my $val1 = $next_cell_arr[0] || die "val1 is undefined!!\n"; 

##</code><code>##

use strict;

my $val1;  # this creates a named storage location for a scalar value,
           # but DOES NOT ASSIGN A VALUE -- its value is undefined.

my $val2 = 0;  # creates a named scalar and assigns a value, so it's defined
               # but the value will evaluate to FALSE in a
               # boolean sense

my $val3 = ''; # similar to $val2: it's defined, it evaluates to false
               # in boolean tests, but in "reality", it's an
               # "empty string" (which $val2 is not)

print "val3 is an empty string\n" if ( $val3 eq '' );
print "val2 is an empty string\n" if ( $val2 eq '' );
print "val1 is (like) an empty string\n" if ( $val1 eq '');
   # this third test would generate a warning in "perl -w"

my $i = 1;
for ( $val1, $val2, $val3 ) {
    print "val$i evaluates to false\n" if ( ! $_ );
    print "val$i is undefined\n" if ( ! defined( $_ ));
    $i++;
}