【WordPress】親カテゴリのスラッグ取得→表示

これやで

<?php 
$cats = get_the_category();
$cat = $cats[0];
if($cat->parent){
$parent = get_category($cat->parent);
echo $parent->slug;
}else{
echo $cat->slug;
}
?>

ちな、一行のやで〜

<?php $cats = get_the_category(); $cat = $cats[0]; if($cat->parent){ $parent = get_category($cat->parent); echo $parent->slug; }else{ echo $cat->slug; } ?>

【2015.04.07追記】スラッグじゃなくてカテゴリ名の場合

<?php
$category = get_the_category();
$cat_id = $category[0]->cat_ID;
$cat_name = $category[0]->cat_name;
$cat_slug = $category[0]->category_nicename;
?>
<?php echo $cat_name; ?>