Also, it can become difficult to distinguish between program and data files. Standard input 3. Pipes are used to take the standard output from one command and use it as standard input to the next command. Redirection, instead of reading or writing to or from standard input or standard output, can be told to write or read from a device or file. Standard input is the keyboard.
Standard output is the screen.
You can tell a command to redirect its output to a file or device. Standard error is also the screen. You can tell standard error to redirect its output to a file or a device. Pipes must have a command on either side of a pipe. Once you have used the redirection symbol, you cannot pipe that output.