If you have to do these checks again and again, you can think of creating a dedicated sub routine for that.

sub all_defined {
    for my $i ( @_ ) {
        #return 0 if !defined $i;
        return if !defined $i;
    }
    return 1;
}

if ( all_defined( $WCkey, $SCkey, $Pkey, $Wkey, $Ukey ) ) {
    print "bla bla";
}
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