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Global Variable
In computer programming, a global variable is a variable with global scope, meaning that it is visible (hence accessible) throughout the program, unless shadowed. The set of all global variables is known as the ''global environment'' or ''global state.'' In compiled languages, global variables are generally static variables, whose extent (lifetime) is the entire runtime of the program, though in interpreted languages (including command-line interpreters), global variables are generally dynamically allocated when declared, since they are not known ahead of time. In some languages, all variables are global, or global by default, while in most modern languages variables have limited scope, generally lexical scope, though global variables are often available by declaring a variable at the top level of the program. In other languages, however, global variables do not exist; these are generally modular programming languages that enforce a module structure, or class-based object-or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Programming
Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of procedures, by writing source code, code in one or more programming languages. Programmers typically use high-level programming languages that are more easily intelligible to humans than machine code, which is directly executed by the central processing unit. Proficient programming usually requires expertise in several different subjects, including knowledge of the Domain (software engineering), application domain, details of programming languages and generic code library (computing), libraries, specialized algorithms, and Logic#Formal logic, formal logic. Auxiliary tasks accompanying and related to programming include Requirements analysis, analyzing requirements, Software testing, testing, debugging (investigating and fixing problems), imple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mutex
In computer science, a lock or mutex (from mutual exclusion) is a synchronization primitive that prevents state from being modified or accessed by multiple threads of execution at once. Locks enforce mutual exclusion concurrency control policies, and with a variety of possible methods there exist multiple unique implementations for different applications. Types Generally, locks are ''advisory locks'', where each thread cooperates by acquiring the lock before accessing the corresponding data. Some systems also implement ''mandatory locks'', where attempting unauthorized access to a locked resource will force an exception in the entity attempting to make the access. The simplest type of lock is a binary semaphore. It provides exclusive access to the locked data. Other schemes also provide shared access for reading data. Other widely implemented access modes are exclusive, intend-to-exclude and intend-to-upgrade. Another way to classify locks is by what happens when the lock stra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exec (Unix)
In computing, exec is a functionality of an operating system that runs an executable file in the context of an already existing process, replacing the previous executable. This act is also referred to as an overlay. It is especially important in Unix-like systems, although it also exists elsewhere. As no new process is created, the process identifier (PID) does not change, but the machine code, data, heap, and stack of the process are replaced by those of the new program. The ''exec'' call or some variant is available for many programming languages including compiled languages and some scripting languages. In command interpreters, the built-in command replaces the shell process with the specified program. Nomenclature Interfaces to ''exec'' and its implementations vary. Depending on programming language it may be accessible via one or more functions, and depending on operating system it may be represented with one or more actual system calls. For this reason, ''exec'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fork (Unix)
In computing, particularly in the context of the Unix operating system and Unix-like, its workalikes, fork is an operation whereby a Computer process, process creates a copy of itself. It is an interface which is required for compliance with the POSIX and Single UNIX Specification standards. It is usually implemented as a C standard library Wrapper library, wrapper to the fork, clone, or other system calls of the kernel (operating system), kernel. Fork is the primary method of process creation on Unix-like operating systems. Overview In multitasking operating systems, processes (running programs) need a way to create new processes, e.g. to run other programs. Fork and its variants are typically the only way of doing so in Unix-like systems. For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the "child process", makes any environment changes the child will need and then calls the exec (system call), exec s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sectors of the computing industry – Windows (unqualified) for a consumer or corporate workstation, Windows Server for a Server (computing), server and Windows IoT for an embedded system. Windows is sold as either a consumer retail product or licensed to Original equipment manufacturer, third-party hardware manufacturers who sell products Software bundles, bundled with Windows. The first version of Windows, Windows 1.0, was released on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs). The name "Windows" is a reference to the windowing system in GUIs. The 1990 release of Windows 3.0 catapulted its market success and led to various other product families ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
COMMAND
Command may refer to: Computing * Command (computing), a statement in a computer language * command (Unix), a Unix command * 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 profess ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, packaged as a Linux distribution (distro), which includes the kernel and supporting system software and library (computing), libraries—most of which are provided by third parties—to create a complete operating system, designed as a clone of Unix and released under the copyleft GPL license. List of Linux distributions, Thousands of Linux distributions exist, many based directly or indirectly on other distributions; popular Linux distributions include Debian, Fedora Linux, Linux Mint, Arch Linux, and Ubuntu, while commercial distributions include Red Hat Enterprise Linux, SUSE Linux Enterprise, and ChromeOS. Linux distributions are frequently used in server platforms. Many Linux distributions use the word "Linux" in their name, but the Free ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bash (Unix Shell)
In computing, Bash (short for "''Bourne Again SHell''") is an interactive command interpreter and command programming language developed for UNIX-like operating systems. Created in 1989 by Brian Fox for the GNU Project, it is supported by the Free Software Foundation and designed as a 100% free alternative for the Bourne shell (sh) and other proprietary Unix shells. Since its inception, Bash has gained widespread adoption and is commonly used as the default login shell for numerous Linux distributions. It holds historical significance as one of the earliest programs ported to Linux by Linus Torvalds, alongside the GNU Compiler ( GCC). It is available on nearly all modern operating systems, making it a versatile tool in various computing environments. As a command-line interface (CLI), Bash operates within a terminal emulator, or text window, where users input commands to execute various tasks. It also supports the execution of commands from files, known as shell scripts, f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Berkeley ( BSD), Microsoft (Xenix), Sun Microsystems ( SunOS/ Solaris), HP/ HPE ( HP-UX), and IBM ( AIX). The early versions of Unix—which are retrospectively referred to as " Research Unix"—ran on computers such as the PDP-11 and VAX; Unix was commonly used on minicomputers and mainframes from the 1970s onwards. It distinguished itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language (in 1973), which allows U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
KornShell
KornShell (ksh) is a Unix shell which was developed by David Korn (computer scientist), David Korn at Bell Labs in the early 1980s and announced at USENIX Annual Technical Conference, USENIX on July 14, 1983. The initial development was based on Bourne shell source code. Other early contributors were Bell Labs developers Mike Veach and Pat Sullivan, who wrote the Emacs and Vi (text editor), vi-style line editing modes' code, respectively. KornShell is backward-compatible with the Bourne shell and includes many features of the C shell, inspired by the requests of Bell Labs users. Features KornShell complies with POSIX#POSIX.2, POSIX.2, Shell and Utilities, Command Interpreter (IEEE Std 1003.2-1992.) Major differences between KornShell and the traditional Bourne shell include: * Job control (Unix), job control, alias (command), command aliasing, and command history designed after the corresponding C shell features; job control was added to the Bourne Shell in 1989 * a choice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shell (computing)
An operating system shell is a computer program that provides relatively broad and direct access to the system on which it runs. The term ''shell'' refers to how it is a relatively thin Abstraction layer, layer around an operating system. A shell is generally a command-line interface (CLI) program although some graphical user interface (GUI) programs are arguably classified as shells too. Overview Operating systems provide various services to their users, including File manager, file management, Process (computing), process management (running and terminating Application program, applications), batch processing, and operating system monitoring and configuration. Most operating system shells are not ''direct'' interfaces to the underlying Kernel (operating system), kernel, even if a shell communicates with the user via peripheral devices attached to the computer directly. Shells are actually special applications that use the kernel API in just the same way as it is used by ot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Operating Systems
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for efficient use of the system and may also include accounting software for cost allocation of Scheduling (computing), processor time, mass storage, peripherals, and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computerfrom cellular phones and video game consoles to web servers and supercomputers. , Android (operating system), Android is the most popular operating system with a 46% market share, followed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
