This sounds like a job for a hash of hashes! Using the code below, you can get at the keys by referring to keys %hash and you can get at all of the values of key2, for example, by referring to keys %{$hash{key2}}

use strict;

my $data = "key1=valuea key2=valuea valueb key3=valuea valueb valuec k
+ey4=valuea key5=valuea key6=valuea valueb";
my %hash = ParseData($data);

print "All of the keys are: ", join(" ",keys %hash),"\n\n";
print "Key2's keys are: ", join(" ",keys %{$hash{key2}});

sub ParseData {
  my $datastring = shift;
  my %data;
  my $currkey;
  foreach (split(' ',$datastring)) {
    if (/=/) {
      my $val;
      ($currkey, $val) = split('=');
      $data{$currkey}{$val}++;
    }
    else {
      $data{$currkey}{$_}++;
    }
  }
  return %data;
}
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