open( ONE, "file1" ) or die "open file1: $!";
open( TWO, "file2" ) or die "open file2: $!";
open( OUT, ">merged" ) or die "open merged: $!";

while( <ONE> ) {
  chomp;
  my $two = <TWO>;
  print OUT $_, (split( " ", $two ))[-1], "\n"
}

close( ONE ); close( TWO ); close( OUT );