Creating Custom Command-Line Tools – Bash

What You’ll Learn 📚

• Understanding the basics of Bash scripting
• Creating simple to advanced command-line tools
• Common pitfalls and how to avoid them
• Troubleshooting tips and tricks

Introduction to Bash and Command-Line Tools

Bash is a powerful scripting language used to automate tasks and manage system operations. Command-line tools are scripts or programs that you can run from the terminal to perform specific tasks. By creating custom tools, you can streamline your workflow and perform complex operations with simple commands.

Key Terminology

• Bash: A Unix shell and command language
• Script: A file containing a series of commands
• Terminal: A text-based interface to interact with your computer
• Command-line tool: A program executed in the terminal

Getting Started: The Simplest Example

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

Running Your Script

1. Save the script to a file, e.g., hello.sh.
2. Make it executable:

   chmod +x hello.sh

3. Run the script:

   ./hello.sh

Lightbulb Moment: The chmod +x command changes the file’s permissions to make it executable. Think of it as giving your script permission to run! 💡

Progressively Complex Examples

Example 2: A Simple Calculator

#!/bin/bash
# Simple calculator script
read -p "Enter first number: " num1
read -p "Enter second number: " num2
sum=$((num1 + num2))
echo "The sum is: $sum"

Note: This script only adds two numbers, but you can expand it to include other operations like subtraction, multiplication, and division!

Example 3: File Organizer

#!/bin/bash
# Organize files by extension
mkdir -p organized
for file in *.*; do
  ext="${file##*.}"
  mkdir -p "organized/$ext"
  mv "$file" "organized/$ext/"
done
echo "Files organized by extension!"

Warning: This script moves files, so make sure you run it in a directory where you can safely organize files!

Example 4: System Monitor

#!/bin/bash
# Simple system monitor
while true; do
  echo "CPU Load: $(uptime | awk '{print $10}')"
  echo "Memory Usage: $(free -m | awk 'NR==2{printf "%.2f%%", $3*100/$2 }')"
  sleep 5
done

Note: Use Ctrl+C to stop the script.

Common Questions and Answers

1. What is Bash?

   Bash is a Unix shell and command language used for scripting and automating tasks.

2. How do I make a script executable?

   Use the command chmod +x scriptname.sh to make your script executable.

3. Why isn’t my script running?

   Ensure the script has execute permissions and the correct path is used.

4. What does #!/bin/bash mean?

   It specifies the interpreter to be used for the script, in this case, Bash.

5. How can I debug a Bash script?

   Use bash -x scriptname.sh to run the script in debug mode.

Troubleshooting Common Issues

• Permission Denied: Ensure your script has execute permissions using chmod +x.
• Command Not Found: Check for typos or ensure the command is installed on your system.
• Unexpected Output: Use echo statements to debug and check variable values.

Practice Exercises

• Create a script that backs up a directory to a specified location.
• Write a script that checks if a website is online and alerts you if it’s down.
• Develop a tool that converts text files from one format to another.

Remember, practice makes perfect! Keep experimenting and building your skills. You’ve got this! 🚀

For more information, check out the Bash Manual and Advanced Bash-Scripting Guide.