=head1 NAME
+X<debug> X<debugger>
perldebug - Perl debugging
=head1 DESCRIPTION
-First of all, have you tried using the B<-w> switch?
+First of all, have you tried using L<C<use strict;>|strict> and
+L<C<use warnings;>|warnings>?
-=head1 The Perl Debugger
+If you're new to the Perl debugger, you may prefer to read
+L<perldebtut>, which is a tutorial introduction to the debugger.
-"As soon as we started programming, we found to our
-surprise that it wasn't as easy to get programs right
-as we had thought. Debugging had to be discovered.
-I can remember the exact instant when I realized that
-a large part of my life from then on was going to be
-spent in finding mistakes in my own programs."
+If you're looking for the nitty gritty details of how the debugger is
+I<implemented>, you may prefer to read L<perldebguts>.
-I< --Maurice Wilkes, 1949>
+=head1 The Perl Debugger
If you invoke Perl with the B<-d> switch, your script runs under the
Perl source debugger. This works like an interactive Perl
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:
+X<-d>
- perl -d -e 42
+ $ perl -d -e 42
-In Perl, the debugger is not a separate program as it usually is in the
+In Perl, the debugger is not a separate program the way it usually is in the
typical compiled environment. Instead, the B<-d> flag tells the compiler
to insert source information into the parse trees it's about to hand off
to the interpreter. That means your code must first compile correctly
for the debugger to work on it. Then when the interpreter starts up, it
-preloads a Perl library file containing the debugger itself.
+preloads a special Perl library file containing the debugger.
The program will halt I<right before> the first run-time executable
statement (but see below regarding compile-time statements) and ask you
line it's I<about> to execute, rather than the one it has just executed.
Any command not recognized by the debugger is directly executed
-(C<eval>'d) as Perl code in the current package. (The debugger uses the
-DB package for its own state information.)
+(C<eval>'d) as Perl code in the current package. (The debugger
+uses the DB package for keeping its own state information.)
+
+Note that the said C<eval> is bound by an implicit scope. As a
+result any newly introduced lexical variable or any modified
+capture buffer content is lost after the eval. The debugger is a
+nice environment to learn Perl, but if you interactively experiment using
+material which should be in the same scope, stuff it in one line.
+
+For any text entered at the debugger prompt, leading and trailing whitespace
+is first stripped before further processing. If a debugger command
+coincides with some function in your own program, merely precede the
+function with something that doesn't look like a debugger command, such
+as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses
+or braces.
+
+=head2 Calling the Debugger
+
+There are several ways to call the debugger:
+
+=over 4
+
+=item perl -d program_name
+
+On the given program identified by C<program_name>.
+
+=item perl -d -e 0
+
+Interactively supply an arbitrary C<expression> using C<-e>.
-Leading white space before a command would cause the debugger to think
-it's I<NOT> a debugger command but for Perl, so be careful not to do
-that.
+=item perl -d:ptkdb program_name
+
+Debug a given program via the C<Devel::ptkdb> GUI.
+
+=item perl -dt threaded_program_name
+
+Debug a given program using threads (experimental).
+
+=back
=head2 Debugger Commands
-The debugger understands the following commands:
+The interactive debugger understands the following commands:
=over 12
+=item h
+X<debugger command, h>
+
+Prints out a summary help message
+
=item h [command]
-Prints out a help message.
+Prints out a help message for the given debugger command.
+
+=item h h
-If you supply another debugger command as an argument to the C<h> command,
-it prints out the description for just that command. The special
-argument of C<h h> produces a more compact help listing, designed to fit
-together on one screen.
+The special argument of C<h h> produces the entire help page, which is quite long.
-If the output of the C<h> command (or any command, for that matter) scrolls
-past your screen, either precede the command with a leading pipe symbol so
-it's run through your pager, as in
+If the output of the C<h h> command (or any command, for that matter) scrolls
+past your screen, precede the command with a leading pipe symbol so
+that it's run through your pager, as in
- DB> |h
+ DB> |h h
-You may change the pager which is used via C<O pager=...> command.
+You may change the pager which is used via C<o pager=...> command.
=item p expr
+X<debugger command, p>
Same as C<print {$DB::OUT} expr> in the current package. In particular,
-because this is just Perl's own
B<print> function, this means that nested
+because this is just Perl's own
C<print> function, this means that nested
data structures and objects are not dumped, unlike with the C<x> command.
