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DB(3pm) 			 Perl Programmers Reference Guide			  DB(3pm)

       DB - programmatic interface to the Perl debugging API (draft, subject to change)

	   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->ret()	       # return from current subroutine
	   CLIENT->backtrace()	       # return the call stack description
	   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->lines()	       # return lines in currently loaded file
	   CLIENT->loadfile(FILE,LINE) # load a file and let other clients know
	   CLIENT->lineevents()        # return info on lines with actions
	   CLIENT->evalcode(STRING)  # eval STRING in executing code's context
	   CLIENT->prestop([STRING]) # execute in code context before stopping
	   CLIENT->poststop([STRING])# execute in code context before resuming

	   # These methods will be called at the appropriate times.
	   # Stub versions provided do nothing.
	   # None of these can block.

	   CLIENT->init()	   # called when debug API inits itself
	   CLIENT->stop(FILE,LINE) # when execution stops
	   CLIENT->idle()	   # while stopped (can be a client event loop)
	   CLIENT->cleanup()	   # just before exit
	   CLIENT->output(LIST)    # called to print any output that API must show

       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 function-
       ality, 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 com-
       mon 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:

       o   data display

       o   command processing

       o   command alias management

       o   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

       Global Variables

       The following "public" global names can be read by clients of this API.	Beware that these
       should be considered "readonly".

	       Name of current executing subroutine.

	       The keys of this hash are the names of all the known subroutines.  Each value is
	       an encoded string that has the sprintf(3) format "("%s:%d-%d", filename, fromline,

	       Single-step flag.  Will be true if the API will stop at the next statement.

	       Signal flag. Will be set to a true value if a signal was caught.  Clients may
	       check for this flag to abort time-consuming operations.

	       This flag is set to true if the API is tracing through subroutine calls.

	       Contains the arguments of current subroutine, or the @ARGV array if in the
	       toplevel context.

	       List of lines in currently loaded file.

	       Actions in current file (keys are line numbers).  The values are strings that have
	       the sprintf(3) format "("%s\000%s", breakcondition, actioncode)".

	       Package namespace of currently executing code.

	       Currently loaded filename.

	       Fully qualified name of currently executing subroutine.

	       Line number that will be executed next.

       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

	       run some more (until a breakpt 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.

	       Usually inherited from DB package.  If no arguments are passed, returns the
	       prestop action string.

	       Called when execution stops (w/ args file, line).

	       Called while stopped (can be a client event loop).

	       Usually inherited from DB package.  If no arguments are passed, returns the post-
	       stop action string.

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

	       Called just before exit.

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

       The interface defined by this module is missing some of the later additions to perl's
       debugging functionality.  As such, this interface should be considered highly experimental
       and subject to 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.

perl v5.8.0				    2002-06-01					  DB(3pm)
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