use strict;
use warnings;
use Benchmark qw/cmpthese/;

my $string = (join '', 'a'..'z') x 10;

my $unpack = sub {
    my @sub_fields = unpack '(A5)*', $string;
};

my $regex1 = sub {
    my @sub_fields = $string =~ /\w{5}/g;
};

my $regex2 = sub {
    my @sub_fields = $string =~ /.{5}/g;
};

my $split = sub { # suggested by Kenosis
    my @sub_fields = split /.{5}\K/, $string;
};

my $substr1 = sub {
    my @sub_fields;
    for ( my $i = 0 ; $i < length $string ; $i += 5 ) {
        push @sub_fields, substr $string, $i, 5;
    }
};

my $substr2 = sub {
    my @sub_fields;
    my $max = (length $string)/5 -1;
    push @sub_fields, substr $string, $_*5, 5  for (0..$max);
};

my $filehandle = sub {
	my (@sub_fields, $var);
	open my $FH, "<", \$string or die "cannot open $string $!";
	push @sub_fields, $var while read $FH, $var, 5;
};

my $c_style_string = sub { # the idea suggested by boftx
	my @sub_fields;
	my @chars = split //, $string;
	while (@chars) { push @sub_fields, join '', splice (@chars, 0, 5)};
};

cmpthese( -1,
    { 	regex1  => sub {$regex1->()},
    	regex2  => sub {$regex2->()},
        unpack => sub {$unpack->()},       
		split  => sub {$split->()},
        substr1 => sub { $substr1->()},
        substr2 => sub {$substr2->()},
        FH => sub {$filehandle->()},
        C_Style => sub { $c_style_string->()}
    }
)

##</code><code>##

           Rate C_Style  regex1  regex2      FH   split substr1 substr2  unpack
C_Style  5598/s      --    -72%    -72%    -78%    -79%    -80%    -80%    -83%
regex1  19690/s    252%      --     -1%    -24%    -28%    -28%    -31%    -39%
regex2  19968/s    257%      1%      --    -23%    -26%    -27%    -30%    -38%
FH      25984/s    364%     32%     30%      --     -4%     -5%     -9%    -20%
split   27161/s    385%     38%     36%      5%      --     -1%     -5%    -16%
substr1 27355/s    389%     39%     37%      5%      1%      --     -4%    -16%
substr2 28523/s    409%     45%     43%     10%      5%      4%      --    -12%
unpack  32428/s    479%     65%     62%     25%     19%     19%     14%      --