Breaking on `die` in Perl debugger

Question

Does the Perl debugger support breaking on die?

I find myself often running a program once to find the die line, then running it a second time to set a breakpoint.

It'd be nice if the debugger could be made to automatically break on die, holding on to the dying context.

Answer 1

You could set a __DIE__ handler and set a breakpoint in it.

$SIG{__DIE__} = sub {
    $DB::single = 1;
    die @_;
};

This isn't a great answer, as inside the __DIE__ handler you don't have the context of the function that called die. But the global package variables will be accessible, and if you have PadWalker installed then with the debugger command y 1 or y 1 <pattern>, you can view the lexical variables in scope when die was called.

Proof-of-concept:

# dying.pl
$SIG{__DIE__} = sub { $DB::single = 1; die @_; };

for my $i (1 .. 10000) {
    my $j = sqrt($i * ($i+1)) - 0.49;
    die "$i $j" if $j - int($j) < 0.1;
}

$ perl -d dying.pl

Loading DB routines from perl5db.pl version 1.37
Editor support available.

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

main::(dying.pl:1):     $SIG{__DIE__} = sub { $DB::single = 1; die @_; };
  DB<1> c
main::CODE(0x1000c918)(dying.pl:1):
1:      $SIG{__DIE__} = sub { $DB::single = 1; die @_; };
  DB<1> y 1 j
$j = 13.000737563232
  DB<2> y 1
$i = 13
$j = 13.000737563232
  DB<3> c
13 13.000737563232 at dying.pl line 5.
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.  
  DB<3>