Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
Use the Tie::IxHash from CPAN.
use Tie::IxHash; tie(%myhash, Tie::IxHash); for ($i=0; $i<20; $i++) { $myhash{$i} = 2*$i; } @keys = keys %myhash; # @keys = (0,1,2,3,...)