Day 2 Quiz & Exercises#

TDS Bridge Bootcamp — Linux & Shell Essentials#

Instructions: Attempt the MCQs without help first. Then do the terminal exercises. The exercises build on each other — do them in order.

Part A — 20 Multiple Choice Questions#

Q1. You type python in the terminal and get “command not found”. Your friend on the same machine has no problem. What is the most likely cause?

  • A) Python is not installed on the system
  • B) Python is installed but its folder is not in your PATH
  • C) You need to use sudo python
  • D) Your terminal is the wrong type
Answer

B — Your PATH doesn’t include Python’s folder

Q2. You run echo $? after a command and see 0. What does this mean?

  • A) The command produced no output
  • B) The command ran successfully
  • C) The command is still running
  • D) There was an error
Answer

B — Exit code 0 = success

Q3. What does tail -f server.log do?

  • A) Deletes the last line of the file
  • B) Shows the last 10 lines and then exits
  • C) Continuously shows new lines as they are added to the file
  • D) Filters the file for lines containing “tail”
Answer

C — -f follows the file live; useful for server logs

Q4. You want to count the number of lines in a file called data.csv. Which command is correct?

  • A) count data.csv
  • B) wc -w data.csv
  • C) wc -l data.csv
  • D) len data.csv
Answer

C — -l counts lines; -w counts words

Q5. Which grep flag makes the search case-insensitive?

  • A) -c
  • B) -n
  • C) -v
  • D) -i
Answer

D — -i = case-insensitive

Q6. You run grep -v "ERROR" app.log. What does this return?

  • A) Only lines containing “ERROR”
  • B) A count of lines containing “ERROR”
  • C) All lines that do NOT contain “ERROR”
  • D) An error because -v is invalid
Answer

C — -v inverts the match — returns non-matching lines

Q7. What is the difference between these two commands?

grep "WARN" app.log > warnings.txt
grep "WARN" app.log >> warnings.txt
  • A) No difference — both do the same thing
  • B) The first overwrites warnings.txt; the second appends to it
  • C) The first appends; the second overwrites
  • D) The second command will fail if the file already exists
Answer

B — > overwrites; >> appends

Q8. You want to see error messages from a Python script separately from its normal output. Which command does this?

  • A) python script.py > all.txt
  • B) python script.py 2> errors.txt
  • C) python script.py | errors.txt
  • D) python script.py >> errors.txt
Answer

B — 2> redirects stderr (error stream)

Q9. What does the pipe | do?

  • A) Saves the output of a command to a file
  • B) Runs two commands at the same time in parallel
  • C) Sends the output of one command as input to the next
  • D) Compares the output of two commands
Answer

C — Pipe feeds stdout of left command into stdin of right

Q10. You run:

cat words.txt | sort | uniq -c | sort -rn | head -10

What does this pipeline produce?

  • A) The 10 shortest lines in the file
  • B) The 10 most frequently occurring lines/words, sorted by count
  • C) 10 random lines from the file
  • D) The alphabetically first 10 unique lines
Answer

B — uniq -c counts; sort -rn sorts by count descending

Q11. Which nano shortcut saves a file?

  • A) Ctrl+S
  • B) Ctrl+O then Enter
  • C) Ctrl+X then Enter
  • D) Esc + :w
Answer

B — Ctrl+O writes (saves); Ctrl+X exits

Q12. You accidentally open a file in vim. You haven’t changed anything. How do you exit?

  • A) Ctrl+C
  • B) Ctrl+Z
  • C) Press Esc, then type :q! and press Enter
  • D) Close the terminal window
Answer

C — :q! force-quits vim without saving

Q13. What is the correct way to copy a folder called project/ (and all its contents) to backup/?

  • A) cp project/ backup/
  • B) cp -r project/ backup/
  • C) mv project/ backup/
  • D) copy -all project/ backup/
Answer

B — -r is required to copy directories recursively

Q14. You run rm -r myfolder/. What happens?

