If you're running a cron job as root, and you're running a homebrew command, you'll need to add homebrew to the root user's path.
sudo su cat ~/.bash_profile
Do you see this?
</usr/local/bin:$PATH/code>? If not, run <code> echo 'export PATH="/usr/local/bin:$PATH"' >> ~/.bash_profile
Test it
source ~/.bash_profile which mycommand