The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of
where STDOUT may be redirected to.
-=item x expr
+=item x [maxdepth] expr
+X<debugger command, x>
+
+Evaluates its expression in list context and dumps out the result in a
+pretty-printed fashion. Nested data structures are printed out
+recursively, unlike the real C<print> function in Perl. When dumping
+hashes, you'll probably prefer 'x \%h' rather than 'x %h'.
+See L<Dumpvalue> if you'd like to do this yourself.
-Evaluates its expression in list context and dumps out the result
-in a pretty-printed fashion. Nested data structures are printed out
-recursively, unlike the C<print> function.
+The output format is governed by multiple options described under
+L</"Configurable Options">.
-The details of printout are governed by multiple C<O>ptions.
+If the C<maxdepth> is included, it must be a numeral I<N>; the value is
+dumped only I<N> levels deep, as if the C<dumpDepth> option had been
+temporarily set to I<N>.
=item V [pkg [vars]]
+X<debugger command, V>
-Display all (or some) variables in package (defaulting to the C<main>
-package) using a data pretty-printer (hashes show their keys and values so
-you see what's what, control characters are made printable, etc.). Make
-sure you don't put the type specifier (like C<$>) there, just the symbol
-names, like this:
+Display all (or some) variables in package (defaulting to C<main>)
+using a data pretty-printer (hashes show their keys and values so
+you see what's what, control characters are made printable, etc.).
+Make sure you don't put the type specifier (like C<$>) there, just
+the symbol names, like this:
V DB filename line
-Use C<~pattern> and C<!pattern> for positive and negative regexps.
+Use C<~pattern> and C<!pattern> for positive and negative regexes.
-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.
+This is similar to calling the C<x> command on each applicable var.
=item X [vars]
+X<debugger command, X>
Same as C<V currentpackage [vars]>.
+=item y [level [vars]]
+X<debugger command, y>
+
+Display all (or some) lexical variables (mnemonic: C<mY> variables)
+in the current scope or I<level> scopes higher. You can limit the
+variables that you see with I<vars> which works exactly as it does
+for the C<V> and C<X> commands. Requires the C<PadWalker> module
+version 0.08 or higher; will warn if this isn't installed. Output
+is pretty-printed in the same style as for C<V> and the format is
+controlled by the same options.
+
=item T
+X<debugger command, T> X<backtrace> X<stack, backtrace>
Produce a stack backtrace. See below for details on its output.
=item s [expr]
+X<debugger command, s> X<step>
-Single step. Executes until it reaches the beginning of another
+Single step. Executes until the beginning of another
statement, descending into subroutine calls. If an expression is
supplied that includes function calls, it too will be single-stepped.
=item n [expr]
+X<debugger command, n>
-Next. Executes over subroutine calls, until it reaches the beginning
+Next. Executes over subroutine calls, until the beginning
of the next statement. If an expression is supplied that includes
function calls, those functions will be executed with stops before
each statement.
-=item E<lt>CRE<gt>
+=item r
+X<debugger command, r>
+
+Continue until the return from the current subroutine.
+Dump the return value if the C<PrintRet> option is set (default).
+
+=item <CR>
Repeat last C<n> or C<s> command.
=item c [line|sub]
+X<debugger command, c>
Continue, optionally inserting a one-time-only breakpoint
at the specified line or subroutine.
=item l
+X<debugger command, l>
List next window of lines.
=item l subname
-List first window of lines from subroutine.
+List first window of lines from subroutine. I<subname> may
+be a variable that contains a code reference.
=item -
+X<debugger command, ->
List previous window of lines.
-=item w [line]
+=item v [line]
+X<debugger command, v>
-List window (a few lines) around the current line.
+View a few lines of code around the current line.
=item .
+X<debugger command, .>
-Return debugger pointer to the last-executed line and
-print it out.
+Return the internal debugger pointer to the line last
+executed, and print out that line.
=item f filename
+X<debugger command, f>
+
+Switch to viewing a different file or C<eval> statement. If I<filename>
+is not a full pathname found in the values of %INC, it is considered
+a regex.
-Switch to viewing a different file or eval statement. If C<filename>
-is not a full filename as found in values of %INC, it is considered as
-a regexp.
