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Process Substitution
In computing, process substitution is a form of inter-process communication that allows the input or output of a command to appear as a file. The command is substituted in-line, where a file name would normally occur, by the command shell. This allows programs that normally only accept files to directly read from or write to another program. History Process substitution was available as a compile-time option for ksh88, the 1988 version of the KornShell from Bell Labs. The rc shell provides the feature as "pipeline branching" in Version 10 Unix, released in 1990. The Bash shell provided process substitution no later than version 1.14, released in 1994. Available in the Gnu source archive of version 1.14.7as of 12 February 2016. Example The following examples use KornShell syntax. The Unix diff command normally accepts the names of two files to compare, or one file name and standard input. Process substitution allows one to compare the output of two programs directly: $ diff ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inter-process Communication
In computer science, interprocess communication (IPC) is the sharing of data between running Process (computing), processes in a computer system. Mechanisms for IPC may be provided by an operating system. Applications which use IPC are often categorized as client–server model, clients and servers, where the client requests data and the server responds to client requests. Many applications are both clients and servers, as commonly seen in distributed computing. IPC is very important to the design process for microkernels and nanokernels, which reduce the number of functionalities provided by the kernel. Those functionalities are then obtained by communicating with servers via IPC, leading to a large increase in communication when compared to a regular monolithic kernel. IPC interfaces generally encompass variable analytic framework structures. These processes ensure compatibility between the multi-vector protocols upon which IPC models rely. An IPC mechanism is either Synchroni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gzip
gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and intended for use by GNU (from which the "g" of gzip is derived). Version 0.1 was first publicly released on 31 October 1992, and version 1.0 followed in February 1993. The decompression of the ''gzip'' format can be implemented as a streaming algorithm, an important feature for Web protocols, data interchange and ETL (in standard pipes) applications. File format gzip is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algorithms which, at the time, limited the usability of the compress utility and other popular archivers. "gzip" also refers to the gzip file format (described in the table below). In sho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anonymous Pipe
In computer science, an anonymous pipe is a simplex FIFO communication channel that may be used for one-way interprocess communication (IPC). An implementation is often integrated into the operating system's file IO subsystem. Typically a parent program opens anonymous pipes, and creates a new process that inherits the other ends of the pipes, or creates several new processes and arranges them in a pipeline. Full-duplex (two-way) communication normally requires two anonymous pipes. Pipelines are supported in most popular operating systems, from Unix and DOS onwards, and are created using the ", " character in many shells. Unix Pipelines are an important part of many traditional Unix applications and support for them is well integrated into most Unix-like operating systems. Pipes are created using the pipe system call, which creates a new pipe and returns a pair of file descriptors referring to the read and write ends of the pipe. Many traditional Unix programs are design ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comparison Of Command Shells
This article catalogs comparable aspects of notable operating system shell (computing), shells. General characteristics {, class="wikitable sortable sticky-header sort-under" style="width: auto; text-align: center; font-size: smaller;" , - !Shell ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! , - !Thompson shell , Unix, UNIX , sh , 1971 , , Unix, UNIX , Unix, UNIX , , , Text-based Command-line interface, CLI , , , , , , , , , , , - !Bourne shell 1977 version , Version 7 Unix, 7th Ed. UNIX , sh , 1977 , , Version 7 Unix, 7th Ed. UNIX , Version 7 Unix, 7th Ed. UNIX, , , , Text-based Command-line interface, CLI , , , , , , , , , , , - !Bourne shell current version , Various Unix, UNIX , sh , 1977 , , SunOS-5.x, FreeBSD , SunOS-5.x , , , Text-based Command-line interface, CLI , , Since mid 1990s. , , , , , , , if compiled with -DACCT. , , - !POSIX shell , POSIX , sh , 1992 , , , POSIX , , , Text-based CLI , , , , , , , {{small, Unspecifi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Command Substitution
In computing, command substitution is a facility that allows a Command-line interpreter, command to be run and its output to be pasted back on the command line as arguments to another command. Command substitution first appeared in the Bourne shell, introduced with Version 7 Unix in 1979, and has remained a characteristic of all later Unix shells. The feature has since been adopted in other programming languages as well, including Perl, PHP, Ruby (programming language), Ruby and Microsoft's Powershell under Windows. It also appears in Microsoft's CMD.EXE in the FOR command and the ( ) command. Syntax and semantics Shells typically implement command substitution by creating a child process to run the first command with its stdout, standard output Pipeline (Unix), piped back to the shell, which reads that output, parsing it into words separated by whitespace character, whitespace. Because the shell can't know it has all the output from the child until the pipe closes or the child ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pipeline (Unix)
