php - Warning: Unexpected character in input: '' (ASCII=92) state=1

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I receive the following error
message:

Warning: Unexpected
            character in input: '\' (ASCII=92)
            state=1

And this is
the line of code that is giving me this
trouble.

$tag_value =
            preg_replace('/\{(.*?)\}/e', '$values[\\1]',
            $tag_value);

I am
using PHP 5.2.9 and upgrading is not an
option.

Regular expression are not my specialty
and I am not able to solve this problem on my own. Any help would be greatly
appreciated.

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class="normal">Answer

You cannot
accomplish this with a simple preg_replace, as array
de-referencing is not done with /e modifier. Instead you can
use preg_replace_callback
function:

$tag_value =
            preg_replace_callback("/\{(.*?)\}/", function($m) use($values){


            return $values[$m[1]];
},
            $tag_value);

This
definitely works in php 5.3, however in 5.2 you may need to define the callback function
explicitly:

function replace($m)
            {
 global $values;
 return
            $values[$m[1]];
}

$tag_value =
            preg_replace_callback("/\{(.*?)\}/", "replace",
            $tag_value);

EDIT:
The error you are seeing is happening because with your original code, your substitution
is being treated literally as $values[\1] (after unescaping the
backslash - in this string, \1 is not the right stuff to put
inside the brackets.