Is there a sort of ternary operator in #Sass ?

background.scss

  //...
  $background: null; // if you don't do this, background is undefined out of the @if/else scope
  @if ($direction) {
    $background: linear-gradient($direction, $color, $color2);
  }
  @else {
    $background: linear-gradient($color, $color2);
  }
  //...
  
  // can we do something like this ?
  $background: $direction ? /* value */ : /* other value */;

Yes, looks like

$background: if($direction, /*value*/, /*other value*/);

Added to SASS 3.1.2 chriseppstein/sass@b9a9e14

you could mimic the behaviour with your own functions like,

@function if($condition, $if-value, $else-value) {
    @if ($condition == true) {
        @return $if-value;
    } @else {
        @return $else-value;
    }
}

In sass 3.3, the if function only evaluates the argument that corresponds to the condition. This makes the if function as powerful as the @if directive.