Perl Programming/Keywords/-z

The -z keyword
-z is a file test that returns true, if the file has zero size (is empty).

It takes one argument, either a FILENAME, a FILEHANDLE, or a DIRHANDLE to test the associated file to see if the file has zero size. If the argument is omitted, it tests $_. -z returns 1 for true and an empty string for false. If the file doesn't exist or can't be examined, it returns <tt>undef</tt> and sets <tt>$!</tt> (<tt>errno</tt>).