$post_message =~ s/\Q[[$1]]/[[$article_id]]/sig;

##</code><code>##

while ($input =~ /\G(.*?)\[\[([^]]+)\]\]/sg) {
   my $link = $2;
   $output .= $1;
   $output .= process($link);
}

##</code><code>##

$post_message =~ s{\[\[([^]]+)\]\]}{
   process($1)
}esg;