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Top 50 Shell Scripting Interview Questions and Answers

Shell scripting is an essential skill for system administrators, DevOps engineers, and software developers. Below is a list of top 50 frequently asked interview questions along with their answers.

Table of Contents

📌 Basic Shell Scripting Questions

1. What is Shell Scripting?

A shell script is a program written using shell commands and scripting constructs to automate tasks in UNIX/Linux.

2. What are different types of shells available in Linux?

  • Bash (Bourne Again Shell) – Default shell in most Linux distros

  • Sh (Bourne Shell) – Original UNIX shell

  • Ksh (Korn Shell) – Extended features of the Bourne Shell

  • Csh (C Shell) – C-like syntax shell

  • Zsh (Z Shell) – Advanced shell with themes and plugins

3. How do you execute a shell script?

bash
bash script.sh

or

bash
chmod +x script.sh
./script.sh

4. How do you define a variable in a shell script?

bash
name="John"
echo "Hello, $name"

5. How do you read user input in a script?

bash
echo "Enter your name: "
read name
echo "Hello, $name!"

6. How do you check if a file exists in a shell script?

bash
if [ -f "file.txt" ]; then
echo "File exists"
else
echo "File does not exist"
fi

7. How do you check if a directory exists?

bash
if [ -d "/path/to/dir" ]; then
echo "Directory exists"
else
echo "Directory does not exist"
fi

📌 Intermediate Shell Scripting Questions

8. How do you write an if-else statement in shell scripting?

bash
if [ "$num" -gt 10 ]; then
echo "Number is greater than 10"
else
echo "Number is 10 or less"
fi

9. How do you use a case statement in shell scripting?

bash
echo "Enter a fruit: "
read fruit

case $fruit in
apple) echo "You chose apple";;
banana) echo "You chose banana";;
orange) echo "You chose orange";;
*) echo "Unknown fruit";;
esac

10. How do you perform arithmetic operations in shell scripting?

bash
num1=10
num2=5
sum=$((num1 + num2))
echo "Sum: $sum"

11. What is the difference between = and == in shell scripting?

  • = is used for string assignment.

  • == is used for string comparison inside [ ] brackets.

12. How do you create and use an array in a shell script?

bash
fruits=("Apple" "Banana" "Cherry")
echo "First fruit: ${fruits[0]}"
echo "All fruits: ${fruits[@]}"

13. How do you loop through an array in shell scripting?

for fruit in "${fruits[@]}"; do
echo "$fruit"
done

14. How do you check if a variable is empty?

if [ -z "$var" ]; then
echo "Variable is empty"
fi

15. How do you define a function in shell scripting?

my_function() {
echo "Hello from function"
}
my_function

16. How do you pass arguments to a shell script?

./script.sh arg1 arg2
echo "First argument: $1"
echo "Second argument: $2"

📌 Advanced Shell Scripting Questions

17. How do you get the last executed command’s exit status?

bash
echo $?

(0 = success, non-zero = failure)

18. How do you redirect output to a file in shell scripting?

bash
echo "Hello" > output.txt

19. How do you append output to a file instead of overwriting?

bash
echo "New line" >> output.txt

20. How do you check if a command executed successfully?

bash
if ls /invalid/path &> /dev/null; then
echo "Success"
else
echo "Command failed"
fi

21. What is the difference between > and >>?

  • > overwrites a file

  • >> appends to a file

22. How do you schedule a cron job in Linux?

bash
crontab -e

Example: Run script every day at 2 AM

bash
0 2 * * * /path/to/script.sh

23. How do you find the number of lines in a file?

bash
wc -l file.txt

24. How do you replace text in a file using sed?

bash
sed -i 's/old-text/new-text/g' file.txt

25. How do you filter output using grep?

bash
grep "error" logfile.txt

📌 Expert-Level Shell Scripting Questions

26. What is the difference between $* and $@?

  • $* treats all arguments as a single string

  • $@ treats arguments as separate words

27. How do you execute multiple commands in one line?

bash
command1 && command2

28. What is the difference between && and ||?

  • && runs the next command only if the first one succeeds

  • || runs the next command only if the first one fails

29. How do you count occurrences of a word in a file?

bash
grep -o "word" file.txt | wc -l

30. What is a here document in shell scripting?

A here document allows multi-line input:

bash
cat << EOF
This is a multi-line text
EOF

31. How do you run a command in the background?

bash
long_running_command &

32. How do you create a log file for a script?

bash
./script.sh > script.log 2>&1

33. How do you kill a process using a script?

bash
kill -9 PID

34. How do you list open network connections?

bash
netstat -tulnp

35. How do you find the disk usage of a directory?

bash
du -sh /path/to/dir

📌 Advanced & Expert-Level Shell Scripting Questions (36-50)

36. How do you find all running processes for a specific user?

bash
ps -u username

Example:

bash
ps -u root

Shows all processes running under the root user.

37. How do you check the CPU and memory usage in Linux?

bash
top

or

bash
htop # (if installed)

For a snapshot of CPU & memory usage:

free -m

38. How do you find and delete files older than 7 days?

find /path/to/directory -type f -mtime +7 -exec rm {} \;

  • -mtime +7 → Finds files older than 7 days

  • -exec rm {} → Deletes the found files

39. How do you write a script that automatically restarts a service if it crashes?

#!/bin/bash
SERVICE="nginx"

if ! pgrep -x "$SERVICE" > /dev/null; then
echo "$SERVICE is not running. Restarting..."
systemctl start $SERVICE
else
echo "$SERVICE is running."
fi

This script checks if nginx is running and restarts it if necessary.

40. How do you extract a column from a text file?

Using awk:

awk '{print $2}' file.txt

This prints the second column from each line of file.txt.

41. How do you replace spaces with underscores in all filenames in a directory?

for file in *\ *; do
mv "$file" "${file// /_}"
done

This renames all files by replacing spaces with underscores.

42. How do you find and replace text in multiple files using sed?

sed -i 's/old-text/new-text/g' *.txt

This replaces "old-text" with "new-text" in all .txt files.

43. How do you create an infinite loop in a shell script?

while true; do
echo "Running..."
sleep 5
done

This runs indefinitely, printing “Running…” every 5 seconds.

44. How do you delete empty files inside a directory?

find /path/to/dir -type f -empty -delete

Deletes all empty files in the specified directory.

45. How do you rename all .txt files to .bak in a folder?

for file in *.txt; do
mv "$file" "${file%.txt}.bak"
done

This renames file.txt to file.bak for all .txt files.

46. How do you run a command as another user inside a script?

Using su (Switch User):

su - username -c "command_to_run"

Example:

su - john -c "ls -l /home/john"

This runs ls -l /home/john as user John.

47. How do you store the output of a command into a variable?

output=$(ls -l)
echo "$output"

This stores the output of ls -l inside the $output variable.

48. How do you schedule a script to run every hour using crontab?

1️⃣ Open crontab:

crontab -e

2️⃣ Add the following line:

0 * * * * /path/to/script.sh

This runs the script every hour at minute 0.

49. How do you extract the filename from a full file path?

file_path="/home/user/file.txt"
filename=$(basename "$file_path")
echo "$filename"

Output:

file.txt

50. How do you create a shell script that runs only once per day?

Use a lock file to prevent multiple executions:

#!/bin/bash
LOCK_FILE="/tmp/myscript.lock"

if [ -e "$LOCK_FILE" ]; then
echo "Script already ran today."
exit 1
fi

# Run the main script tasks here
echo "Running the script..."

# Create a lock file
touch "$LOCK_FILE"

Then, schedule it in crontab to run daily:

0 0 * * * /path/to/script.sh