If the lines are long
Digest::MD5 might be able to solve your problem.
#!/usr/bin/perl
use strict;
use Digest::MD5;
my $file = shift;
my ($input, $check);
open($input, $file) or die "Could not open $file: $!";
open($check, $file) or die "Could not open $file: $!";
my %hash;
while (!eof($input)) {
my $location = tell($input);
my $line = readline($input);
chomp $line;
my $digest = Digest::MD5::md5($line);
# $digest = length($line);
if (defined(my $ll = $hash{$digest})) {
my $d = 0;
for my $l (@$ll) {
seek($check, $l, 0);
my $checkl = readline($check);
chomp $checkl;
if ($checkl eq $line) {
print "DUP $line\n";
$d = 1;
last;
}
}
if ($d == 0) {
push(@{$hash{$digest}}, $location);
}
} else {
push(@{$hash{$digest}}, $location);
}
}
The seek is really over kill in this case, but would be needed if you used a checksum in place of the Digest::MD5 method.
Note: This will only save memory if the average line length is longer than 16 bytes.
UPDATE: Changed code to correctly handle problem pointed out by Corion.
Solution for wojtyk. This will let you have up to 256 passes. It does assume that there is a random distribution of the first byte of the Digest.
#!/usr/bin/perl
use strict;
use Digest::MD5;
my $file = shift;
my ($input, $check);
open($input, $file) or die "Could not open $file: $!";
open($check, $file) or die "Could not open $file: $!";
my %hash;
my $passes = 2;
for (my $pass = 0; $pass < $passes; $pass++) {
while (!eof($input)) {
my $location = tell($input);
my $line = readline($input);
chomp $line;
my $digest = Digest::MD5::md5($line);
my $p = ord($digest);
if ($p % $passes != $pass) {
next;
}
if (defined(my $ll = $hash{$digest})) {
my $d = 0;
for my $l (@$ll) {
seek($check, $l, 0);
my $checkl = readline($check);
chomp $checkl;
if ($checkl eq $line) {
print "DUP $line\n";
$d = 1;
last;
}
}
if ($d == 0) {
push(@{$hash{$digest}}, $location);
}
} else {
push(@{$hash{$digest}}, $location);
}
}
seek($input, 0, 0);
}
-- gam3
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