+C<eval>ed strings (when accessible) are considered to be filenames:
+C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string
+(in the order of execution). The bodies of the currently executed C<eval>
+and of C<eval>ed strings that define subroutines are saved and thus
+accessible.
=item /pattern/
-Search forwards for pattern; final / is optional.
+Search forwards for pattern (a Perl regex); final / is optional.
+The search is case-insensitive by default.
=item ?pattern?
Search backwards for pattern; final ? is optional.
+The search is case-insensitive by default.
-=item L
+=item L [abw]
+X<debugger command, L>
-List all breakpoints and actions.
+List (default all) actions, breakpoints and watch expressions
-=item S [[!]pattern]
+=item S [[!]regex]
+X<debugger command, S>
-List subroutine names [not] matching pattern.
+List subroutine names [not] matching the regex.
-=item t
+=item t [n]
+X<debugger command, t>
-Toggle trace mode (see also C<AutoTrace> C<O>ption).
+Toggle trace mode (see also the C<AutoTrace> option).
+Optional argument is the maximum number of levels to trace below
+the current one; anything deeper than that will be silent.
-=item t expr
+=item t [n] expr
+X<debugger command, t>
-Trace through execution of expr. For example:
+Trace through execution of C<expr>.
+Optional first argument is the maximum number of levels to trace below
+the current one; anything deeper than that will be silent.
+See L<perldebguts/"Frame Listing Output Examples"> for examples.
- $ perl -de 42
- Stack dump during die enabled outside of evals.
+=item b
+X<breakpoint>
+X<debugger command, b>
- Loading DB routines from perl5db.pl patch level 0.94
- Emacs support available.
+Sets breakpoint on current line
- Enter h or `h h' for help.
-
- main::(-e:1): 0
- DB<1> sub foo { 14 }
+=item b [line] [condition]
+X<breakpoint>
+X<debugger command, b>
- DB<2> sub bar { 3 }
+Set a breakpoint before the given line. If a condition
+is specified, it's evaluated each time the statement is reached: a
+breakpoint is taken only if the condition is true. Breakpoints may
+only be set on lines that begin an executable statement. Conditions
+don't use C<if>:
- DB<3> t print foo() * bar()
- main::((eval 172):3): print foo() + bar();
- main::foo((eval 168):2):
- main::bar((eval 170):2):
- 42
+ b 237 $x > 30
+ b 237 ++$count237 < 11
+ b 33 /pattern/i
-or, with the C<O>ption C<frame=2> set,
+If the line number is C<.>, sets a breakpoint on the current line:
- 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
+ b . $n > 100
-=item b [line] [condition]
+=item b [file]:[line] [condition]
+X<breakpoint>
+X<debugger command, b>
-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 be set on only lines
-that begin an executable statement. Conditions don't use B<if>:
+Set a breakpoint before the given line in a (possibly different) file. If a
+condition is specified, it's evaluated each time the statement is reached: a
+breakpoint is taken only if the condition is true. Breakpoints may only be set
+on lines that begin an executable statement. Conditions don't use C<if>:
- b 237 $x > 30
- b 237 ++$count237 < 11
- b 33 /pattern/i
+ b lib/MyModule.pm:237 $x > 30
+ b /usr/lib/perl5/site_perl/CGI.pm:100 ++$count100 < 11
=item b subname [condition]
+X<breakpoint>
+X<debugger command, b>
-Set a breakpoint at the first line of the named subroutine.
+Set a breakpoint before the first line of the named subroutine. I<subname> may
+be a variable containing a code reference (in this case I<condition>
+is not supported).
=item b postpone subname [condition]
+X<breakpoint>
+X<debugger command, b>
-Set breakpoint at first line of subroutine after it is compiled.
+Set a breakpoint at first line of subroutine after it is compiled.
=item b load filename
+X<breakpoint>
+X<debugger command, b>
-Set breakpoint at the first executed line of the file. Filename should
-be a full name as found in values of %INC.
+Set a breakpoint before the first executed line of the I<filename>,
+which should be a full pathname found amongst the %INC values.
=item b compile subname
+X<breakpoint>
+X<debugger command, b>
-Sets breakpoint at the first statement executed after the subroutine
-is compiled.
+Sets a breakpoint before the first statement executed after the specified
+subroutine is compiled.
-=item d [line]
+=item B line
+X<breakpoint>
+X<debugger command, B>
-Delete a breakpoint at the specified line. If line is omitted, deletes
-the breakpoint on the line that is about to be executed.
