Your code is IO bound (most of the work goes to reading and writing, and even if the file is in memory you have to convert strings to numbers, etc.). Of course you're not going to see any difference between my and implicit operators.

Try this: 

#!/usr/local/bin/perl -w

use strict;

use Benchmark;


timethese(-2,
      { default =>
        sub {
          $_="the quick brown fox";
          s/brown/black/
        },
        my =>
        sub {
          my $x="the quick brown fox";
          $x =~ s/brown/black/
        }
      });

[download]
I get a 2% speed difference; localising $_ makes the `my' version 4% faster.

Duplicating the string 10_000 times and performing global substitution makes the `my' version 11% faster.

In reply to Re: The speed of $_ versus a lexical by ariels
in thread The speed of $_ versus a lexical by grinder

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.