If you invoke Perl with the B<-d> switch, your script runs under the
Perl source debugger. This works like an interactive Perl
environment, prompting for debugger commands that let you examine
-source code, set breakpoints, get stack backtraces, change the values of
+source code, set breakpoints, get stack back-traces, change the values of
variables, etc. This is so convenient that you often fire up
the debugger all by itself just to test out Perl constructs
interactively to see what they do. For example:
=item p expr
-Same as C<print DB::OUT expr> in the current package. In particular,
-since this is just Perl's own B<print> function, this means that nested
+Same as C<print {$DB::OUT} expr> in the current package. In particular,
+because this is just Perl's own B<print> function, this means that nested
data structures and objects are not dumped, unlike with the C<x> command.
=item x expr
-Evals its expression in list context and dumps out the result
+Evaluates its expression in list context and dumps out the result
in a pretty-printed fashion. Nested data structures are printed out
recursively, unlike the C<print> function.
+The details of printout are governed by multiple C<O>ptions.
+
=item V [pkg [vars]]
Display all (or some) variables in package (defaulting to the C<main>
Nested data structures are printed out in a legible fashion, unlike
the C<print> function.
+The details of printout are governed by multiple C<O>ptions.
+
=item X [vars]
Same as C<V currentpackage [vars]>.
=item T
-Produce a stack backtrace. See below for details on its output.
+Produce a stack back-trace. See below for details on its output.
=item s [expr]
Repeat last C<n> or C<s> command.
-=item c [line]
+=item c [line|sub]
Continue, optionally inserting a one-time-only breakpoint
-at the specified line.
+at the specified line or subroutine.
=item l
=item L
-List all breakpoints and actions for the current file.
+List all breakpoints and actions.
=item S [[!]pattern]
=item t
-Toggle trace mode.
+Toggle trace mode (see also C<AutoTrace> C<O>ption).
=item t expr
main::foo((eval 168):2):
main::bar((eval 170):2):
42
- DB<4> q
+
+or, with the C<O>ption C<frame=2> set,
+
+ DB<4> O f=2
+ frame = '2'
+ DB<5> t print foo() * bar()
+ 3: foo() * bar()
+ entering main::foo
+ 2: sub foo { 14 };
+ exited main::foo
+ entering main::bar
+ 2: sub bar { 3 };
+ exited main::bar
+ 42
=item b [line] [condition]
Set a breakpoint. If line is omitted, sets a breakpoint on the line
that is about to be executed. If a condition is specified, it's
evaluated each time the statement is reached and a breakpoint is taken
-only if the condition is true. Breakpoints may only be set on lines
+only if the condition is true. Breakpoints may be set on only lines
that begin an executable statement. Conditions don't use B<if>:
b 237 $x > 30
+ b 237 ++$count237 < 11
b 33 /pattern/i
=item b subname [condition]
Set a breakpoint at the first line of the named subroutine.
+=item b postpone subname [condition]
+
+Set breakpoint at first line of subroutine after it is compiled.
+
+=item b load filename
+
+Set breakpoint at the first executed line of the file.
+
=item d [line]
Delete a breakpoint at the specified line. If line is omitted, deletes
Set an action to be done before the line is executed.
The sequence of steps taken by the debugger is
-=over 3
-
-=item 1
-
-check for a breakpoint at this line
-
-=item 2
-
-print the line if necessary (tracing)
-
-=item 3
-
-do any actions associated with that line
-
-=item 4
-
-prompt user if at a breakpoint or in single-step
-
-=item 5
-
-evaluate line
-
-=back
+ 1. check for a breakpoint at this line
+ 2. print the line if necessary (tracing)
+ 3. do any actions associated with that line
+ 4. prompt user if at a breakpoint or in single-step
+ 5. evaluate line
For example, this will print out C<$foo> every time line
53 is passed:
beginning with a C<|> character.) By default,
C<$ENV{PAGER}> will be used.
+=item tkRunning
+
+Run Tk while prompting (with ReadLine).
+
+=item signalLevel, warnLevel, dieLevel
+
+Level of verbosity.
