H
# empty append at address 0 should set the current address to 0
0a
.
+4a
# this is not a comment
.
# empty append at current address should not modify the current address
a
.
a
hello world!
.
a
hello world!!
.
0a
hello world!!!
.
!read one	# shell escape should not modify the current address
text for the read shell command above
a
shell escape marker
.
$a
hello world!!!!
.
u
u
a
hello world!!!!!
.
a
to be undone
.
u
w out.o