You could try using Tie::File with a Fisher-Yates shuffle in place:
#!perl
use strict;
use warnings;
use Tie::File;
my $filename = shift;
die 'No file' unless $filename;
my $tie = tie my @file, 'Tie::File', $filename, memory => 20_000_000;
die "Couldn't tie $filename: $!" unless $tie;
$tie->defer();
shuffle(\@file);
$tie->flush();
undef $tie;
untie @file;
sub shuffle {
my $deck = shift; # $deck is a reference to an array
my $i = @$deck;
while (--$i) {
my $j = int rand ($i+1);
@$deck[$i,$j] = @$deck[$j,$i];
}
}
__END__
This worked well enough for me using a simple text file containing 1 million lines of random numbers.
