Thanks, that saves the action of setting a breakpoint.
But even better, I could shift the signal handler code into the debugger initialization file .perldb. Then I do not have to modify the original source code. Works great!
This is the content of file .perldb (place it in the current or in the home directory):
sub afterinit
{
$::SIG{'__WARN__'} = sub {
my $warning = shift;
if ( $warning =~ m{\s at \s \S+ \s line \s \d+ \. $}xms ) {
$DB::single = 1; # debugger stops here automatically
}
warn $warning;
};
print "sigwarn handler installed!\n";
return;
}