Here’s an example of quick script I wrote in PHP and added as a cronjob to backup some mysql databases:
// dump database tables to sql text files //
exec('mysqldump -uroot -pPasswordHere music > /tmp/music.sql');
exec('mysqldump -uroot -pPasswordHere taskfreak > /tmp/taskfreak.sql');
// pack into tarballs //
exec("tar -cf /tmp/music.sql.tar /tmp/music.sql");
exec("tar -cf /tmp/taskfreak.sql.tar /tmp/taskfreak.sql");
// gzip tarballs //
exec("gzip /tmp/music.sql.tar");
exec("gzip /tmp/taskfreak.sql.tar");