Parallel download of rpm packages
I completely changed the approach which resulted in faster downloads, and improved functionality. The overall approach of the initial version works well for a generic solution looking for adding concurrency to independent jobs.


Removed zypper list-updates. This format is easier for machine consumption, but it's not intended for Tumbleweed. Replaced with zypper dup/inr/in --details;
Removed background jobs and waits. Replaced with aria2 which handles the maximum number of concurrent connections;
It pays off learning more about awk capabilities, in order to replace sequences of grep/awk/tr with a single awk;
The main job of the script became building a plain text file with URIs and target directory for each .rpm file


aria2 is really great tool. Superb quality. curl is not reliable in its native concurrent download capabilities.