+Delete a breakpoint from the specified I<line>.
-=item D
+=item B *
+X<breakpoint>
+X<debugger command, B>
Delete all installed breakpoints.
-=item a [line] command
-
-Set an action to be done before the line is executed.
-The sequence of steps taken by the debugger is
-
- 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 $foo every time line
-53 is passed:
-
- a 53 print "DB FOUND $foo\n"
-
-=item A
-
-Delete all installed actions.
-
-=item W [expr]
-
-Add a global watch-expression.
-
-=item W
-
-Delete all watch-expressions.
-
-=item O [opt[=val]] [opt"val"] [opt?]...
-
-Set or query values of options. val defaults to 1. opt can
-be abbreviated. Several options can be listed.
-
-=over 12
-
-=item C<recallCommand>, C<ShellBang>
-
-The characters used to recall command or spawn shell. By
-default, these are both set to C<!>.
-
-=item C<pager>
-
-Program to use for output of pager-piped commands (those
-beginning with a C<|> character.) By default,
-C<$ENV{PAGER}> will be used.
-
-=item C<tkRunning>
-
-Run Tk while prompting (with ReadLine).
-
-=item C<signalLevel>, C<warnLevel>, C<dieLevel>
-
-Level of verbosity. By default the debugger is in a sane verbose mode,
-thus it will print backtraces on all the warnings and die-messages
-which are going to be printed out, and will print a message when
-interesting uncaught signals arrive.
-
-To disable this behaviour, set these values to 0. If C<dieLevel> is 2,
-then the messages which will be caught by surrounding C<eval> are also
-printed.
-
-=item C<AutoTrace>
-
-Trace mode (similar to C<t> command, but can be put into
-C<PERLDB_OPTS>).
-
-=item C<LineInfo>
-
-File or pipe to print line number info to. If it is a pipe (say,
-C<|visual_perl_db>), 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<ornaments>
-
-affects screen appearance of the command line (see L<Term::ReadLine>).
-
-=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. If C<frame & 8>, overloaded C<stringify> and
-C<tie>d C<FETCH> are enabled on the printed arguments. If C<frame &
-16>, the return value from the subroutine is printed as well.
-
-The length at which the argument list is truncated is governed by the
-next option:
-
-=item C<maxTraceLen>
-
-length at which the argument list is truncated when C<frame> option's
-bit 4 is set.
-
-=back
-
-The following options affect what happens with C<V>, C<X>, and C<x>
-commands:
-
-=over 12
-
-=item C<arrayDepth>, C<hashDepth>
-
-Print only first N elements ('' for all).
-
-=item C<compactDump>, C<veryCompact>
+=item disable [file]:[line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
-Change style of array and hash dump. If C<compactDump>, short array
-may be printed on one line.
-
-=item C<globPrint>
+Disable the breakpoint so it won't stop the execution of the program.
+Breakpoints are enabled by default and can be re-enabled using the C<enable>
+command.
-Whether to print contents of globs.
+=item disable [line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
-=item C<DumpDBFiles>
+Disable the breakpoint so it won't stop the execution of the program.
+Breakpoints are enabled by default and can be re-enabled using the C<enable>
+command.
-Dump arrays holding debugged files.
+This is done for a breakpoint in the current file.
-=item C<DumpPackages>
+=item enable [file]:[line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
-Dump symbol tables of packages.
+Enable the breakpoint so it will stop the execution of the program.
-=item C<DumpReused>
+=item enable [line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
-Dump contents of "reused" addresses.
+Enable the breakpoint so it will stop the execution of the program.
-=item C<quote>, C<HighBit>, C<undefPrint>
+This is done for a breakpoint in the current file.
-Change style of string dump. Default value of C<quote> is C<auto>, one
-can enable either double-quotish dump, or single-quotish by setting it
-to C<"> or C<'>. By default, characters with high bit set are printed
-I<as is>.
+=item a [line] command
+X<debugger command, a>
-=item C<UsageOnly>
+Set an action to be done before the line is executed. If I<line> is
+omitted, set an action on the line about to be executed.
+The sequence of steps taken by the debugger is
-I<very> rudimentally per-package memory usage dump. Calculates total
-size of strings in variables in the package.
