my $outfile = "$accession_$biotype";

##</code><code>##

my $outfile = '$accession_$biotype';

##</code><code>##

$outfile = "${accession}_${biotype}";

##</code><code>##

$outfile = $accession . '_' . $biotype;

##</code><code>##

use strict;
use warnings;

my $genfile = "c:\bemisia_coi.gb";
my $outfile;
my ($OUT, $IN);

print "Input: $genfile\n";
open $IN, '<', $genfile or die "cannot open $genfile: $!\n";

while (<$IN>) {
   $_ = lc $_; #case insensitive
   my @tokens = split m{//};
   for my $token (@tokens) {
         my ($accession) = ($token =~ /locus\s*([a-z]{8})/);
         my ($biotype)   = ($token =~ /biotype: ([a-z]{1})/);
         my ($sequence)  = ($token =~ /origin(\*+)\/\//);
            $sequence =~ s/\s//g; #Removing spaces
            $sequence =~ s/\d//g; #Removing numbers

        $outfile = "${accession}_${biotype}";
        open $OUT, '>' $outfile or die "cannot open $outfile: $!\n";
        print "Printing to $outfile \n";
        print $OUT, ">$outfile/n^^/n$sequence");
   }
}