Some weird with that }; ?

simple_trace.pl

$ cat test.pl
#!/usr/bin/perl -dl

{
  use DB;
  *DB::DB = sub {
    my ($p, $f, $l) = caller;
    print "> " . @{"::_<$f"}[$l] unless caller(1);
  };
};

*foo = sub {
   "bar";
};

print foo();

$ perl test.pl

Loading DB routines from perl5db.pl version 1.49
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

> };

> print foo();

bar