Scripting languages

With the advent of technologies such as the Web, scripting languages are enjoying considerable success. They enable the rapid implementation of sometimes complex programs, thanks to their own qualities, the libraries at their disposal and the efficiency of computers.

But what is a script and what is a scripting language? What characteristics do scripting languages have in common, and what are the special features of the best-known of them? Let's start by formulating some answers to these questions.

Traditionally, the term "script" refers to the transcription of a film or action. Computers soon became capable of chaining together program executions, and so developed languages to describe these sequences. As early as the 1950s, the description of such a sequence of tasks was called a "script". The execution of a script stored in a file made it possible to run these sequences without requiring the presence of the operator.

The Unix operating system made this notion commonplace by developing an interactive language dedicated to scripting, the "shell", and offering it as an interface with the user. A shell script is a file that can be made executable and parameterized with arguments, thus becoming a new command.

The Unix shell is just another scripting language, but two of its features are characteristic of languages in this family:

• 1. it's a language whose programs – scripts – are easy to implement: no explicit compilation is required, and a script is ready to run straight away;

• 2. it's a language with powerful primitive operations, such as pattern matching or command pipelining, and access to a large library, since a shell script can use any other Unix command as a library function.

When faced with a conventional programming language, the programmer has to finely adapt his own data structures to his problem, choose the constructs offered by the language according to their execution cost in order to control the complexity of his algorithms, and compile his program in order to benefit from the various checks performed by the compiler and produce an optimized executable.

On the other hand, writing a script must be fast, and the language is expected to provide very high-level functionalities, in the form of language constructs, primitives or libraries, so that the problem to be solved can be solved by as short a script as possible. In the same way, certain development techniques may require the execution of scripts whose components have yet to be defined, for example to test or present certain aspects. Such flexibility often leads designers of scripting languages to endow them with...