How do I prevent tar from overwriting an existing archive?

Question

I backup files a few times a day on Ubuntu/Linux with the command tar -cpvzf ~/Backup/backup_file_name.tar.gz directory_to_backup/, (the file name contains the date in YYYY-MM-DD format and a letter from a to z - a is the first backup for this date etc.) but I want to create a new archive, not overwrite the archive if it already exists. How do I prevent tar from overwriting an existing archive? If the archive exists, I want tar to exit without doing anything (and if possible, display an error message).

Answer 1

Check the existence of the file beforehand:

if [ -f ~"/Backup/[backup_file_name].tar.gz" ]; then
    echo "ooops backup file was already here"
    exit
fi
tar -cpvzf ~/Backup/[backup_file_name].tar.gz directory_to_backup/

Note that the ~ has to be outside the double quotes if you want it to be expanded.

---

Update

Thanks. Do you know how to make the archive file name and directory to backup as command line arguments? The file name includes the full path.

You can use $1, $2 and so on to indicate the parameters. For instance:

if [ -f $1 ]; then
    echo "ooops backup file was already here"
    exit
fi
tar -cpvzf $1 $2

And then call the script with:

./script.sh file backup_dir

Answer 2

I created the file ~/scripts/tar.sh:

#!/bin/bash

if [ -f $1 ]; then
    echo "Oops! backup file was already here."
    exit
fi
tar -cpvzf $1 $2 $3 $4 $5

Now I just have to type:

~/scripts/tar.sh ~/Backup/backup_file_name_`date +"%Y-%m-%d"`_a.tar.gz directory_to_backup/

And the backup file is created if the file doesn't exist.