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

#Populate the hash the first way.
my @keys = qw(a b c d e f);
my %hash; 
@hash{@keys} = (1,1,1,1,1,1);

# first verse.
print Dumper(\%hash);

#clear %hash. 
for (keys %hash) {
delete $hash{$_};
}
print Dumper(\%hash);

#Populate the hash the second way, using scalars and arrays.
${hash}{a} = 1;
$hash{b} = 1; # proving brackets optional when setting hash values in $calar mode.
@{hash}{('c','d')} = (1,1);
@hash{'e','f'} = (1,1); # proving brackets optional when setting hash values in @rray mode

# second verse, same as the first.
print Dumper(\%hash);