As I understand your task (which seems to be different from BrowserUk), this should do it:

#!/usr/bin/perl -w
use strict;

my %hash = (a=>2, b=>1, c=>5, d=>3, e=>4);

my $input = "abcdaeec";

for (2, 3) {
    print "n=$_: ";
    my $n = $_ - 1;

    my @sums;
    while ( $input =~ /(.)(?=.{$n}(.))/g ) {
        push @sums, $hash{$1} + $hash{$2};
    }
    print "@sums\n";
}

__END__
n=2: 7 4 7 7 6 9
n=3: 5 3 9 7 7
[download]

Update: let YAPE::Regex::Explain explain what the regex does:

use YAPE::Regex::Explain;

print YAPE::Regex::Explain->new( qr/(.)(?=.{1}(.))/ )->explain;

__END__
The regular expression:

(?-imsx:(.)(?=.{1}(.)))

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    .                        any character except \n
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  (?=                      look ahead to see if there is:
----------------------------------------------------------------------
    .{1}                     any character except \n (1 times)
----------------------------------------------------------------------
    (                        group and capture to \2:
----------------------------------------------------------------------
      .                        any character except \n
----------------------------------------------------------------------
    )                        end of \2
----------------------------------------------------------------------
  )                        end of look-ahead
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

And see perlop for what m//g does in scalar context (like the while (...) here).

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.