use warnings;
use strict;
use Benchmark qw[ cmpthese ];

my @fields = (
    { name => 'name1', start =>  0, len=>  4 },
    { name => 'name2', start =>  3, len=>  7 },
    { name => 'name3', start =>  8, len=>  3 },
    { name => 'name4', start =>  0, len=> 10 },
    { name => 'name5', start =>  5, len=> 20 },
    { name => 'name6', start => 11, len=> 14 },
    { name => 'name7', start =>  9, len=> 13 },
    { name => 'name8', start =>  2, len=>  2 },
    { name => 'name9', start =>  1, len=> 10 },
);

open FH, '<', $ARGV[ 0 ] or die $!;

cmpthese -3, {
    'unpack' => sub {
    my $unpack = "";
    my $position = 0;

    for ( @fields ) {
        $unpack .= $_->{start} < $position ? 'X' . ( $position   - $_->{start} ) :
                   $_->{start} > $position ? 'x' . ( $_->{start} - $position   ) :
                   '';

        $unpack .= 'A' . $_->{len};

        $position = $_->{start}+$_->{len};
    }
        seek FH, 0, 0;
        while( my $text = <FH> ) {
            my @a = unpack $unpack, $text;
        }
    },
    'substr' => sub {
        seek FH, 0, 0;
        while( my $text = <FH> ) {
            my @a = map{ substr $text, $_->{start}, $_->{len} } @fields;
        }
    }
};

close FH;
__END__
C:\test>for /l %i in (1,1,6) do holli data\alpha.1e%i

C:\test>holli data\alpha.1e1
           Rate unpack substr
unpack  28603/s     --   -80%
substr 140302/s   391%     --

C:\test>holli data\alpha.1e2
        Rate substr unpack
substr 400/s     --   -26%
unpack 540/s    35%     --

C:\test>holli data\alpha.1e3
         Rate substr unpack
substr 40.3/s     --   -27%
unpack 54.9/s    36%     --

C:\test>holli data\alpha.1e4
         Rate substr unpack
substr 4.06/s     --   -28%
unpack 5.61/s    38%     --

C:\test>holli data\alpha.1e5
            (warning: too few iterations for a reliable count)
            (warning: too few iterations for a reliable count)
       s/iter substr unpack
substr   2.47     --   -27%
unpack   1.80    37%     --

C:\test>holli data\alpha.1e6
            (warning: too few iterations for a reliable count)
            (warning: too few iterations for a reliable count)
       s/iter substr unpack
substr   25.3     --   -29%
unpack   18.0    40%     --