# warning: untested code

# A string that will sort beyond any returned file (they all start with /)
use constant INFINITY => chr(ord("/")+1);

open(local *YESTERDAY, "<", $yesterday_file) || 
    die "Could not open $yesterday_file: $!";
open(local *CURRENT, "find / $search_files -print | sort") ||
    die "Could not start find: $!";
open(local *TODAY, ">", $today_file) ||
    die "Could not create $today_file: $!";
my $yesterday = <YESTERDAY> || INFINITY;

local $_;
while (<CURRENT>) {
    print TODAY $_;
    while ($yesterday lt $_) {
        print "Lost file $yesterday";
        $yesterday = <YESTERDAY> || INFINITY;
    }
    # Now $yesterday ge $_
    if ($yesterday gt $_) {
        print "New file $_";
    } else {
        $yesterday = <YESTERDAY> || INFINITY;
    }
}
if ($yesterday ne INFINITY) {
    print "Lost file $yesterday";
    print "Lost file $_" while <YESTERDAY>;
}