Here is my go at it. I think a bunch of your logic at the bottom is difficult to read at first glance, so I tried to simplify it based upon the first numbered picture being 1 (and thus not 0).

The logic for previous, next, and this picture all works, unless there are no files (and thus my die statement when reading the number of pictures, if it is 0). It might be even better to break that math out into some subroutines, especially if you will be doing it in more than one place.

This is untested, as I didn't take the time to write the accessory templates, but this should be a good starting place. (comments added where I deemed necessary) 

## Modules and setup
use CGI;
use HTML::Template;
use strict;

$CGI::POST_MAX=1024 * 1;   # max 1k post
$CGI::DISABLE_UPLOADS = 1; # No uploads

# Your script name is already a property,
# so this isn't generally necessary -
# just call $ENV{SCRIPT_NAME}
# instead of $ThisScript;
my $ThisScript = $ENV{SCRIPT_NAME};

# better to create new CGI object this way with ->new()
my $q = CGI->new();

my $template = HTML::Template->new(
   filename => "./template.html"
);

# instead of making variables that we'll later use
# only once, let's just do the math when defining
# the template params:
$template->param(
   PreviousPicture =>
      $q->param('Picture') - 1 || NumberOfPictures(),
   PictureToView   =>
      $q->param('Picture') || 1,
   NextPicture =>
      $q->param('Picture') % NumberOfPictures() + 1,
);

print $q->header, $template->output();

{
   # we'll go ahead and cache the number for
   # future calls without re-reading the directory
   # we don't need a global variable for this, so
   # we'll limit the scope of this cached variable to
   # this block.

   my $cached_number_of_pics;

   sub NumberOfPictures {
      return $cached_number_of_pics
         if defined $cached_number_of_pics;

      opendir(DIR, "./")
         || die "Couldn't open directory: $@\n";

      my @LFiles = grep {
         not /^(\.\.?|template\.html|pictureview\.cgi)$/
      } readdir(DIR);

      closedir(DIR);

      # We don't really have a reason to continue
      # if there are no files, so die.
      die "No files -- I have no idea what to do\n"
         unless @LFiles;

      $cached_number_of_pics = @LFiles;

      # probably not necessary to force scalar
      # context, but...
      return scalar @LFiles;
   }
}

[download]

In reply to Re: How can it be done better? by perlguy
in thread How can it be done better? by SilverB1rd

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.