Editing Standard streams (section)

==Standard input (stdin)==<!-- This section is linked from [[COMMAND.COM]] -->
Standard input is a stream from which a program reads its input data. The program requests data transfers by use of the ''read'' operation. Not all programs require stream input. For example, the ''[[dir (command)|dir]]'' and ''[[ls]]'' programs (which display file names contained in a directory) may take [[Command-line interface#Arguments|command-line arguments]], but perform their operations without any stream data input.

Unless [[Redirection (computing)|redirected]], standard input is inherited from the parent process.  In the case of an interactive shell, that is usually associated with the input device of a [[Computer terminal|terminal]] (or [[Pseudoterminal|pseudo terminal]]) which is ultimately linked to a user's [[Keyboard (computing)|keyboard]].

On [[POSIX]] systems, the [[file descriptor]] for standard input is 0 (zero); the [[POSIX]] <code><unistd.h></code> definition is <code>STDIN_FILENO</code>; the corresponding C <code><stdio.h></code> abstraction is provided via the <code>FILE* stdin</code> global variable. Similarly, the global C++  <code>std::cin</code> variable of type <code><iostream></code> provides an abstraction via [[Input/output_(C%2B%2B)#Input/output_streams|C++ streams]]. Similar abstractions exist in the standard I/O libraries of practically every [[programming language]].