Standard Input, Output, and Error

Linux programs use three data streams:

Stream	Name	Description
stdin	Standard Input	Input data (usually from keyboard or another command)
stdout	Standard Output	Normal output of a command
stderr	Standard Error	Error messages

Example:

ls > files.txt

Redirects output (stdout) to files.txt.

ls /root 2> errors.txt

Redirects error messages (stderr) to errors.txt.