my $start_dir;
my $file_name = "mjnload.cmm";
opendir(DIR, "$start_dir");
@plf_files = grep(/\.plf$/,readdir(DIR));
print "PLF FILES\n";
print "@plf_files\n";--->there are no duplicates 
closedir(DIR);
foreach my $plf (@plf_files) {
chomp($plf);
open my $match, '<',"$start_dir\\$plf" or die "could not open '$plf' $!";
my @file_lines = <$match>;
$Hash_filenames{$plf}=\@file_lines;
}

open my $hash, '>>', "hash.txt";
print $hash Dumper( \%Hash_filenames );