Just to illustrate I have rewritten your script to use DBI.
Note that I don't have access to Oracle so I haven't tested it.

The rewrite is quite simple:

#!/usr/bin/perl -w

use strict;
use DBI;
use Env;

my $DB = "DBNAME";
my $UN = "USERNAME";
my $PW = "PASSWORD";
my ($dbh,$sth,$clli,$c);

$dbh = DBI->connect("dbi:Oravel:$DB",$UN,$PW,
     {AutoCommit => 0, RaiseError => 1) or
              die("Oracle login FAILED, $DBI::errstr");

$sth = $dbh->prepare("select distinct(clli) from gvc_traffic30");
$sth->execute;

$sth->bind_col(1, \$clli);
while ($sth->fetchrow_arrayref ) {
    $c++;
    if ($clli =~ /\W/ ) {
      print "Found bad character in line $c.";
    } else {
      print "This clli appears to be OK.";
    }
    print " : $clli\n";
}
[download]

Note that I don't do any error checking. This is because I set $dbh->{RaiseError} in the connect call, so the DBI will do all neccessary errorchecking for me!

Check the DBI documentation to see what this does.

Happy DBI'ing