A scripting language, script language or extension language is a programming language that allows some control of a single or many software application(s). "Scripts" are often treated as distinct from "programs", which execute independently from any other application.At the same time they are distinct from the core code of the application, which is usually written in a different language, and by being accessible to the end-user they enable the behavior of the application to be adapted to the user's needs.

Scripts are often, but not always, interpreted from the source code or "semi-compiled" to byte code which is interpreted, unlike the applications they are associated with, which are traditionally compiled to native machine code for the system on which they run. Scripting languages are nearly always embedded in the application with which they are associated.

The name "script" is derived from the written script of the performing arts, in which dialogue is set down to be spoken by human actors. Early script languages were often called batch languages or job control languages. Such early scripting languages were created to shorten the traditional edit-compile-link-run process.

Type of Scripting Languages

Web browsers

Web browsers are typically used to render HTML, but in time a host of special-purpose languages has developed to control their operation. These include ECMAScript, a very versatile procedural scripting language superficially resembling Java; Cascading Style Sheets, which enable style metadata to be abstracted from content; XML which can be used for content in conjunction with style metadata, as an alternative to HTML; VBScript by Microsoft, which only works in Internet Explorer; and XSLT, a presentation language that transforms XML content into a new form. Techniques involving the combination of XML and JavaScript scripting to improve the user's subjective impression of responsiveness have become significant enough to acquire a name: AJAX. The Document Object Model standard ensures that all browsers respond in a predictable manner to the same JavaScript.

The Mozilla project has developed its own system for extending the user interface of the browser itself, called XUL.

Web servers

On the server side of the HTTP link, application servers and other dynamic content servers such as Web content management systems provide content through a large variety of techniques and technologies typified by the scripting approach. Particularly prominent in this area are PHP, ColdFusion, JSP and ASP, but other developments such as Ruby on Rails have carved out a niche.

Text processing languages

The processing of text-based records is one of the oldest uses of scripting languages. Many, such as UNIX's AWK (The name AWK is derived from the family names of its authors — Alfred Aho, Peter Weinberger, and Brian Kernighan; however, it is not commonly pronounced as a string of separate letters but rather to sound the same as the name of the bird, auk) were originally designed to aid programmers in automating tasks that involved Unix text-based configuration and log files. Of primary importance here is the regular expression, a language developed for the formal description of the lexical structure of text, and used by all of these tools.

Perl was originally designed to overcome the limitations of these tools and has grown to be one of the most widespread general purpose languages.

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 web browsers; however, the standardization of the language as ECMAScript has made it popular as a general purpose embeddable language. In particular, the Mozilla implementationSpiderMonkey is embedded in several environments such as the Yahoo! Widget Engine. Other applications embedding ECMAScript implementations include the Adobe products Adobe Flash (Action Script) and Adobe Acrobat (for scripting PDF files).