#print
I hope you have been checking the effects of your
substitutions by using the 'p' command before and
after the changes.  This is so often desired that
you may type the 'p' on the same line, after the 's'
command.  Thus
  s/ab/cd/p
changes 'ab' to 'cd' and prints the line after the change.
In this directory there is a file named 'tree'.  Try changing
the fourth line, which now reads
   spruxx
to read
   spruce
and then rewrite the file, and type 'ready'.
#create Ref
pine
fir
hemlock
spruce
birch
beech
hickory
maple
#create tree
pine
fir
hemlock
spruxx
birch
beech
hickory
maple
#user
#cmp Ref tree
#log
#next
32.1a 10
31.2b 5