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";
}