Bash Script to Backup Files Easily and Safely

Use a Bash script like cp -r /path/to/source /path/to/backup/backup_$(date +%Y%m%d_%H%M%S) to copy files into a timestamped backup folder.

Examples

Input/home/user/documents

OutputCopies all files from /home/user/documents to /home/user/backup/backup_YYYYMMDD_HHMMSS

Input/var/log

OutputCopies all log files from /var/log to /var/backups/backup_YYYYMMDD_HHMMSS

Input/tmp/emptyfolder

OutputCreates an empty backup folder /backup/backup_YYYYMMDD_HHMMSS with no files if source is empty

How to Think About It

To backup files with a Bash script, think about copying the source files to a safe place. Use a timestamp in the backup folder name to avoid overwriting old backups. The script should handle folders and files recursively.

Algorithm

1

Get the source directory path from the user or set it in the script

2

Create a backup directory with a timestamp to keep backups unique

3

Copy all files and folders from the source to the backup directory

4

Print a message confirming the backup location

Code

bash

#!/bin/bash

SOURCE_DIR="$1"
BACKUP_DIR="$HOME/backup/backup_$(date +%Y%m%d_%H%M%S)"

mkdir -p "$BACKUP_DIR"
cp -r "$SOURCE_DIR"/* "$BACKUP_DIR"/
echo "Backup completed to $BACKUP_DIR"

Output

Backup completed to /home/username/backup/backup_20240601_123456

Dry Run

Let's trace backing up /home/user/docs through the script

1

Set source and backup paths

SOURCE_DIR="/home/user/docs" BACKUP_DIR="/home/user/backup/backup_20240601_123456"

2

Create backup directory

mkdir -p /home/user/backup/backup_20240601_123456

3

Copy files

cp -r /home/user/docs/* /home/user/backup/backup_20240601_123456/

Step	Action	Value
1	SOURCE_DIR	/home/user/docs
1	BACKUP_DIR	/home/user/backup/backup_20240601_123456
2	mkdir	Created backup directory
3	cp	Copied all files from source to backup

Why This Works

Step 1: Create unique backup folder

Using $(date +%Y%m%d_%H%M%S) adds a timestamp so each backup folder is unique and old backups are not overwritten.

Step 2: Copy files recursively

The cp -r command copies all files and subfolders from the source to the backup folder, preserving the structure.

Step 3: Confirm backup completion

Printing a message with the backup path helps the user know where the files were saved.

Alternative Approaches

Using tar to create a compressed backup

bash

#!/bin/bash
SOURCE_DIR="$1"
BACKUP_FILE="$HOME/backup/backup_$(date +%Y%m%d_%H%M%S).tar.gz"
tar -czf "$BACKUP_FILE" -C "$SOURCE_DIR" .
echo "Backup archive created at $BACKUP_FILE"

Creates a compressed archive, saving space but requires extraction to restore files.

Using rsync for incremental backup

bash

#!/bin/bash
SOURCE_DIR="$1"
BACKUP_DIR="$HOME/backup/backup_$(date +%Y%m%d_%H%M%S)"
mkdir -p "$BACKUP_DIR"
rsync -av --delete "$SOURCE_DIR"/ "$BACKUP_DIR"/
echo "Backup completed with rsync to $BACKUP_DIR"

Efficiently copies only changed files, good for large backups but requires rsync installed.

Complexity: O(n) time, O(n) space

Time Complexity

The script copies all files and folders once, so time grows linearly with the number of files (n).

Space Complexity

Backup requires space proportional to the size of the source files, so space is O(n).

Which Approach is Fastest?

Using rsync is faster for repeated backups because it copies only changed files, while cp copies everything every time.

Approach	Time	Space	Best For
cp recursive copy	O(n)	O(n)	Simple full backups
tar compressed archive	O(n)	Less than O(n)	Space-saving backups
rsync incremental backup	O(changed files)	O(n)	Efficient repeated backups