use strict;
use warnings;

my %hashOfVals;
open(my $tmp, "<", "NC_001903.gbk.txt") || die "Could not open $!";
undef @hashOfVals{map {chomp; $_} <$tmp>};
close($tmp);

open(my $tmpFile, "<", "cp26_diffexpr.txt") || die "Could not open $!";
my @arrayFromCSV = <$tmpFile>;
chomp @arrayFromCSV;
close($tmpFile);

for (0..$#arrayFromCSV-1) {
    print "$1: $arrayFromCSV[$_+1]\n" 
        if $arrayFromCSV[$_] =~ /locus_tag="(.*)"/ and exists $hashOfVals{$1};
}