If your strings could contain embedded commas then use Text::CSV_XS or similar to split it into an array, then all or any from List::Util to check that none or some are blank.

use Text::CSV_XS;
use List::Util qw /any/;
my $csv = Text::CSV_XS->new;

my @strings = (
    'a,b,c,d,e,f',
    'a,b,,d,e,f',
    'a,b,"c,and,some,commas",d,e,f',
    'a,b,c,d,e',
);

foreach my $string (@strings) {
    print "Checking $string\n";
    my $status = $csv->parse ($string);
    my @array  = $csv->fields;
    warn ($csv->error_input) 
      if !$status;
    
    print "Did not get six entries in $string\n"
      if not @array == 6;
    
    print "one entry in $string is zero length\n"
      if any {!length $_} @array;
          
    print join ':', @array;
    print "\n\n";
}
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