TopolearnEvery PHP program, from a CLI script to a Laravel app, starts as a file the interpreter executes top to bottom.
A PHP file is plain text that the interpreter runs from top to bottom. Code lives between the opening tag <?php and an optional closing tag ?>. Anything outside the tags is sent to the output unchanged, which is how PHP was originally used to sprinkle code into HTML pages.
For a file that contains only PHP (classes, scripts, config), leave out the closing `?>`. A stray newline after it would be sent as output and can break headers or downloads.
Run a script with php hello.php, try a one-liner with php -r 'echo 2 + 2;', or open an interactive shell with php -a. Check your version with php -v.
echoprints one or more strings;printdoes the same but takes one argument.- Statements end with a semicolon.
- Comments are
//,#or/* ... */. var_dump($x)shows a value with its type, which is the quickest debugging tool you have.
In a web setting the same script is executed once per HTTP request by a web server (PHP-FPM behind nginx, Apache, or FrankenPHP), and whatever it echoes becomes the response body. Each request starts with a clean slate: variables do not survive between requests.
Example
<?php
// hello.php: run with `php hello.php`
echo "Hello, PHP!\n"; // Hello, PHP!
echo "Version: ", PHP_MAJOR_VERSION, "\n"; // Version: 8
$answer = 6 * 7;
var_dump($answer); // int(42)
var_dump("42" === $answer); // bool(false)
# pure-PHP files end without a closing tagRemember
- Code goes inside <?php ... and pure-PHP files omit the closing ?>
- Run scripts with php file.php; php -a gives an interactive shell
- var_dump shows a value and its type
Watch out for
- Adding a closing ?> followed by whitespace, which sends unexpected output before headers.