+ 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
-=back
+For example, this will print out $foo every time line
+53 is passed:
-During startup options are initialized from C<$ENV{PERLDB_OPTS}>.
-You can put additional initialization options C<TTY>, C<noTTY>,
-C<ReadLine>, and C<NonStop> there.
+ a 53 print "DB FOUND $foo\n"
-Example rc file:
+=item A line
+X<debugger command, A>
- &parse_options("NonStop=1 LineInfo=db.out AutoTrace");
+Delete an action from the specified line.
-The script will run without human intervention, putting trace information
-into the file I<db.out>. (If you interrupt it, you would better reset
-C<LineInfo> to something "interactive"!)
+=item A *
+X<debugger command, A>
-=over 12
+Delete all installed actions.
-=item C<TTY>
+=item w expr
+X<debugger command, w>
-The TTY to use for debugging I/O.
+Add a global watch-expression. Whenever a watched global changes the
+debugger will stop and display the old and new values.
-=item C<noTTY>
+=item W expr
+X<debugger command, W>
-If set, goes in C<NonStop> mode, and would not connect to a TTY. If
-interrupt (or if control goes to debugger via explicit setting of
-$DB::signal or $DB::single from the Perl script), connects to a TTY
-specified by the C<TTY> option at startup, or to a TTY found at
-runtime using C<Term::Rendezvous> module of your choice.
+Delete watch-expression
-This module should implement a method C<new> which returns an object
-with two methods: C<IN> and C<OUT>, returning two filehandles to use
-for debugging input and output correspondingly. Method C<new> may
-inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at
-startup, or is C<"/tmp/perldbtty$$"> otherwise.
+=item W *
+X<debugger command, W>
-=item C<ReadLine>
+Delete all watch-expressions.
-If false, readline support in debugger is disabled, so you can debug
-ReadLine applications.
+=item o
+X<debugger command, o>
-=item C<NonStop>
+Display all options.
-If set, debugger goes into noninteractive mode until interrupted, or
-programmatically by setting $DB::signal or $DB::single.
+=item o booloption ...
+X<debugger command, o>
-=back
+Set each listed Boolean option to the value C<1>.
-Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
+=item o anyoption? ...
+X<debugger command, o>
- $ PERLDB_OPTS="N f=2" perl -d myprogram
+Print out the value of one or more options.
-will run the script C<myprogram> without human intervention, printing
-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 (with exception of
-C<Dump*> options).
+=item o option=value ...
+X<debugger command, o>
-Other examples may include
+Set the value of one or more options. If the value has internal
+whitespace, it should be quoted. For example, you could set C<o
+pager="less -MQeicsNfr"> to call B<less> with those specific options.
+You may use either single or double quotes, but if you do, you must
+escape any embedded instances of same sort of quote you began with,
+as well as any escaping any escapes that immediately precede that
+quote but which are not meant to escape the quote itself. In other
+words, you follow single-quoting rules irrespective of the quote;
+eg: C<o option='this isn\'t bad'> or C<o option="She said, \"Isn't
+it?\"">.
- $ PERLDB_OPTS="N f A L=listing" perl -d myprogram
+For historical reasons, the C<=value> is optional, but defaults to
+1 only where it is safe to do so--that is, mostly for Boolean
+options. It is always better to assign a specific value using C<=>.
+The C<option> can be abbreviated, but for clarity probably should
+not be. Several options can be set together. See L</"Configurable Options">
+for a list of these.
-- runs script noninteractively, 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"!)
+=item < ?
+X<< debugger command, < >>
+List out all pre-prompt Perl command actions.
- $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram
+=item < [ command ]
+X<< debugger command, < >>
-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
+Set an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines.
- $ sleep 1000000
+=item < *
+X<< debugger command, < >>
-See L<"Debugger Internals"> below for more details.
+Delete all pre-prompt Perl command actions.
-=item E<lt> [ command ]
+=item << command
+X<< debugger 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.
+Add an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backwhacking the newlines.
-=item E<lt>E<lt> command
+=item > ?
+X<< debugger command, > >>
-Add an action (Perl command) to happen before every debugger prompt.
-A multi-line command may be entered by backslashing the newlines.
+List out post-prompt Perl command actions.
-=item E<gt> command
+=item > command
+X<< debugger command, > >>
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.
+command may be entered by backslashing the newlines (we bet you
+couldn't have guessed this by now).
