A file descriptor is a small integer assigned to every open file in UNIX. The file descriptors for standard input, standard output, and standard error are 0, 1, and 2. The I/O and error redirection can be performed with the help of file descriptors by using file descriptors for standard file with the < and > operator, as in 0<, 1>, and 2>, for input, output, and error redirections, respectively. For example, cat 1>letter 2>save 0letter 2>/dev/null cat 2>save1 0save2 1>letter For the second command line, give one case that some messages will be output into file "save1", and give another case that some messages will be output into file "save2". You should make two demonstrable cases in a computer. Take the screenshots to show the two cases in your homework submission.