my $file_name = CGI::param('file_field');
$file_name =~ s:^.*[\\/](.*)$:$1:;  # remove path if present
my $fh = CGI::upload('file_field');
if ( $fh ) {
  open(OUT, '>', "/dir/to/save/$file_name");
  while (<$fh>) { print OUT $_; }
  close OUT;
} else {
  # handle the error
}