Something along the lines of ...

use warnings;
use strict;

use Data::Dumper;

use Text::xSV;

my $sv = Text::xSV->new(sep => '|', fh => *DATA);
my $res = {};

while (my $row = $sv->get_row()) {
    $res->{shift @$row} = [ @$row ];
}

print Dumper $res;


__DATA__
UserID001|username1|password1|displayname1|
UserID002|username2|password2|displayname2|
UserID003|username3|password3|displayname3|
[download]

when run, gives

$ perl tst.pl
$VAR1 = {
          'UserID001' => [
                           'UserID001',
                           'username1',
                           'password1',
                           'displayname1',
                           undef
                         ],
          'UserID002' => [
                           'UserID002',
                           'username2',
                           'password2',
                           'displayname2',
                           undef
                         ],
          'UserID003' => [
                           'UserID003',
                           'username3',
                           'password3',
                           'displayname3',
                           undef
                         ]
        };
[download]

Is that the sort of thing you're after (with a bit of fettling to suit your individual needs) ??