usr/lib/learn/editor/L15.2a

#print
So far you have learned how to
copy and print existing files, and now
you probably want to know how to add new text
to a file.  The "a" (append) command lets
you do that.  For example, the sequence
  ed file
  a
  A man, a plan, a canal - Panama.
  .
  w
  q
will append the line
  A man, a plan, a canal - Panama.
to the editor buffer, and write it on file "file".
(If "file" didn't exist already, the editor will
warn you.  It's not an error, just a warning.)
Try that.  Then say "cat file" to check what was written,
and then type "ready".
#create Ref
A man, a plan, a canal - Panama.
#user
#cmp file Ref
#log
#next
15.2b 5
15.3b 2