Standard output is the device where commands send information. Standard output is generally set to the screen but it can be any output device. Standard output is set during the login procedure. Standard output is also known by 1. 4. Standard input is the device where commands receive information.
Standard input is generaly set to the keyboard but it can be any input device.
Standard input is set during the login procedure. To the shell standard input is also known by 0. 5. Standard error is the output device where error messages are sent. Generally it is set to the screen but can be any output device. The file pointer for standard error is 'stderr'.