12:30 >perl -e "printf qq[%f\n], $x;"
0.000000

12:31 >perl -e "use warnings; printf qq[%f\n], $x;"
Name "main::x" used only once: possible typo at -e line 1.
Use of uninitialized value $x in printf at -e line 1.
0.000000

12:31 >perl -e "use warnings FATAL => 'all'; printf qq[%f\n], $x;"
Name "main::x" used only once: possible typo at -e line 1.
Use of uninitialized value $x in printf at -e line 1.

12:31 >