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In computing, redirection is a form of interprocess communication, and is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations. The concept of redirection is quite old, dating back to the earliest operating systems (OS).
Process substitution can also be used to capture output that would normally go to a file, and redirect it to the input of a process. The Bash syntax for writing to a process is >(command). Here is an example using the tee, wc and gzip commands that counts the lines in a file with wc -l and compresses it with gzip in one pass:
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. Unless redirected , standard input is inherited from the parent process.
Version 1 AT&T UNIX dd: Filesystem Mandatory Convert and copy a file Version 5 AT&T UNIX delta: SCCS Optional (XSI) Make a delta (change) to an SCCS file PWB UNIX df: Filesystem Mandatory Report free disk space Version 1 AT&T UNIX diff: Text processing Mandatory Compare two files; see also cmp Version 5 AT&T UNIX dirname: Filesystem Mandatory
An important aspect of this, setting Unix pipes apart from other pipe implementations, is the concept of buffering: for example a sending program may produce 5000 bytes per second, and a receiving program may only be able to accept 100 bytes per second, but no data is lost. Instead, the output of the sending program is held in the buffer.
Rsh originated as part of the BSD Unix operating system, along with rcp, as part of the rlogin package on 4.2BSD in 1983. rsh has since been ported to other operating systems. The rsh command has the same name as another common UNIX utility, the restricted shell , which first appeared in PWB/UNIX ; in System V Release 4 , the restricted shell ...
The Thompson shell was the first Unix shell, introduced in the first version of Unix in 1971, and was written by Ken Thompson. [1] It was a simple command interpreter, not designed for scripting, but nonetheless introduced several innovative features to the command-line interface and led to the development of the later Unix shells.
UUCP (Unix-to-Unix Copy) [1] is a suite of computer programs and protocols allowing remote execution of commands and transfer of files, email and netnews between computers.. A command named uucp is one of the programs in the suite; it provides a user interface for requesting file copy operations.