Filing this against libsigrok though users will perceive this issue from
either of the applications.
When drivers require or support the conn= spec, the current implementation
is rather strict and expects a full user provided value which connection to
use to communicate to the device. Usability could get improved by accepting
abbreviated serial port specs like ttyACM0 instead of /dev/ttyACM0, as well
as ambiguous values like ttyUSB when multiple devices are connected to the
same kind of serial port and all of them should be used.
There may be individual device drivers which support this feature already
(uni-t dmms come to mind, though not all of them universally). Ideally the
feature would be common and applicable to a larger set of drivers. Neither
is this limited to serial ports, could also apply to USB VID/PID specs, or
BLE address specs, etc.