If you want a general answer, you can use named pipes, created by the mknod command. They solve the following problem: one can use pipes to divert the standard output of a program to the standard input of another one, but sometimes, one may want several programs (or several copies of the same program) to write to the standard input of a single program, one after the other. A named pipe look like a file, several programs may write to it, and a program reading from it would get the stream of data as if it came from a single file. But this Unix-specific mechanism is quite old---I wouldn't really advise using it for serious stuff.