-=item E<gt>E<gt> command
+=item > *
+X<< debugger command, > >>
+
+Delete all post-prompt Perl command actions.
+
+=item >> command
+X<<< debugger 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 { ?
+X<debugger command, {>
+
+List out pre-prompt debugger commands.
+
=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.
+A multi-line command may be entered in the customary fashion.
+
+Because this command is in some senses new, a warning is issued if
+you appear to have accidentally entered a block instead. If that's
+what you mean to do, write it as with C<;{ ... }> or even
+C<do { ... }>.
+
+=item { *
+X<debugger command, {>
+
+Delete all pre-prompt debugger commands.
=item {{ command
+X<debugger command, {{>
Add an action (debugger command) to happen before every debugger prompt.
-A multi-line command may be entered by backslashing the newlines.
+A multi-line command may be entered, if you can guess how: see above.
=item ! number
+X<debugger command, !>
-Redo a previous command (default previous command).
+Redo a previous command (defaults to the previous command).
=item ! -number
+X<debugger command, !>
-Redo number'th-to-last command.
+Redo number'th previous command.
=item ! pattern
+X<debugger command, !>
Redo last command that started with pattern.
-See C<O recallCommand>, too.
+See C<o recallCommand>, too.
=item !! cmd
+X<debugger command, !!>
+
+Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See
+C<o shellBang>, also. Note that the user's current shell (well,
+their C<$ENV{SHELL}> variable) will be used, which can interfere
+with proper interpretation of exit status or signal and coredump
+information.
-Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT)
-See C<O shellBang> too.
+=item source file
+X<debugger command, source>
+
+Read and execute debugger commands from I<file>.
+I<file> may itself contain C<source> commands.
=item H -number
+X<debugger command, H>
Display last n commands. Only commands longer than one character are
-listed. If number is omitted, lists them all.
+listed. If I<number> is omitted, list them all.
=item q or ^D
+X<debugger command, q>
+X<debugger command, ^D>
-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.
+Quit. ("quit" doesn't work for this, unless you've made an alias)
+This is the only supported way to exit the debugger, though typing
+C<exit> twice might work.
-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.
+Set the C<inhibit_exit> option to 0 if you want to be able to step
+off the end the script. You may also need to set $finished to 0
+if you want to step through global destruction.
=item R
+X<debugger command, R>
-Restart the debugger by B<exec>ing a new session. It tries to maintain
-your history across this, but internal settings and command line options
+Restart the debugger by C<exec()>ing a new session. We try to maintain
+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>.
+The following setting are currently preserved: history, breakpoints,
+actions, debugger options, and the Perl command-line
+options B<-w>, B<-I>, and B<-e>.
=item |dbcmd
+X<debugger command, |>
-Run debugger command, piping DB::OUT to current pager.
+Run the debugger command, piping DB::OUT into your current pager.
=item ||dbcmd
+X<debugger command, ||>
-Same as C<|dbcmd> but DB::OUT is temporarily B<select>ed as well.
-Often used with commands that would otherwise produce long
-output, such as
-
- |V main
+Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well.
=item = [alias value]
+X<debugger command, =>
Define a command alias, like
=item command
-Execute command as a Perl statement. A missing semicolon will be
-supplied.
+Execute command as a Perl statement. A trailing semicolon will be
+supplied. If the Perl statement would otherwise be confused for a
+Perl debugger, use a leading semicolon, too.
=item m expr
+X<debugger command, m>
-The expression is evaluated, and the methods which may be applied to
-the result are listed.
-
-=item m package
-
-The methods which may be applied to objects in the C<package> are listed.
-
-=back
-
-=head2 Debugger input/output
-
-=over 8
-
-=item Prompt
-
-The debugger prompt is something like
+List which methods may be called on the result of the evaluated
+expression. The expression may evaluated to a reference to a
+blessed object, or to a package name.
- DB<8>
+=item M
+X<debugger command, M>
-or even
+Display all loaded modules and their versions.
- DB<<17>>
+=item man [manpage]
+X<debugger command, man>
-where that number is the command number, which you'd use to access with
-the builtin 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, or you step into an
-expression via C<s/n/t expression> command.
