# data file is open to read on the FOO handle
my @lines = <FOO>;

# option A.
my @lines = sort {  substr( $a, 0, 1) cmp substr( $b, 0, 1)
                    or substr( $b, 1) cmp substr( $a, 1)
            } @lines;
#  option B.
my @ary;
push @{$ary[ substr( $_, 0, 1)]}, substr( $_, 1) for @lines;
@ary = map {[ reverse sort @$_ ]} @ary;