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Top Forums Shell Programming and Scripting Honey, I broke awk! (duplicate line removal in 30M line 3.7GB csv file) Post 302895685 by Chubler_XL on Tuesday 1st of April 2014 07:22:33 PM
Old 04-01-2014
This updated version checks for different lines that have the same MD5 and fails with an exit code so at least you can be confident nothing is wrong. This needs a filename parameter as it needs random access and streams don't support that.

Code:
#!/usr/bin/perl -w
use Digest::MD5 qw(md5);
open(DATA, "<", $ARGV[0]) || die "Can't open $ARGV[0]: $!";

my %seen;
while (1) {
  my $pos = tell DATA;
  my $line=<DATA>;
  last unless defined $line;
  my $crc= md5($line);
  if(!$seen{$crc}) {
     $seen{$crc}=$pos+1;
         print $line;
  } else {
      $pos = tell DATA;
      seek DATA, $seen{$crc}-1, 0;
          $!=255;
          die "Duplicate CRC found" unless (<DATA> eq $line);
          seek DATA, $pos, 0;
  }
}

This User Gave Thanks to Chubler_XL For This Post:
 

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SessionX::Generate::MD5(3pm)				User Contributed Perl Documentation			      SessionX::Generate::MD5(3pm)

NAME
Apache::Session::Generate::MD5 - Use MD5 to create random object IDs SYNOPSIS
use Apache::SessionX::Generate::MD5; $id = Apache::SessionX::Generate::MD5::generate($string); DESCRIPTION
This module fulfills the ID generation interface of Apache::SessionX. If you don't give the argument $string, the IDs are generated using a two-round MD5 of a random number, the time since the epoch, the process ID, and the address of an anonymous hash. The resultant ID number is highly entropic on Linux and other platforms that have good random number generators. You are encouraged to investigate the quality of your system's random number generator if you are using the generated ID numbers in a secure environment. If you give $string the ID is the MD5 hash of that string. This module can also examine session IDs to ensure that they are, indeed, session ID numbers and not evil attacks. The reader is encouraged to consider the effect of bogus session ID numbers in a system which uses these ID numbers to access disks and databases. This modules takes one argument in the usual Apache::Session style. The argument is IDLength, and the value, between 0 and 32, tells this module where to truncate the session ID. Without this argument, the session ID will be 32 hexadecimal characters long, equivalent to a 128-bit key. AUTHOR
This module was written by Jeffrey William Baker <jwbaker@acm.org> and modified by Gerald Richter <richter@dev.ecos.de>. SEE ALSO
Apache::Session perl v5.14.2 2005-11-10 SessionX::Generate::MD5(3pm)
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