$ cat t.pl
#!/usr/bin/perl
use 5.14.0;
use warnings;
use autodie;
use DBI;

my $orig_SQL="select * from table ";

my @ex = (
    [ qw( apple ) ],
    [ qw( cart horse ) ],
    [ qw( a quick red fox ) ],
);

for (@ex) {

    my $num_args = @$_;
    my $SQL = $orig_SQL
            . " where col in ("
            . join(", ", ("?") x $num_args)
            . ")";
    print "\n\nSQL: $SQL\n\n";
    print "execute(", join(", ", @$_), ")\n";

    # my $ST = $DB->prepare($SQL . $where_clause);
    # $ST->execute(@$_);
    # ... process results ...
}

$ perl t.pl

SQL: select * from table  where col in (?)

execute(apple)


SQL: select * from table  where col in (?, ?)

execute(cart, horse)


SQL: select * from table  where col in (?, ?, ?, ?)

execute(a, quick, red, fox)