How to get linux command results in php

public function get_server_ip() {
 	if (PHP_SAPI === 'cli'){
	 	$buffer = "";
		 $handle = popen("ifconfig eth0|grep 'inet addr'|awk -F'[ :]' '{print $13}'", 'r');
			while(!feof($handle)) {
			 $buffer.=fgets($handle);
			}
			pclose($handle);
		 $server_ip = rtrim($buffer);
 	}else{
	 	if (isset($_SERVER)) { 
		  if($_SERVER['SERVER_ADDR']) {
		   $server_ip = $_SERVER['SERVER_ADDR']; 
		  } else { 
		   $server_ip = $_SERVER['LOCAL_ADDR']; 
		  } 
		 } else { 
		  $server_ip = getenv('SERVER_ADDR');
		 }
 	}
	 return $server_ip; 
	}