#!/usr/bin/perl -wT
use strict;

my @a       = (1..16);   # test array
my $atatime = 3;         # number of elements to loop over

for my $i (0..$#a/$atatime) {  # loop through @a/$atatime times
  my $min = $i*$atatime;       # index of low element
  my $max = $min+$atatime-1;   # index of high element
  $max = $#a if $max > $#a;    # make sure we don't fall off the end
  print join(", ", @a[$min..$max]),"\n";  # do something with our slice
}

# Verify that we haven't munged our values
print "\nStill There: ", join(' ',@a), "\n";

=output
1, 2, 3
4, 5, 6
7, 8, 9
10, 11, 12
13, 14, 15
16

Still There: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16