I’m a little surprised there’s no references to the gnu coreutil yes source. I love speculation as much as the next guy but a lot of it could be satisfied by reading the source code. It’s fascinating that the BSD code is linked but not the primary subject!

Source for yes which does all the buffer malarkey: https://github.com/coreutils/coreutils/blob/master/src/yes.c

Source for the actual output: https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob_pla...