$ perl -Mstrict -Mwarnings -E 'my ($u, $p) = (qq{W$X}, qq{Y@Z}); say for $u, $p'
Possible unintended interpolation of @Z in string at -e line 1.
Global symbol "$X" requires explicit package name (did you forget to declare "my $X"?) at -e line 1.
Global symbol "@Z" requires explicit package name (did you forget to declare "my @Z"?) at -e line 1.
Execution of -e aborted due to compilation errors.