Running maintenance commands in pbuilder chroot using cron

We run an automated build system using pbuilder-dist. We use it to build our open source project [Snap Websites](https://sourceforge.net/p/snapcpp/code/ci/master/tree/) to produce nightly builds. Currently we are building against Ubuntu "trusty." The issue we face is that periodically the packages in Ubuntu are updated and our chroot environment needs to be updated. In short, we want to run commands from cron within the chroot like so: # apt-get update # apt-get upgrade # apt-get autoremove However, I don't see a way to do this. Yes there are pbuilder hooks, but I don't see a way to do this from a cron script: # pbuilder-dist trusty login --save-after-login ...and then feed it commands like above. Any ideas? I've looked at the documentation for pbuilder but I don't see a clean and obvious way, so I thought I'd ask here.