https://www.youtube.com/watch?v=Zpdo6We-_e0
ed test.txt #ed is terse as it was cost effective as it was often printed on paper.
ed -p ":" /tmp/test.txt
# add verbose errors
:H
# ed in the 60s
# vi came around in the 70s
#ed has command mode and insert mode
:a
# append
This is line one.
.
# the period ends the insert
:,p
# is shorthand for
:1,$p
:a
This is line 2.
.
:,p
:,n
#will print line numbers
:n
# will print current line
:p
:i
#insert:- p # print previous line :4c #changes line 4 :1d
#deletes line 1 :u #undo the last command (only 1 life) :2t0 #copy line
2 to 0 :1m2 #move line 1 to 2 :/This #show lines with :/This