Introduction

In the previous chapter, we saw how to deal with user input using PHP superglobals and applied sanitization and validation in order to secure the application. We also learned how to keep the user's session on the server and built a small application. In that application, we used the session to store data, which vanished with every session destroyed (or logout).

In this chapter, we will learn how we can store and read persistent data using PHP. Specifically, we will learn how to handle file I/O (open, read, and write) and disk operations (change the current directory, create a new file/directory, remove a file or directory, and so on). This is useful when you would like to use the filesystem for precious application logs, to generate all kinds of reports, to handle uploaded user images, and so on. We will also learn how to connect to a MySQL database and how to query the data, insert new records, and update or delete data from the database. This is helpful when...