DB<1> use Scalar::Util 'readonly' DB<2> p readonly 1 134217728 DB<3> p readonly \1 0 DB<4> *one = \1 DB<5> p readonly $one 134217728 DB<6> $rone = \1 DB<7> p readonly $$rone 134217728 DB<8> $one = 2 Modification of a read-only value attempted at (eval 16)[/usr/share/perl/5.20/perl5db.pl:732] line 2. DB<9> $$rone = 2 Modification of a read-only value attempted at (eval 17)[/usr/share/perl/5.20/perl5db.pl:732] line 2.