PHP is a scripting language that is often used for server side creation of web pages. But PHP can be used in command line mode.

PHP is a popular general-purpose scripting language that is especially suited to web development. Fast, flexible and pragmatic, PHP powers everything from your blog to the most popular websites in the world. From the PHP web site at https://www.php.net/ .

For installation details, see PHP .

The current version is 7 though 5 is still popular. Version 6 was never released.

Version 7 adds more Unicode support.

As a programming language designed for non-programmers, PHP has a large number of quirks and design defects.

PHP is very usable despite having many quirks and design defects, but those quirks and design defects can be very annoying.

PHP was created by Rasmus Lerdorf in 1994.

PHP started out standing for "Personal Home Page" but now stands for "PHP Hypertext Processor". (a self-referential definition)

PHP started as a server side web page development system in 1994, hooking into the CGI (Common Gateway Interface) model.

PHP is designed to pass text through to a web page but have interspersed PHP code that customizes what is inserted.

PHP can be used in command line mode as a general programming language.

Some PHP features, or quirks, include the following.

Note: As with many languages, I pick a subset of the language that works as expected and then use that subset, avoiding as many bad parts as needed.

This is not as easy in PHP as in other languages.

If an integer overflows, most languages ignore the error (cycling around to the opposite end of the integer range) or raise an exception.

PHP converts the integer to a float (with a bigger integer range) and continues execution, without a way to easily detect that it has happened.

The equality operator "==" and "!=="have many quirks.

Instead, one should use "===" or "!===".

PHP does not have true and false types (that act as expected) so one may want to use 0 for false and 1 for true appropriately.

Variable names are case-sensitive.

Function and class names are not case-sensitive.

Variables are not declared but created on first use. If a variable that does not exist is used, it is created with a null value and then used.

Variable names start with a dollar sign (even though an analysis of the program could determine which identifiers are variables).

• The dollar sign name is recognized in strings that use formatted output and inserted. For a real dollar sign, escape the dollar sign.

Global variables cannot be accessed inside a function unless they are declared there as global.

Without the global declaration, any global variable is considered a local variable, created locally, given a null value, and used.

Module variables need to be declared as global to access them, even at the top level of modules and programs.

• Class methods need a special syntax even though a static analysis could determine this relationship.
• Module method/routines have a special reference syntax even though a static analysis could determine this relationship.

PHP lists (arrays) and dictionaries (hashed arrays) are somewhat similar and can be easily confused.

When used, these structures do a copy rather than update the list or dict, so one must be very careful about the order in which updates are made to lists and/or dicts.

PHP has (at least) 13 functions for sorting an array in various ways. Why so many?

Functions as arguments is handled by passing the function name as a string and doing appropriate processing or calls.

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