+
+=item AutoTrace
+
+Where to print all the breakable points in the executed program
+(similar to C<t> command, but can be put into C<PERLDB_OPTS>).
+
+=item LineInfo
+
+File or pipe to print line number info to. If it is a
+pipe, then a short, "emacs like" message is used.
+
+=item C<inhibit_exit>
+
+If 0, allows I<stepping off> the end of the script.
+
+=item C<PrintRet>
+
+affects printing of return value after C<r> command.
+
+=item C<frame>
+
+affects printing messages on entry and exit from subroutines. If
+C<frame & 2> is false, messages are printed on entry only. (Printing
+on exit may be useful if inter(di)spersed with other messages.)
+
+If C<frame & 4>, arguments to functions are printed as well as the
+context and caller info.
+
=back
The following options affect what happens with C<V>, C<X>, and C<x>
Change style of string dump.
-=item tkRunning
+=back
-Run Tk while prompting (with ReadLine).
+During startup options are initialized from C<$ENV{PERLDB_OPTS}>.
+You can put additional initialization options C<TTY>, C<noTTY>,
+C<ReadLine>, and C<NonStop> there.
-=item signalLevel, warnLevel. dieLevel
+Example rc file:
-Level of verbosity.
+ &parse_options("NonStop=1 LineInfo=db.out AutoTrace");
-=back
+The script will run without human intervention, putting trace information
+into the file I<db.out>. (If you interrupt it, you would better reset
+C<LineInfo> to something "interactive"!)
-The option C<PrintRet> affects printing of return value after C<r>
-command, The option C<frame> affects printing messages on entry and exit
-from subroutines. If C<frame> is 1, messages are printed on entry only;
-if it's set to more than that, they'll will be printed on exit as well,
-which may be useful if interdispersed with other messages.
+=over 12
-During startup options are initialized from $ENV{PERLDB_OPTS}.
-You can put additional initialization options C<TTY>, C<noTTY>,
-C<ReadLine>, and C<NonStop> there. Here's an example of using
-the C<$ENV{PERLDB_OPTS}> variable:
+=item C<TTY>
+
+The TTY to use for debugging I/O.
+
+=item noTTY
+
+If set, goes in C<NonStop> mode. On interrupt if TTY is not set uses the
+value of C<noTTY> or "/tmp/perldbtty$$" to find TTY using
+C<Term::Rendezvous>. Current variant is to have the name of TTY in this
+file.
+
+=item C<noTTY>
+
+If set, goes in C<NonStop> mode, and would not connect to a TTY. If
+interrupt (or if control goes to debugger via explicit setting of
+$DB::signal or $DB::single from the Perl script), connects to a TTY
+specified by the C<TTY> option at startup, or to a TTY found at
+runtime using C<Term::Rendezvous> module of your choice.
+
+This module should implement a method C<new> which returns an object
+with two methods: C<IN> and C<OUT>, returning two filehandles to use
+for debugging input and output correspondingly. Method C<new> may
+inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at
+startup, or is C<"/tmp/perldbtty$$"> otherwise.
+
+=item C<ReadLine>
+
+If false, readline support in debugger is disabled, so you can debug
+ReadLine applications.
+
+=item C<NonStop>
+
+If set, debugger goes into non-interactive mode until interrupted, or
+programmatically by setting $DB::signal or $DB::single.
+
+=back
+
+Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
$ PERLDB_OPTS="N f=2" perl -d myprogram
out the call tree with entry and exit points. Note that C<N f=2> is
equivalent to C<NonStop=1 frame=2>. Note also that at the moment when
this documentation was written all the options to the debugger could
-be uniquely abbreviated by the first letter.
+be uniquely abbreviated by the first letter (with exception of
+C<Dump*> options).
-See "Debugger Internals" below for more details.
+Other examples may include
-=item E<lt> command
+ $ PERLDB_OPTS="N f A L=listing" perl -d myprogram
+
+- runs script non-interactively, printing info on each entry into a
+subroutine and each executed line into the file F<listing>. (If you
+interrupt it, you would better reset C<LineInfo> to something
+"interactive"!)
