if ( "ok" eq eval { process_upload_as_excel($upload); "ok" } )
{
    # Do stuff, report success.
}
elsif ( $@ )
{
    my $first_err = $@;
    if ( "ok" eq eval { process_upload_as_cvs($upload); "ok" } )
    {
        # Do stuff, report success.
    }
    else
    {
        die "Couldn't process as Excel or CVS...";
        # Include $first_err and (new one) $@. Or don't.
        # I'm a code comment, not a cop.
    }
}
else
{
    die "Unknown failure!";
}