  • A) The folder is moved to the Recycle Bin
  • B) Only empty folders inside are removed
  • C) The folder and all its contents are permanently deleted
  • D) You’ll be asked to confirm each file before deletion
Answer

C — rm -r is permanent — no recycle bin

Q15. You add this line to .bashrc:

MY_KEY="abc123"

Then open a new terminal and run echo $MY_KEY. What do you see?

  • A) abc123 — the variable is available
  • B) Nothing — you forgot export
  • C) An error — variables cannot be stored in .bashrc
  • D) MY_KEY — the name is printed, not the value
Answer

B — Without export, the variable isn’t inherited by child processes or new shells

Q16. What is the correct command to apply changes you just made to .bashrc without closing the terminal?

  • A) reload ~/.bashrc
  • B) bash ~/.bashrc
  • C) source ~/.bashrc
  • D) apply ~/.bashrc
Answer

C — source re-executes the file in the current shell

Q17. What is the difference between these two lines?

MY_VAR="hello"
export MY_VAR="hello"
  • A) No difference
  • B) The first sets the variable only for the current shell; export also makes it available to programs launched from this shell
  • C) export saves the variable permanently; the first only lasts for this command
  • D) The first works in Bash; export only works in zsh
Answer

B — export shares the variable with child processes

Q18. In Python, you want to read an API key stored as an environment variable called API_KEY. Which code is correct?

  • A) api_key = "API_KEY"
  • B) api_key = env.get("API_KEY")
  • C) api_key = os.environ["API_KEY"]
  • D) api_key = os.getenv.API_KEY
Answer

C — os.environ["KEY"] is the standard way

Q19. You run ls -la and see a file called .env. What is true about this file?

  • A) It is a system file you should never touch
  • B) It is hidden because its name starts with .
  • C) It is an error — filenames can’t start with .
  • D) It will not appear with ls -la
Answer

B — Dot-prefixed files are hidden; ls -la reveals them

Q20. You want to search all .py files in ~/tds/ for the word import. Which command works?

  • A) grep "import" ~/tds/
  • B) grep -r "import" ~/tds/
  • C) find "import" ~/tds/*.py
  • D) cat ~/tds/**/*.py | grep "import"
Answer

B — -r searches recursively through directories

Q21. Which command shows the current user logged into the terminal?

  • A) whoami
  • B) user
  • C) name
  • D) id -u
Answer

A — whoami prints the current user.

Q22. What does chmod +x script.sh do?

  • A) Deletes the script
  • B) Makes the script executable
  • C) Hides the script
  • D) Copies the script
Answer

B — +x adds execute permission.

Q23. How do you view the manual/help page for the ls command?

  • A) ls --help or man ls
  • B) help ls
  • C) info ls
  • D) All of the above
Answer

A — man ls or ls --help are the standard ways.

Q24. You want to clear the terminal screen. What command or shortcut works?

  • A) clear or Ctrl+L
  • B) clean
  • C) cls
  • D) reset
Answer

A — clear or Ctrl+L clears the screen.

Q25. What is the purpose of the sudo command?

  • A) To switch users
  • B) To run a command with superuser (administrator) privileges
  • C) To install software
  • D) To shutdown the system
Answer

B — sudo executes a command as root/superuser.

Q26. What does df -h show?

  • A) Disk space usage in human-readable format
  • B) Memory usage
  • C) Network interfaces
  • D) Directory files
Answer

A — df shows disk free space, -h makes it readable.

Q27. You want to find where the python executable is located. Which command do you use?

  • A) locate python
  • B) which python
  • C) find python
  • D) search python
Answer

B — which locates a command in the PATH.

Q28. What does history do in the terminal?

  • A) Shows recently modified files
  • B) Prints a list of previously executed commands
  • C) Re-runs the last command
  • D) Clears old commands
Answer

B — history displays the command history.

Q29. How can you re-run the exact command you ran 3 steps ago without retyping it?

