FYI @deldesir and @EMG70 this PR was tested to show live (real-time) display of "percentage download progress" in the web front-end's "Tasks" view.

While carefully avoiding the pollution of /var/log/calibre-web.log and /var/log/xklb.log — as subprocesses' STDERR and STDIN streams were polluting log files with duplicate/triplicate (and definitely ugly!) messages.

So hopefully this PR (or similar) can be merged in short order if @deldesir's testing reconfirms this is on the right track! 🛤️

@deldesir please in future feel free to improve on these REGEX's (preferably keeping all 3 aligned!) if there's a specific need ✅

Many Thanks to @EMG70 who reconfirmed — on Lines 1035-1316 here:

https://sprunge.us/1D9ieU?en#n-1035

I forgot to mention:

This PR also changed log label "Warning" to "Debug" in /var/log/xklb.log

As discussed earlier:

• Suggested improvements for scripts/lb-wrapper [refactor logging & subprocess substitution, etc] #87 (comment)