-Set an action to happen before every debugger prompt. A multiline
-command may be entered by backslashing the newlines.
+
+ $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram
+
+may be useful for debugging a program which uses C<Term::ReadLine>
+itself. Do not forget detach shell from the TTY in the window which
+corresponds to F</dev/ttyc>, say, by issuing a command like
+
+ $ sleep 1000000
+
+See L<"Debugger Internals"> below for more details.
+
+=over 12
+
+=item E<lt> [ command ]
+
+Set an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines. If
+C<command> is missing, resets the list of actions.
+
+=item E<lt>E<lt> command
+
+Add an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines.
=item E<gt> command
-Set an action to happen after the prompt when you've just given a
-command to return to executing the script. A multiline command may be
-entered by backslashing the newlines.
+Set an action (Perl command) to happen after the prompt when you've
+just given a command to return to executing the script. A multi-line
+command may be entered by backslashing the newlines. If C<command> is
+missing, resets the list of actions.
+
+=item E<gt>E<gt> command
+
+Adds an action (Perl command) to happen after the prompt when you've
+just given a command to return to executing the script. A multi-line
+command may be entered by backslashing the newlines.
+
+=item { [ command ]
+
+Set an action (debugger command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines. If
+C<command> is missing, resets the list of actions.
+
+=item {{ command
+
+Add an action (debugger command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines.
=item ! number
=item q or ^D
-Quit. ("quit" doesn't work for this.)
+Quit. ("quit" doesn't work for this.) This is the only supported way
+to exit the debugger, though typing C<exit> twice may do it too.
+
+Set an C<O>ption C<inhibit_exit> to 0 if you want to be able to I<step
+off> the end the script. You may also need to set C<$finished> to 0 at
+some moment if you want to step through global destruction.
=item R
your history across this, but internal settings and command line options
may be lost.
+Currently the following setting are preserved: history, breakpoints,
+actions, debugger C<O>ptions, and the following command-line
+options: B<-w>, B<-I>, and B<-e>.
+
=item |dbcmd
Run debugger command, piping DB::OUT to current pager.
DB<<17>>
where that number is the command number, which you'd use to access with
-the built-in B<csh>-like history mechanism, e.g. C<!17> would repeat
+the built-in B<csh>-like history mechanism, e.g., C<!17> would repeat
command number 17. The number of angle brackets indicates the depth of
the debugger. You could get more than one set of brackets, for example, if
you'd already at a breakpoint and then printed out the result of a
-function call that itself also has a breakpoint.
+function call that itself also has a breakpoint, or you step into an
+expression via C<s/n/t expression> command.
If you want to enter a multi-line command, such as a subroutine
definition with several statements, you may escape the newline that would
Note that this business of escaping a newline is specific to interactive
commands typed into the debugger.
-Here's an example of what a stack backtrace might look like:
+Here's an example of what a stack back-trace might look like:
$ = main::infested called from file `Ambulation.pm' line 10
@ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7
If you have any compile-time executable statements (code within a BEGIN
block or a C<use> statement), these will C<NOT> be stopped by debugger,
-although C<require>s will. From your own Perl code, however, you can
+although C<require>s will (and compile-time statements can be traced
+with C<AutoTrace> option set in C<PERLDB_OPTS>). From your own Perl
+code, however, you can
transfer control back to the debugger using the following statement,
which is harmless if the debugger is not running:
=head2 Debugger Customization
-If you want to modify the debugger, copy F<perl5db.pl> from the Perl
-library to another name and modify it as necessary. You'll also want
-to set your PERL5DB environment variable to say something like this:
-
- BEGIN { require "myperl5db.pl" }
+Most probably you not want to modify the debugger, it contains enough
+hooks to satisfy most needs. You may change the behaviour of debugger
+from the debugger itself, using C<O>ptions, from the command line via
+C<PERLDB_OPTS> environment variable, and from I<customization files>.
