Perl Programming/Keywords/-T

The -T keyword
-T is a file test that tests if the filehandle is opened to a TTY.

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