tee for splitting output in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of tee command?

Consider the command:
echo "Hello World" | tee file.txt
What will be the output on the terminal?

Linux CLI

echo "Hello World" | tee file.txt

A file.txt

B Hello World

C No output

D Error: tee command not found

💡 Hint

tee prints the input to both the file and the terminal.

The tee command reads from standard input and writes to standard output and files. So the text is shown on the terminal and saved to file.txt.

💻 Command Output

intermediate

What happens when tee is used with -a option?

Given the command:
echo "New Line" | tee -a file.txt
What is the effect on file.txt?

Linux CLI

echo "New Line" | tee -a file.txt

A file.txt is overwritten with 'New Line'

B file.txt is deleted

C file.txt is appended with 'New Line'

D Error: invalid option -a

💡 Hint

The -a option means append.

The -a option tells tee to append the output to the file instead of overwriting it.

💻 Command Output

advanced

What is the output of tee with multiple files?

What will be the result of:
echo "Data" | tee file1.txt file2.txt
on the terminal and files?

Linux CLI

echo "Data" | tee file1.txt file2.txt

A Outputs 'Data' on terminal and writes to file1.txt and file2.txt

B Outputs 'Data' only on terminal, files remain empty

C Writes 'Data' only to file1.txt, no terminal output

D Error: tee accepts only one file

💡 Hint

tee can write to multiple files at once.

tee writes the input to standard output and all specified files.

💻 Command Output

advanced

What error occurs with invalid tee usage?

What error message appears when running:
echo "Test" | tee -z file.txt?

Linux CLI

echo "Test" | tee -z file.txt

A tee: invalid option -- 'z'

B Test

C No output, no error

D file.txt contains 'Test'

💡 Hint

Invalid options cause an error message.

The -z option is not valid for tee, so it prints an invalid option error.

🚀 Application

expert

How to save and display command output simultaneously?

You want to run ls -l and save its output to listing.txt while also seeing it on the terminal. Which command achieves this?

A ls -l >> listing.txt

B ls -l > listing.txt

C tee listing.txt < ls -l

D ls -l | tee listing.txt

💡 Hint

tee duplicates output to file and terminal.

Using tee after the pipe sends output to both the file and terminal.

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