Possible combination trick

Let’s say I have this:

to you the dog
to that the dog
was to the dog
and you the dog
you and the dog
and that the dog
and he the dog
he and the dog
and was the dog

and I want this

to you and this
to that and this
was to and this
and you and this
you and and this
and that and this
and he and this
he and and this
and was and this

How do you change every the dog to and this with a command. Then have it
sent to a .rb without changing them manually one by one.

Sounds like you need the gsub function: http://www.ruby-doc.org/core/classes/String.html#M001186

…then you write the changed lines to a new file, close the new file, delete the old file, and rename the new file to the old file name. You can use Tempfile to come up with a new filename that won’t clash with any existing filenames.