Another one using a hash, this is a modified character frequency example from perlretut. This will sort and also handle negative numbers. Comments on where I can improve this code and what practices I should stay away from are appreciated.

use strict;

local $/;
my $f = <DATA>;
my %chars;

$f =~ s/(.+)/$chars{$1}++;$1/eg;  # final $1 replaces char with itself
print "'$_'\n" foreach (sort {$a <=> $b} keys %chars);

__DATA__
1
1
2
2
3
3
4
5
6
7
8
9
10
11
12
13
-12
-3
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