Feature: dry mode that lists packages that can be upgraded

[Merinorus]

Hello,

First of all, many thanks for this tool which is easy and convenient to use!

Is there a possibility to have a kind-of dry mode that lists only packages to be upgraded?

For instance:

$> pur -r requirements.txt -d
fastapi: 0.80.0 -> 0.82.0
python-dotenv: 0.20.0 -> 0.21.0
2 package upgrade(s) available.

I tried something like:

$> pur -n -r requirements.txt -d | sed '$ d' | diff --suppress-common-lines -y requirements.txt -
                                                              > ==> requirements.txt <==
fastapi==0.80.0                                               | fastapi==0.82.0
python-dotenv==0.20.0                                         | python-dotenv==0.21.0

Or maybe there is another tool that already provides this information.

Thank you!