I assume what you really want is to ignore all comment lines completely (not just changes to comment lines).
Diff won't do this directly, but that's what [named] pipes are for :)

try this:
diff <(grep -v '^//' file1) <(grep -v '^//' file2)

On 10/22/2012 01:59 PM, Eric Cope wrote:
> Hi all,
> I am trying to diff between two sets of files. I want to ignore comments
> (lines that start with //).
> I've tried
> 
>    - diff -I "//" file1 file2
>    - diff -I "\/\/" file1 file2
>    - diff -I "//.* file1 file2
> 
> among others. Has anyone successfully used diff and its ignore option?
> 
> Thanks,
> Eric
> 
> 
> 
> 
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