man Devel::ebug (3): A simple, extensible Perl debugger

SYNOPSIS

use Devel::ebug;
my $ebug = Devel::ebug->new;
$ebug->program("calc.pl");
$ebug->load;
print "At line: " . $ebug->line . "\n";
print "In subroutine: " . $ebug->subroutine . "\n";
print "In package: " . $ebug->package . "\n";
print "In filename: " . $ebug->filename . "\n";
print "Code: " . $ebug->codeline . "\n";
$ebug->step;
$ebug->step;
$ebug->next;
my($stdout, $stderr) = $ebug->output;
my $actual_line = $ebug->break_point(6);
$ebug->break_point(6, '$e == 4');
$ebug->break_point("t/Calc.pm", 29);
$ebug->break_point("t/Calc.pm", 29, '$i == 2');
$ebug->break_on_load("t/Calc.pm");
my $actual_line = $ebug->break_point_subroutine("main::add");
$ebug->break_point_delete(29);
$ebug->break_point_delete("t/Calc.pm", 29);
my @filenames = $ebug->filenames();
my @break_points = $ebug->break_points();
my @break_points = $ebug->break_points("t/Calc.pm");
my @break_points = $ebug->break_points_with_condition();
my @break_points = $ebug->break_points_with_condition("t/Calc.pm");
my @break_points = $ebug->all_break_points_with_condition();
$ebug->watch_point('$x > 100');
my $codelines = $ebug->codelines(@span);
$ebug->run;
my $pad = $ebug->pad;
foreach my $k (sort keys %$pad) {
my $v = $pad->{$k};
print "Variable: $k = $v\n";
}
my $v = $ebug->eval('2 ** $exp');
my( $v, $is_exception ) = $ebug->eval('die 123');
my $y = $ebug->yaml('$z');
my @frames = $ebug->stack_trace;
my @frames2 = $ebug->stack_trace_human;
$ebug->undo;
$ebug->return;
print "Finished!\n" if $ebug->finished;

DESCRIPTION

A debugger is a computer program that is used to debug other programs. Devel::ebug is a simple, extensible Perl debugger with a clean API. Using this module, you may easily write a Perl debugger to debug your programs. Alternatively, it comes with an interactive debugger, ebug.

perl5db.pl, Perl's current debugger is currently 2,600 lines of magic and special cases. The code is nearly unreadable: fixing bugs and adding new features is fraught with difficulties. The debugger has no test suite which has caused breakage with changes that couldn't be properly tested. It will also not debug regexes. Devel::ebug is aimed at fixing these problems and delivering a replacement debugger which provides a well-tested simple programmatic interface to debugging programs. This makes it easier to build debuggers on top of Devel::ebug, be they console-, curses-, GUI- or Ajax-based.

There are currently two user interfaces to Devel::debug, ebug and ebug_http. ebug is a console-based interface to debugging programs, much like perl5db.pl. ebug_http is an innovative web-based interface to debugging programs.

Note that if you're debugging a program, you can invoke the debugger in the program itself by using the INT signal:

  kill 2, $$ if $square > 100;

Devel::ebug is a work in progress.

Internally, Devel::ebug consists of two parts. The frontend is Devel::ebug, which you interact with. The frontend starts the code you are debugging in the background under the backend (running it under perl -d:ebug code.pl). The backend starts a TCP server, which the frontend then connects to, and uses this to drive the backend. This adds some flexibilty in the debugger. There is some minor security in the client/server startup (a secret word), and a random port is used from 3141-4165 so that multiple debugging sessions can happen concurrently.

CONSTRUCTOR

new

The constructor creats a Devel::ebug object:

  my $ebug = Devel::ebug->new;

program

The program method selects which program to load:

  $ebug->program("calc.pl");

load

The load method loads the program and gets ready to debug it:

  $ebug->load;

METHODS

break_point

The break_point method sets a break point in a program. If you are run-ing through a program, the execution will stop at a break point. Break points can be set in a few ways.

A break point can be set at a line number in the current file:

  my $actual_line = $ebug->break_point(6);

A break point can be set at a line number in the current file with a condition that must be true for execution to stop at the break point:

  my $actual_line = $ebug->break_point(6, '$e = 4');

A break point can be set at a line number in a file:

  my $actual_line = $ebug->break_point("t/Calc.pm", 29);

A break point can be set at a line number in a file with a condition that must be true for execution to stop at the break point:

  my $actual_line = $ebug->break_point("t/Calc.pm", 29, '$i == 2');

Breakpoints can not be set on some lines (for example comments); in this case a breakpoint will be set at the next breakable line, and the line number will be returned. If no such line exists, no breakpoint is set and the function returns "undef".

break_on_load

Set a breakpoint on file loading, the file name can be relative or absolute.

break_point_delete

The break_point_delete method deletes an existing break point. A break point at a line number in the current file can be deleted:

  $ebug->break_point_delete(29);

A break point at a line number in a file can be deleted:

  $ebug->break_point_delete("t/Calc.pm", 29);

break_point_subroutine

The break_point_subroutine method sets a break point in a program right at the beginning of the subroutine. The subroutine is specified with the full package name:

  my $line = $ebug->break_point_subroutine("main::add");
  $ebug->break_point_subroutine("Calc::fib");

The return value is the line at which the break point is set.

break_points

The break_points method returns a list of all the line numbers in a given file that have a break point set.

