C:\test>perl
my @d = qw(AAA30 BBC5 SHT12H DAL33B BBC49 AAA31 DAL33A BBC6 SHT12G BBC50);

my $last = "";
foreach my $v ( sort {$a cmp $b} @d)
{
        my $l1 = $last;
        my $l2 = chop $l1;
        print "$last,$v\n" if $v eq $l1.++$l2;
        $last = $v;
}
^Z
AAA30,AAA31
DAL33A,DAL33B
SHT12G,SHT12H