use strict;
use warnings;
use Digest::MD5;

my $md5file = shift;
my @files   = @ARGV;

die "Usage: addmd5 <md5sumfile> <files>\n" if !defined $md5file or ! -e $md5file or !@files;

# Read existing MD5 sums
open (MD5FILE, '<', $md5file) or die "Couldn't open '$md5file'.\n";
my %md5files = map { chomp; substr($_, 34) => 1 } <MD5FILE>;
close (MD5FILE);

# Append new MD5 sums
open (MD5FILE, '>>', $md5file) or die "Couldn't open '$md5file' for appending.\n";

foreach my $file (@files) {
    next if exists $md5files{$file};
    my $ctx = Digest::MD5->new;
    open (my $fh, '<', $file) or die "Couldn't open data file '$file'\n";
    $ctx->addfile($fh);
    close ($fh);
    my $line = sprintf "%s  %s\n", $ctx->hexdigest(), $file;
    print $line;
    print MD5FILE $line;
}

close (MD5FILE);

__END__