Creating Interactive Scripts – in Shell Scripting

What You’ll Learn 📚

• Core concepts of shell scripting
• Key terminology and definitions
• How to create simple interactive scripts
• Progressively complex examples
• Common questions and troubleshooting tips

Introduction to Shell Scripting

Shell scripting is a powerful way to automate tasks and manage your system efficiently. It allows you to write scripts that can execute commands in sequence, handle files, and interact with the user. By making your scripts interactive, you can create more dynamic and responsive programs that can ask for user input and make decisions based on that input.

Key Terminology

• Shell: A command-line interface that allows users to interact with the operating system.
• Script: A file containing a series of commands that can be executed by the shell.
• Interactive: A script that requires user input to function.

Starting with the Basics

#!/bin/bash
# This script asks for your name and greets you

# Prompt the user for their name
echo "What's your name?"
read name

# Greet the user
echo "Hello, $name! Nice to meet you!"

What's your name?
John
Hello, John! Nice to meet you!

Progressively Complex Examples

#!/bin/bash
# A simple calculator script

echo "Enter first number:"
read num1
echo "Enter second number:"
read num2
echo "Choose operation (+, -, *, /):"
read op

# Perform the calculation
case $op in
  +) result=$(echo "$num1 + $num2" | bc);;
  -) result=$(echo "$num1 - $num2" | bc);;
  *) result=$(echo "$num1 * $num2" | bc);;
  /) result=$(echo "scale=2; $num1 / $num2" | bc);;
  *) echo "Invalid operation"; exit 1;;
esac

echo "Result: $result"

Enter first number:
5
Enter second number:
3
Choose operation (+, -, *, /):
+
Result: 8

#!/bin/bash
# Simple user authentication script

# Predefined username and password
username="student"
password="password123"

# Prompt user for credentials
echo "Enter username:"
read input_username
echo "Enter password:"
read -s input_password

# Check credentials
if [ "$input_username" == "$username" ] && [ "$input_password" == "$password" ]; then
  echo "Access granted!"
else
  echo "Access denied!"
fi

Enter username:
student
Enter password:
Access granted!

Common Questions and Troubleshooting

1. Why do I need to make scripts executable?

   Scripts need executable permissions to run. Use chmod +x script.sh to make your script executable.

2. What if my script doesn’t run?

   Check for syntax errors, ensure the script is executable, and verify the shebang line (#!/bin/bash).

3. How can I debug my script?

   Use bash -x script.sh to run your script with debugging output.

4. What is the bc command?

   bc is a command-line calculator that supports basic arithmetic operations.

5. How do I handle invalid input?

   Use conditional statements to check for valid input and provide feedback to the user.

Troubleshooting Common Issues

Ensure your script starts with the correct shebang line (#!/bin/bash) to specify the shell interpreter.

If your script isn’t working as expected, try adding set -x at the top to enable debugging output.

Practice Exercises

• Create a script that asks for a user’s favorite color and responds with a fun fact about that color.
• Modify the calculator script to support more operations like modulus and exponentiation.
• Write a script that prompts the user for a file name and checks if the file exists.

Remember, practice makes perfect! Keep experimenting with your scripts and don’t hesitate to explore new ideas. You’ve got this! 🚀

Additional Resources

• Bash Reference Manual
• Advanced Bash-Scripting Guide