...
my $csv = Text::CSV_XS->new();
   open (CSV, "<", $file_to_parse) or die "Could not open '$file' $!<br>";

     while (my $line = <CSV>) {
       chomp $line;

           if ($csv->parse($line)) {
              my @columns = $csv->fields();
              #check user file format been uploaded TEST: perl -le 'print "1234567" =~ /^[[:alnum:]]+$/ ? "OK" : "BAD"'

              if( ($columns[0]!~/^[[:alnum:]]+$/) && ($columns[2]!~/^[[:alnum:]]+$/) ) {

               # wrong format
              exit;

           }else{
              my $err = $csv->error_input;
              print "<br><b>Failed to parse line, please call for help!</b><br>";
             }
     }
...