#!/usr/bin/perl -w

use strict;
use Bio::DB::GenBank;
use Bio::SeqIO;
use File::Basename;

# configuration information
my $outfile  = 'outfile';
my $progname = basename $0;

# usage information
my $usage = "usage:  $0 accession1 [accession2 ...]\n";
die $usage unless @ARGV;

# start program flow
my $gb = new Bio::DB::GenBank( 
   -retrievaltype => 'tempfile', 
   -format => 'Fasta'
);

my $seqout = Bio::SeqIO->new( -file => ">$outfile", -format => 'FASTA' );

my $seqio = $gb->get_Stream_by_acc( @ARGV );
while( my $sequence =  $seqio->next_seq ) {
   $seqout->write_seq($sequence);
}