Normally the 's' command only changes
the first instance on a line of the expression
it is looking for. Sometimes you want to change
more than one instance. If you put a 'g' after the
all instances of 'cat' will be changed to 'dog'. To
print the result you must say
('pg' at the end doesn't work, sorry).
Edit file 'stuff' in this directory to change every
instance of 'green' to 'red' on every line.
Then rewrite the file and type "ready".
red book, red paper, red pencil
red car, red sign, redhorn
green light, village green
green book, green paper, green pencil
green car, green sign, greenhorn