#!/usr/bin/perl -w

use strict;
use Data::Dumper;

my %data;


while (<DATA>) {
  chomp;
  my ($val, @keys) = split;

  my $lastkey = pop @keys;

  my $hashref = \%data;

  foreach my $k (@keys) {
    $hashref->{$k} ||= {};
    $hashref = $hashref->{$k};
  }

  $hashref->{$lastkey} = $val;
}


print Dumper \%data;

__END__
val1 keyA keyX foo key1
val2 keyA keyY bar key2
val3 keyB keyZ baz key3