use Data::Dumper;
my @array = ();
$array[0] = [1];
$array[2] = [2];
@array = sort { $$a[0] cmp $$b[0]} @array;
print Dumper \@array;

##</code><code>##

use strict;
use warnings;
use Data::Dumper;

my @courselist = ( 
    ["UM", "CS 34", ],
    ["AC", "PHIL 13", ],
    ["UM", 'BIO 567', ],
    ["UA", 'BIO 999', ],
    ["UM", 'BIO 1', ],
);  


@courselist = sort {$$a[0] cmp $$b[0] or $$a[1] cmp $$b[1]} @courselist;
print Dumper(\@courselist);