If you can install Swissknife, you don't have to write your own parser for UniProt and a program similar to the following might do what you need.

use strict;
use warnings;
use Data::Dumper;

#
# SWISS::Entry is part of Swissknife
# Available from http://swissknife.sourceforge.net/
# See: http://swissknife.sourceforge.net/docs/
#
use SWISS::Entry;

my %entries;

# Change the line termination string so we read an entire entry at a t
+ime
local $/ = "\n//\n";


# Read in all the entries and fill %entries 
while (<>) {
    my $entry = SWISS::Entry->fromText($_);

    #
    # Add this entry to %entries once for each IDentifier, DEscription
    # and Gene Name in the entry, all keys converted to lower case.
    # The hash values are pointers to anonymous arrays, so push the
    # entries onto the arrays.
    #
    foreach my $key (
         $entry->IDs->elements,
         map { $_->text }
            $entry->DEs->elements,
            map { ( $_->Name, $_->Synonyms ) } $entry->GNs->elements ,
    ) {
        push( @{$entries{lc($key)}}, $entry);
    }
}


#
# Now report on each key in %entries
#
foreach my $key (sort keys %entries) {
    print "\n\n----------------------\n";
    print "DUPLICATE " if ( @{$entries{$key}} > 1);
    print "key $key\n";
    foreach my $entry ( @{$entries{$key}} ) {

        print "\n";

        print "  IDs " . join(", ", $entry->IDs->elements) . "\n"
            if($entry->IDs);

        print "  DEs " .
            join(", ", map { $_->text } $entry->DEs->elements) .
            "\n"
            if($entry->DEs);

        print "  GNs " .
            join(", ", map { $_->text }
                map { ($_->Name, $_->Synonyms) }$entry->GNs->elements)
+ .
            "\n"
            if($entry->GNs);
    }
}
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