For fun I ran a quick benchmark test in my Ubuntu 16.04 VM. I’ve noticed programs with a lot of output tend to go slower in eshell, so I ran the following command in both eshell in a fresh Emacs instance and gnome-terminal, both with my default login shell (zsh). It repeatedly prints y\n for 5 seconds, displaying the results and writing to a file.
$ timeout 5 yes | tee -a $file
Comparing the number of lines printed to each file:
~ $ wc -l emacs
1148639 emacs
~ $ wc -l gnome-terminal
5963776 gnome-terminal
~ $ (/ 5963776 1148639.0)
5.19203683663884
Gnome-terminal did 5x more work than eshell.
