It certainly helps that Perl is freely available and distributable, but that hardly explains the fantstic popularity of Perl, since many freeware packages fail to thrive
It is one of the most portable languages around. It will run on just about any operating system you could care to name (including MS-DOS, VMS, OS/2, Plan 9, Macintosh, any variety of Windows you please, and of course, all the flavors of the operating system it was born on, UNIX.
Perl is fantastic for developing web applications. 80% of all webmasters prefer Perl to any of the other "web programming " languages like Java, VBscript etc. Perl is still the tool of choice for adding interactivity to web pages.
Many of Perl's ideas are borrowed from natural language. It's creator Larry Wall describes it in terms of concepts like "nouns", "verbs" and "indirect object kind of constructs" in his extremely readable and thorough book "Programming Perl".
Perl is simple. Doing things like manipulating numbers and text, files and directories, computers and networks is a breeze.
Though simple in many ways, Perl is also a rich language. There is a lot to learn. Navigating files, scanning large amounts of text, creating and obtaining dynamic data and printing easily formattable reports based on that data were features that even the pioneer version of Perl had. But Perl has grown to be a language for file system manipulation, process management, database administration, client server programming, secure programming, web based information management, and even for object oriented and functional programming.
All the above functionality was not just slapped onto the side of Perl - but each feature works synergistically with the rest. Perl has always been a "glue" language. And Perl is designed to be modularly extensible.
You can embed Perl in other languages, and you can embed other languages in Perl.
CPAN, or the Comprehensive Perl Archive Network, a replicated archive of Perl modules, documentation, scripts, ports, development releases and just about anything else that you can think of related to Perl. This repository can be found at many places on the web, one of them being http://www.cpan.org.This repository is the closest that the world has come to the fabled "Software ICs" mentioned by Brad Cox and Lamar Ledbetterr in their classic June 1985 article of the same name. This repository reduces the amount of energy wasted on competing, incompatible implementations of functionality.
But the most endearing aspect of Perl is the Perl community, some of the most helpful folks around the world. You can meet them on USENET or via mailing lists, 24 / 7 / 365.
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