My first thought was "emacs editing characters already work on the command line."

Then I thought, maybe there are commands you want to be really really sure of before submitting them?

Then I realized I very frequently use very long commands with loops and pipes that might benefit, like:

  for i in *.py; do mv $i AA_$i; done

  find . -type f |while read f; do if cmp -s "$f" ../new/"$f"; then rm -f "$f"; fi ;done