Regex escaping question

How can I escape the $ in the replaced section in the following statement?

$tmp_code = preg_replace('/(<\?=\$([a-zA-Z0-9\_]+)\?>)/me','"{$$2}"',$tmp_code);

The replaced text should like like {$te开发者_开发知识库st} however I can't figure out how to escape the first $. I've tried \$ but that didn't do anything.

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Generally you should prefer preg_replace_callback over the /e expression modifier. But depending on what you want to do, there are multiple workarounds.

You can split up the string expression:

 '"{"."$"."$2"."}"', $tmp

Or use the alternative placeholder syntax and escape the {$ so it does not get interpreted as variable variable within the double quotes:

 '"{\\\$\2}"'

(No, I didn't know that. Just tinkered around.)