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of process (computing), processes chained together by their standard streams, so that the output text of each process (''stdout'') is passed directly as input (''stdin'') to the next one. The second process is started as the first process is still executing, and they are executed concurrency (computer science), concurrently. The concept of pipelines was championed by Douglas McIlroy at Unix's ancestral home of Bell Labs, during the development of Unix, shaping its Unix philosophy, toolbox philosophy. It is named by analogy to a physical pipeline transport, pipeline. A key feature of these pipelines is their "hiding of internals". This in turn allows for more clarity and simplicity in the system. The pipes in the pipeline are anonymous pipes (as opposed to named pipes), where data written by one process is buffered by the operating system un ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix File Types
The Unix file types are the categories of file formats that a Unix-based system uses to provide context-sensitive behavior of file system items all of which called ''files'' in Unix-based systems. POSIX defines categories: regular, Directory (computing), directory, symbolic link, Named pipe, FIFO special, Device file, block special, character special, and Unix domain socket, socket. An operating system may define additional categories (e.g. Solaris Doors (computing), doors). A regular file is any file format that the file system does not know and relies on applications to manipulate. The other categories are for file formats that the file system inherently knows and can manipulate. The ls, ls -l command reports a file's category via the character before the File-system permissions#Notation of traditional Unix permissions, permissions information. The File (command), file command reports file format information; even for regular files. Representations Numeric The type of a f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Random Access
Random access (also called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any other, no matter how many elements may be in the set. In computer science it is typically contrasted to sequential access which requires data to be retrieved in the order it was stored. For example, data might be stored notionally in a single sequence like a row, in two dimensions like rows and columns on a surface, or in multiple dimensions. However, given all the coordinates, a program can access each record about as quickly and easily as any other. In this sense, the choice of datum is arbitrary in the sense that no matter which item is sought, all that is needed to find it is its address, i.e. the coordinates at which it is located, such as its row and column (or its track and record number on a magnetic drum). At first, the term "random access" was used because th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fseek
The C (programming language), C programming language provides many standard library subroutine, functions for computer file, file input/output, input and output. These functions make up the bulk of the C standard library header file, header . The functionality descends from a "portable I/O package" written by Mike Lesk at Bell Labs in the early 1970s, and officially became part of the Unix operating system in Version 7 Unix, Version 7. The I/O functionality of C is fairly low-level by modern standards; C abstracts all file operations into operations on stream (computing), streams of bytes, which may be "input streams" or "output streams". Unlike some earlier programming languages, C has no direct support for random access, random-access data files; to read from a record in the middle of a file, the programmer must create a stream, fseek, seek to the middle of the file, and then read bytes in sequence from the stream. The stream model of file I/O was popularized by Unix, which was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiprocessing
Multiprocessing (MP) is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There are many variations on this basic theme, and the definition of multiprocessing can vary with context, mostly as a function of how CPUs are defined ( multiple cores on one die, multiple dies in one package, multiple packages in one system unit, etc.). A multiprocessor is a computer system having two or more processing units (multiple processors) each sharing main memory and peripherals, in order to simultaneously process programs. A 2009 textbook defined multiprocessor system similarly, but noted that the processors may share "some or all of the system’s memory and I/O facilities"; it also gave tightly coupled system as a synonymous term. At the operating system level, ''multiprocessing'' is sometimes used to refer to the executi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wc (Unix)
(short for word count) is a command in Unix, Plan 9, Inferno, and Unix-like operating systems. The program reads either standard input or a list of computer files and generates one or more of the following statistics: newline count, word count, and byte count. If a list of files is provided, both individual file and total statistics follow. Example Sample execution of wc: $ wc foo bar 40 149 947 foo 2294 16638 97724 bar 2334 16787 98671 total The first column is the count of newlines, meaning that the text file foo has 40 newlines while bar has 2294 newlines- resulting in a total of 2334 newlines. The second column indicates the number of words in each text file showing that there are 149 words in foo and 16638 words in bar giving a total of 16787 words. The last column indicates the number of characters in each text file, meaning that the file foo has 947 characters while bar has 97724 characters 98671 characters all in all. Newer versions o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
