tee for splitting output in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the tee command do in Linux?

The tee command reads from standard input and writes the output to both standard output (screen) and one or more files at the same time.

beginner

How do you use tee to append output to a file instead of overwriting it?

Use the -a option with tee. For example: command | tee -a filename appends the output to filename.

beginner

Why is tee useful when running commands in the terminal?

tee lets you see the output on the screen and save it to a file at the same time. This is like watching a live TV show while recording it for later.

beginner

What happens if you run ls | tee file.txt?

The list of files from ls will be shown on the screen and also saved into file.txt. You get both at once.

intermediate

Can tee write to multiple files at once? How?

Yes. You can list multiple files after tee. For example: command | tee file1.txt file2.txt writes the output to both files and the screen.

What does the tee command do?

A Splits output to screen and file(s)

B Deletes files

C Changes file permissions

D Compresses files

tee sends output to both the screen and one or more files.

How do you append output to a file using tee?

A Use <code>-d</code> option

B Use <code>-o</code> option

C Use <code>-a</code> option

D Use <code>-r</code> option

The -a option appends output instead of overwriting.

Which command shows output on screen and saves it to log.txt?

A command | tee log.txt

B command > log.txt

C command >> log.txt

D tee command log.txt

Using tee after a pipe sends output to screen and file.

Can tee write to multiple files at once?

A No, it only writes to screen

B No, only one file at a time

C Yes, but only with <code>-m</code> option

D Yes, by listing files after <code>tee</code>

You can specify multiple files after tee to write output to all.

What will ls | tee file.txt do?

A Only save files to file.txt

B Show files on screen and save to file.txt

C Only show files on screen

D Delete file.txt

Output goes to both screen and file.txt with tee.

Explain how the tee command helps when you want to see command output and save it at the same time.

Think about watching and recording a live show.

Describe how to use tee to append output to a file and why this might be useful.

Appending is like adding pages to a notebook without erasing old pages.

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