# Unit 1: Introduction to PHP (CA314) ## What is PHP - **PHP** (originally Personal Home Page, now **PHP: Hypertext Preprocessor**) is an open-source, **server-side scripting language** embedded in HTML, created by Rasmus Lerdorf (1994). - Runs on Apache/Nginx with the PHP interpreter; supports MySQL and many databases; cross-platform (Windows, Linux, macOS). **XAMPP/WAMP/LAMP** bundle Apache, MySQL, PHP. - Advantages: free, easy to learn, fast, platform independent, large community, many frameworks. ## Uses of PHP - **In web applications**: dynamic pages, forms, login systems, shopping carts, CMS (WordPress). - **For database applications**: connecting to MySQL, PostgreSQL, Oracle, SQLite to store and retrieve data. - **With the file system**: create, read, write, upload and delete files and directories. - **For system commands**: `exec()`, `system()`, `shell_exec()` to run OS commands. - Others: email sending, sessions, image generation (GD library), XML/JSON handling, command-line scripts. ## Understanding the Working of PHP 1. Browser requests a `.php` page. 2. Web server passes it to the PHP engine. 3. Engine runs the PHP code (and queries the database if needed). 4. Output (pure HTML) is returned to the browser; the PHP code is never seen by the client. **[Figure: PHP request cycle]** Browser -> web server -> PHP interpreter -> database; HTML result returned to browser. ## PHP as General-Purpose Language and for the Web - Beyond the web, PHP can be used for command-line scripting and desktop apps (PHP-CLI); yet its main strength is the web: access to form data (`$_GET`, `$_POST`), cookies, sessions, headers, and HTML output. ## Keeping Up with Changes; PHP 5 - PHP evolved through versions 3, 4, 5, 7 (big speed gains) and 8 (JIT, union types, attributes, match expression). Follow **php.net** release notes. - **PHP 5** introduced a new **object model** (visibility, abstract classes, interfaces, exceptions), **PDO/MySQLi**, SimpleXML and better OOP support. ## Writing PHP Statements - Statements end with a **semicolon**; PHP tags ``; short echo tag ``. - Case sensitivity: variables are case sensitive; function and keyword names are not. - Example: `` ## Adding PHP Sections to an HTML File - PHP code can be embedded anywhere inside HTML file saved with `.php`: `

` - Multiple PHP blocks may appear in one file; HTML between them is output as is. ## PHP Output Statements - **echo**: language construct; can print multiple comma-separated strings; no return value; slightly faster. - **print**: construct returning 1; one argument. - **printf()** for formatted output; `print_r()` and `var_dump()` for arrays/debugging. - Single quotes print text literally; double quotes interpolate variables. ## Documenting Scripts (Comments) - Single line: `// comment` or `# comment`; multiline: `/* ... */`; **DocBlock** `/** ... */` used by phpDocumentor. Good practice: comment purpose, parameters and author. ## Likely Exam Questions 1. What is PHP? Mention its features and uses. 2. Explain the working of PHP with a diagram. 3. How is PHP code embedded in HTML? 4. Differentiate between echo and print. 5. Explain the types of comments in PHP. 6. What are the new features in PHP 5?