stop form action from going to page if search field is empty

I have a search field in a form that looks like this on my index.php page.

 

 <form action="search.php" method="post">

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The search function is working fine but I don't want the page to actually go to search.php if the search field is empty i.e.: they just click "search" without actually inputting anything.

I tried this above the form:

 $error = "";
		  
		  if($_SERVER['REQUEST_METHOD'] == "POST"){
			  
			  if (empty($_POST['search'])){
				  
				  $error .="Please enter a search term";
				  
			  } 
		  }

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But it still posts the search.php page and shows the error there. Is it possible to stop the page from redirecting to search.php if the search input is empty?