my $nline = "\n";
my $comma = ",";
...
     print OUTPUT $column[4],$comma,$column[5],$comma,$column[7],$comma,$column[8],$comma,$A,$comma,$B,$comma,$nline;

##</code><code>##

# $/ = "\n" # Input RS already defined
$, = ",";
...
     print OUTPUT $column[4],$column[5],$column[7],$column[8],$A,$B;
     print $/; # or use 'say' as it was said.

##</code><code>##

     print OUTPUT "$column[4],$column[5],$column[7],$column[8],$A,$B\n";