$ perl -le " print fileno($_) for STDIN, STDOUT, STDERR "
0
1
2


##</code><code>##

$ perl -le " print 0+-t $_  for STDIN, STDOUT, STDERR "
1
1
1


##</code><code>##

$ perl -le " print 0+-t $_  for STDIN, STDOUT, STDERR "  < NUL
0
1
1



##</code><code>##

$ perl -le " print 0+-t $_  for STDIN, STDOUT, STDERR "  < NUL  2> NUL
0
1
0



##</code><code>##

$ perl -le " print 0+-t $_  for STDIN, STDOUT, STDERR " > out.txt

$ cat out.txt
1
0
1