Well unless theres a version issue going on here then I would write that benchamrk like this 
use Benchmark 'cmpthese';
for $size (2, 200, 20_000) {
    $s = "." x $len;
    print "\nDATASIZE = $size\n";
    cmpthese -5,{
        chop2   => '$t = $s; chop $t; chop $t;',
        subs    => '($t = $s) =~ s/..\Z//s;',
        lsubstr => '$t = $s; substr($t, -2) = "";',
        rsubstr => '$t = substr($s, 0, length($s)-2);',
    };
}

[download]
There are a few more ways, but this is a direct but less verbose copy of what you posted. The -5 argument indicates that the benchmarking for each item should take at minimum 5 seconds. (It may take longer) If you used a positive argument then it does that many runs of the given code. It will warn if you dont use enough iterations for it to get a "reasonable" sample.

Please consult the Benchmark documentation as I suspect the interface has moved on since the edition of Programming Perl that you are using. I say this because your code does work, but it looks like Benchmark has been updated to do that idiom automatically.

cheers

--- demerphq
my friends call me, usually because I'm late....

In reply to Re: Re: Re: Benchmarking File Retrevial by demerphq
in thread Benchmarking File Retrevial by jpfarmer

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.