My main problem with this is that it would require me to store my password, in clear text, in a shell script.
I'm no security expert but that raises a red flag for me. I'd rather have some way of entering my password each time I want to back up, but this would also make the cron process impossible.
See gmvault as mentioned in the comments here, it just saves an oauth token. Still can be used to access your mail but at least it can be easily revoked and isn't your clear text password.
If it's a shared box, you'd still have to hide the --pwd argument from `ps` process listings. You'd have to do something like make a ~/.gmail-pass file with the content "--pwd foobar", and call the script like this:
I'm no security expert but that raises a red flag for me. I'd rather have some way of entering my password each time I want to back up, but this would also make the cron process impossible.