Syntax, tags & structure

Tags, statements, expressions, blocks, comments and the escaping rules — the grammar everything else is written in.

PHP's grammar is small. Almost everything is a statement ending in ;, statements group into blocks with { }, and the whole thing lives inside <?php … ?> tags.

Tags: code inside text

A PHP file starts as text. <?php switches to code; ?> switches back.

<?php

$name = 'Ada';
?>
Hello, <?= $name ?>!
<?php

echo "\nBack in code.\n";

<?= is shorthand for <?php echo — always available, and the normal way to print a value inside markup.

Statements and semicolons

A statement is an instruction. The ; terminates it. The last statement before ?> may omit it, because the tag terminates it — but do not rely on that.

<?php

$a = 1; $b = 2;          // two statements on one line is legal
$sum =
    $a
    + $b;                // one statement across three lines is legal too

echo $sum, "\n";

Whitespace and newlines carry no meaning. Indentation is for humans; the lexer throws it away.

Expressions: anything with a value

An expression is anything that evaluates to a value. 1, $a + $b, strlen($s), $x = 5 — assignment is itself an expression, which is why $a = $b = 0 works.

<?php

$b = 0;
$a = $b = 5;             // assignment returns the assigned value
echo $a, ' ', $b, "\n";

$ok = ($a > 1);          // comparison is an expression
var_dump($ok);

echo (int) ('7 apples' === '7 apples'), "\n";

Blocks

Curly braces group statements into a block. if, while, for, foreach, functions and classes all take one.

<?php

$scores = [12, 7, 30];

foreach ($scores as $s) {
    if ($s > 10) {
        echo $s, " is high\n";
    } else {
        echo $s, " is low\n";
    }
}

PHP also has an alternative syntax that replaces { with : and } with endif / endforeach / endwhile / endfor / endswitch. It exists for templates, where a stray } is easy to lose in markup.

<?php

$items = ['tea', 'coffee'];
?>
<ul>
<?php foreach ($items as $item): ?>
  <li><?= $item ?></li>
<?php endforeach; ?>
</ul>

Comments

<?php

// a single-line comment, to the end of the line
# also a single-line comment, rarely used

/*
   a block comment
   over several lines
*/

/** A doc comment. Tools and reflection read these. */
function greet(string $who): string {
    return "Hello, $who";
}

echo greet('world'), "\n";
echo (new ReflectionFunction('greet'))->getDocComment(), "\n";

Case sensitivity

This catches everyone once:

<?php

function Shout(string $s): string { return strtoupper($s); }

echo SHOUT('quiet'), "\n";       // calling with different case: fine

$name = 'Ada';
$Name = 'Grace';
echo $name, ' and ', $Name, "\n";   // two different variables

Escaping from a string

Inside double quotes, \n, \t, \\, \" and \$ are escapes, and $name is interpolated. Inside single quotes only \\ and \' mean anything — everything else is literal.

<?php

$who = 'world';

echo "double: hello $who\n";
echo 'single: hello $who', "\n";
echo "a tab\there, a dollar \$here\n";

Reference: Basic syntax in the PHP Manual.