Variables and Strings

So far, everything you echoed was typed by hand. Real websites are more interesting than that: they greet users by name, show product titles, and display messages that change. To do any of that, PHP needs a way to remember values. That is what variables are for.

Making a variable

In PHP, every variable starts with a dollar sign. You create one by giving it a name and a value with the equals sign:

<?php
$name = "Ada";
$greeting = "Welcome back";
echo $greeting;
?>

Read $name = "Ada"; as: put the text Ada into a box labeled name. From then on, whenever PHP sees $name, it looks in the box and uses whatever is inside.

Naming rules

• Every variable starts with $.
• After the dollar sign, start with a letter or underscore, never a number. $user2 is fine; $2user is not.
• Names are case sensitive: $Name and $name are two different boxes.
• Pick names that describe the contents. Future you will thank present you for $customerEmail instead of $x.

Strings: text in quotes

A piece of text in quotes is called a string. PHP accepts single quotes and double quotes, and the difference actually matters.

With double quotes, PHP looks inside the string for variables and swaps in their values:

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

This prints Hello, Ada! because PHP replaced $name with its value. With single quotes, PHP takes the text completely literally:

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

This prints Hello, $name! with the dollar sign and all. Beginners usually reach for double quotes so that variables work inside them.

Gluing strings together

You can join strings with a dot, which PHP calls concatenation:

<?php
$first = "Grace";
$last = "Hopper";
$full = $first . " " . $last;
echo "The full name is " . $full . ".";
?>

The dot simply sticks one string onto the end of another. Here we glued the first name, a space, and the last name into $full, then built a sentence around it.

Variables can change

The value in a variable is not locked in. Assign again and the old value is replaced:

<?php
$mood = "sleepy";
$mood = "caffeinated";
echo $mood;
?>

This prints caffeinated, because the second assignment overwrote the first. That ability to change is exactly why they are called variables.