How can I test for a serialized variable? Without throwing E_NOTICE if string is not serialized

I am coding my own var_dump to meet certain requirements which probably only apply to me and have a problem.

The code checks for objects, arrays, etc and finally gets to a stage where it reckons it is left with a number, a string or a boolean.

Of course, a string can actually be a serialized variable, so I want to heck for that ...

if (is_string($variable))
{
   // check if it is serialzed; if so, unserialize & dump as an array, \
   // with a suitable header indicating that it was serialized
   try
   {
      $old_error_level= error_reporting(E_ALL ^ E_NOTICE);
      $unserialized_varaible = @unserialize($variable);
      $result .= my_dump($unserialized_varaible, ... <some params&开发者_如何学编程gt;); // recursive call
      $old_error_level= error_reporting($old_error_level);
   }

   catch(Exception $e)    // Treat it as a string
   {
       $old_error_level= error_reporting($old_error_level);
       $result .= GetHtmlForSimpleVariable($variable, ... <some params>);
   }
}

But, what I get when trying to dump a simple, non-serialized, string is

Problem type Notice "unserialize() 
  [<a href='function.unserialize'>function.unserialize</a>]:
  Error at offset 0 of 14 bytes" at line 362 in file my_dump.php<br><br>

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Update: the point there is that I want to suppress that E_NOTICE when a string is not a serialized string. I had thought that the @on @unserizlize() would do that, but ...

If the string is serialized then everything is hunky dory. If not, then not.

---

When you try to unserialize it, it returns false if it is not serialized. It also returns a an E_NOTICE which is where that output is coming from.

From the manual:

In case the passed string is not unserializeable, FALSE is returned and E_NOTICE is issued.

Check if the return value of unserialize ===false