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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:
Standard output is a stream to which a program writes its output data. The program requests data transfer with the write operation. Not all programs generate output.
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
The many advantages include easy program or file selection, quick start, and interactive debugging. A shell script can be used to provide a sequencing and decision-making linkage around existing programs, and for moderately sized scripts the absence of a compilation step is an advantage.
Console redirection Stream redirection Configurability Startup/shutdown scripts Batch scripts Logging Available as statically linked, independent single file executable Thompson shell: UNIX: sh 1971 — UNIX: UNIX — Yes Text-based CLI: No No — Yes — — — — — — Bourne shell 1977 version 7th Ed. UNIX: sh 1977 Yes [1] 7th Ed. UNIX ...
m4 is a general-purpose macro processor included in most Unix-like operating systems, and is a component of the POSIX standard. The language was designed by Brian Kernighan and Dennis Ritchie for the original versions of UNIX. It is an extension of an earlier macro processor, m3, written by Ritchie for an unknown AP-3 minicomputer. [1]
In computer networking, STREAMS is the native framework in Unix System V for implementing character device drivers, network protocols, and inter-process communication.In this framework, a stream is a chain of coroutines that pass messages between a program and a device driver (or between a pair of programs).