splice is the answer. Consider:

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

my @array = qw( 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 );

do_something (splice @array, 0, 3) while @array;


sub do_something {
    print "@_\n";
}
[download]

Prints:

1 2 3
4 5 6
7 8 9
10 11 12
13 14 15
16 17 18
19 20
[download]