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Automation with Shell Scripting

In DevOps, our goal is to Automate Everything. Shell scripting is the simplest and most powerful way to glue different tools together.

1. The Anatomy of a Script​

Every Bash script must start with a Shebang (#!). This tells the computer which interpreter to use to run the code.

Create a file named hello.sh:

#!/bin/bash

# This is a comment
echo "Hello, A Master! Welcome to Shell Scripting."

Making it Executable​

By default, new files aren't allowed to "run" as programs. You must grant permission:

chmod +x hello.sh
./hello.sh

2. Variables and Inputs​

Just like in JavaScript, you can store data in variables. Note: In Bash, there must be NO spaces around the = sign.

#!/bin/bash

NAME="CodeHarborHub"
VERSION=1.0

echo "Deploying $NAME version $VERSION..."

# Taking User Input
echo "Enter your environment (dev/prod):"
read ENV
echo "Deploying to $ENV environment..."

3. Conditionals (If/Else)​

Conditionals allow your script to make decisions. Pay close attention to the spaces inside the brackets [ ].

#!/bin/bash

FILE="config.json"

if [ -f "$FILE" ]; then
    echo "$FILE exists. Proceeding with setup..."
else
    echo "Error: $FILE not found! Creating default config..."
    touch "$FILE"
fi

4. Loops​

Loops are perfect for processing multiple files or repeating tasks.

#!/bin/bash

# Creating 5 backup folders
for i in {1..5}
do
   mkdir "backup_folder_$i"
   echo "Created backup_$i"
done

🏗️ 5. A Real-World DevOps Example: Auto-Backup​

Here is a script that a "Master" might use to back up a project folder and add a timestamp.

#!/bin/bash

# Define variables
SOURCE="/home/ajay/my-project"
DEST="/home/ajay/backups"
DATE=$(date +%Y-%m-%d_%H-%M-%S)

# Create destination if it doesn't exist
mkdir -p $DEST

# Create a compressed archive (tarball)
tar -czf $DEST/project_backup_$DATE.tar.gz $SOURCE

echo "Backup completed successfully on $DATE!"

6. Why Bash for DevOps?​

  1. Native: It runs on almost every Linux/Unix server without installing anything.
  2. Fast: It interacts directly with the OS kernel.
  3. Integration: It easily combines tools like Git, Docker, and Nginx.

Practice: The Automation Challenge​

  1. Create a script named setup-project.sh.
  2. The script should:
  • Create a folder named my-app.
  • Inside that folder, create index.html and styles.css.
  • Write <h1>Hello World</h1> into the HTML file using echo.
  • Print a success message in the terminal.
  1. Run the script and verify the files were created!
Exit Codes

Every command in Linux returns an "Exit Code." 0 means success, and anything else means an error. You can check the exit code of the last command using echo $?. A true "Master" script always checks if a command succeeded before moving to the next step!