You didn't convert the file names into shell string literals when you created the shell command. There are two simpler alternatives:

You can use the multi-arg form of system which passes the arguments to the child without serializing them*:

system('cp', $oldname, "renamed/$newname")
   or die("cp: $!/$?\n");
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You can use File::Copy:

copy($oldname, "renamed/$newname")
   or die("copy: $!\n");
[download]

* — Serialization will occur in Windows, but Perl will handle quoting and escaping for you (within the limits of Windows's command line abilities).