I have a folder for scripts in ~/.bin and added that folder to my $PATH. I put the following script into ~/.bin/resolution and made executable with chmod +x ~/.bin/resolution.

This allows me to quickly get the current resolution of the connected screens (including the interal MacBook screen) by just running the command resolution in my terminal.

system_profiler SPDisplaysDataType | grep Resolution | sed -e 's/^[^R]*//g'