PHP keep me from eval ;) Variables inside string - php

Question

For reasons I'd rather not get into right now, I have a string like so:
<div>$title</div>
that gets stored in a database using mysql_real_escape_string.
During normal script execution, that string gets parsed and stored in a variable $string and then gets sent to a function($string).
In this function, I am trying to:
function test($string){
$title = 'please print';
echo $string;
}
//I want the outcome to be <div>please print</div>
This seems like the silliest thing, but for the life of me, I cannot get it to "interpret" the variables.
I've also tried,
echo html_entity_decode($string);
echo bin2hex(html_entity_decode($string)); //Just to see what php was actually seeing I thought maybe the $ had a slash on it or something.
I decided to post on here when my mind kept drifting to using EVAL().
This is just pseudocode, of course. What is the best way to approach this?

Answer 1

Your example is a bit abstract. But it seems like you could do pretty much what the template engines do for these case:
function test($string){
$title = 'please print';
$vars = get_defined_vars();
$string = preg_replace('/[$](\w{3,20})/e', '$vars["$1"]', $string);
echo $string;
}
Now actually, /e is pretty much the same as using eval. But at least this only replaces actual variable names. Could be made a bit more sophisticated still.

Answer 2

I don't think there is a way to get that to work. You are trying something like this:
$var = "cute text";
echo 'this is $var';
The single quotes are preventing the interpreter from looking for variables in the string. And it is the same, when you echo a string variable.
The solution will be a simple str_replace.
echo str_replace('$title', $title, $string);
But in this case I really suggest Template variables that are unique in your text.

Answer 3

You just don't do that, a variable is a living thing, it's against its nature to store it like that, flat and dead in a string in the database.
If you want to replace some parts of a string with the content of a variable, use sprintf().
Example
$stringFromTheDb = '<div>%s is not %s</div>';
Then use it with:
$finalString = sprintf($stringFromTheDb, 'this', 'that');
echo $finalString;
will result in:
<div>this is not that</div>

Answer 4

If you know that the variable inside the div is $title, you can str_replace it.
function test($string){
$title = 'please print';
echo str_replace('$title', $title, $string);
}
If you don't know the variables in the string, you can use a regex to get them (I used the regex from the PHP manual).
function test($string){
$title = 'please print';
$vars = '/(?<=\$)[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*/';
preg_match_all($vars, $string, $replace);
foreach($replace[0] as $r){
$string = str_replace('$'.$r, $$r, $string);
}
echo $string;
}