#!/usr/bin/perl

use strict;
use warnings;

while (<DATA>) {
    s/<# \{(.*?)\} #>/$1/eeg;
    print;
}

__DATA__
<# { $a = 3; $b = 3; if ($a == $b) { "a=b"; } } #>
<# { 4*3;  } #>

##</code><code>##

a=b
12