Newline removed
   after, not before
        |      |
        |      |
        v      v
's/\n^$|\n^dn:*$//mg','s/cn: //g','s/\norclnetdescstring: /=/g'
's/\n^$|^dn:.*\n//mg; s/cn: //g; s/\norclnetdescstring: /=/g
            ^        ^
            |        |
           Missing   |
           dot      Optional: no need to switch between Perl and shell,
                    using semicolons instead of commas.