Isn't PHP that horrible language?
Among some developers who use other languages, you can often hear snarky remarks about PHP and how it's "a terrible language", "badly designed" or just "ugly" which is rarely backed up by actual arguments.
Most of that resentment probably comes from a time, somewhere around the early 2000s, when PHP was the only option in server-side web development that people had. Web hosting companies didn't usually offer any alternatives and PHP was the only language of it's kind that you could find substantial helpful resources on the web.
Back then, PHP 4 was the current major version and it was indeed not a good language. It's object system was rudimentary, it's APIs were inconsistent because over the years, people had added features to it without adhering to a consistent style.
When Ruby (mostly through Rails) became popular, many people left PHP and never looked back. So now, a lot of people compare the languages and frameworks they use today, in 2015, with what they used in PHP around 2006, almost a decade ago.
So much has changed since then ...
With PHP 5 and especially it's minor releases 5.2 and 5.3 a lot of things were improved. There's now a much better object model, there are important built-in data structures that were missing before, higher order functions were added, performance has greatly increased and some weird configuration options that were outright dangerous have been deprecated and removed.
Composer, a new package manager for PHP, has fixed the tedious installation of third party libraries. The popular application frameworks from the Ruby world now have PHP equivalents (Rails -> Symfony, Sinatra -> Silex).
PHP is flawed, sure, just like most other languages/platforms. And just like the others, it's worth learning it.
So, why learn PHP?
With countless alternatives to choose from, why should you learn PHP? Well, the most likely reason is that you have a project that you want to work on or a job that simply requires it. There are tons of PHP projects out there that are actively maintained and many companies that have been in web development for a while probably have PHP code that's actively in use.
If you run into problems and need help, it's very likely, someone else has already asked your question on StackOverflow and there are probably already very good answers that are still correct.
The main upside of PHP however is operations. Since it has been in very wide spread use for such a long time, it's supported by practically every hosting company and running PHP on your own production server is a very well known and well documented topic. Also, PHP tends to be very stable in terms of backwards compatibility and not break existing code with its minor updates.
How to use this guide
We will start with how to install PHP and Composer and then go through a small example program to get familiar with the syntax and general look and feel of PHP.
Then we'll make a "Hello world" web application using a minimalist framework called "Silex". This will serve as an introduction on how to install and use third party dependencies.
In the following chapters, we will explore the features of PHP in more detail. The chapters are intended to be read in the correct order since they are based on previous chapters.