The issue you've run into here is that each hash key can only be associated with a single value, so the second assignment to $hash{one} overwrites its previous value. Or, as spazm put it in the comment you were replying to,

My solutions below assume that you have unique key values, or are un-interested in collisions. In the case of a collision, the last reference to the key wins.

However, the single value held by the hash doesn't have to be a simple scalar. If you use an array reference there (giving you a "hash of arrays" or "HoA"), then the code will be a little more complex, but you'll be able to store as many values as you like with each key:

#!/usr/bin/perl

use strict;
use warnings;

my @value_pairs = qw( one abc two xyz one def );
my %hash;

while (@value_pairs) {
  my $key = shift @value_pairs;
  my $value = shift @value_pairs;
  push @{$hash{$key}}, $value;
}

for my $key (keys %hash) {
  print "key $key has values: ", join(', ', @{$hash{$key}}), "\n";
}
__END__
key one has values: abc, def
key two has values: xyz
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