Perl Programming/Keywords/-p

The -p keyword
-p is a file test that tests, if the file is a named pipe (FIFO), or filehandle is a pipe.

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 $_. -p returns 1 for true and an empty string for false. If the file doesn't exist or can't be examined, it returns <tt>undef</tt> and sets <tt>$!</tt> (errno).