#!/usr/bin/perl -w
        use strict;

        open FIRST,"file1" or die "Can't open file1: $!\n";
   open LAST,"file2" or die "Can't open file2: $!\n";

        my ( $Flag, @Last, @First,  %Hash );

        chomp ( @First = <FIRST> );
        chomp ( @Last= <LAST> ) ;

        $Flag = 0;

        foreach my $record ( @First )
        {
                $record =~/^(\S*) (\d*)$/;
                $Hash{$1} = $2 ;
        }

        foreach my $record ( @Last )
        {
                $record =~ /^(\S*) (\d*)$/;
                 unless ( exists $Hash{$1} )
                        {
                          $Flag++;
                          $Hash{$1} = $2;
                        }
        }

        if ( $Flag ) # This condition checking avoids unwanted creation of the new file. Hope it will add value to the code.
        {
                          open NEW,">file3" or die "Can't open file3: $!\n";
                          map { print NEW "$_ $Hash{$_}\n"} sort keys %Hash ;
                          close NEW;
        }

   close FIRST;
   close LAST;