Whenever a UNIX command is executed, it opens three standard files for standard input and output. UNIX uses file descriptor 0 for standard input (stdin), 1 for standard output ( stdout ), and 2 for standard error (stderr) messages. In this chapter, you learned the meaning of standard input, output, and error and how to redirect them. You used the output redirection symbol > , input redirection symbol < , and error redirection symbol 2> . In addition, you learned how to append output of a command to a file with the >> symbol. You also used 2>&1 to redirect standard output and standard error to one place.
Use of pipes was the other important matter discussed in the chapter. You used the pipe symbol " " and also used the tee command to pipe output of a command to more than one place.