other necessary files included. cmd+alt+b will select the line and make it a full comment block
awk '{print "#" $0}' *.tf
perl -pi -e's/^/#/' *.tf
# try this out
perl -e "print '#'x42 . \"\n#\n\" . '#'x42" | pbcopy
node -p 'fs = require("fs");fs.readdirSync(".").filter(x => x.endsWith(".tf")).forEach(y => {fs.readFile(y, "utf8", function (e,z) {if (e) {return console.log(e);};z.split("\n").forEach(l => console.log(`# ${l}`));});})'
Yp - duplicate current line, leaving the cursor at the lower of the two
V - enter visual line mode
k - go up and select both lines
r# - replace every selected character with #. Leaves visual mode and leaves cursor at the upper line.
p - put the yanked line (the original) on the next line.