Day 9 Shell Scripting Challenge Directory Backup with Rotation📂🔄

Task: Shell Scripting Challenge - Directory Backup with Rotation. This script will create timestamped backups of a specified directory and manage the backups by keeping only the last three.

Backup Script: vim backup_with_rotation.sh

#!/bin/bash

<< readme
This is a script for backup with a 3-day rotation.

Usage:
./backup.sh <path to your source> <path to backup folder>
readme

# Function to display usage information
function display_usage {
    echo "Usage: ./backup.sh <path to your source> <path to backup folder>"
    echo "./backup.sh <what to backup> <where to backup>"
}

# Check if no arguments are provided
if [ $# -eq 0 ]; then
    display_usage
    exit 1
fi

# Assign command line arguments to variables
source_dir=$1
timestamp=$(date '+%Y-%m-%d-%H-%M-%S')
backup_dir=$2

# Function to create a backup
function create_backup {
    zip -r "${backup_dir}/backup_${timestamp}.zip" "${source_dir}" > /dev/null

    if [ $? -eq 0 ]; then
        echo "Backup generated successfully for ${timestamp}"
    else
        echo "Error creating backup."
        exit 1
    fi
}

# Function to perform backup rotation
function perform_rotation {
    backups=($(ls -t "${backup_dir}/backup_"*.zip 2>/dev/null))

    if [ "${#backups[@]}" -gt 3 ]; then
        echo "Performing rotation for 3 backups"

        backups_to_remove=("${backups[@]:3}")  # Keep backups after the first 3

        for backup in "${backups_to_remove[@]}"; do
            rm -f "${backup}"
        done
        echo "Old backups removed."
    fi
}

# Run the functions
create_backup
perform_rotation

Line-by-Line Explanation

1. Shebang:

    #!/bin/bash
   

   Specifies that the script should be executed using the Bash shell.

2. Multi-line Comment:

    << readme
    This is a script for backup with a 3-day rotation.
    ...
    readme
   

   Describes the script and its usage. It utilizes a document for multi-line comments.

3. Function to Display Usage Information:

    function display_usage {
        echo "Usage: ./backup.sh <path to your source> <path to backup folder>"
        echo "./backup.sh <what to backup> <where to backup>"
    }
   

   This function outputs instructions on using the script if the required arguments are not provided.

4. Argument Check:

    if [ $# -eq 0 ]; then
        display_usage
        exit 1
    fi
   

   Check if the number of arguments passed to the script is zero. If true, it calls the display_usage function and exits.

5. Variable Assignments:

    source_dir=$1
    timestamp=$(date '+%Y-%m-%d-%H-%M-%S')
    backup_dir=$2
   

   • source_dir=$1: Stores the first argument (source directory) in source_dir.

   • timestamp=$(date '+%Y-%m-%d-%H-%M-%S'): Generates a timestamp for naming the backup file.

   • backup_dir=$2: Stores the second argument (backup directory) in backup_dir.

6. Function to Create Backup:

    function create_backup {
        zip -r "${backup_dir}/backup_${timestamp}.zip" "${source_dir}" > /dev/null
   
        if [ $? -eq 0 ]; then
            echo "Backup generated successfully for ${timestamp}"
        else
            echo "Error creating backup."
            exit 1
        fi
    }
   

   This function zips the source directory into a timestamped zip file in the backup directory and checks if the operation was successful.

7. Function to Perform Backup Rotation:

    function perform_rotation {
        backups=($(ls -t "${backup_dir}/backup_"*.zip 2>/dev/null))
   
        if [ "${#backups[@]}" -gt 3 ]; then
            echo "Performing rotation for 3 backups"
   
            backups_to_remove=("${backups[@]:3}")  # Keep backups after the first 3
   
            for backup in "${backups_to_remove[@]}"; do
                rm -f "${backup}"
            done
            echo "Old backups removed."
        fi
    }
   

   • This function lists all zip files in the backup directory, sorted by modification time.

   • It checks if there are more than three backups and removes the oldest ones if necessary.

8. Run the Functions:

    create_backup
    perform_rotation
   

   Calls the create_backup function to create a new backup and then perform_rotation to manage old backups.

   Functionality Breakdown

   • Directory Check: The script checks if a directory is provided and if it exists.

   • Timestamp Creation: It generates a timestamp to name the backup folder.

   • Backup Creation: It copies all files from the specified directory to the new backup folder.

   • Backup Rotation: It checks the number of existing backup folders and removes the oldest ones if there are more than three.

Summary

This script efficiently backs up a specified source directory, creating a timestamped zip file in a designated backup directory. It ensures that only the three most recent backups are kept, automatically deleting older backups as necessary. You can easily modify it for your specific needs, such as changing the backup format or the rotation policy.