Perl for Web Site Management

The map Function

There’s one more really cool thing in this script. Buried in its latter half, where the top-level page is being created to list all the results stored in the %data HoH, there is the following somewhat scary-looking line:

my @engine_links = map { qq{<A HREF="#$_">$_</A>} } sort @engines;

This is our first use of Perl’s map function. The map function is another one of those things, like the conditional operator (walnuts ? rutabagas : watermelons), that serves to separate the accidental programmers from the real ones. It took me years, literally, before I was comfortable enough with Perl to begin using the map function, but now that I’m familiar with it I can’t imagine life without it. Larry Rosler, one of the nicest members of the extended Perl community when it comes to helping out beginners, called the map function “beautiful” in a session I attended at one of O’Reilly’s Perl conferences, and after working with it for a while I can appreciate why he feels that way.

The map function is one of those Perl shortcuts, a diagonal path offering a more efficient route from point A to point B. In effect, it lets us take a foreach loop and squash it down into a single line. To be more specific, map lets us specify a block of code to be executed for each element in a list. The map function processes the list, running the block of code on each element, and returns a list consisting of the results of all those blocks’ execution.

An example will clarify what I’m describing. Let’s ...