get specific lines from a repeated range pattern in a text file

Question

Wow, this sounds so complicated in the title, but I assume it is not quite so.

I have text files that have basically this layout:

Stimulus ...
...
...
...
Response
Stimulus ...
...
...
...
Response

I used sed to get everything in between and then further extracted information I needed.

sed -n -e '/Stimulus/,/Response/ p'

However, sometimes the participants do not respond, in which case the file looks like this:

Stimulus ...
...
...
...
Stimulus ...
...
...
...
Response

In this special case, my script will not get what I am looking for. So, I am looking for a way to extract the information if and only if the pattern1 is followed by pattern2, not pattern1 again.

Let me know, if I formulated it unclear. I am more then happy to provide further information.

Answer 1

One dirty way, although it seemed to work in my test, could be to reverse the file content, search from Response to Stimulus and reverse again the result.

Assuming following input data:

Stimulus 1...
...
...
...
Stimulus 2...
...
...
...
Response 2
Stimulus 3...
...
...
...
Response 3
Stimulus 4...
...
...
...
Stimulus 5...

The command:

tac infile | sed -ne '/Response/,/Stimulus/ p' | tac -

Yields:

Stimulus 2...
...
...
...
Response 2
Stimulus 3...
...
...
...
Response 3

---

EDIT: For an example with isolated Response parts. There is to filter twice (based on a comment of the OP):

tac infile | 
  sed -ne '/Response/,/Stimulus/ p' | 
  tac - | 
  sed -ne '/Stimulus/,/Response/ p'