Command for printing derivations that will be built?

[Rodrigo Morales <moralesrodrigo1100@gmail.com>]

From what I understand in the output of `guix package -u' (see below),
whenever I execute it, some derivations that exist in `/gnu/store' are
passed to `guix build' and so they are built. Am I correct?

If I'm correct, I would like to know how I can print the list that is
reported by `guix package -u' below "The following derivations will be
built". I know I can execute `guix package -u' and press `C-c' in the
next 5 seconds. However, I'd like to do this the right way. That is,
write a command that only prints that list and does nothing more.

The reason I'm asking is because sometimes I want to build specific
derivations in order to have those packages advertised in my local
network in the order that I feel it's the best for me.

,----
| $ guix package -u
| The following packages will be upgraded:
|    (... list of packages ...)
|
| The following derivations will be built:
|    (... list of derivations in /gnu/store ...)
|
| building (... a derivation ...)
| - 'unpack' phase
`----