+Despite its name, this calls your system's default documentation
+viewer on the given page, or on the viewer itself if I<manpage> is
+omitted. If that viewer is B<man>, the current C<Config> information
+is used to invoke B<man> using the proper MANPATH or S<B<-M>
+I<manpath>> option. Failed lookups of the form C<XXX> that match
+known manpages of the form I<perlXXX> will be retried. This lets
+you type C<man debug> or C<man op> from the debugger.
-=item Multiline commands
+On systems traditionally bereft of a usable B<man> command, the
+debugger invokes B<perldoc>. Occasionally this determination is
+incorrect due to recalcitrant vendors or rather more felicitously,
+to enterprising users. If you fall into either category, just
+manually set the $DB::doccmd variable to whatever viewer to view
+the Perl documentation on your system. This may be set in an rc
+file, or through direct assignment. We're still waiting for a
+working example of something along the lines of:
-If you want to enter a multi-line command, such as a subroutine
-definition with several statements, or a format, you may escape the
-newline that would normally end the debugger command with a backslash.
-Here's an example:
-
- DB<1> for (1..4) { \
- cont: print "ok\n"; \
- cont: }
- ok
- ok
- ok
- ok
-
-Note that this business of escaping a newline is specific to interactive
-commands typed into the debugger.
-
-=item Stack backtrace
-
-Here's an example of what a stack backtrace via C<T> command 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
- $ = main::pests('bactrian', 4) called from file `camel_flea' line 4
-
-The left-hand character up there tells whether the function was called
-in a scalar or list context (we bet you can tell which is which). What
-that says is that you were in the function C<main::infested> when you ran
-the stack dump, and that it was called in a scalar context from line 10
-of the file I<Ambulation.pm>, but without any arguments at all, meaning
-it was called as C<&infested>. The next stack frame shows that the
-function C<Ambulation::legs> was called in a list context from the
-I<camel_flea> file with four arguments. The last stack frame shows that
-C<main::pests> was called in a scalar context, also from I<camel_flea>,
-but from line 4.
-
-Note that if you execute C<T> command from inside an active C<use>
-statement, the backtrace will contain both C<require>
-frame and an C<eval>) frame.
-
-=item Listing
-
-Listing given via different flavors of C<l> command looks like this:
-
- DB<<13>> l
- 101: @i{@i} = ();
- 102:b @isa{@i,$pack} = ()
- 103 if(exists $i{$prevpack} || exists $isa{$pack});
- 104 }
- 105
- 106 next
- 107==> if(exists $isa{$pack});
- 108
- 109:a if ($extra-- > 0) {
- 110: %isa = ($pack,1);
-
-Note that the breakable lines are marked with C<:>, lines with
-breakpoints are marked by C<b>, with actions by C<a>, and the
-next executed line is marked by C<==E<gt>>.
-
-=item Frame listing
-
-When C<frame> option is set, debugger would print entered (and
-optionally exited) subroutines in different styles.
-
-What follows is the start of the listing of
-
- env "PERLDB_OPTS=f=n N" perl -d -V
-
-for different values of C<n>:
-
-=over 4
-
-=item 1
-
- entering main::BEGIN
- entering Config::BEGIN
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- Package lib/Config.pm.
- entering Config::TIEHASH
- entering Exporter::import
- entering Exporter::export
- entering Config::myconfig
- entering Config::FETCH
- entering Config::FETCH
- entering Config::FETCH
- entering Config::FETCH
-
-=item 2
-
- entering main::BEGIN
- entering Config::BEGIN
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- exited Config::BEGIN
- Package lib/Config.pm.
- entering Config::TIEHASH
- exited Config::TIEHASH
- entering Exporter::import
- entering Exporter::export
- exited Exporter::export
- exited Exporter::import
- exited main::BEGIN
- entering Config::myconfig
- entering Config::FETCH
- exited Config::FETCH
- entering Config::FETCH
- exited Config::FETCH
- entering Config::FETCH
-
-=item 4
-
- in $=main::BEGIN() from /dev/nul:0
- in $=Config::BEGIN() from lib/Config.pm:2
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:644
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li
- in @=Config::myconfig() from /dev/nul:0
- in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'SUBVERSION') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574
-
-=item 6
-
- in $=main::BEGIN() from /dev/nul:0
- in $=Config::BEGIN() from lib/Config.pm:2
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- out $=Config::BEGIN() from lib/Config.pm:0
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:644
- out $=Config::TIEHASH('Config') from lib/Config.pm:644
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
- out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
- out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- out $=main::BEGIN() from /dev/nul:0
- in @=Config::myconfig() from /dev/nul:0
- in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
- out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
- out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574
- out $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'SUBVERSION') from lib/Config.pm:574
-
-=item 14
-
- in $=main::BEGIN() from /dev/nul:0
- in $=Config::BEGIN() from lib/Config.pm:2
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- out $=Config::BEGIN() from lib/Config.pm:0
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:644
- out $=Config::TIEHASH('Config') from lib/Config.pm:644
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
- out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
- out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- out $=main::BEGIN() from /dev/nul:0
- in @=Config::myconfig() from /dev/nul:0
- in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
- out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
- in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
- out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
-
-=item 30
-
- in $=CODE(0x15eca4)() from /dev/null:0
- in $=CODE(0x182528)() from lib/Config.pm:2
- Package lib/Exporter.pm.
