$ perl -MO=Deparse -le '
> sub DEBUG () { 1 }
> if(DEBUG) { print "Debug" }
> print "Done";
> '
BEGIN { $/ = "\n"; $\ = "\n"; }
do {
    print 'Debug'
};
print 'Done';
-e syntax OK

$ perl -MO=Deparse -le '
> sub DEBUG () { 0 }
> if(DEBUG) { print "Debug" }
> print "Done";
> '
BEGIN { $/ = "\n"; $\ = "\n"; }
'???';
print 'Done';
-e syntax OK