How to identify that the string is a path to any file, using PHPcode?

Using P开发者_如何学GoHP, How to identify that the string is a path to any file?

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http://pt.php.net/is_file

$path = 'string';
if(is_file($path)){
  // look, it's a file!
}

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is_file($filename)
is_dir($filename)

Will return true if the string points to an existing file or directory.