[SPOILER] Minimalistic (but CPAN-enabled) solution

Here's a solution using IO::All and the Uniq modules which implements the uniq 
function:

<<<
#!/usr/bin/perl

use strict;
use warnings;
use IO::All;
use Uniq;

io($ARGV[1])->print(uniq(
    sort { $a cmp $b }
    map { my $s = $_; $s=~s{[A-Z]$}{M}; ($_, $s) }
    io($ARGV[0])->getlines()
    ));
>>>

There's exactly one statement except for all the use ones.

Regards,

        Shlomi Fish
-- 

---------------------------------------------------------------------
Shlomi Fish      shlomif-ik1l9ssToec+JF/nGntIXQ@xxxxxxxxxxxxxxxx
Homepage:        http://www.shlomifish.org/

Knuth is not God! It took him two days to build the Roman Empire.