Variable interpolation in double quotes

Learn how variables are interpolated inside double-quoted strings and the use of {} braces.

Variable interpolation in double quotes

In PHP, when you write a variable name inside a double-quoted string, PHP places the variable's value into the string. For example, $name = "Alex"; echo "Hello $name"; outputs "Hello Alex". This is called variable interpolation.

In single quotes, $name is written as is; echo 'Hello $name'; outputs "Hello $name". This difference helps you choose which quote to use.

When do you need curly braces?

Inside a double-quoted string, writing $variable is usually enough. But when a letter comes right after the variable name, PHP gets confused. For example, "$names" makes PHP look for a variable named $names; you may have wanted to append the letter s to $name.

Curly braces {} solve this: "{$name}s" outputs Alexs. The same rule applies to array elements and property access. In complex expressions, always use {} to be safe.

Exercise Build a message with interpolation

Assign "Alex" to $name. Assign "Hello, $name!" to $msg using double quotes (use variable interpolation). Then print it with echo $msg;.

Show example solution

Use double quotes; $name inside the string is replaced by its value.
Example solution:
<?php
$name = "Alex";
$msg = "Hello, $name!";
echo $msg;

Test yourself

$city = "Paris"; echo "City: $city"; what is the output?
```
$city = "Paris";
echo "City: $city";
```
- City: $city
- City: Paris
- City:
- It errors
Show answer

City: Paris — Correct. Double quotes place the value of $city: "City: Paris".

Insert the variable with curly braces

$product = 'Coffee';
echo "Product: ____";

Show answer

$product = 'Coffee';
echo "Product: {$product}";

Match each syntax to its behavior

'$name'

No interpolation
"$name"

Interpolates the variable
"{$name}"

Curly-brace interpolation

Next lesson: Escape sequences

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