$ perl -Mstrict -Mwarnings -E 'my $x; eval { my $y = defined $x ? 1 : 0; }; say $@ if $@; say $y;'
Global symbol "$y" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.

$ perl -Mstrict -Mwarnings -E 'my $x; my $y = eval { defined $x ? 1 : 0; }; say $@ if $@; say $y;'
0