It's not enough to check whether $! is set. From "perldoc perlvar":
> Many system or library calls set "errno" if they fail, to
> indicate the cause of failure. They usually do not set "errno"
> to zero if they succeed and may set "errno" to a non-zero value
> on success. This means "errno", hence $!, is meaningful only
> *immediately* after a failure:
To protect against potential issues, check the return value of unlink
and only check $! if it failed.
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>