You can do some customization by setting up a F<.perldb> file which
contains initialization code. For instance, you could make aliases
$DB::alias{'ps'} = 's/^ps\b/p scalar /';
$DB::alias{'quit'} = 's/^quit(\s*)/exit\$/';
+One changes options from F<.perldb> file via calls like this one;
+
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2");
+
+(the code is executed in the package C<DB>). Note that F<.perldb> is
+processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the
+subroutine C<afterinit>, it is called after all the debugger
+initialization ends. F<.perldb> may be contained in the current
+directory, or in the C<LOGDIR>/C<HOME> directory.
+
+If you want to modify the debugger, copy F<perl5db.pl> from the Perl
+library to another name and modify it as necessary. You'll also want
+to set your C<PERL5DB> environment variable to say something like this:
+
+ BEGIN { require "myperl5db.pl" }
+
+As the last resort, one can use C<PERL5DB> to customize debugger by
+directly setting internal variables or calling debugger functions.
+
=head2 Readline Support
As shipped, the only command line history supplied is a simplistic one
the Devel::DProf package) can be used to interpret the information which is
in that profile.
-=head2 Debugger Internals
+=head2 Debugger support in perl
When you call the B<caller> function from package DB, Perl sets the
C<@DB::args> array to contain the arguments that stack frame was called
-with. It also maintains other magical internal variables, such as
-C<@DB::dbline>, an array of the source code lines for the currently
-selected (with the debugger's C<f> command) file. Perl effectively
-inserts a call to the function C<DB::DB>(I<linenum>) in front of every
-place that can have a breakpoint. Instead of a subroutine call it calls
-C<DB::sub> setting C<$DB::sub> being the called subroutine. It also
-inserts a C<BEGIN {require 'perl5db.pl'}> before the first line.
+with.
-Note that no subroutine call is possible until C<&DB::sub> is defined
-(for subroutines defined outside this file). In fact, the same is
-true if C<$DB::deep> (how many levels of recursion deep into the
-debugger you are) is not defined.
+If perl is run with B<-d> option, the following additional features
+are enabled:
-At the start, the debugger reads your rc file (F<./.perldb> or
-F<~/.perldb> under UNIX), which can set important options. This file may
-define a subroutine C<&afterinit> to be executed after the debugger is
-initialized.
+=over
-After the rc file is read, the debugger reads environment variable
-PERLDB_OPTS and parses it as a rest of C<O ...> line in debugger prompt.
+=item *
-The following options can only be specified at startup. To set them in
-your rc file, call C<&parse_options("optionName=new_value")>.
+Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require
+'perl5db.pl'}> if not present) before the first line of the
+application.
-=over 12
+=item *
-=item TTY
+The array C<@{"_<$filename"}> is the line-by-line contents of
+$filename for all the compiled files. Same for C<eval>ed strings which
+contain subroutines, or which are currently executed. The C<$filename>
+for C<eval>ed strings looks like C<(eval 34)>.
-The TTY to use for debugging I/O.
+=item *
-=item noTTY
+The hash C<%{"_<$filename"}> contains breakpoints and action (it is
+keyed by line number), and individual entries are settable (as opposed
+to the whole hash). Only true/false is important to Perl, though the
+values used by F<perl5db.pl> have the form
+C<"$break_condition\0$action">. Values are magical in numeric context:
+they are zeros if the line is not breakable.
-If set, goes in C<NonStop> mode. On interrupt if TTY is not set uses the
-value of C<noTTY> or "/tmp/perldbtty$$" to find TTY using
-C<Term::Rendezvous>. Current variant is to have the name of TTY in this
-file.
+Same for evaluated strings which contain subroutines, or which are
+currently executed. The C<$filename> for C<eval>ed strings looks like
+C<(eval 34)>.
-=item ReadLine
+=item *
-If false, dummy ReadLine is used, so you can debug
-ReadLine applications.
+The scalar C<${"_<$filename"}> contains C<"_<$filename">. Same for
+evaluated strings which contain subroutines, or which are currently
+executed. The C<$filename> for C<eval>ed strings looks like C<(eval
+34)>.
