> perl -s -e'print"{@a[grep$a&2**$_,0..@a]}"while$a++<2**(@a=qw/0 1 2/)'
{0}{1}{0 1}{2}{0 2}{1 2}{0 1 2}{}

> perl -Mstrict -e'print"{@x[grep$x&2**$_,0..@x]}"while$x++<2**(@x=qw/0 1 2/)'
Global symbol "@x" requires explicit package name at -e line 1.
Global symbol "$x" requires explicit package name at -e line 1.
Global symbol "@x" requires explicit package name at -e line 1.
Global symbol "$x" requires explicit package name at -e line 1.
Global symbol "@x" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.