Server :: Causing Crontab To Not Email Blank Emails

I've currently got a crontab line that looks like the following:

Code:
*/5 * * * * /usr/bin/php -q /etc/backend/cron.php | mail -s "Cron script output" whiteydude@gmail.com

The script works fine - it runs every 5 minutes and checks if certain environmental variables are set in place - if they are, it prints an output. If they're not, it dies.

The problem is that when it dies, it still sends me a blank email - one every 5 minutes, every time the cron job runs.

telling it not to send if it's blank?

I'm assuming some type of dirty awk script could do this, but I don't really know my shell well enough to do that.

I'm not good at putting these things into words, so let me write some psuedo code to explain what I mean:

Code:
*/5 * * * * /usr/bin/php -q /etc/backend/cron.php | if (STDOUT != '') { mail -s "Cron script output" whiteydude@gmail.com }

EDIT: Unfortunately I'm running on CentOS, so I can't use mail -E . Apparently that's a FreeBSD thing.