C:\test>perl -le"use constant DEBUG=>0; print 'hi'; DEBUG and print 'debugging'; print 'bye'"
hi
bye

C:\test>perl -MO=Deparse -le"use constant DEBUG=>0; print 'hi'; DEBUG and print 'debugging'; print 'bye'"
BEGIN { $/ = "\n"; $\ = "\n"; }
use constant ('DEBUG', 0);
print 'hi';
'???';
print 'bye';
-e syntax OK