for (@array) {
    if (condition($_)) {
        $_ = transform($_);
    }
}

##</code><code>##

$_ = transform($_) for grep condition($_), @array;

##</code><code>##

my @array = qw( John Jake and Jasper );
$_ = uc($_) for grep /^a/, @array;
print("@array\n");  # John Jake AND Jasper