Whats the difference between {$var} and $var?

Question

I would like to know when and why should I use {$var}

echo \"This is a test using {$var}\";

and when (and why) should I use the simple form

Answer 1

The brackets allow you to remove ambiguity for the PHP parser in some special cases. In your case, they are equivalent.

But consider this one:

$foobar = 'hello';
$foo = 'foo';
echo "${$foo . 'bar'}"; // hello

Without the brackets, you will not get the expected result:

echo "$$foo . 'bar'"; // $foo . 'bar'

For clarity purposes, I would however strongly advise against this syntax.