Re^3: bsd_glob does not reset $!

[ikegami]

Unfortunately it is not set to a value other than zero when the globbing produced no result

No matches is not an error. You could check for that condition explicitely.

if (GLOB_ERROR || !@list) {
   ... error or no match ...
}

But then, why is it reset with $pat4 in the above example??

The value of $! is meaningless on success. It could be zero, non-zero, undef, etc.