PHP

PHP uses a blend of interpretation and compilation in order to provide the best mix of performance and flexibility to programmers.

Behind the scenes, PHP compiles your script down to a series of instructions (called opcodes) whenever it is accessed. These instructions are then executed one by one until the script terminates. This is different from conventional compiled languages such as C++ where the code is compiled down to native executable code then that executable is run from then on. Instead, PHP re-compiles your script each time it is requested.

This constant recompilation may seem a waste of processor time, but it is actually not all that bad because you no longer need to worry about hand recompiling your scripts when you make any changes. On the flip side, many scripts take longer to compile than they do to execute!

Furthermore, it provides very quick feedback during development. If you have an error somewhere in your file, PHP will refuse to compile the page until you have fixed the problem, and you are able to step through execution of your code line by line until you find the problem.

The speed hit of regular compilation is nullified entirely by the use of PHP accelerators.

One major advantage to having interpreted code is that all memory used by the script is managed by PHP, and the language automatically cleans up after every script has finished. This means that you do not need to worry about closing database links, freeing memory assigned to images, and so on, because PHP will do it for you. That is not to say you should be lazy and make PHP do all the work - good programmers clean up themselves, and let PHP work as backup in case something is missed.

Perl

Perl is the most popular of the PHP alternatives out there, arguably because it is also the oldest. There is a large installed base of Perl out there; many open-source projects require Perl to be installed to work properly. It has the advantages of being very (very!) flexible, and also having a large collection of modules already written for it. However, it is let down by the fact that it is very easy to write obfuscated and confusing Perl without really realising you are doing so, and this has resulted in such marvels as the annual Obfuscated Perl Contest.

Well-written Perl scripts often look fairly like their PHP equivalent. The major cause for Perl's messy appearance is that many Perl programmers rely on "one-liners" - packing large amounts of functionality into just one line of code. Perl was once described very accurately by its creator, Larry Wall, when he argued that the front cover for his O'Reilly book on Perl should be a camel, saying that Perl was ugly but serviceable, and able to go long distances without much nourishment.

Perl is often a better choice when you want to take advantage of some of the pre-written libraries. CPAN, Perl's library repository, is very big, and there is a huge range of code for you to take, customise, and re-use. Perl also has a very active - and very cool - hacker community around it that's a whole lot of fun to be part of and is really a bedrock of support when you need it. Larry Wall and Damian Conway (both core Perl developers) are both rightfully revered as "alpha geeks" - people who really push the envelope of programming by doing cool new things. They are both very friendly, and and attend many conferences year round - go ahead and introduce yourself if you meet them, because they really are fascinating to talk to.

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