my %user_passwds = (
   joe  => ...,
   jeff => ...,
   john => ...,
);

##</code><code>##

my %user = (
   id       => 'joe',
   name     => 'Joe',
   passwd   => ...,
   home_dir => ...,
);

##</code><code>##

my %unique;
++$unique{$_} foreach @list;
@list = keys %unique;