pyCardDAV is a simple to use CardDAV CLI client. It has built in support for mutt's query_command but also works very well solo (and with other MUAs).
pyCardDAV consists of pycardsyncer, a program for syncing your CardDAV resource into a local database and of pc_query, a program for querying the local database. pyCardDAV is some ugly python code (actually, it's not that bad anymore…) that holds together vobject, lxml, requests and pysqlite.
(or rather: limitations)
Please do provide feedback if pyCardDAV works for you or even more importantly if it doesn't. You can reach me by email at pycarddav (at) lostpackets (dot) de , by jabber/XMPP at geier (at) jabber (dot) lostpackets (dot) de or via github.
pyCardDAV is released under the Expat/MIT License:
Copyright (c) 2011-2013 Christian Geier and contributors
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.