my $t = 1;
print grep {$t} qw( a b c d e ); 
What do you think that means?

this is the same as:
grep{1}qw( a b c d e );
and yields the exact same output as input list (a b c d e) 

grep {0} qw( a b c d e ); 
yields nothing! 
because this means foreach(a b c d e), pass each
item to the output (to the left) if the thing within
grep{} is true. BUT {0} is NOT true! So nothing is
passed to your print.


my $True_false = "False";
foreach (qw ( a b c d e ))
{
   print if ($True_false eq "True");
   print "" && $_; #another way
   #either way prints nothing!!!
}


Your very cute use of XOR is well, cute.

my $t = 1;
print grep {$t^=1} qw( a b c d e );