Not much about Perl is unique; what it can do, so can other languages. Nevertheless, Perl stands out because its expressiveness and particular blend of features give it an attractive cost model. Simply put, Perl lets programmers do more work with less effort.

After using a language for a few jobs, programmers form an intuitive model of the language's costs; some things are pricey; others, inexpensive. While programmers rarely talk about these models explicitly, they do as a community come to an understanding of languages' relative costs.

The Perl community, for example, says that Perl "makes easy things easy and hard things possible." This is a crude yet fair statement of Perl's cost model. For most trivial and small problems, Perl imposes the lowest costs that I know of. Because there are more small problems than large ones, more trivial problems than small, Perl often offers the lowest-cost solutions to common problems. Since programmers solve large problems by breaking them into small problems, Perl also has a respectably low cost for larger problems.

Further, the Perl language has been tuned for common problem domains such as text processing and web programming, which represent a large portion of many modern projects. Testing, something most serious projects invest in, is another domain where a little Perl goes a long way. In other areas Perl's cost model is not so well tuned but still better than most. For example, functional programming in Perl costs less than in more popular languages.

In short, solving common problems is usually less expensive in Perl than in more popular languages. As it turns out, this is a great feature to have in a programming language.  ;-)

Cheers,
Tom