#! perl
use strict;
use warnings;
use Data::Dump;

my @array;

while (<DATA>)
{
    chomp;
    push @array, $_;
}

dd \@array;
    @array = clean(@array);     # or clean(\@array);
dd \@array;

sub clean
{
    my   @array_with_duplicates = wantarray ? @_ : @{$_[0]};
    my  (@array_no_duplicates, %hash);

    for (@array_with_duplicates)
    {
        unless (exists $hash{$_})
        {
            push @array_no_duplicates, $_;
            $hash{$_} = undef;
        }
    }

    return @array_no_duplicates if wantarray;
    @{ $_[0] } = @array_no_duplicates;
}

__DATA__
Frieda
Adele
Briony
Hermione
Cathy
Dorothy
Cathy
Erin
Ida
Frieda
Frieda
Gertrude
Hermione