UNIX for Advanced & Expert Users

This is something I've given a lot of thought to and come up with no answer.

Say you have a data stream passing from a file, through process A, into process B. Process A only modifies a few bytes of the stream, then prints the rest of the stream unmodified. Is there any way to stream the file into process B directly instead of doing redundant reads and writes?

Not sure what you want to do

Do you have a better example.....

May depend on what you what to do?

Do you know the position of the changes in advance?

Position? It's a pipe.

I've thought of lots of applications for this idea, but the original one was a sort of temporary automatic buffer. One process produces data and writes it to the next, the next buffers it, the third reads from the buffer. When the buffer bottoms out, the process joins the input and output pipes together then quits.

It was a stream in your original post.

The reason I asked this, was without being able to correlate changes and raw data, I don't see how you could avoid the duplicated read, ie you need to know in the final stream reader what bytes to read from the source and which to read from the pipe.