> But calling stat on a pipe makes no sense, as Perl has no idea what file(s) the command opens and processes.

I didn't realize that. In the example from my code where I call stat on the pipe opened to zcat, if I call stat() on the filename and stat() on the open pipe handle and compare the mtime values (last modified), the filename's mtime value is the last modified value as reported in Linux, but the handle's last modified value is the time the pipe was opened.