PHP String interpolation
You can also use interpolation to interpolate (insert) a variable within a string. Interpolation works in double quoted strings and the heredoc syntax only.
$name = 'Joel';
// $name will be replaced with `Joel`
echo "<p>Hello $name, Nice to see you.</p>";
#> "<p>Hello Joel, Nice to see you.</p>"
// Single Quotes: outputs $name as the raw text (without interpreting it)
echo 'Hello $name, Nice to see you.'; # Careful with this notation
#> "Hello $name, Nice to see you."The complex (curly) syntax format provides another option which requires that you wrap your variable within curly braces {}. This can be useful when embedding variables within textual content and helping to prevent possible ambiguity between textual content and variables.
$name = 'Joel';
// Example using the curly brace syntax for the variable $name
echo "<p>We need more {$name}s to help us!</p>";
#> "<p>We need more Joels to help us!</p>"
// This line will throw an error (as `$names` is not defined)
echo "<p>We need more $names to help us!</p>";The {} syntax only interpolates variables starting with a $ into a string. The {} syntax does not evaluate arbitrary PHP expressions.
// Example tying to interpolate a PHP expression
echo "1 + 2 = {1 + 2}";Output
// Example using a constant
define("HELLO_WORLD", "Hello World!!");
echo "My constant is {HELLO_WORLD}";
#> "My constant is {HELLO_WORLD}"
// Example using a function
function say_hello() {
return "Hello!";
};
echo "I say: {say_hello()}";Output
However, the {} syntax does evaluate any array access, property access and function/method calls on variables,
array elements or properties:
// Example accessing a value from an array — multidimensional access is allowed
$companions = [0 => ['name' => 'Amy Pond'], 1 => ['name' => 'Dave Random']];
echo "The best companion is: {$companions[0]['name']}";Output
// Example of calling a method on an instantiated object
class Person {
function say_hello() {
return "Hello!";
}
}
$max = new Person();
echo "Max says: {$max->say_hello()}";Output
// Example of invoking a Closure — the parameter list allows for custom expressions
$greet = function($num) {
return "A $num greetings!";
};
echo "From us all: {$greet(10 ** 3)}";Output
Notice that the dollar $ sign can appear after the opening curly brace { as the above examples, or, like in Perl or Shell Script, can appear before it:
$name = 'Joel';
// Example using the curly brace syntax with dollar sign before the opening curly brace
echo "<p>We need more ${name}s to help us!</p>";Output
We need more Joels to help us!
The Complex (curly) syntax is not called as such because it's complex, but rather because it allows for the use of 'complex expressions'.