FreeBSD® Unleashed

File Descriptors

File descriptors are numbered IDs that are set up each time the kernel starts a process. These numbers are what the process uses to write output and read input. There are three file descriptors that are opened by default:

F.D. 0	STDIN. This is where standard input comes from. It is normally the keyboard, but it can be redirected to read from a file or some other source.
F.D. 1	STDOUT. This is where standard output goes. It is normally the screen, but as you have seen it can be redirected.
F.D. 2	STDERR. This is where standard error messages go. Once again, it is normally the screen, but it can also be redirected.

File descriptors can be used in shell programs to make your programs both more efficient and easier to write. The ...