Benchmark: running BufferedFileHandle, chunk, linebyline, each for at least 3 CP
U seconds...
BufferedFileHandle:  3 wallclock secs ( 3.22 usr +  0.08 sys =  3.30 CPU) @  <b>2.73/s</b> (n=9)
     chunk:  4 wallclock secs ( 2.89 usr +  0.32 sys =  3.21 CPU) @  <b>4.36/s</b> (n=14)
linebyline:  4 wallclock secs ( 3.25 usr +  0.06 sys =  3.31 CPU) @  <b>2.72/s</b> (n=9)


##</code><code>##

#!/usr/bin/perl

use Benchmark;
use strict;
use FileHandle;

timethese(0, { 'linebyline' => \&linebyline, 
               'chunk' => \&chunk ,
               'BufferedFileHandle' => \&BufferedFileHandle });

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

sub chunk {
  my($buf, $leftover, @lines);
  open(FILE, "file");
  while(read FILE, $buf, 64*1024) {
    $buf = $leftover.$buf;
    @lines = split(/\n/, $buf);
    $leftover = ($buf !~ /\n$/) ? pop @lines : "";
    foreach (@lines) { }
 }
 close(FILE);
}

sub BufferedFileHandle{
  my $fh=new FileHandle;
  my $buffer_var;
  $fh->open("file");
  $fh->setvbuf($buffer_var, _IOLBF, 64*1024);
  while(<$fh>) { }
  close(FILE);
}