use Benchmark;
my @arr = (1 .. 10000);
timethese(1000, {
test_a => sub {
my $x = @arr;
for (my $i = 0; $i < $x ; $i++) { }
},
test_b => sub {
foreach (@arr) { }
},
test_c => sub {
my $n = 0;
for (@arr) { $n++; }
}
});

Benchmark: timing 1000 iterations of test_a, test_b, test_c...
test_a: 2 wallclock secs ( 1.88 usr + 0.00 sys = 1.88 CPU) @ 533.33/s (n=1000)
test_b: 1 wallclock secs ( 1.23 usr + 0.00 sys = 1.23 CPU) @ 810.37/s (n=1000)
test_c: 2 wallclock secs ( 1.86 usr + 0.00 sys = 1.86 CPU) @ 537.63/s (n=1000)

aで$n++する意味がわからん。