DBI connection problem

Hi, all
I am trying to write Perl script using DBI module to manupulate the database
on our virtual server.

I wrote the following code:

#! /usr/bin/perl5

use DBI;
$dbHandle = DBI->connect("DBI:Pg:dbname=best",'','') or $DBI::errstr;
$sql ="SELECT * FROM sample";
$statementHandle = $dbHandle->prepare($sql);
$statementHandle->excute() || die $statementHandle->errstr;

$arrayRef = $statementHandle->fetchall_arrayref;
$dbHandle->disconnect();

print $arrayRef ;

after compiling, I got the following error message:

connectDB() failed: Is the postmaster running and accepting connections at 'UNIX
Socket' on port '5432'?
at sample.pl line 4

but when I run
% psql

in the shell, everything works just OK.

Why my script cannot connect to the database? What I need to do for this?

Thanks a lot.

James