$ perl -le '
    BEGIN { my $x = 1; }
    print defined $x
          ? "defined"
          : "undefined";'
undefined

##</code><code>##

$ perl -Mstrict -le '
    BEGIN { my $x = 1; }
    print $x;'
Global symbol "$x" requires explicit package name at -e line 2.
Execution of -e aborted due to compilation errors.