$ perl -d -e '42'

Loading DB routines from perl5db.pl version 1.39_10
Editor support available.

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

main::(-e:1):	42
  DB<1> x @ACan't use string ("::") as a HASH ref while "strict refs" in use at /System/Library/Perl/5.18/perl5db.pl line 9513.   
 at /System/Library/Perl/5.18/perl5db.pl line 9513.
	DB::db_complete('@A', 'x @A', 2) called at sub readline::completion_matches line 10
	readline::completion_matches('CODE(0x7fcfa1bb1988)', '@A', 'x @A', 2) called at sub readline::complete_internal line 27
	readline::complete_internal('\x{9}') called at sub readline::F_Complete line 16
	readline::F_Complete(1, 9) called at /Library/Perl/5.18/Term/ReadLine/readline.pm line 1669
	readline::readline('  DB<1> ') called at /Library/Perl/5.18/Term/ReadLine/Perl.pm line 11
	Term::ReadLine::Perl::readline('Term::ReadLine::Perl=ARRAY(0x7fcfa182c4b8)', '  DB<1> ') called at /System/Library/Perl/5.18/perl5db.pl line 7281
	DB::readline('  DB<1> ') called at /System/Library/Perl/5.18/perl5db.pl line 1831
	DB::_DB__read_next_cmd(undef) called at /System/Library/Perl/5.18/perl5db.pl line 2741
	DB::DB called at -e line 1
Debugged program terminated.  Use q to quit or R to restart,
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.