Devel::Trepan customized DB package. Down the line this should be split off and merged with DB that perl5db.pl and other uses similar ilk.


These routines are used to store (and restore) lists of items in environment variables during a restart.


Set_list packages up items to be stored in a set of environment variables (VAR_n, containing the number of items, and VAR_0, VAR_1, etc., containing the values). Values outside the standard ASCII charset are stored by encoding then as hexadecimal values.


Reverse the set_list operation: grab VAR_n to see how many we should be getting back, and then pull VAR_0, VAR_1. etc. back out.


DB - programmatic interface to the Perl debugging API


    package CLIENT;
    use DB;
    @ISA = qw(DB);

    # these (inherited) methods can be called by the client

    CLIENT->register()      # register a client package name
    CLIENT->done()          # de-register from the debugging API
    CLIENT->skippkg('hide::hide')  # ask DB not to stop in this package
    CLIENT->cont([WHERE])       # run some more (until BREAK or another breakpt)
    CLIENT->step()              # single step
    CLIENT->next()              # step over
    CLIENT->finish()            # stop before finishing the current subroutine
    CLIENT->ready()             # call when client setup is done
    CLIENT->trace_toggle()      # toggle subroutine call trace mode
    CLIENT->subs([SUBS])        # return subroutine information
    CLIENT->files()             # return list of all files known to DB
    CLIENT->loadfile(FILE,LINE) # load a file and let other clients know
    CLIENT->evalcode(STRING)  # eval STRING in executing code's context

    # These methods you should define; They will be called by the DB
    # when appropriate. The stub versions provided do nothing. You should
    # Write your routine so that it doesn't block.

    CLIENT->init()          # called when debug API inits itself
    CLIENT->idle(BOOL, EVENT, ARGS)  # while stopped (can be a client event loop)
    CLIENT->cleanup()       # just before exit
    CLIENT->output(STRING)   # called to print any output that API must show
    CLIENT->warning(STRING) # called to print any warning output that API
                            # must show
    CLIENT->showfile(FILE,LINE) # called to show file and line before idling


Perl debug information is frequently required not just by debuggers, but also by modules that need some "special" information to do their job properly, like profilers.

This module abstracts and provides all of the hooks into Perl internal debugging functionality, so that various implementations of Perl debuggers (or packages that want to simply get at the "privileged" debugging data) can all benefit from the development of this common code. Currently used by Swat, the perl/Tk GUI debugger.

Note that multiple "front-ends" can latch into this debugging API simultaneously. This is intended to facilitate things like debugging with a command line and GUI at the same time, debugging debuggers etc. [Sounds nice, but this needs some serious support -- GSAR]

In particular, this API does not provide the following functions:

  • data display

  • command processing

  • command alias management

  • user interface (tty or graphical)

These are intended to be services performed by the clients of this API.

This module attempts to be squeaky clean w.r.t use strict; and when warnings are enabled.

API Methods

The following are methods in the DB base class. A client must access these methods by inheritance (*not* by calling them directly), since the API keeps track of clients through the inheritance mechanism.


register a client object/package


eval STRING in executing code context


ask DB not to stop in these packages


continue some more (until a breakpoint is reached)


single step


step over


de-register from the debugging API

Client Callback Methods

The following "virtual" methods can be defined by the client. They will be called by the API at appropriate points. Note that unless specified otherwise, the debug API only defines empty, non-functional default versions of these methods.


Called after debug API inits itself.


Called while stopped (can be a client event loop or REPL). If called after the idle program requested an eval to be performed, BOOLEAN will be true. False otherwise. See evalcode below. ARGS are any


Usually inherited from DB package. Ask for a STRING to be eval-ed in executing code context.

In order to evaluate properly, control has to be passed back to the DB subroutine. Suppose you would like your idle program to do this:

    until $done {
        $command = read input
        if $command is a valid debugger command,
           run it
           evaluate it via CLIENT->evalcode($command) and print
           the results.

Due to the limitation of Perl, the above is not sufficient. You have to break out of the until to get back to DB::sub to have the eval run. After that's done, DB::sub will call idle again, from which you can then retrieve the results.

One other important item to note is that one can only evaluation reliably current (most recent) frame and not frames further down the stack.

That's probably why the stock Perl debugger doesn't have frame-switching commands.


Called just before exit.


Called when API must show a message (warnings, errors etc.).


The interface defined by this module is missing a number of Perl's debugging functionality. As such, this interface is subject to (possibly incompatible) change.


Gurusamy Sarathy gsar@activestate.com

This code heavily adapted from an early version of perl5db.pl attributable to Larry Wall and the Perl Porters.

Further modifications by R. Bernstein rocky@cpan.org