like so?

use strict;
use warnings;

my %hash;

while (<DATA>)
{
    if ( /(\w) (.+)/ )
    {
        $hash{$1} .= $2;
    }
}
for ( sort keys %hash )
{
    print "$_ $hash{$_}\n";
}
__DATA__
A A_
B B_
C C_
D D_
E E_
A A*
B B*
C C*
D D*
E E*
A A-
B B-
C C-
D D-
E E-
A AB
B BB
C CC
D DD
[download]

prints:

A A_A*A-AB
B B_B*B-BB
C C_C*C-CC
D D_D*D-DD
E E_E*E-
[download]