use strict;
use warnings;
use diagnostics;
use Benchmark qw(cmpthese);
cmpthese(-60,{a=>sub{for (0..786500){my $array = '1'; undef $array;}},
             b=>sub{for (0..786500){my $array = '1'; $array = ''; }}});
    
cmpthese(0,{a=>sub{for (0..10){my $array = '1';
                               open OUT, ">>tmp";
                               print OUT "$array";
                               undef $array;
                               close OUT;}},
             b=>sub{open OUT, ">>tmp"; for (0..10){my $array = '1';
                                                   print OUT "$array";
                                                   undef $array;}}});    

__END__
Benchmark: running a, b, each for at least 60 CPU seconds...
         a: 62 wallclock secs (60.50 usr +  0.00 sys = 60.50 CPU) @  1.69/s (n=102)
         b: 64 wallclock secs (62.31 usr +  0.00 sys = 62.31 CPU) @  1.97/s (n=123)
    Rate    a    b
a 1.69/s   -- -15%
b 1.97/s  17%   --

Benchmark: running a, b, each for at least 3 CPU seconds...
         a: 11 wallclock secs ( 0.03 usr +  3.75 sys =  3.78 CPU) @  2.12/s (n=8)
         b:  8 wallclock secs ( 0.00 usr +  3.14 sys =  3.14 CPU) @ 23.24/s (n=73)
    Rate    a    b
a 2.12/s   -- -91%
b 23.2/s 998%   --