$! is only set to a useful value if the function that you call fails. If it succeeds, you cannot draw conclusions from the value of $!. If you look at the source code of File::Copy, you see that the move command first tries a rename(). If that fails, it tries copying and unlinking. But if the rename() fails, rename() sets $! Even if the copy and unlink() succeeds.

The right way to test whether move() succeeds is by checking its return value.

Abigail