[GNU diff] new (?) conditional diff functionality

[Frédéric Conrotte]

Hello,

 

I'm working in a company that put tags in its COBOL source code

to identify a maintenance.

 

I'd like to do some "diff" between old and new sources

where diff reports differences only IF the new source's code line includes this tag.

That's what I call the "conditional diff functionality"

 

It could be called a "conditional left diff", where "left" is the new source.

 

I've been looking for this functionality in diff options (and diff.c)

but for what I've understood this option is not yet available.

 

Can you just tell me if this functionality already exists in the GNU diff tool ?

 

thank you,

 

Fred