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autostopping the debugger

Lets assume, you want to use the debugger. Then the problem might be to get the debugger to break after a warning condition happened.

The warnings contain a line number which is fine, but when the line is part of a loop, this is not enough information. We would want a stop with the current context. Only then can we examine the state of the program in the context that produced the problem.

So what to do?
I replace the signal handler for SIGWARN with my own handler that checks for the typical format of a Perl warning. I do that because I am interested only in warnings from the Perl interpreter. If this format has been detected, the code branches into a special path where we can setup the debugger. We want the debugger to stop and to return to the caller, where there warning was caused. So we set a variable that causes the debugger to stop. This will take effect when the signal handler has returned. After that setup stage, the warning message is printed as before the modification.

The signal handler code should go into the debugger initialization file .perldb. Then I do not have to modify the original source code.

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 automatically after
            # the line that caused the warning.
        }
        warn $warning;
    };
    print "sigwarn handler installed!\n";
    return;
}
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