  • A) Press the UP arrow key 3 times
  • B) Run repeat 3
  • C) Run undo 3
  • D) It is impossible
Answer

A — The UP arrow cycles through history.

Q30. What does mkdir -p a/b/c do?

  • A) Creates a directory c inside b inside a, creating a and b if they don’t exist
  • B) Fails if a and b do not exist
  • C) Creates three separate directories: a, b, and c
  • D) Prints the path a/b/c
Answer

A — -p creates parent directories as needed.

Full Answer Key (spoilers)
QAnswer
1B
2B
3C
4C
5D
6C
7B
8B
9C
10B
11B
12C
13B
14C
15B
16C
17B
18C
19B
20B
21A
22B
23A
24A
25B
26A
27B
28B
29A
30A

Part B — Terminal Exercises#

Do these in order. Each builds on the previous one.

Exercise 1 — Navigate and inspect#

# 1. Go to your home directory
cd ~

# 2. List all files including hidden ones
ls -la

# 3. How many items do you see? Count with:
ls -la | wc -l

# 4. Go into your tds/bootcamp folder
cd ~/tds/bootcamp

Write down: What hidden files did you spot in your home directory?

Exercise 2 — Create and populate a file#

cd ~/tds/bootcamp

# Create a log file with some sample content
echo "INFO: server started on port 8000" > app.log
echo "INFO: connected to database" >> app.log
echo "WARN: disk usage at 80%" >> app.log
echo "ERROR: failed to read config.json" >> app.log
echo "INFO: request received from 127.0.0.1" >> app.log
echo "ERROR: database connection lost" >> app.log
echo "WARN: retrying connection..." >> app.log
echo "INFO: connection restored" >> app.log

Now answer these using only terminal commands (no opening the file in an editor):

  1. How many lines does app.log have?
  2. What are the last 3 lines?
  3. How many lines contain ERROR?
  4. Show only the WARN lines.

Exercise 3 — Pipes in action#

Using the app.log file from Exercise 2:

# Save all ERROR lines to a separate file
grep "ERROR" app.log > errors.txt

# Confirm it worked
cat errors.txt

# Count errors and warnings separately
echo "Errors:" && grep -c "ERROR" app.log
echo "Warnings:" && grep -c "WARN" app.log

Now try this pipeline — predict what it does before running it:

cat app.log | grep -v "INFO" | wc -l

Question: What did it count? Why?

Exercise 4 — Edit with nano#

nano ~/tds/bootcamp/app.log

Inside nano:

  1. Add a new line at the very top: # Log file for my TDS project
  2. Save with Ctrl+O then Enter
  3. Exit with Ctrl+X
  4. Verify the change: head -1 app.log

Exercise 5 — Environment variables#

# 1. Set a variable for this session
export MY_LOG_FILE="$HOME/tds/bootcamp/app.log"

# 2. Use it
cat $MY_LOG_FILE

# 3. Count errors using the variable
grep -c "ERROR" $MY_LOG_FILE

# 4. Now make it permanent — open .bashrc
nano ~/.bashrc

At the bottom of .bashrc, add:

export MY_LOG_FILE="$HOME/tds/bootcamp/app.log"
export MY_NAME="your-name-here"

Save, exit, then:

source ~/.bashrc
echo $MY_NAME

Confirm: Does echo $MY_NAME print your name?

Bonus Exercise — One pipeline challenge#

Using only terminal commands (no Python, no editor), find the most frequent word in your app.log file.

Hint: you’ll need cat, tr, sort, uniq -c, sort -rn, and head.

Write your pipeline in day2.md under a “My Pipeline” section.

End of Day 2 Quiz & Exercises

Exercise 6 — Additional Practice#

  1. Run whoami and note the output.
  2. Run history | tail -5 to see your last 5 commands.
  3. Try which python to see where your Python is installed.

Question to answer: Why is the output of which python important when working with virtual environments?