In case anyone else reads this and needs a workaround, here is function to expand any embedded variables of the form "$name" found inside a given string. Note: this uses the global scope, even if called from inside a function.

// Expand global variables if found in a string
// ExpandVars ver=1/24/08
function ReplaceVarCallback($M)
	{
	if (!isset($GLOBALS[$M[1]]))
		die("Variable ".@$M[0]." is undefined.");
	return $GLOBALS[$M[1]];
	} // ReplaceVarCallback
function ExpandVars($Str)
	{
	for (;;)
		{
		$Res=preg_replace_callback('#\$([A-Za-z_][A-Za-z0-9_]*)#',
			"ReplaceVarCallback",$Str);
		if ($Res==$Str)
			break;
		$Str=$Res;
		}
	return $Str;
	} // ExpandVars

I wrote two functions to display ways of accomplishing this already (although a built-in function would be nice).

This function is very restrictive and requires you to pass a hash (name=>value) as $vars.  I prefer and use this function to build page layout with predefined variables to be placed in a template file (I put stuff like <div id="content">$content</div> where a page's specific content should go).  I consider this a safer way to string expand as you are explicitly limiting what can be expanded.  Some improvements can be done to it to handle arrays, but I haven't had a need for it yet.


function stringExpand($subject, array $vars) {
	// loop over $vars map
	foreach ($vars as $name => $value) {
		// use preg_replace to match ${`$name`} or $`$name`
		$subject = preg_replace(sprintf('/\$\{?%s\}?/', $name), $value, $subject);
	}
	// return variable expanded string
	return $subject;
}


This second function accomplishes the same task only using eval() and variables in the current symbol table (with the help of extract()).  I opted to use heredoc with optionally a randomly generated delimiter. This allows access to all variables available to the function (static members, globals, $vars, etc) so it could potentially allow access to preferably private data.  I won't even go into the security implications of using eval() to accomplish this, it's probably better to use something like the above.  here it is:
	
function stringExpandDangerous($subject, array $vars = array(), $random = true) {
	
	// extract $vars into current symbol table
	extract($vars);
		
	$delim;
	// if requested to be random (default), generate delim, otherwise use predefined (trivially faster)
	if ($random)
		$delim = '___' . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . chr(mt_rand(65,90)) . '___';
	else
		$delim = '__ASDFZXCV1324ZXCV__';  // button mashing...
		
	// built the eval code
	$statement = "return <<<$delim\n\n" . $subject . "\n$delim;\n";
		
	// execute statement, saving output to $result variable
	$result = eval($statement);
		
	// if eval() returned FALSE, throw a custom exception
	if ($result === false)
		throw new EvalException($statement);
		
	// return variable expanded string
	return $result;
}
	
As you can see you can easily (and dangerously) accomplish this task using eval() or you can cautiously accomplish it using a variant of regex.  I would recommend limiting the access of your string expansion script as well as avoiding eval(), you can capture variable names & values easily using compact().  I wouldn?t allow your script access to $GLOBALS like the above comment, you might not want that data as accessible as you?re making it.

The "Zend mechanism for this that is already there" is, well, eval(). It's a feature of the lexer parsing source code, there's no magical internal function we could easily expose. Also, you can call functions within string escapes, so this is just as dangerous as eval() anyway.

If you really want something like this, do it yourself with preg_match and some variable variables ($$).

I came up with a string like

"\115\x6f\172\x69\x6c\154\x61\x2f\x35\x2e\x30\40\x28\127\151\156\144\x6f\x77\163\40\x4e\x54\x20\61\60\56\x30\x3b\x20\127\x4f\127\x36\x34\x3b\x20\x72\x76\x3a\64\63\56\x30\x29\x20\x47\x65\x63\153\157\57\x32\x30\x31\60\60\x31\x30\x31\x20\106\151\162\145\x66\x6f\170\x2f\64\x33\56\x30"

and wanted it to get the real decoded characters. An echo in the console works, but I need the content to be in a variable.

Using ob_start() and echo() did not work, because it gave the same escaped string back. Also with print or printf.

Solution for me was to use stripcslashes() which gave me the unescaped result.