I'm a newbie to Raspberry Pi's, but one of the things I was thinking about doing is running it off batteries (I see many people do this) - that led me to concerns about shutting down gracefully. Is there a software only solution that would allow me to detect input voltage?
you'll need some external circuitry to do that, because afaik the raspberry does not provide the battery voltage anywhere in the system: http://raspi.tv/tag/raspberry-pi-monitoring-its-own-battery-voltage
vcgencmd will show the internal voltages for
vcgencmd measure_volts core
The output will look something like this:
The following shell commands will display all the voltages:
for id in core sdram_c sdram_i sdram_p do echo -e "$id:\t$(vcgencmd measure_volts $id)" done
No, but MoPi is a tidy little board that provides the capability.