


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


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.



perl v5.10.1                2009-10-12                          1





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


       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



perl v5.10.1                2009-10-12                          2





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


               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 "("%s\000%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



perl v5.10.1                2009-10-12                          3





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


       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 v5.10.1                2009-10-12                          4


