Stage 4: Script Champion

Teach learners how to write and execute shell scripts to automate repetitive tasks. Build confidence in scripting fundamentals like variables, loops, conditionals, and execution permissions - skills often tested in interviews.

Hackbook Overview

1. What is a Shell Script?

• A text file containing a sequence of commands.
• Automates tasks that would otherwise be run manually.
• Commonly written in Bash.

2. Creating and Running Scripts

• Create a file: nano script.sh.
• Make executable: chmod +x script.sh.
• Run: ./script.sh.

Add commands:

#!/bin/bash
echo "Hello, Linux!"

3. Variables

• Store values for reuse.

Example:

NAME="Shubham"
echo "Hello $NAME"

4. Conditionals

• Use if, else, elif.

Example:

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

5. Loops

While loop:

while true; do
  echo "Running..."
  break
done

For loop:

for i in 1 2 3; do
  echo "Number $i"
done

6. Why This Matters in Interviews

• Shows ability to automate tasks and think like an engineer.
• Demonstrates practical knowledge beyond just running commands.
• Often tested in DevOps, Cloud, and SysAdmin interviews.

Hands‑On Practice

• Write a script that prints today’s date.
• Write a script that checks if a file exists.
• Write a script that loops through numbers 1–5 and prints them.
• Write a script that backs up a directory into a .tar.gz file.

Interview Question Bank

Conceptual

• Q1. What is a shell script and why is it useful?
  A1. A shell script is a file containing commands executed by the shell. It automates repetitive tasks, saving time and reducing errors.
• Q2. How do you make a script executable?
  A2. Use chmod +x script.sh and run it with ./script.sh.
• Q3. What is the purpose of #!/bin/bash at the top of a script?
  A3. It’s called a shebang. It tells the system which interpreter to use (here, Bash).

Practical

Q6. How do you check if a file exists in a script?
A6.bash

if [ -f filename ]; then
  echo "File exists"
fi

Q5. How do you pass arguments to a script?
A5. Arguments are accessed as $1, $2, etc. Example:bash

echo "First argument: $1"

Q4. Write a script that prints “Hello World.”
A4.bash

#!/bin/bash
echo "Hello World"

Scenario‑Based

• Q7. You need to automate log cleanup every day. How would you do it?
  A7. Write a script that deletes old logs and schedule it with cron.

Q9. How would you write a script that checks disk usage and alerts if it’s above 80%?
A9.bash

#!/bin/bash
usage=$(df / | grep / | awk '{print $5}' | sed 's/%//')
if [ $usage -gt 80 ]; then
  echo "Disk usage above 80%!"
fi

Q8. You want to back up /home/user into /backup. How do you script it?
A8.bash

#!/bin/bash
tar -czf /backup/home_backup.tar.gz /home/user

Behavioral Based

• Q10. Tell me about a time you automated a task with a script.
  A10. Example: “I wrote a script to monitor log files and alert when errors appeared, which reduced downtime during deployments.”

Cheatsheet (Quick Notes)

• Create Script: nano script.sh → add commands → chmod +x script.sh → ./script.sh.
• Shebang: #!/bin/bash defines interpreter.
• Variables: VAR=value, access with $VAR.
• Conditionals: if [ condition ]; then … fi.
• Loops: for, while.
• Arguments: $1, $2, etc.