> PERLDB_OPTS="TTY=`tty`  ReadLine=0" xterm -e perl -d ./calc_TRL.pl

Loading DB routines from perl5db.pl version 1.33
Editor support available.

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

main::(./calc_TRL.pl:2):	my $term = Term::ReadLine->new('Simple Perl calc');
  DB<1> l
2==>	my $term = Term::ReadLine->new('Simple Perl calc');
3:	my $prompt = "Enter code: ";
4:	my $OUT = $term->OUT || \*STDOUT;
5:	while ( $_ = $term->readline($prompt) ) {
6:	  my $res = eval($_);
7:	  warn $@ if $@;
8:	  print $OUT $res, "\n" unless $@;
9:	  $term->addhistory($_) if /\S/;
10 	}
11 	  
  DB<1> b 9
  DB<2> c
main::(./calc_TRL.pl:9):	  $term->addhistory($_) if /\S/;
  DB<2> c 
main::(./calc_TRL.pl:9):	  $term->addhistory($_) if /\S/;
  DB<3> 

##</code><code>##

Enter code: 1+2
3
Enter code: 4+4
8

##</code><code>##

> cat ./calc_TRL.pl
use Term::ReadLine;
my $term = Term::ReadLine->new('Simple Perl calc');
my $prompt = "Enter code: ";
my $OUT = $term->OUT || \*STDOUT;
while ( $_ = $term->readline($prompt) ) {
  my $res = eval($_);
  warn $@ if $@;
  print $OUT $res, "\n" unless $@;
  $term->addhistory($_) if /\S/;
}