Question

I’m a bit confuse with

$hello = "hello";
echo "Say $hello";
echo "Say {$hello}";
echo "Say ${hello}";

and the output is same Say hello. When should I use {$hello} and ${hello}? and why it cannot be used in single quote?

Answer 1

$animal = 'cat';
echo "I have 14 $animals";

This may lead to problems, thus you will “escape” it

echo "I have 14 ${animal}s";

or

echo "I have 14 {$animal}s";

In single caused variables/expression were never substituted.