Scripting language

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. A script is usually interpreted rather than compiled.

Many such languages are quite sophisticated and have been used to write elaborate programs, which are often still called scripts even though they go well beyond automating simple computer tasks. A script language can be found at almost every level of a computer system. Besides being found at the level of the operating system, they appear in computer games, web applications, word processing documents, network software and more. In many ways, the terms high-level programming language and scripting language have become entwined, and there is no clear delineation between the two.

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 often implemented with interpreters rather than compilers; and they are strong at communication 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 many relevant 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). In most modern systems, the latter case is very seldom recommendable, since one or more suitable script languages is usually available.

Types of scripting languages

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 internet web pages. Such languages are specialized for internet communication and use web browsers for their user interface. However, most modern web programming languages are powerful enough for general-purpose programming.

ColdFusion (Application Server)
Lasso
Miva
SMX

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 small 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.

Ch (C/C++ interpreter)
ECMAScript a.k.a. DMDScript, JavaScript, JScript
GameMonkeyScript
Guile
ICI
Squirrel
Lua
Tcl
RBScript (REALbasic Script)
Z-Script

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.

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.