my $element;
foreach $element(@Elements){
    &process($element) or die;
}

sub process{
   chdir("$path_to_the_data_directory")or die;
   my $outfile;
   #the $outfile name depends on $reg;
   open my $OUTFILE, q{>}, $outfile;
   my $infile = "data.txt";
   open my $INFILE, q{<}, $infile;
   while (my $line = <$INFILE>){
   # several operations which produce "$results"
   print $OUTFILE "$results\n";
   }
   close $OUTFILE;
   chdir("$path_to_the_script_directory") or die;
}