Detailed explanation of setting method of PHP general return value

<?php
define("return_val", "return array(&#39;code&#39; => 0, &#39;msg&#39; => &#39;&#39;, &#39;data&#39; => &#39;&#39;);");

define("RETURN_SUCCESS",    0); 
define("RETURN_RUNTIME_ERR",  1); 
define("RETURN_FILE_NOT_EXIST", 2); 

class ReturnConf{
  public static function CommonReturn(){
    return eval(return_val);
  }  
}
?>

<?php
require_once("Return.conf.php");

function get_file_line($filename){
  $result = ReturnConf::CommonReturn();
  
  $cmd = "wc -l $filename | awk &#39;{print $1}&#39;";
  exec($cmd, $output, $code);
  if (RETURN_SUCCESS !== $code){
    $result[&#39;code&#39;] = RETURN_RUNTIME_ERR;
    $result[&#39;msg&#39;] = "exec $cmd err";
    return $result; 
  }  

  $result[&#39;data&#39;] = $output[0];
  return $result;
}

print_r(get_file_line("test.php"));
?>