cat << EOF > file.txt
# [[content here]]
EOF
On a more serious note: Neovim for quick file-edits, doom-emacs as my IDE.
Doom-emacs does most of the stuff you are already using out of the box, is highly configurable and it lets you use vim-keybindings. It’s also free (as in freedom) software!
Dijkstra wants to have a word with you
I’d say going with C is not a bad idea at all—I for one would be interested. C is not going to become obsolete any time soon and is an immensly useful language to be proficient in.
When I tried to learn C I felt like I’m doing everything wrong because the C-way of doing things is very different to what one is used to from more modern languages (header files, make etc). Bridging the gap between the “I can solve project euler challenges” stage and actually being able to organize and implement proper projects is difficult without a mentor, so why not share your expertise?
In the end, go with what you feel most like doing, there will be an audience either way. So pick what is most fun to you!
Have you tried
ed?