Standard Streams

These are the ways a process is allowed to interact with the external environment.

stdin - Defaults to keyboard stdout - Defaults the screen connected. stderr - Defaults the screen connected.

Standard streams inherited

For new processes/commands, standard stream file descriptors are inherited in the new process. This is exactly why the command output is simply written to same place from where the command is executed.

Information in File Descriptors

Every process has a file descriptor for all IO as well. The first 3 file descriptors for any process are 0, 1 and 2 which is stdin, stdout and stderr respectively.

The file descriptors fo these standard streams are address to a buffer object (backed by arrays or linked lists) from which the data is read or written.