How to use a regular expression to match a regular expression?

There are several things in a long string: {$ var}, {$ wtf}, {$ mdzz}. I want to use a preg_replace to replace them with {code ...} how do I write this regular expression? There are several things in a long string:
{$var},{$wtf},{$mdzz}
I want to replace them with a preg_replace

How do I write this regular expression?

Reply content:

There are several things in a long string:
{$var},{$wtf},{$mdzz}
I want to replace them with a preg_replace

How do I write this regular expression?

Replace with the following match:
$msg = preg_replace("/{$var}/g", ' ', $msg);


Single quotes'The code in is not parsed.

preg_replace('/{\$([a-zA-Z]+)}/','
  ',$filestr);

Why?echo "{$a},{$b},{$c}"And

echo $a; echo ','; echo $b; echo ','; echo $c;

Is completely equivalent.