Without these, output under USB error conditions looks like:
$ teensy_loader_cli --mcu=mk20dx256 -w -v blink_slow_Teensy31.hex
Teensy Loader, Command Line, Version 2.0
Read "blink_slow_Teensy31.hex": 14324 bytes, 5.5% usage
Unable to claim interface, check USB permissionsWaiting for Teensy device...
(hint: press the reset button)
Unable to claim interface, check USB permissionsUnable to claim interface, check USB permissionsUnable to …
Without these, output under USB error conditions looks like: