$string_out = foo($string_in);

##</code><code>##

use strict;
use warnings;
use Benchmark qw(:all);
use constant COUNT => 200000;

my($str, $tmp, $len);

sub in1 ($) {
    $tmp = length($_[0]);
}

sub in2 ($) {
    $tmp = length(${$_[0]});
}

sub out1 () {
    return($str);
}

sub out2 () {
    return(\$str);
}

sub fun1 ($) {
    my $new = $_[0] . "x";
    return($new);
}

sub fun2 ($) {
    my $new = ${ $_[0] } . "x";
    return(\$new);
}

foreach $len (1, 10, 100) {
    $str = "A" x ($len * 1000);
    timethese(10, {
	"in1x$len"  => sub { for (1 .. COUNT) { in1($str) } },
	"in2x$len"  => sub { for (1 .. COUNT) { in2(\$str) } },
	"out1x$len" => sub { for (1 .. COUNT) { $tmp = out1() } },
	"out2x$len" => sub { for (1 .. COUNT) { $tmp = out2() } },
	"fun1x$len" => sub { for (1 .. COUNT) { $tmp = fun1($str) } },
	"fun2x$len" => sub { for (1 .. COUNT) { $tmp = fun2(\$str) } },
    });
}

##</code><code>##

Benchmark: timing 10 iterations of fun1x1, fun2x1, in1x1, in2x1, out1x1, out2x1...
    fun1x1:  4 wallclock secs ( 4.31 usr +  0.01 sys =  4.32 CPU) @  2.31/s (n=10)
    fun2x1:  5 wallclock secs ( 4.92 usr +  0.00 sys =  4.92 CPU) @  2.03/s (n=10)
     in1x1:  2 wallclock secs ( 1.08 usr +  0.00 sys =  1.08 CPU) @  9.26/s (n=10)
     in2x1:  1 wallclock secs ( 1.48 usr +  0.00 sys =  1.48 CPU) @  6.76/s (n=10)
    out1x1:  3 wallclock secs ( 2.40 usr +  0.00 sys =  2.40 CPU) @  4.17/s (n=10)
    out2x1:  1 wallclock secs ( 1.58 usr +  0.00 sys =  1.58 CPU) @  6.33/s (n=10)
Benchmark: timing 10 iterations of fun1x10, fun2x10, in1x10, in2x10, out1x10, out2x10...
   fun1x10: 16 wallclock secs (15.72 usr +  0.04 sys = 15.76 CPU) @  0.63/s (n=10)
   fun2x10: 12 wallclock secs (12.33 usr +  0.01 sys = 12.34 CPU) @  0.81/s (n=10)
    in1x10:  1 wallclock secs ( 1.08 usr +  0.00 sys =  1.08 CPU) @  9.26/s (n=10)
    in2x10:  2 wallclock secs ( 1.47 usr +  0.00 sys =  1.47 CPU) @  6.80/s (n=10)
   out1x10:  6 wallclock secs ( 6.62 usr +  0.00 sys =  6.62 CPU) @  1.51/s (n=10)
   out2x10:  2 wallclock secs ( 1.59 usr +  0.00 sys =  1.59 CPU) @  6.29/s (n=10)
Benchmark: timing 10 iterations of fun1x100, fun2x100, in1x100, in2x100, out1x100, out2x100...
  fun1x100: 119 wallclock secs (118.82 usr +  0.03 sys = 118.85 CPU) @  0.08/s (n=10)
  fun2x100: 89 wallclock secs (87.76 usr +  0.05 sys = 87.81 CPU) @  0.11/s (n=10)
   in1x100:  1 wallclock secs ( 1.10 usr +  0.00 sys =  1.10 CPU) @  9.09/s (n=10)
   in2x100:  1 wallclock secs ( 1.49 usr +  0.01 sys =  1.50 CPU) @  6.67/s (n=10)
  out1x100: 43 wallclock secs (43.27 usr +  0.04 sys = 43.31 CPU) @  0.23/s (n=10)
  out2x100:  2 wallclock secs ( 1.57 usr +  0.00 sys =  1.57 CPU) @  6.37/s (n=10)