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

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

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

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

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

sub subarray {
    my ($a, $b) = @_;
...
}

subarray(\@a, \@b);

sub subarray {
    my ($a, $b) = @_;
...
}

subarray(\@a, \@b);

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