<===> input.scss
$media1: screen;
$media2: print;
$var: -webkit-min-device-pixel-ratio;
$val: 20;
@media #{$media1} and ($var: $val), only #{$media2} {a {b: c}}

<===> output.css
@media screen and (-webkit-min-device-pixel-ratio: 20), only print {
  a {
    b: c;
  }
}