#! perl -slw
use strict;

our $LINES ||= 1000;

## Gen some test data to a simulated file
my @a = qw[ one two three four five six seven eight nine ];;
my @lines = map{ join '_', @a[ map{ rand @a } 1 .. 2+rand 3 ] } 1 .. $LINES;

warn "Processing " . @lines . " start: " . localtime;

## Index the lines
my %index;
for my $idx ( 0 .. $#lines ) {
	$index{ $_ }{ $idx }++ for split '_', $lines[ $idx ];
}

my @keys = keys %index;

while( my $first = pop @keys ) {
	for my $second ( @keys ) {
		print "$first/$second: ", join "\n\t", 
			@lines[ 
				grep{ 
					exists $index{ $second }{ $_ } 
				} keys %{ $index{ $first } } 
			];
	}
}

warn "Processing " . @lines . " stop:  " . localtime;

__END__
P:\test>392861 -LINES=100000 >nul
Processing 100000 start: Wed Sep 22 19:58:46 2004 at P:\test\392861.pl line 10.
Processing 100000 stop:  Wed Sep 22 19:58:50 2004 at P:\test\392861.pl line 31.