#!/usr/bin/perl
use strict;
use warnings;
BEGIN {
    # This BEGIN block must come before "use DBI" and before "use DBD::Oracle", or this trick won't work!
    $ENV{'WHATEVER_ORACLE_WANTS'}='is set here';
    $ENV{'MAYBE_EVEN_SEVERAL'}='environment variables';
}
use DBI qw( ... ); # maybe hidden in your database handling module