#!usr/bin/perl
my $a = 1;
%hash = map { $_ , undef } 0 .. 3;	
@h = sort {$a <=> $b} keys %hash;
print "@h\n";

__END__
0 3 2 1

##</code><code>##

@h = sort {$a <=> $b} @arr = keys %hash; # doesn't sort
@h = sort {$a <=> $b}        0 .. 3;     # do      sort
@h = sort {$a <=> $b} @arr = 0 .. 3;     # do      sort