My first idea was a "merge sort" (well, at least the "merge" part of it). Luckilly you say that the files are already sorted so this is easy. But I still don't think it is as easy as extending what gaspodethewonderdog came up with (since you said in the chatterbox that you wanted both additions and deletions). 

sub compare {
    my( $old, $new )= @_;
    open OLD, "< $old"  or  die "Can't read $old: $!\n";
    open NEW, "< $new"  or  die "Can't read $new: $!\n";
    my %old;
    while(  <OLD>  ) {
        chomp;
        $old{$_}++;
    }
    close OLD;
    my @new;
    while(  <NEW>  ) {
        chomp;
        push @new, $_   if  delete $old{$_};
    }
    close NEW;
    my @old= sort keys %old;
    print "New sites:\n\t", join("\n\t",@new), $/;
    print "Old sites:\n\t", join("\n\t",@old), $/;
}

[download]

Then use Alabanach's idea for deciding which order to compare the files in.

        - tye (but my friends call me "Tye")

In reply to (tye)Re3: Comparison Of Files by tye
in thread Comparison Of Files by ImpalaSS

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.