shows output live.

3. Step 3: Eliminate incorrect options

   uname -a | tee sysinfo.log overwrites file. Options C and D misuse command order and redirection.

4. Final Answer:

   uname -a | tee -a sysinfo.log -> Option B

5. Quick Check:

   Pipe output to tee -a to append and show = A [OK]

Hint: Use pipe and tee -a to append and display output live [OK]

Common Mistakes:

• Forgetting -a causes overwrite
• Placing tee before command
• Using > redirection incorrectly with tee