problem with perl dbi

from html form,I fill in details and wish to compare certain data in mysql.

my dbi code is run normally from the command line.but run under httpd,it fails.

its seem like the httpd process usually runs under the user id of nobody,which implies there is no configured environment.I was wondering that is the problem of making my perl script is not running properly.

here is my code:
$temp=$ENV{'CONTENT_LENGTH'};
@pairs=split(/&/,$temp);
..
..
.. #skip the foraech statement

use DBI;
$dbh=DBI->connect('DBI:mysql:$databasename:localhost','','');
$cursor=$dbh->prepare("select * from $tablename");
$cursor->execute;
while(..) #skip the fecthrow statement
{
}
$cursor->finish;
$dbh->disconnect;

hope someone can help me.
thank.

Does your DB not have a username/password? What does the apache error_log say if anything?