my $emptyfile; #structure file, new.
my $previous; #structure file, alternative conformation.

my @emptyfiles = grep { /^\d+$/ } grep { -f } glob '*';

$previous = ($emptyfile)-1); #set that $previous is the previous alternative conformation.
#print "previous is $previous \n";

#push (@emptyfiles, $emptyfile);
#push (@emptyfiles, $previous);

foreach (@emptyfiles) {

 if (-z "$emptyfile") {
 print "found previous conformation: $previous \n";
 print "found new conformation: $emptyfile \n";
 } # if -z loop.

} #foreach loop.