Return the list of breakpoints in the current file:

  my @break_points = $ebug->break_points();

Return the list of breakpoints in a given file:

  my @break_points = $ebug->break_points("t/Calc.pm");

break_points_with_condition

The break_points method returns a list of break points for a given file.

Return the list of breakpoints in the current file:

  my @break_points = $ebug->break_points_with_condition();

Return the list of breakpoints in a given file:

  my @break_points = $ebug->break_points_with_condition("t/Calc.pm");

Each element of the list has the form

  { filename  => "t/Calc.pm",
    line      => 29,
    condition => "$foo > 12",
    }

where "condition" might not be present.

all_break_points_with_condition

Like "break_points_with_condition" but returns a list of break points for the whole program.

codeline

The codeline method returns the line of code that is just about to be executed:

  print "Code: "          . $ebug->codeline   . "\n";

codelines

The codelines method returns lines of code.

It can return all the code lines in the current file:

  my @codelines = $ebug->codelines();

It can return a span of code lines from the current file:

  my @codelines = $ebug->codelines(1, 3, 4, 5);

It can return all the code lines in a file:

  my @codelines = $ebug->codelines("t/Calc.pm");

It can return a span of code lines in a file:

  my @codelines = $ebug->codelines("t/Calc.pm", 5, 6);

eval

The eval method evaluates Perl code in the current program and returns the result. If the evalutation results in an exception, $@ is returned.

  my $v = $ebug->eval('2 ** $exp');

In list context, eval also returns a flag indicating if the evalutation resulted in an exception.

  my( $v, $is_exception ) = $ebug->eval('die 123');

filename

The filename method returns the filename of the currently running code:

  print "In filename: "   . $ebug->filename   . "\n";

filenames

The filenames method returns a list of the filenames of all the files currently loaded:

  my @filenames = $ebug->filenames();

finished

The finished method returns whether the program has finished running:

  print "Finished!\n" if $ebug->finished;

line

The line method returns the line number of the statement about to be executed:

  print "At line: "       . $ebug->line       . "\n";

The next method steps onto the next line in the program. It executes any subroutine calls but does not step through them.

  $ebug->next;

output

The output method returns any content the program has output to either standard output or standard error:

  my($stdout, $stderr) = $ebug->output;

package

The package method returns the package of the currently running code:

  print "In package: "    . $ebug->package    . "\n";

pad

  my $pad  = $ebug->pad;
  foreach my $k (sort keys %$pad) {
    my $v = $pad->{$k};
    print "Variable: $k = $v\n";
  }

return

The return subroutine returns from a subroutine. It continues running the subroutine, then single steps when the program flow has exited the subroutine:

  $ebug->return;

It can also return your own values from a subroutine, for testing purposes:

  $ebug->return(3.141);

run

The run subroutine starts executing the code. It will only stop on a break point or watch point.

  $ebug->run;

step

The step method steps onto the next line in the program. It steps through into any subroutine calls.

  $ebug->step;

subroutine

The subroutine method returns the subroutine of the currently working code:

  print "In subroutine: " . $ebug->subroutine . "\n";

stack_trace

The stack_trace method returns the current stack trace, using Devel::StackTrace. It returns a list of Devel::StackTraceFrame methods:

  my @traces = $ebug->stack_trace;
  foreach my $trace (@traces) {
    print $trace->package, "->",$trace->subroutine,
    "(", $trace->filename, "#", $trace->line, ")\n";
  }

stack_trace_human

The stack_trace_human method returns the current stack trace in a human-readable format:

  my @traces = $ebug->stack_trace_human;
  foreach my $trace (@traces) {
    print "$trace\n";
  }

undo

The undo method undos the last action. It accomplishes this by restarting the process and passing (almost) all the previous commands to it. Note that commands which do not change state are ignored. Commands that change state are: break_point, break_point_delete, break_point_subroutine, eval, next, step, return, run and watch_point.

  $ebug->undo;

It can also undo multiple commands:

  $ebug->undo(3);

watch_point

The watch point method sets a watch point. A watch point has a condition, and the debugger will stop run-ing as soon as this condition is true:

  $ebug->watch_point('$x > 100');

yaml

The eval method evaluates Perl code in the current program and returns the result of YAML's Dump() method:

  my $y = $ebug->yaml('$z');

BUGS

Devel::ebug does not quite work under 5.8.0.

Devel::ebug does not handle signals under Windows.

AUTHOR

Latest releases by Brock Wilcox, "<[email protected]>"

Leon Brocard, "<[email protected]>"

COPYRIGHT

LICENSE

This module is free software; you can redistribute it or modify it under the same terms as Perl itself.