How to list all packages installed as optional dependencies only?

[enihcam]

I know paru -Qdt can list all dependency packages that are neither required nor optionally required by any currently installed package, but how to list all packages installed only as optional dependency but not required? Thanks.

[eclairevoyant]

Don't think paru is the tool for this. I would suggest installing expac instead.

If you want to print out all packages that are optdeps of some package:

comm -12 <(expac -l"\n" "%o" | sort -u) <(expac -l"\n" "%n\n%S" | sort -u)

If you want to print out all packages that are optdeps of some package and not a hard dep of any package:

comm -12 <(expac -l"\n" "%o" | sort -u) <(expac -l"\n" "%n\n%S" | sort -u) | comm -23 - <(expac -l"\n" "%D" | sort -u)

Adapted from this SO answer (which answers kind of the opposite question) by @Sunday: https://unix.stackexchange.com/a/218990/36254