Small improvement (easy if you keep a template on hand)

#!/usr/bin/perl --
use strict;
use warnings;

use DBI;
use CGI::Carp qw(fatalsToBrowser);

Main(@ARGV);
exit(0);

sub Main {
    print "Content-type:text/html\n\n";

    my $db   = "database";
    my $user = "username";
    my $pass = "password";
    my $host = "localhost";

    my $dbh = DBI->connect( "DBI:mysql:$db:$host", $user, $pass )
      or die "Connecting to MySQL database failed: $DBI::errstr";

    my $query = ( "
    SELECT 
    username 
    FROM 'sessions' 
    WHERE uid='1'
" );

    my $start = $dbh->prepare($query)
      or die "Preparing MySQL query failed: $DBI::errstr";

    $start->execute()
      or die "The execution of the MySQL query failed: $DBI::errstr";

    my $result;
    while ( $result = $start->fetchrow_hashref() ) {
        print "Ta-da!:" . "$result->{username}\n";
    }

    $dbh->disconnect();

}
[download]