• TUX



Perl 5 version 22.0 documentation
Recently read



DB - programmatic interface to the Perl debugging API


  1. package CLIENT;
  2. use DB;
  3. @ISA = qw(DB);
  4. # these (inherited) methods can be called by the client
  5. CLIENT->register() # register a client package name
  6. CLIENT->done() # de-register from the debugging API
  7. CLIENT->skippkg('hide::hide') # ask DB not to stop in this package
  8. CLIENT->cont([WHERE]) # run some more (until BREAK or
  9. # another breakpointt)
  10. CLIENT->step() # single step
  11. CLIENT->next() # step over
  12. CLIENT->ret() # return from current subroutine
  13. CLIENT->backtrace() # return the call stack description
  14. CLIENT->ready() # call when client setup is done
  15. CLIENT->trace_toggle() # toggle subroutine call trace mode
  16. CLIENT->subs([SUBS]) # return subroutine information
  17. CLIENT->files() # return list of all files known to DB
  18. CLIENT->lines() # return lines in currently loaded file
  19. CLIENT->loadfile(FILE,LINE) # load a file and let other clients know
  20. CLIENT->lineevents() # return info on lines with actions
  21. CLIENT->set_break([WHERE],[COND])
  22. CLIENT->set_tbreak([WHERE])
  23. CLIENT->clr_breaks([LIST])
  24. CLIENT->set_action(WHERE,ACTION)
  25. CLIENT->clr_actions([LIST])
  26. CLIENT->evalcode(STRING) # eval STRING in executing code's context
  27. CLIENT->prestop([STRING]) # execute in code context before stopping
  28. CLIENT->poststop([STRING])# execute in code context before resuming
  29. # These methods will be called at the appropriate times.
  30. # Stub versions provided do nothing.
  31. # None of these can block.
  32. CLIENT->init() # called when debug API inits itself
  33. CLIENT->stop(FILE,LINE) # when execution stops
  34. CLIENT->idle() # while stopped (can be a client event loop)
  35. CLIENT->cleanup() # just before exit
  36. CLIENT->output(LIST) # called to print any output that
  37. # the 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 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.

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.).


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

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