my $bookIDList = "abc,ghj,zxc,bnm,qwe,rty,iop,sdf,ert";
my $param = {
                 IDs => [ split /,/, $bookIDList ], 
                 sort => "AUTHOR",
                 maxResults => 100
              };

##</code><code>##

my @bookIDList = ( "abc", "ghj", "zxc", "bnm", "qwe", "rty", "iop", "sdf", "ert" );
my $param = {
                 IDs => \@bookIDList, 
                 sort => "AUTHOR",
                 maxResults => 100
              };