Thank you so much, Peter and Roger, for those excellent and clear explanations.

In particular, the description of how process substitution works is super interesting. I wonder if it actually create a physical temp file, and if the temp file automatically gets cleaned up by the operating system. I'll google it and do more research.

The thing about running "sh script.sh" totally makes sense, and that's pretty much what I figured was happening as soon as you pointed out that there's a difference between "sh" and "bash" (and remembered that the script was being launched by "sh").

Thanks!