(Update: the above solution using reverse is cooler and better than this one.

I would suggest using splice rather than delete for this purpose, but either way you're going to have to use something other than for over the array.

Like a lot of things the "three-part" or "C-style" for loop should be avoided in general, but used when needed. Don't feel that you must never use it.

my @foo = (1,2,2,1) x 5;
my @bar = (2) x 20;

for (my $i = 0; $i < @foo; $i++) {
  print "$i\n";
  if ($foo[$i] % $bar[$i]) {  
    splice @foo, $i, 1; $i--
  }
}

print "@foo\n";
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Because you're removing the element at $i when you use splice, you have to decrement it so that the next time you find the element that used to be at $i + 1. The splice will change the size of @foo, so the comparison in the for loop will refer to the current list size.

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