This how we override the UNIX default predefined I/O defaults.
This is not part of C but operating system dependent. We will do redirection from the command line.
> - redirect stdout to a file.
So if we have a program, out, that usually prints to the screen then
out > file1
will send the output to a file, file1.
< - redirect stdin from a file to a program.
So if we are expecting input from the keyboard for a program, in we can read similar input from a file
in < file2.
| - pipe: puts stdout from one program to stdin of another
prog1 | prog2
e.g. Sent output (usually to console) of a program direct to printer:
out | lpr