Shell Scripting Challenge Directory Backup with Rotation

In the realm of DevOps, automation ensures reliability and consistency in managing systems and applications. A critical automation task involves backing up directories. While backups are vital for data protection, managing them can be challenging with numerous files. Here's how a Bash script automates directory backups with a rotation mechanism to retain only the last three backups.

Objectives

Our script will:

Take a directory path as a command-line argument.
Create a timestamped backup folder inside the specified directory.
Copy all files from the specified directory into the backup folder.
Implement a rotation mechanism to keep only the last three backups, removing older ones.

The Script

Below is the Bash script named backup_with_rotation.sh that implements the described functionality:

#!/bin/bash

<<readme
This script takes backup of a directory with timestamped folders and implements rotation.
Usage:
./backup_with_rotation.sh <path of directory>
readme

# Ensure correct number of arguments
if [ $# -ne 1 ]; then
    echo "Usage: $0 <path of directory>"
    exit 1
fi

source_dir="$1"
target_dir="${source_dir}"

# Create target directory if it does not exist
if [ ! -d "$target_dir" ]; then
    mkdir -p "$target_dir"
fi

timestamp=$(date '+%Y-%m-%d_%H-%M-%S')

backup_dir="${target_dir}/backup_${timestamp}"

function create_backup {
    # Create the backup
    zip -r "${backup_dir}.zip" "${source_dir}" > /dev/null

    if [ $? -eq 0 ]; then
        echo "Backup created: ${backup_dir}.zip"
    else
        echo "Backup was not performed for $timestamp"
    fi
}

function perform_rotation {
    # List backups, sorted by modification time, newest first
    backups=($(ls -t "${target_dir}/backup_"*.zip))

    if [ "${#backups[@]}" -gt 3 ]; then
        backups_to_remove=("${backups[@]:3}")
        for backup in "${backups_to_remove[@]}"; do
            rm -f -- "$backup"
            if [ $? -eq 0 ]; then
                echo "Removed old backup: $backup"
            else
                echo "Failed to remove old backup: $backup"
            fi
        done
    fi
}

create_backup
perform_rotation

Understanding the Script

#!/bin/bash

<<readme
This script takes backup of a directory with timestamped folders and implements rotation.
Usage:
./backup_with_rotation.sh <path of directory>
readme

Shebang: #!/bin/bash specifies that the script should be executed using the Bash interpreter.
Here Document: <<readme ... readme is used for multi-line comments. It provides a description of the script's purpose and usage.

# Ensure correct number of arguments
if [ $# -ne 1 ]; then
    echo "Usage: $0 <path of directory>"
    exit 1
fi

Argument Handling: if [ $# -ne 1 ]; then ... fi checks if the script is provided exactly one argument (the directory path). If not, it prints usage instructions and exits with an error code.

source_dir="$1"
target_dir="${source_dir}"

# Create target directory if it does not exist
if [ ! -d "$target_dir" ]; then
    mkdir -p "$target_dir"
fi

Directory Setup: source_dir="$1" assigns the first argument (directory path) to source_dir. target_dir="${source_dir}" sets target_dir to the same path as source_dir.
Directory Creation: If target_dir doesn't exist (if [ ! -d "$target_dir" ]; then ... fi), it creates it using mkdir -p "$target_dir".

timestamp=$(date '+%Y-%m-%d_%H-%M-%S')

backup_dir="${target_dir}/backup_${timestamp}"

Timestamp Generation: timestamp=$(date '+%Y-%m-%d_%H-%M-%S') uses date command to generate a timestamp in the format YYYY-MM-DD_HH-MM-SS.
Backup Directory: backup_dir="${target_dir}/backup_${timestamp}" sets backup_dir to a directory path with the current timestamp appended.

function create_backup {
    # Create the backup
    zip -r "${backup_dir}.zip" "${source_dir}" > /dev/null

    if [ $? -eq 0 ]; then
        echo "Backup created: ${backup_dir}.zip"
    else
        echo "Backup was not performed for $timestamp"
    fi
}

Backup Creation: create_backup function compresses (zip -r) source_dir into ${backup_dir}.zip. Redirects output to /dev/null to suppress zip command output.
Backup Status: Checks if the backup operation was successful (if [ $? -eq 0 ]; then ... fi) and prints appropriate messages.

function perform_rotation {
    # List backups, sorted by modification time, newest first
    backups=($(ls -t "${target_dir}/backup_"*.zip))

    if [ "${#backups[@]}" -gt 3 ]; then
        backups_to_remove=("${backups[@]:3}")
        for backup in "${backups_to_remove[@]}"; do
            rm -f -- "$backup"
            if [ $? -eq 0 ]; then
                echo "Removed old backup: $backup"
            else
                echo "Failed to remove old backup: $backup"
            fi
        done
    fi
}

Rotation Mechanism: perform_rotation function lists existing backups (ls -t "${target_dir}/backup_"*.zip), sorts them by modification time (newest first).
Backup Removal: If more than 3 backups exist (if [ "${#backups[@]}" -gt 3 ]; then ... fi), it removes older backups (rm -f -- "$backup").

create_backup
perform_rotation

Execution: Finally, it calls create_backup to create a new backup and perform_rotation to manage existing backups.

How to Use the Script

Save the Script: Save the script as backup_with_rotation.sh.
Make the Script Executable: Run the following command to make the script executable:
```
 chmod +x backup_with_rotation.sh
```
Execute the Script: Run the script with the directory path as an argument:
```
 ./backup_with_rotation.sh /path/to/directory
```