Dynamic variables were not used in preg_replace().
I want searching html code for the tag "<usr my_var>" and want to replace this tag by the HTTP_POST or HTTP_GET var "my_var", but it doesn't work.

Here is my regexp:
$modified = '[...]<usr my_var>[...]';
$my_var = 'content';

$modified = preg_replace("/<usr\s+?(.*?)\s*?>/ims", ${"$1"}, $modified, -1);
Output: [...][...] (replaced by empty string)

This expression match to <usr my_var> and if i do the following preg_replace works correct:
$modified = preg_replace("/<usr\s+?(.*?)\s*?>/ims", "$1", $modified, -1);
Output: [...]my_var[...]

And this also doesn't work:
$modified = preg_replace("/<usr\s+?(.*?)\s*?>/ims", ${$my_var}, $modified, -1);
Output: [...][...] (replaced by empty string)

This is the problem.