You asked in the OP what is different about your command and why isn't the 'or die' clause working in your open command. I provided documentation that shows if you open a pipe it returns the pid instead of just non-zero or zero like with opening a file. That is the difference and the answer to your question.

I wasn't telling you to do anything with the pid, only that it is the return value and the reason why your code didn't work as expected.

I don't think this example should be included in the documentation for open since it doesn't work as expected for pipes.