将功能输出与数字进行比较。消失的结果

Question

我试图比较这个，无论是否有进程，结果始终为false

 output=$(minikube ssh 'ps -ef | grep dashboard | grep -v grep | wc -l')
 if [[ "$output" == 0 ]]; then
   echo "Starting minikube dashboard"
 else
   echo "Minikube dashboard already has been started"
 fi

有趣的时刻：

$echo $output
1
$echo "$output smth"
 smth

那么功能输出是怎么回事？