A tied handle is a Perl variable that Perl presents as a file handle, but isn't. When a program passes a tied handle to a Perl IO function, Perl calls a subroutine instead of doing IO calls. There's no way for Perl to cause a child process (that might not even be a Perl program) to call a sub in its parent instead of writing to a handle. As such, children cannot inherit tied handles or any other handle without a fileno.