Given encouragement to try tmux, here is what I've come up with as a "one-liner" (script) that does what I was originally looking for:
#!/bin/sh
tmux new-session -d -s split_screen_grep \; \
send-keys "/bin/sh -c '$1' | tee /tmp/split_screen_grep.txt" C-m \; \
split-window -h \; \
select-pane -t 1 \; \
send-keys "tail -f /tmp/split_screen_grep.txt | grep '$2'" C-m \;
tmux attach-session -t split_screen_grep
I use it as follows, first arg is a command, second arg is a pattern to search for:
$ ./split-grep "cat big_file.txt" "tmux"
This is the case for me as well. I tried NixOS this weekend, and even though it has more adoption than Guix, it still does not have 100% coverage of all software I wanted. That said, the packages I did install were pretty up-to-date. I guess NixOS is as close to "critical mass" as we've got when it comes to this type of OS. But if I were a wizard devops type person with more time, I'd probably enjoy Guix more.