use Fatal qw/open/;
my %h;
open my $fh, '<', '/tmp/file1';
while ( defined ($_ = <$fh>)){
  /^([\d.]+)/ and $h{$1}++;
}
open  $fh, '<', '/tmp/file2';
while ( defined ($_ = <$fh>)){
  /^([\d.]+)/ and delete $h{$1};
}
print join "\n", keys %h;