Question

Both stdin and stdout file descriptors point to it. How does it work? Can some one point to a good resource for understanding UNIX terminals and system calls that interact with it.

Answer 1

dev/tty is a file system object that represents the current console. Copying files into this “directory” from the command line prints out the content of these files to your console:

cp myfile.txt /dev/tty

is equivalent to

cat myfile.txt

These objects are there to let you use the familiar file APIs to interact with console. It is a clever way to unify console API with file API. You can use fopen, fprintf, etc. to interact with the console in the same way that you interact with regular files.

This example writes "Hello, world\n" to the terminal:

#include <stdio.h>

int main (int argc, const char * argv[]) {
    FILE *f = fopen("/dev/tty", "w");
    fprintf(f, "Hello, world!\n");
    return 0;
}