This is the complex (curly) syntax for string interpolation. From the manual:
Complex (curly) syntax
This isn’t called complex because the syntax is complex, but because
it allows for the use of complex expressions.Any scalar variable, array element or object property with a string
representation can be included via this syntax. Simply write the
expression the same way as it would appear outside the string, and
then wrap it in{
and}
. Since{
can not be escaped, this syntax
will only be recognised when the$
immediately follows the{
. Use
{\$
to get a literal{$
. Some examples to make it clear:<?php // Show all errors error_reporting(E_ALL); $great="fantastic"; // Won't work, outputs: This is { fantastic} echo "This is { $great}"; // Works, outputs: This is fantastic echo "This is {$great}"; echo "This is ${great}"; // Works echo "This square is {$square->width}00 centimeters broad."; // Works, quoted keys only work using the curly brace syntax echo "This works: {$arr['key']}"; // Works echo "This works: {$arr[4][3]}"; // This is wrong for the same reason as $foo[bar] is wrong outside a string. // In other words, it will still work, but only because PHP first looks for a // constant named foo; an error of level E_NOTICE (undefined constant) will be // thrown. echo "This is wrong: {$arr[foo][3]}"; // Works. When using multi-dimensional arrays, always use braces around arrays // when inside of strings echo "This works: {$arr['foo'][3]}"; // Works. echo "This works: " . $arr['foo'][3]; echo "This works too: {$obj->values[3]->name}"; echo "This is the value of the var named $name: {${$name}}"; echo "This is the value of the var named by the return value of getName(): {${getName()}}"; echo "This is the value of the var named by the return value of \$object->getName(): {${$object->getName()}}"; // Won't work, outputs: This is the return value of getName(): {getName()} echo "This is the return value of getName(): {getName()}"; ?>
Often, this syntax is unnecessary. For example, this:
$a="abcd";
$out = "$a $a"; // "abcd abcd";
behaves exactly the same as this:
$out = "{$a} {$a}"; // same
So the curly braces are unnecessary. But this:
$out = "$aefgh";
will, depending on your error level, either not work or produce an error because there’s no variable named $aefgh
, so you need to do:
$out = "${a}efgh"; // or
$out = "{$a}efgh";