The easy way to get rid of the \n at the end of a line is chomp.  Chomp deletes the last char from a sting IF that char is a \n.
$good_iput = chomp($input);

A neat discussion of pointers in Perl (called references) can be found at http://www.sitecircus.com/tricks/scalars.html.

This code is wrong.  Split just returns the items split in a scalar context, or the items in a list context.  But it does not return true/false
$count = split(/-/, $nations);
@n = split(/-/, $nations);
@n = split(/-/, $nations) or die "This is bad code!!";

#!/usr/bin/perl
# connect to db
my $dbh = DBI->connect(bla..bla..bla);
my $sql_q = "SHOW COLUMNS FROM $table";
my $sth = $dbh->prepare($sql_q);
$sth->execute;
while (@row = $sth->fetchrow_array){
           print"Field    Type     Null     Key     Default    Extra\n";
           print"----------------------------------------------------\n";
           print"$row[0]  $row[1]  $row[2]  $row[3] $row[4]    $row[5]\n";
}

# This will return one row which contains
# the number of rows found
my $sql = q(select count(*) from $table where field = ?);
my $sth = $dbh->prepare($sql);
$sth->execute('$value');
my $rows = $sth->fetchrow_arrayref->[0];
$sth->finish;w do I get the number of rows a query might generate?

You can Join the Same Table Twice

mysql> select A.name, B.name, length from borders, nations A, nations B where code1 = "rs" and code2 = "ch" and A.code = code1 and B.code = code2;
+--------+-------+---------+
| name   | name  | length  |
+--------+-------+---------+
| Russia | China | 2259.90 |
+--------+-------+---------+

Another way to fetch from a database is

         my($id, $name, $phone);
      $sth->bind_columns(undef, \$id, \$name, \$phone);

      for my $month (@months) {
          print "People born in $month:\n";

          # Execute the statement for this $month
          $sth->execute();

          # Fetch each row and print out the values
          while ($sth->fetch) {
              print "\t", join("\t", $id, $name, $phone), "\n";
          }
      }

If Perl is going to run out of Apache, then you can use Apachi:DBI to cache the database connections.  See  http://www.perlmonks.org/index.pl?node=Tricks%20with%20DBI&lastnode_id=954 .

        Some databases need to be told whether to commit or abort the transaction.  Other times for your own reasons you might want to cause a rollback.
    sub new_employee {
        # Arguments: database handle; first and last names of new employee;
        # department ID number for new employee's work assignment
        my ($dbh, $first, $last, $department) = @_;
        my ($insert_handle, $update_handle);

        my $insert_handle =
             $dbh->prepare_cached('INSERT INTO employees VALUES (?,?,?)');
        my $update_handle =
             $dbh->prepare_cached('UPDATE departments
                                   SET num_members = num_members + 1
                                   WHERE id = ?');

        die "Couldn't prepare queries; aborting"
             unless defined $insert_handle && defined $update_handle;
        my $success = 1;
        $success &&= $insert_handle->execute($first, $last, $department);
        $success &&= $update_handle->execute($department);

        my $result = ($success ? $dbh->commit : $dbh->rollback);
        unless ($result) {
             die "Couldn't finish transaction: " . $dbh->errstr
        }
        return $success;
     }
Automatic Error Handling

When you make the connect call, you can specify a RaiseErrors option that handles errors for you automatically. When an error occurs, DBI will abort your program instead of returning a failure code. If all you want is to abort the program on an error, this can be convenient:

my $dbh = DBI->connect('DBI:Oracle:payroll',
                      {RaiseError => 1},)
           or die "Couldn't connect to database: " . DBI->errstr;
 

People are always writing code like this:

while ($lastname = <>) {
    my $sth = $dbh->prepare("SELECT * FROM people WHERE lastname = '$lastname'");
    $sth->execute();
    # and so on ...
}

Here we interpolated the value of $lastname directly into the SQL in the prepare call.

This is a bad thing to do for three reasons.

First, prepare calls can take a long time. The database server has to compile the SQL and figure out how it is going to run the query. If you have many similar queries, that is a waste of time.

Second, it will not work if $lastname contains a name like O'Malley or D'Amico or some other name with an '. The ' has a special meaning in SQL, and the database will not understand when you ask it to  prepare a statement that looks like
 SELECT * FROM people WHERE lastname = 'O'Malley'

It will see that you have three 's and complain that you don't have a fourth matching ' somewhere else.

Finally, if you're going to be constructing your query based on a user input, as we did in the example program, it's unsafe to simply interpolate the input directly into the query, because the user can construct a strange input in an attempt to trick your program into doing something it didn't expect. For example, suppose the user enters the following bizarre value for $input:

x' or lastname = lastname or lastname = 'y

Now our query has become something very surprising:

SELECT * FROM people WHERE lastname = 'x' or lastname = lastname or lastname = 'y'

The part of this query that our sneaky user is interested in is the second or clause. This clause selects all the records for which lastname is equal to lastname; that is, all of them. We thought that the user was only going to be able to see a few records at a time, and now they've found a way to get them all at once. This probably wasn't what we wanted.

Solution
$sth = $dbh->prepare("select * from table where name = ?")
then
$sth->execute($userinput);