I'm surprised no one mentioned Berkeley DB when you wanted a fast, simple, and hash-like DB.

See On-disk hash/array data structures for db_ref().

use warnings;
use strict;

my $randomword = db_ref("HASH");
my $numofwords = 50000000;
my @chars = ("A" .. "Z", "a" .. "z", 0 .. 9, qw(! @ $ % ^ & *));

for my $i (0 .. $numofwords - 1)
{
    my $rin = join("" => @chars[map { rand @chars } (1 .. 5)]);

    if (defined $randomword->{$rin})
    {
        $randomword->{$rin} .= ",$i";
    }
    else
    {
        $randomword->{$rin} = $i;
    }
}

## do some stuff with $randomword

untie %{ $randomword }; # when you're done
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