Standard streams

Originally I/O happened via a physically connected system console (input via keyboard, output via monitor), but standard streams abstract this.

In most operating systems predating Unix, programs had to explicitly connect to the appropriate input and output devices.

On many systems it was necessary to obtain control of environment settings, access a local file table, determine the intended data set, and handle hardware correctly in the case of a punch card reader, magnetic tape drive, disk drive, line printer, card punch, or interactive terminal.

Older operating systems forced upon the programmer a record structure and frequently non-orthogonal data semantics and device control.

Another Unix breakthrough was to automatically associate input and output to terminal keyboard and terminal display, respectively, by default[citation needed] — the program (and programmer) did absolutely nothing to establish input and output for a typical input-process-output program (unless it chose a different paradigm).

In contrast, previous operating systems usually required some—often complex—job control language to establish connections, or the equivalent burden had to be orchestrated by the program.

For example, the dir and ls programs (which display file names contained in a directory) may take command-line arguments, but perform their operations without any stream data input.

For example, the file rename command (variously called mv, move, or ren) is silent on success.

The usual destination is the text terminal which started the program to provide the best chance of being seen even if standard output is redirected (so not readily observed).

In the C programming language, the standard input, output, and error streams are attached to the existing Unix file descriptors 0, 1 and 2 respectively.

Ken Thompson (designer and implementer of the original Unix operating system) modified sort in Version 5 Unix to accept "-" as representing standard input, which spread to other utilities and became a part of the operating system as a special file in Version 8.

[9] Basic read and write capabilities for the stdin and stdout streams are also accessible directly through the class System.Console (e.g. System.Console.WriteLine() can be used instead of System.Console.Out.WriteLine()).

System.Console.In, System.Console.Out and System.Console.Error are System.IO.TextReader (stdin) and System.IO.TextWriter (stdout, stderr) objects, which only allow access to the underlying standard streams on a text basis.

GUIs created with scripting tools like Zenity and KDialog by KDE project[10] make use of stdin, stdout, and stderr, and are based on simple scripts rather than a complete GUI programmed and compiled in C/C++ using Qt, GTK, or other equivalent proprietary widget framework.

The Common Lisp Interface Manager paradigm "presents" GUI elements sent to an extended output stream.