$ perl -d -e 1

Loading DB routines from perl5db.pl version 1.28
Editor support available.

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

main::(-e:1):   1
Can't ioctl TIOCGETP: Invalid argument
Consider installing Term::ReadKey from CPAN site nearby
        at http://www.perl.com/CPAN
Or use
        perl -MCPAN -e shell
to reach CPAN. Falling back to 'stty'.
        If you do not want to see this warning, set PERL_READLINE_NOWARN

##</code><code>##

 at /scratch/testfrank/lib/perl5/Term/ReadLine/readline.pm line 1730
        readline::SetTTY() called at /scratch/testfrank/lib/perl5/Term/ReadLine/readline.pm line 1580
        eval {...} called at /scratch/testfrank/lib/perl5/Term/ReadLine/readline.pm line 1580
        readline::readline('  DB<1> ') called at /scratch/testfrank/lib/perl5/Term/ReadLine/Perl.pm line 11
        Term::ReadLine::Perl::readline('Term::ReadLine::Perl=ARRAY(0xd744740)', '  DB<1> ') called at /usr/lib/perl5/5.8.8/perl5db.pl line 6367
        DB::readline('  DB<1> ') called at /usr/lib/perl5/5.8.8/perl5db.pl line 2203
        DB::DB called at -e line 1
  DB<1> 

##</code><code>##

DB<3> b 1580
DB<4> x readline::readline('  FOO ')
readline::readline(/scratch/testfrank/lib/perl5/Term/ReadLine/readline.pm:1580):
1580:       if (!eval {SetTTY()}) {     ## Put into raw mode.
auto(-1)  DB<<5>> v
1577:       $lastdelta = 0;             ## Cursor was nowhere
1578:       $si = 0;                    ## Want line to start left-justified
1579:       $force_redraw = 1;          ## Want to display with brute force.
1580==>b            if (!eval {SetTTY()}) {     ## Put into raw mode.
1581:           warn $@ if $@;
1582:           $dumb_term = 1;
1583:           return readline_dumb;
1584        }
1585 
1586:       *KeyMap = $var_EditingMode;
DB<<5>> x eval{SetTTY()}
0  1
DB<<6>> x $@
0  ''
DB<<7>>