You can get a list of the files this way:

chdir $logdir;
@files = glob 'audit_*_010000.csv';
[download]

They probably should be in sorted order, but if occasionally that's not the case, you can do:

@files = sort glob 'audit_*_010000.csv';
[download]

Now files[-1] will be the name of the most recent file and $files[-2] the one of the previous file, assuming @files >= 2. So now, you can compare them.