# phpman > perldoc > DB

## 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](https://www.chedong.com/phpMan.php/perldoc/hide%3A%3Ahide/markdown)')  # 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:

    *   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](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Asub/markdown)
            Name of current executing subroutine.

    %[DB::sub](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Asub/markdown)
            The keys of this hash are the names of all the known subroutines. Each value is an
            encoded string that has the [sprintf(3)](https://www.chedong.com/phpMan.php/man/sprintf/3/markdown) format "("%s:%d-%d", filename, fromline,
            toline)".

    $[DB::single](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Asingle/markdown)
            Single-step flag. Will be true if the API will stop at the next statement.

    $[DB::signal](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Asignal/markdown)
            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](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Atrace/markdown)
            This flag is set to true if the API is tracing through subroutine calls.

    @[DB::args](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Aargs/markdown)
            Contains the arguments of current subroutine, or the @ARGV array if in the toplevel
            context.

    @[DB::dbline](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Adbline/markdown)
            List of lines in currently loaded file.

    %[DB::dbline](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Adbline/markdown)
            Actions in current file (keys are line numbers). The values are strings that have the
            [sprintf(3)](https://www.chedong.com/phpMan.php/man/sprintf/3/markdown) format "("%s\000%s", breakcondition, actioncode)".

    $[DB::package](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Apackage/markdown)
            Package namespace of currently executing code.

    $[DB::filename](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Afilename/markdown)
            Currently loaded filename.

    $[DB::subname](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Asubname/markdown)
            Fully qualified name of currently executing subroutine.

    $[DB::lineno](https://www.chedong.com/phpMan.php/perldoc/DB%3A%3Alineno/markdown)
            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](https://www.chedong.com/phpMan.php/perldoc/D%3A%3Ahide/markdown)')
            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.