Install and use vimdiff. Its superior in every way. 

http://vimcasts.org/episodes/comparing-buffers-with-vimdiff/

Or

man diff

But use vimdiff

> On Oct 7, 2017, at 12:16 AM, joe@actionline.com wrote:
> 
> When I try to use 'diff' to compare two htm files,
> diff shows all lines including all identical lines.
> 
> How can I get diff to show only lines that are different?
> 
> 
> 
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