13.6. Redirection and Pipes
Normally, standard output (stdout) from a command goes to the screen, standard input (stdin) comes from the keyboard, and error messages (stderr) go to the screen. The shell allows you to use the special redirection metacharacters to redirect the input/output to or from a file. The redirection operators (<, >, >>, >&) are followed by a filename. This file is opened by the shell before the command on the left-hand side is executed.
Pipes, represented by a vertical bar (|) symbol, allow the output of one command to be sent to the input of another command. The command on the left-hand side of the pipe is called the writer because it writes to the pipe. The command on the right-hand side of the pipe is the reader because ...
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