I don't think there's a way to do exactly what you want and pull out X number of lines in one shot. You're better off doing something like limitting the number of bytes you read in at a time. I threw together a bit of code (posted below) which reads in a certain amount of bytes, splits that into an array, and then processes those lines. Used with a reasonable size of bytes to read in, it seems to consistently be about 1.5 times faster. 
#!/usr/bin/perl

use Benchmark;
use strict;

timethese(10, { 'linebyline' => \&linebyline, 'chunk' => \&chunk });

sub linebyline {
   open(FILE, "file");
   while(<FILE>) { }
   close(FILE);
}

sub chunk {
   my($buf, $leftover, @lines);

   open(FILE, "file");

   while(read FILE, $buf, 10240) {
      $buf = $leftover.$buf;
      @lines = split(/\n/, $buf);
      $leftover = ($buf !~ /\n$/) ? pop @lines : "";
      foreach (@lines) { }
   }

   close(FILE);
}

Benchmark: timing 10 iterations of chunk, linebyline...
     chunk: 60 wallclock secs (55.20 usr +  3.48 sys = 58.68 CPU)
linebyline: 95 wallclock secs (91.67 usr +  2.16 sys = 93.83 CPU)

[download]
These tests were run on a 25 meg file with roughly 1 million lines in it. This code is not guaranteed to work 100%, but I believe it is correct enough to serve benchmarking purposes well.

In reply to Re: read X number of lines? by plaid
in thread read X number of lines? by eduardo

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