This week, alumni like me get to spend time at Hacker School. Since I work on MediaWiki-related documentation and I've never programmed in PHP before, I decided to start understanding just enough PHP to be able to read it better. Jordan Orelli from Etsy, a fellow alumnus, was kind enough to give me several pointers, and to especially help me understand how a PHP programmer's experience differs from my experience as a Python programmer.

I have learned, for instance:

• The PHP REPL (command-line interpreter/environment) is not as verbose/helpful as, say, the Ruby and Python ones. You get to it by doing php -a at the command line.


• For people like me who want a reasonably recent PHP and are on Ubuntu, apt-get install php5 is a good way to install PHP.


• PHP is a templating language that - in its design - kind of always implicitly assumes that it's in the context of an HTML page. For instance, by default, it autoescapes HTML characters such that output from a bit of PHP will be suitable for including in an HTML page. And within an HTML page, serverside, you might have something like

  <p><?php echo "I am leet!"; ?></p>

  which the server will execute, thanks to something like Apache's mod_php plugin, and then send to the browser as the HTML

  <p>I am leet!</p>



• What I as a Python programmer would call a dictionary, PHP folks call an associative array.


• PHP is completely single-threaded. This is why you never have race conditions in PHP! Every time you execute PHP within mod_php, you execute it within a sandbox just for that HTTP request! And that means that "the global namespace" really means "the global namespace for the current HTTP request" so "global" sort of has a different meaning, and thus I understand better why people are more okay with using "global" variables and the "argh, global data is bad" aversion is weaker in the world of PHP programming.

  But you also cannot share state this way! So you should use caches & the database & job queues & other persistence layers.



• A lot of the time, you want a pretty URL for the user to see, like https://www.mediawiki.org/wiki/Performance_guidelines , but the work is being done by app logic in, say, index.php plus query parameters, e.g. https://www.mediawiki.org/w/index.php?title=Performance_guidelines . So, if you're using Apache, mod_rewrite uses the .htaccess &/or .htdocs files (need to double-check this), which contain just a giant list of "if this then that" regexes, to rewrite the URLs of HTTP request headers.


• Many things in PHP are inconsistent or unintuitive, and it's not your fault if you don't get it. For instance, some method names have underscores and some don't, and the pattern isn't intuitive.

Much thanks, Jordan! This is all oversimplified for clarity, etc., etc. I think next up I am going to try to understand a bit of PHP syntax, and the role of PEAR.