#!/usr/bin/perl -w
use Memory::Usage;
use vars qw ($muse);
$muse = Memory::Usage->new();

my $name = "bigfile"; # file size: 640MB
my $READIN = qw (<);
my $EXT;
my @data = ();
my $d = \@data;
die "Error opening file: $name" if ( !open $EXT, $READIN, $name );
$muse->record('Begin');

@data = <$EXT>; # option 1
#@$d = <$EXT>;  # option 2

close($EXT);
$muse->record('After file read');
$muse->dump();

##</code><code>##

$ perl test_read.pl
  time    vsz (  diff)    rss (  diff) shared (  diff)   code (  diff)   data (  diff) 
     0  78300 ( 78300)   2120 (  2120)   1412 (  1412)     12 (    12)   1164 (  1164) Begin 
    12  4538324 ( 4460024)  4373332 ( 4371212)   1428 (    16)     12 (     0)  4461188 ( 4460024) After file read 

##</code><code>##

$ perl test_read.pl
  time    vsz (  diff)    rss (  diff) shared (  diff)   code (  diff)   data (  diff) 
     0  78300 ( 78300)   2116 (  2116)   1412 (  1412)     12 (    12)   1164 (  1164) Begin 
    17  6461328 ( 6383028)  6296400 ( 6294284)   1428 (    16)     12 (     0)  6384192 ( 6383028) After file read