The link function in PHP creates a link for a target. The hard link created for the target means that if a link is created for a file, the file can still be accessed after it has been deleted. The general syntax for link is as follows: link(string $target, string $link): bool.

A function is a piece of code that takes another input in the form of a parameter, processes it, and then returns a value. A PHP Function feature is a piece of code that can be used over and over again and accepts argument lists as input, and returns a value. PHP comes with thousands of built-in features.

Pass by reference: When variables are passed by reference, use & (ampersand) symbol need to be added before variable argument. For example: function( &$x ). Scope of both global and function variable becomes global as both variables are defined by same reference.

User-defined functions ¶ Any valid PHP code may appear inside a function, even other functions and class definitions. Function names follow the same rules as other labels in PHP. A valid function name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.