The results surprise me. To a number of decimal places, there is absolutely no speed difference between these two routines.

#! /usr/bin/perl -w

use strict;
use Benchmark;

my $scratch = '/tmp/foo';

# create a really big file
open OUT, ">$scratch" or die "$scratch: $!\n";
print OUT join( "\n", 1..1000000 ), "\n";
close OUT;

timethese( shift || 20,
    {
        '$_' => sub {
            my $count = 0;
            open IN, $scratch or die "$scratch input: $!\n";
            while( <IN> ) {
                chomp;
                $count += $_;
            }
            close IN;
        },
        'my' => sub {
            my $count = 0;
            open IN, $scratch or die "$scratch input: $!\n";
            my $rec;
            while( defined( $rec = <IN> )) {
                chomp $rec;
                $count += $rec;
            }
            close IN;
        },
    }
);
unlink $scratch;
[download]

Is there any assumption I'm overlooking? I've looping through a large file, hopefully large enough to avoid OS caching problems. Maybe there's a more pathological example that highlights a speed difference between $_ and a lexical, but I can't find it (and I can't find the original message in my mail archive).

Does anyone know of a case where $_ is slower than a lexical (and no, I'm not talking about local issues). Thanks.

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g r i n d e r