#!/usr/bin/perl

use strict;
use warnings;

my $line = "a||c|\t|  |d||e";
my @fields = split(/\|/, $line);
my @null;

for my $i (0..$#fields){
  push @null, $i unless $fields[$i];
}

print "null fields: ", scalar @null, "\n";
print "at field: ";
print ++$_, ", " for @null;

# output
# null fields: 2
# at field: 2, 7,