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Stdout
In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin), standard output (stdout) and standard error (stderr). Originally I/O happened via a physically connected system console (input via keyboard, output via monitor), but standard streams abstract this. When a command is executed via an interactive shell, the streams are typically connected to the text terminal on which the shell is running, but can be changed with redirection or a pipeline. More generally, a child process inherits the standard streams of its parent process. Application Users generally know standard streams as input and output channels that handle data coming from an input device, or that write data from the application. The data may be text with any encoding, or binary data. In many modern systems, the standard error str ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redirection (computing)
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. In Unix-like operating systems, programs do redirection with the system call, or its less-flexible but higher-level stdio analogues, and . Redirecting standard input and standard output Redirection is usually implemented by placing certain characters between commands. Basic Typically, the syntax of these characters is as follows, using < to redirect input, and > to redirect output. command > file1 executes , placing the output in , as opposed to displaying it at the terminal, which is the usual destination for standard output. This will clobber any existing data in . Using command > file1. To read from a stream literal (an inline file, passed to the standard input), one can use a here document, using the << operator: $ tr a-z A-Z uno dos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Descriptor
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have non-negative integer values, with negative values being reserved to indicate "no value" or error conditions. File descriptors are a part of the POSIX API. Each Unix process (except perhaps daemons) should have three standard POSIX file descriptors, corresponding to the three standard streams: Overview In the traditional implementation of Unix, file descriptors index into a per-process maintained by the kernel, that in turn indexes into a system-wide table of files opened by all processes, called the . This table records the ''mode'' with which the file (or other resource) has been opened: for reading, writing, appending, and possibly other modes. It also indexes into a third table called the inode table that describes the actual u ... [...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 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 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 toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals" (Ritchie & Thompson, 1974). This in turn allows for more clarity and simplicity in the system. This article is about anonymous pipes, where data written by one process is buffered by the operating system until it is read by the next process, and this uni-directional channel disappears when the processes ... [...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 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 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 toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals" (Ritchie & Thompson, 1974). This in turn allows for more clarity and simplicity in the system. This article is about anonymous pipes, where data written by one process is buffered by the operating system until it is read by the next process, and this uni-directional channel disappears when the processes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System Console
One meaning of system console, computer console, root console, computer operator, operator's console, or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the Kernel (computer science), kernel, from the init system and from the syslog, system logger. It is a physical device consisting of a keyboard and a screen, and traditionally is a text terminal, but may also be a graphical terminal. System consoles are generalized to computer terminals, which are abstracted respectively by virtual consoles and terminal emulators. Today communication with system consoles is generally done abstractly, via the standard streams (stdin, stdout, and stderr), but there may be system-specific interfaces, for example those used by the system kernel. Another, older, meaning of system console, computer console, hardware console, operator's console or simply console is a hardware component used by an operator to control ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Command-line Interface
A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and providing information to them as to what actions they are to perform. In some cases the invocation is conditional based on conditions established by the user or previous executables. Such access was first provided by computer terminals starting in the mid-1960s. This provided an interactive environment not available with punched cards or other input methods. Today, many users rely upon graphical user interfaces and menu-driven interactions. However, some programming and maintenance tasks may not have a graphical user interface and use a command line. Alternatives to the command-line interface include text-based user interface menus (for example, IBM AIX SMIT), keyboard shortcuts, and various desktop metaphors centered on the pointer (usual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Programming
Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms (usually in a chosen programming language, commonly referred to as coding). The source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, which is directly executed by the central processing unit. The purpose of programming is to find a sequence of instructions that will automate the performance of a task (which can be as complex as an operating system) on a computer, often for solving a given problem. Proficient programming thus usually requires expertise in several different subjects, including knowledge of the application domain, specialized algori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
End-of-file
In computing, end-of-file (EOF) is a condition in a computer operating system where no more data can be read from a data source. The data source is usually called a file or stream. Details In the C standard library, the character reading functions such as getchar return a value equal to the symbolic value (macro) EOF to indicate that an end-of-file condition has occurred. The actual value of EOF is implementation-dependent and must be negative (but is commonly −1, such as in glibc). Block-reading functions return the number of bytes read, and if this is fewer than asked for, then the end of file was reached or an error occurred (checking of errno or dedicated function, such as ferror is required to determine which). EOF character Input from a terminal never really "ends" (unless the device is disconnected), but it is useful to enter more than one "file" into a terminal, so a key sequence is reserved to indicate end of input. In UNIX the translation of the keystroke to EOF is pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Job Control Language
Job Control Language (JCL) is a name for scripting languages used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem. More specifically, the purpose of JCL is to say which programs to run, using which files or devices for input or output, and at times to also indicate under what conditions to skip a step. Parameters in the JCL can also provide accounting information for tracking the resources used by a job as well as which machine the job should run on. There are two distinct IBM Job Control languages: * one for the operating system lineage that begins with DOS/360 and whose latest member is z/VSE; and * the other for the lineage from OS/360 to z/OS, the latter now including JES extensions, Job ''Entry'' Control Language (JECL). They share some basic syntax rules and a few basic concepts, but are otherwise very different. The VM operating system does not have JCL as such; the CP and CMS components each have command ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced like the letter c'') is a General-purpose language, general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted CPUs. It has found lasting use in operating systems, device drivers, protocol stacks, though decreasingly for application software. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems. A successor to the programming language B (programming language), B, C was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of the measuring programming language popularity, most widely used programming languages, with C compilers avail ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keyboard (computing)
A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Replacing early punched cards and paper tape technology, interaction via teleprinter-style keyboards have been the main input method for computers since the 1970s, supplemented by the computer mouse since the 1980s. Keyboard keys (buttons) typically have a set of characters engraved or printed on them, and each press of a key typically corresponds to a single written symbol. However, producing some symbols may require pressing and holding several keys simultaneously or in sequence. While most keys produce characters (letters, numbers or symbols), other keys (such as the escape key) can prompt the computer to execute system commands. In a modern computer, the interpretation of key presses is generally left to the software: the information sent to the computer, the scan code, tells it only wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
COMMAND
Command may refer to: Computing * Command (computing), a statement in a computer language * COMMAND.COM, the default operating system shell and command-line interpreter for DOS * Command key, a modifier key on Apple Macintosh computer keyboards * Command pattern, a software design pattern in which objects represent actions * Voice command, in speech recognition Military * Military command (instruction) or military order * Command responsibility, the doctrine of hierarchical accountability in cases of war crimes * Command (military formation), an organizational unit * Command and control, the exercise of authority in a military organization * Command hierarchy, a group of people dedicated to carrying out orders "from the top" Music * ''Command'' (album), a 2009 album by Client * Command Records, a record label Sports * Command (baseball), the ability of a pitcher to throw a pitch where he intends to * Kansas City Command, a former professional arena football team * Commands (hors ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
