I have removed the spaces around the "=" and the code works fine. Using spaces around = is an old habit, but I'll stop doing that in these cases, and watch out for it as potential cause of errors.
Thanks a million to ripat, jojopi and Trev for getting back to me so quickly and for being so helpful.

Hi Trev here is my code - borrowed from Eben Upton's RPi user guide ... #! /bin/bash #RPi User Guide pp245 while true do echo $PATH filename = `date +%Y%m%dT%H%M%S`.jpg raspistill -w 1920 -h 1080 -t 0 -o $filename echo Image captured sleep 30 done

I've had my Pi a couple of weeks now and currently am working through some simple Picam projects. I'm using BASH, Python and CLI and most stuff seems to be going ok. I've hit a problem with an example project which makes use of the filename command to set up a ddmmyy filename within a bash script. I...