while( @letters > 2 ){
while( @dirs ){
while( @files ){
while( @ARGV ){
while( @nodes ){
...

##</code><code>##

$ perl  -MData::Dump -e " my @f = ( 1, 0, undef, 6 ); while( my($q)=shift @f ){ dd( $q ); $r++; die if $r > 10; } "
1
0
undef
6
undef
undef
undef
undef
undef
undef
undef
Died at -e line 1.