I needed this to work on the command line since I use the print screen key as a hotkey to take screenshots. Looks like the -a combined with -f does what I want. Here's my command for an example: shutter -a -f -o screenshot_%Y-%m-%d_%T.png

Excellent answer! I tried to use this to run spotify as a non-privileged system user. Your answers, especially for running a GUI app, worked for me. However, I did neet to pass in my DISPLAY var through sudo using the -E flag. Also, I was ignorant and didn't realize localuser is that literal string. Finally, a gui app may fail to various other issues with expecting a normal user's profile. HTH

It's better to do something like ^[[:space:]]$ instead of just a newline since there are DOS, Linux, and Mac kinds of newlines that will mess you up if you just try to strip out one kind of them.