Perl

Perl is commonly considered an interpreted language, namely that is interpreted when it runs. In fact, the first thing that the interpreter has do is to convert the source code in an intermediate graph, and this graph is the one to be interpreted. This approach allows you to run it faster.

Born in a Unix environment and distributed with the GPL and Artistic Licenses, it is also available for Windows and MacOS (not Mac OS X version which belongs to the family Unix). The most used implementation for Windows is distributed by ActiveState which offers an open source license for Windows while selling the integrated development environments both for Perl and other open source languages such as Tcl and Python.

Although it is considered to be one of the great innovations in the developers world, assessments  from the community are different. It's judged negatively because of the fact that facilitates writing software hard to read and maintain  (to the point that the name of the language has been reinterpreted as Pathologically Eclectic Rubbish Lister), but it's appreciated for the easiness of the writing mechanism that allows the developer to use the semantic he prefers. Infact, there is not only one way of doing things in PERL.
Another positive aspect that attracts developers is the wide availability of modules released with open source licenses. These modules are often well documented, and the language itself offers the Pod, a way to include the documentation within the code, ensuring the documentation along with the module. The community has created a site called CPAN which organizes in topics the modules considered particularly valid. The forms themselves are not stored at that site, but remain on the sites chosen by their authors. Finally, as interpreted language and therefore always distributed with the source code, favours the liberal practice.

One of the most important features of Perl are the regular expressions, allowing the search and the replacement of text strings described with special characters. Regular expressions are not a PERL privilege, and indeed were derived from existing text, but those of Perl are the most powerful and  numerous languages emulate them through the library functions or external modules.

The language and the interpreter are developed by a group of about a hundred developers, led by Wall, which takes final decisions on what to include in the code. The developers have created the Perl Institute to facilitate the development of Perl, improve the visibility and organize conferences about it. Wall himself works for an editor who actively supports the Open Source movement.

Perl is part of the standard tools of Unix operating systems. Its updating can be done either through Internet or through distribution of free operating systems such as Linux, Open-BSD, and so on. The Windows versions can also be found on line. Some guides to Perl are accompanied by a CD-Rom including different versions and all forms included in the CPAN.