$text =~ s/(.*)$nbsp(.*)//g;  # this is your problem

##</code><code>##

$text = "test of &nbsp;this # ? my 0923&nbsp;5834t674";

$text =~ s{(.*?)(\&nbsp;)?}{($x=$1)=~tr/ /./c; "$x$2"}ge;

print "$text\n";

__OUTPUT__
.... .. &nbsp;.... . . .. ....&nbsp;........