This script and variations of it have been around for several years. I found that you will get a blank SQL file if the permissions are not set right for the database user.
Try this. You need the following permissions: SELECT, RELOAD, FILE, SHOW DATABASES, SUPER, LOCK TABLES, SHOW VIEW
It is a good idea to set up a separate DB user for backups. These are not standard settings.
One of the basic security rules for DB user permissions is that you never grant anything more than the minimal requirements to any DB user.
There may be other reasons for a blank file, but this is what fixed my backups when I first encountered the problem.
Another problem you might run into is with e-mailing large databases. Some ISPs place limits on e-mail file sizes. The --all-databases option may not work if the databases are large. I've also seen problem trying to e-mail WordPress backups if you have the wassup plugin installed and you do not set time limits on the data it retains. By default, wassup saves all the history and the tables can become very large very quickly.
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