Backup Script

This Bash script automates creating and encrypting a backup archive. It tars (optionally compresses) the specified directory and encrypts the resulting archive with AES-256 via OpenSSL.

Features

1. Positional and Named Arguments

• Positional: ./backup.sh <DIRECTORY> [<COMPRESSION>] [<OUTPUT_FILE>]
• Named: ./backup.sh -i <DIRECTORY> [-c <COMPRESSION>] [-o <OUTPUT_FILE>]

2. Compression: Available algorithms are gzip, bzip2, xz. Defaults to none if not specified. In case of none, archiving works without compression.

3. Encryption: Encrypts the archive using OpenSSL with -aes-256-cbc -pbkdf2 and produces a final file ending in .enc unless an explicit filename is provided.

4. Error Logging: All error messages (stderr) are timestamped and logged in error.log. Warnings and errors—such as missing directories or invalid compression—go here.

5. Help Option: -h or --help available anywhere in the arguments to show usage instructions.

6. Debug Mode: By default, DEBUG=1, so script variables are printed to the terminal. If you set DEBUG=0, all normal script output is suppressed, and only errors are logged to error.log.

Usage

You can run the script in two ways: positional or named arguments.

Positional Mode

./backup.sh <DIRECTORY> [<COMPRESSION>] [<OUTPUT_FILE>]

• <DIRECTORY>: Required. Must be an existing directory.
• <COMPRESSION>: (Optional) One of none (default), gzip, bzip2, xz.
• <OUTPUT_FILE>: (Optional) The final name for the encrypted backup. Defaults to <DIRECTORY>.backup.enc.

Examples

1. Minimal (no compression, default output):

./backup.sh /var/www/html

Produces html.backup.enc in the current directory.

2. Specify compression:

./backup.sh /home/user gzip

Tar + gzip compresses /home/user, then encrypts into user.backup.enc.

3. Fully specify:

./backup.sh /srv/data xz data_archive.tar.xz

Creates data_archive.tar.xz (tar + xz), then encrypts into data_archive.tar.xz.

Named Arguments Mode

./backup.sh -i <DIRECTORY> [-c <COMPRESSION>] [-o <OUTPUT_FILE>]

• -i / --input <DIRECTORY>: Required directory path to back up.
• -c / --compression <COMPRESSION>: Optional. Defaults to none.
• -o / --output <OUTPUT_FILE>: Optional. Defaults to <DIRECTORY>.backup.enc if omitted.

Examples

1. Minimal:

./backup.sh -i /var/log

Uses no compression; final file log.backup.enc.

2. Specify compression & output:

./backup.sh -i /var/log -c bzip2 -o logs_backup.tar.bz2

Compresses with bzip2, then encrypts into logs_backup.tar.bz2.

3. Help:

./backup.sh -h
./backup.sh --help

Shows usage instructions and exits.

Debug/Verbose Mode

The script has a DEBUG variable near the top:

DEBUG=1

• DEBUG=0 (default, quiet mode): Normal output is redirected to /dev/null; only errors and warnings show up in error.log.
• DEBUG=1 (verbose mode): Prints internal variables (BACKUP_DIR, COMPRESSION, etc.) to stdout (for troubleshooting).

To enable verbose mode (i.e., keep normal output visible and print debugging info about the script’s variables) add -v or --verbose parameter while running the script.

Outputs

After running successfully, you end up with an encrypted file (e.g., mydata.backup.enc). If you specified an output name (like myarchive.tar.gz), that’s the file you’ll see (still encrypted). The unencrypted tar is removed automatically.

How to Restore / Unpack

1. Decrypt:

openssl enc -d -aes-256-cbc -pbkdf2 -in <encrypted_backup> -out <decrypted_backup>

You’ll be prompted for the passphrase used to create the backup.

2. Extract:

• If uncompressed (none), just:

tar -xf <decrypted_backup>

• If compressed with gzip:

tar -xzf <decrypted_backup>

• If compressed with bzip2:

tar -xjf <decrypted_backup>

• If compressed with xz:

tar -xJf <decrypted_backup>

(You can also do tar -xaf <decrypted_backup> and many modern tar versions will auto-detect the compression.)

Logging & Error Handling

Errors and warnings (e.g., invalid compression type, missing directory) are timestamped in error.log. If you ever need to see normal script messages while debugging, use verbose mode.

Requirements

• Bash (and basic Unix utilities like tar).
• OpenSSL installed and accessible in PATH.