The answers in the FAQ don't modify the array in-place. In case that's what you need, you can do the following:

my @a = qw( a a b c c c d e f e f e a f g h h h );

my %seen;
for ( my $i = 0; $i <= $#a ; )
{
    splice @a, --$i, 1
        if $seen{$a[$i++]}++;
}

print "@a\n";
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This can be wrapped in a sub like so:

sub remove_duplicates(\@)
{
    my $ar = shift;
    my %seen;
    for ( my $i = 0; $i <= $#{$ar} ; )
    {
        splice @$ar, --$i, 1
            if $seen{$ar->[$i++]}++;
    }
}

my @a = qw( a a b c c c d e f e f e a f g h h h );
remove_duplicates( @a );
print "@a\n";
[download]