my @a=qw( wilma fred barney betty pebbels dino ); 
for (my ($i,$p,$c,$n)=(0,undef,@a);
     $i < scalar @a;
     $i++,($p,$c,$n) = ($c,$n,$a[$i+1])){
 print  qq($i  Prev=$p \tCurr=$c \tNext=$n\n)
}

-- Output -- 

0  Prev=        Curr=wilma      Next=fred
1  Prev=wilma   Curr=fred       Next=barney
2  Prev=fred    Curr=barney     Next=betty
3  Prev=barney  Curr=betty      Next=pebbels
4  Prev=betty   Curr=pebbels    Next=dino
5  Prev=pebbels         Curr=dino       Next=