All assuming that the key value is unique! Sorry about the long lines ...

#!

# Just For A Lark

use strict;
use warnings;
use Digest::MD5;


# Hash for X
my %X_h;
{
    open(my $IN,'<','X')
        or die "Can't open 'X'! $!";
    # Populate hash with third field and SizeAndMD5
    while (<$IN>) {
        chomp;
        $X_h{(split('|'))[2]}=SizeAndMD5($_);
         };
    close($IN)
        or die "Can't close 'X'! $!";
     };
### %X_h

# Processing Y
# Hash for Y
my %Y_h;
{
    open(my $IN,'<','Y')
        or die "Can't open 'Y'! $!";
    open(my $OUT,'>','Y.new')
        or die "Can't open 'Y.new'! $!";
    # Populate hash with third field and SizeAndMD5
    while (<$IN>) {
        chomp;
        $Y_h{my $key=(split('|'))[2]}=SizeAndMD5($_);
        unless (exists $X_h{$key}) { # No key in X so append a "D"
            print $OUT "$_|D\n";
             }
        elsif ($Y_h{$key} ne $X_h{$key}) { # The corresponding record 
+in X is different
            print $OUT "$_|U\n";
             }
        else { # The corresponding record in X is the same
            print $OUT "$_|\n";
             };
         };
    close($OUT)
        or die "Can't close 'Y.new'! $!";
    close($IN)
        or die "Can't close 'Y'! $!";
     };
### %Y_h

# Re-processing X
{
    open(my $IN,'<','X')
        or die "Can't open 'X'! $!";
    open(my $OUT,'>','X.new')
        or die "Can't open 'X.new'! $!";
    # Populate hash with third field and SizeAndMD5
    while (<$IN>) {
        chomp;
        my $key=(split('|'))[2];
        unless (exists $Y_h{$key}) { # No key in X so append a "I"
            print $OUT "$_|I\n";
             }
        elsif ($X_h{$key} ne $Y_h{$key}) { # The corresponding record 
+in Y is different
            print $OUT "$_|U\n";
             }
        else { # The corresponding record in Y is the same
            print $OUT "$_|\n";
             };
         };
    close($OUT)
        or die "Can't close 'X.new'! $!";
    close($IN)
        or die "Can't close 'X'! $!";
     };

exit;

    # Returns Size and MD5 of the string as "%8.8lx%32.32s"
    sub SizeAndMD5 {
        return sprintf("%8.8lx%32.32s",length($_[0]),Digest::MD5::md5_
+hex($_[0]));
         };
[download]

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