PHP String formatting String interpolation
Example
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>";
#> "Notice: Undefined variable: names"
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}";
#> "1 + 2 = {1 + 2}"
// 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()}";
#> "I say: {say_hello()}"
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']}";
#> "The best companion is: Amy Pond"
// 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()}";
#> "Max says: Hello!"
// 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)}";
#> "From us all: A 1000 greetings!"
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>";
#> "<p>We need more Joels to help us!</p>"
The
Complex (curly) syntaxis not called as such because it's complex, but rather because it allows for the use of 'complex expressions'. Read more aboutComplex (curly) syntax
