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

NAME

       DB - programmatic interface to the Perl debugging API

SYNOPSIS

	   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->set_break([WHERE],[COND])
	   CLIENT->set_tbreak([WHERE])
	   CLIENT->clr_breaks([LIST])
	   CLIENT->set_action(WHERE,ACTION)
	   CLIENT->clr_actions([LIST])
	   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

DESCRIPTION

       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:

       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 enabled.

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

       $DB::sub
	       Name of current executing subroutine.

       %DB::sub
	       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, toline)".

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

       $DB::signal
	       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.

       $DB::trace
	       This flag is set to true if the API is tracing through subroutine calls.

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

       @DB::dbline
	       List of lines in currently loaded file.

       %DB::dbline
	       Actions in current file (keys are line numbers).  The values are strings that have the sprintf(3) format "("%s00%s",
	       breakcondition, actioncode)".

       $DB::package
	       Package namespace of currently executing code.

       $DB::filename
	       Currently loaded filename.

       $DB::subname
	       Fully qualified name of currently executing subroutine.

       $DB::lineno
	       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.

       CLIENT->register()
	       register a client object/package

       CLIENT->evalcode(STRING)
	       eval STRING in executing code context

       CLIENT->skippkg('D::hide')
	       ask DB not to stop in these packages

       CLIENT->run()
	       run some more (until a breakpt is reached)

       CLIENT->step()
	       single step

       CLIENT->next()
	       step over

       CLIENT->done()
	       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.

       CLIENT->init()
	       Called after debug API inits itself.

       CLIENT->prestop([STRING])
	       Usually inherited from DB package.  If no arguments are passed, returns the prestop action string.

       CLIENT->stop()
	       Called when execution stops (w/ args file, line).

       CLIENT->idle()
	       Called while stopped (can be a client event loop).

       CLIENT->poststop([STRING])
	       Usually inherited from DB package.  If no arguments are passed, returns the poststop action string.

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

       CLIENT->cleanup()
	       Called just before exit.

       CLIENT->output(LIST)
	       Called when API must show a message (warnings, errors etc.).

BUGS

       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.

AUTHOR

       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 v5.16.2							    2012-10-11								   DB(3pm)