my $found=0;
while(<USERPREF>) {
    chomp;      
    if (exists($update_words{$_})) {
        print "found $_ \n";
        $found=1;
    }
}

if (not $found) {
   print "not found $_ \n";
   #write
}

##</code><code>##

while (<$fh>) {
  chomp;
  my $comparevalue= split(/,/,$_);
  $update_words{$comparevalue}= $_;
  print "$_\n";
}
...
while(<USERPREF>) {
    chomp;
    my $comparevalue= split(/,/,$_);   
    if (exists($update_words{$comparevalue})) {
        print "found $_ \n";
        $found=1;
        print OUTFILE $update_words{$comparevalue}
    }
    else {
        print OUTFILE $_;
    }
}