Standard Input/Output/Error

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Programs need to get input, and output results or error messages if any. In Unix-like systems such as GNU/Linux, the system provides the interfaces, or links for those purposes.

  • The link for input is called standard input. By default, it is connected to the keyboard.
  • The link for normal output is called standard output. By default, it is connected to the screen.
  • The link for error message output is called standard error. By default, it is also connected to the screen.

In Unix-like systems, everything is treated as a file. every file has a file descriptor (an index number). So are standard input, output, and error.

File Descriptor
stdin 0
stdout 1
stderr 2

The endpoints, or files, they connect to can be changed, this action is called redirection.

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