$a[$_] -= $b[$_] for 0..$#a;

##</code><code>##

$a[$_] -= $b[$_] for (),0..$#a;

##</code><code>##

map { $a[$_] -= $b[$_] } 0..$#a;

##</code><code>##

my $i = @a; $a[$i] -= $b[$i] while $i--;

##</code><code>##

my $i = @a;
goto CHECK;
BODY:  $a[$i] -= $b[$i];
CHECK: goto BODY if $i--;

##</code><code>##

sub subarray {
    my ($a, $b) = @_;
    local *_helper = sub {
        my $i = $_[0];
        return if !$i--;
        $a->[$i] -= $b->[$i];
        _helper($i);
    };
    _helper(0+@$a);
}

subarray(\@a, \@b);

##</code><code>##

sub subarray {
    my ($a, $b) = @_;
    local *_helper = sub {
        return if !@_;
        $_[0] -= $_[-1];
        shift; pop;
        &_helper;
    };
    _helper(@$a, reverse(@$b));
}

subarray(\@a, \@b);

##</code><code>##

use List::MoreUtils qw( pairwise );
@a = pairwise { $a - $b } @a, @b;