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a neat little Perl debugger hook that can be placed in code for automatic breakpoints.

Instead of stepping through code until all the modules are loaded, and then continuing to a line number or a specific method in a module , you can continue to a pre-defined breakpoint. To add such a breakpoint use :

$DB::single = 2;

Here’s some explanatory text on it from Programming Perl:

You can exert a little control over the Perl debugger from within your Perl program itself. You might do this, for example, to set an automatic breakpoint at a certain subroutine whenever a particular program is run under the debugger. From your own Perl code, however, you can transfer control back to the debugger using the following statement, which is harmless if the debugger is not running:

$DB::single = 1;

If you set $DB::single to 2, it’s equivalent to the n command, whereas a value of 1 emulates the s command. The $DB::trace variable should be set to 1 to simulate the t command.