$ sudo apt install khal
…
Unpacking khal (0.8.4-3) ...
…
$ (echo 1;echo 0;echo y;echo 0; echo y; echo n; echo y; echo y)  | khal configure
…
Do you want to write the config to /home/user/.config/khal/khal.conf? (Choosing `No` will abort) [y/N]: Successfully wrote configuration to /home/user/.config/khal/khal.conf
$ wget https://anonscm.debian.org/cgit/debconf-data/dc17.git/plain/misc/until-dc17.ics
…
HTTP request sent, awaiting response... 200 OK
Length: 6120 (6.0K) [text/plain]
Saving to: ‘until-dc17.ics’
…
$ khal import --batch -a private until-dc17.ics
$ khal agenda --days 14
Today:
16:30-17:30: DebConf Weekly Meeting ⟳

27-02-2017
16:30-17:30: DebConf Weekly Meeting ⟳

khal is available in stretch and newer and is probably best run from cron piping into '/usr/bin/mail' :-) Thanks to Gunnar Wolf for figuring it all out.