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Scripting redirects here. For other uses, see script. Scripting languages (commonly called scripting programming languages or script languages) are computer programming languages created to shorten the traditional edit-compile-link-run process. The name comes from a written script such as a screenplay, where dialog is repeated verbatim for every performance. Early script languages were often called batch languages or job control languages. Scripting languages can be interpreted or compiled, but because interpreters are simpler to write than compilers, they are interpreted at least as often as they are compiled. The term scripting language is not technical, though embedding and dependence on a larger system are usually criteria. In computer games, scripts extend game logic, tailoring the game engine to particular game data. Scripts also make applications programmable from within, so that repetitive tasks can be quickly automated. Of course, not every scripting system that grows beyond its original design and delegation acquires a new name. Full-blown in-game languages such as UnrealScript exist, and JavaScript is a very influential standard, supported by virtually every browser on the market. Description Computer languages are created for varying purposes and tasks — different kinds and styles of programming. One common programming task is known as scripting, or connecting diverse pre-existing components to accomplish a new related task. Those languages which are suited to scripting are typically called scripting languages. Many languages for this purpose have common properties: they favor rapid development over efficiency of execution; they are normally implemented with interpreters rather than compilers; and they are strong at communicating with program components written in other languages. Many scripting languages emerged as tools for executing one-off tasks, particularly in system administration. One way of looking at scripts is as "glue" that puts several components together; thus they are widely used for creating graphical user interfaces or executing a series of commands that might otherwise have to be entered interactively through keyboard at the command prompt. The operating system usually offers some type of scripting language by default, widely known as a shell script language. Scripts are typically stored only in their plain text form (as ASCII) and interpreted, or compiled each time prior to being invoked. Some scripting languages are designed for a specific domain, but often it is possible to write more general programs in that language. In many large-scale projects, a scripting language and a lower level programming language are used together, each lending its particular strengths to solve specific problems. Scripting languages are often designed for interactive use, having many commands that can execute individually, and often have very high level operations (for example, in the classic UNIX shell (sh), most operations are programs themselves). Such high level commands simplify the process of writing code. Programming features such as automatic memory management and bounds checking can be taken for granted. In a 'lower level' or non-scripting language, managing memory and variables, and creating data structures tends to consume more programmer effort and lines of code to complete a given task. In some situations this is well worth it for the resulting fine-grained control. The scripter typically has less flexibility to optimize a program for speed or to conserve memory. For the reasons noted above, it is usually faster to program in a scripting language, and script files are typically much smaller than, say, equivalent C program files. The flip side can be a performance penalty: scripting languages, often interpreted, may be significantly slower to execute and may consume more memory when running. In some cases, however, e.g. with small scripts of some tens of lines, the write-time advantage far outweighs the run-time disadvantage. Also, this argument gets stronger with rising programmer salaries and falling hardware costs. However, the boundary between scripting languages and regular programming languages tends to be vague, and is blurring ever more with the emergence of new languages and integrations in this fast-changing area. In some scripting languages, an experienced programmer can accomplish a good deal of optimization if they choose. And in general, it is possible to write a script in any language (including C or assembly language). This is not recommended, however, for scripting languages whose interpreters are to be marketed, such as languages for macros or for web development. Job control languages and shells A major class of scripting languages has grown out of the automation of job control -- starting and controlling the behavior of system programs. Many of these languages' interpreters double as command line interfaces, such as the Unix shell or the MS-DOS COMMAND.COM. Others, such as AppleScript, add scripting capability to computing environments lacking a command-line interface. GUI Scripting With the advent of Graphical user interfaces came a specialized kind of scripting language for controlling a computer. These languages interact with the same graphic windows, menus, buttons and such that a person does. They are typically used to automate repetitive actions or configure a standard state. In principle they could be used to control any application running on a GUI-based computer, but in practice the support for such languages depend on the application and operating system. Such languages are also called "macro languages" when the control is through keyboard interaction. Application-specific languages Many large application programs include an idiomatic scripting language tailored to the needs of the application user. Likewise, many computer game systems use a custom scripting language to express the programmed actions of non-player characters and the game environment. Languages of this sort are designed for a single application and, while they may superficially resemble a specific general-purpose language (e.g. QuakeC, modeled after C) they have custom features which distinguish them. Web programming languages An important type of application-specific scripting language is one used to provide custom functionality to dynamic web pages. Such languages are specialized for web applications and other Internet uses . However, most modern web programming languages are powerful enough for general-purpose programming. Text processing languages The processing of text-based records is one of the oldest uses of scripting languages. Many, such as Unix's awk and, later, Perl, were originally designed to aid system administrators in automating tasks that involved Unix text-based configuration and log files. Perl is a special case -- originally intended as a report-generation language, it has grown into a full-fledged applications language in its own right. General-purpose dynamic languages Some languages, such as Perl, began as scripting languages but developed into programming languages suitable for broader purposes. Other similar languages -- frequently interpreted, memory-managed, dynamic -- have been described as "scripting languages" for these similarities, even if they are more commonly used for applications programming. They are usually not called "scripting languages" by their own users. Extension/embeddable languages A number of languages have been designed for the purpose of replacing application-specific scripting languages, by being embeddable in application programs. The application programmer (working in C or another systems language) includes "hooks" where the scripting language can control the application. These languages serve the same purpose as application-specific extension languages, but with the advantage of allowing some transfer of skills from application to application. JavaScript began as and primarily still is a language for scripting inside of web browsers, however, the standardization of the language as ECMAScript has made it popular as a general purpose embeddable language. In particular, the Mozilla implementation SpiderMonkey is embedded in several environments such as the Yahoo! Widget Engine. Other applications embedding ECMAScript implementations include the Adobe products Adobe Flash (ActionScript) and Adobe Acrobat (for scripting pdf files). Tcl was created as an extension language but has come to be used more frequently as a general purpose language in roles similar to Python, Perl, and Ruby. Others See also | |||||||
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