local undef $/;

Thatīll first clear $/, then localize it. Legal syntax, but not probably what you meant.

$ perl -wle'$_ = "x"; { local undef $_ } print'
Use of uninitialized value in print at -e line 1.

$ perl -wle'$_ = "x"; { undef local $_ } print'
x
[download]

Makeshifts last the longest.