-=item NonStop
+=item *
-If true, no I/O is performed until an interrupt.
+After each C<require>d file is compiled, but before it is executed,
+C<DB::postponed(*{"_<$filename"})> is called (if subroutine
+C<DB::postponed> exists). Here the $filename is the expanded name of
+the C<require>d file (as found in values of C<%INC>).
-=item LineInfo
+=item *
-File or pipe to print line number info to. If it is a
-pipe, then a short, "emacs like" message is used.
+After each subroutine C<subname> is compiled existence of
+C<$DB::postponed{subname}> is checked. If this key exists,
+C<DB::postponed(subname)> is called (if subroutine C<DB::postponed>
+exists).
-Example rc file:
+=item *
- &parse_options("NonStop=1 LineInfo=db.out");
- sub afterinit { $trace = 1; }
+A hash C<%DB::sub> is maintained, with keys being subroutine names,
+values having the form C<filename:startline-endline>. C<filename> has
+the form C<(eval 31)> for subroutines defined inside C<eval>s.
-The script will run without human intervention, putting trace information
-into the file I<db.out>. (If you interrupt it, you would better reset
-C<LineInfo> to something "interactive"!)
+=item *
+
+When execution of the application reaches a place that can have
+a breakpoint, a call to C<DB::DB()> is performed if any one of
+variables $DB::trace, $DB::single, or $DB::signal is true. (Note that
+these variables are not C<local>izable.) This feature is disabled when
+the control is inside C<DB::DB()> or functions called from it (unless
+C<$^D & 1 E<lt>E<lt> 30>).
+
+=item *
+
+When execution of the application reaches a subroutine call, a call
+to C<&DB::sub>(I<args>) is performed instead, with C<$DB::sub> being
+the name of the called subroutine. (Unless the subroutine is compiled
+in the package C<DB>.)
=back
+Note that no subroutine call is possible until C<&DB::sub> is defined
+(for subroutines outside of package C<DB>). (In fact, for the
+standard debugger the same is true if C<$DB::deep> (how many levels of
+recursion deep into the debugger you can go before a mandatory break)
+is not defined.)
+
+=head2 Debugger Internals
+
+At the start, the debugger reads your rc file (F<./.perldb> or
+F<~/.perldb> under UNIX), which can set important options. This file may
+define a subroutine C<&afterinit> to be executed after the debugger is
+initialized.
+
+After the rc file is read, the debugger reads environment variable
+PERLDB_OPTS and parses it as a rest of C<O ...> line in debugger prompt.
+
+It also maintains magical internal variables, such as C<@DB::dbline>,
+C<%DB::dbline>, which are aliases for C<@{"::_<current_file"}>
+C<%{"::_<current_file"}>. Here C<current_file> is the currently
+selected (with the debugger's C<f> command, or by flow of execution)
+file.
+
+Some functions are provided to simplify customization. See L<"Debugger
+Customization"> for description of C<DB::parse_options(string)>. The
+function C<DB::dump_trace(skip[, count])> skips the specified number
+of frames, and returns an array containing info about the caller
+frames (all if C<count> is missing). Each entry is a hash with keys
+C<context> (C<$> or C<@>), C<sub> (subroutine name, or info about
+eval), C<args> (C<undef> or a reference to an array), C<file>, and
+C<line>.
+
+The function C<DB::print_trace(FH, skip[, count[, short]])> prints
+formatted info about caller frames. The last two functions may be
+convenient as arguments to C<E<lt>>, C<E<lt>E<lt>> commands.
+
=head2 Other resources
You did try the B<-w> switch, didn't you?
=head1 BUGS
-If your program exit()s or die()s, so too does the debugger.
-
You cannot get the stack frame information or otherwise debug functions
that were not compiled by Perl, such as C or C++ extensions.
If you alter your @_ arguments in a subroutine (such as with B<shift>
-or B<pop>, the stack backtrace will not show the original values.
-
+or B<pop>, the stack back-trace will not show the original values.
projects / p5sagit/p5-mst-13.2.git / blobdiff