Functions & Practical Examples

Functions help you organize your scripts into reusable blocks of code.

1. Defining Functions

Functions can take arguments just like scripts, using $1, $2, etc.

#!/bin/bash
 
# Define function
greet_user() {
    echo "Hello, $1! Welcome to the server."
}
 
# Call function
greet_user "John"

2. Practical Automation: Log Backup

Here is a script that combines everything: variables, conditionals, and functions.

#!/bin/bash
 
LOG_DIR="/var/log/myapp"
BACKUP_DIR="/tmp/backups"
DATE=$(date +%Y-%m-%d)
 
# Function to check directory
ensure_dir() {
    if [[ ! -d "$1" ]]; then
        echo "Creating $1..."
        mkdir -p "$1"
    fi
}
 
echo "--- Starting Backup ---"
ensure_dir "$BACKUP_DIR"
 
if ls "$LOG_DIR"/*.log 1> /dev/null 2>&1; then
    tar -czf "$BACKUP_DIR/logs-$DATE.tar.gz" "$LOG_DIR"/*.log
    echo "Backup successful: logs-$DATE.tar.gz"
else
    echo "No logs found to backup."
fi

3. Setting Up Your Script

To run your script professionally:

1. Add Shebang: Ensure #!/bin/bash is at the top.
2. Permissions: chmod +x script.sh.
3. Run: ./script.sh.

DevOps Automation Checklist

• Does the script have a shebang?
• Are variables quoted?
• Is there basic error checking (e.g., checking if a file exists)?
• Is the output clear for the user?

[!IMPORTANT] Exit Codes Use exit 0 for success and exit 1 (or higher) for failures. This allows other scripts or CI/CD pipelines to know if your script succeeded.