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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 breakpointt)
           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
                                   # the 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 "("%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 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 AT activestate.com
       This code heavily adapted from an early version of perl5db.pl
       attributable to Larry Wall and the Perl Porters.
perl v5.26.3                      2018-03-01                           DB(3pm)