(Attribution is questionable, but as a geezer I feel the need to make sure the younger generations at least are familiar with this:)

ed is the standard text editor

Let's look at a typical novice's session with the mighty ed:

  golem> ed

  ?
  help
  ?
  ?
  ?
  quit
  ?
  exit
  ?
  bye
  ?
  hello? 
  ?
  eat flaming death
  ?
  ^C
  ?
  ^C
  ?
  ^D
  ?

  ---
  Note the consistent user interface and error reportage.  Ed is
  generous enough to flag errors, yet prudent enough not to overwhelm
  the novice with verbosity.

(As a geezer, I also have to say I really am impressed with ed in some ways, and you should never be afraid to try it when you have a specific and known edit you want to do.)