- out $=CODE(0x182528)() from lib/Config.pm:0
- scalar context return from CODE(0x182528): undef
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:628
- out $=Config::TIEHASH('Config') from lib/Config.pm:628
- scalar context return from Config::TIEHASH: empty hash
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
- out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
- scalar context return from Exporter::export: ''
- out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
- scalar context return from Exporter::import: ''
-
-
-=back
-
-In all the cases indentation of lines shows the call tree, if bit 2 of
-C<frame> is set, then a line is printed on exit from a subroutine as
-well, if bit 4 is set, then the arguments are printed as well as the
-caller info, if bit 8 is set, the arguments are printed even if they
-are tied or references, if bit 16 is set, the return value is printed
-as well.
-
-When a package is compiled, a line like this
-
- Package lib/Carp.pm.
-
-is printed with proper indentation.
+ $DB::doccmd = 'netscape -remote http://something.here/';
=back
-=head2 Debugging compile-time statements
-
-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 (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:
-
- $DB::single = 1;
-
-If you set C<$DB::single> to the value 2, it's equivalent to having
-just typed the C<n> command, whereas a value of 1 means the C<s>
-command. The C<$DB::trace> variable should be set to 1 to simulate
-having typed the C<t> command.
-
-Another way to debug compile-time code is to start debugger, set a
-breakpoint on I<load> of some module thusly
-
- DB<7> b load f:/perllib/lib/Carp.pm
- Will stop on load of `f:/perllib/lib/Carp.pm'.
-
-and restart debugger by C<R> command (if possible). One can use C<b
-compile subname> for the same purpose.
-
-=head2 Debugger Customization
-
-Most probably you do 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
-like these (the last one is one people expect to be there):
-
- $DB::alias{'len'} = 's/^len(.*)/p length($1)/';
- $DB::alias{'stop'} = 's/^stop (at|in)/b/';
- $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
-that checks for leading exclamation points. However, if you install
-the Term::ReadKey and Term::ReadLine modules from CPAN, you will
-have full editing capabilities much like GNU I<readline>(3) provides.
-Look for these in the F<modules/by-module/Term> directory on CPAN.
-
-A rudimentary command line completion is also available.
-Unfortunately, the names of lexical variables are not available for
-completion.
-
-=head2 Editor Support for Debugging
-
-If you have GNU B<emacs> installed on your system, it can interact with
-the Perl debugger to provide an integrated software development
-environment reminiscent of its interactions with C debuggers.
-
-Perl is also delivered with a start file for making B<emacs> act like a
-syntax-directed editor that understands (some of) Perl's syntax. Look in
-the I<emacs> directory of the Perl source distribution.
+=head2 Configurable Options
-(Historically, a similar setup for interacting with B<vi> and the
-X11 window system had also been available, but at the time of this
-writing, no debugger support for B<vi> currently exists.)
+The debugger has numerous options settable using the C<o> command,
+either interactively or from the environment or an rc file.
+(./.perldb or ~/.perldb under Unix.)
-=head2 The Perl Profiler
-
-If you wish to supply an alternative debugger for Perl to run, just
-invoke your script with a colon and a package argument given to the B<-d>
-flag. One of the most popular alternative debuggers for Perl is
-B<DProf>, the Perl profiler. As of this writing, B<DProf> is not
-included with the standard Perl distribution, but it is expected to
-be included soon, for certain values of "soon".
-Meanwhile, you can fetch the Devel::Dprof module from CPAN. Assuming
-it's properly installed on your system, to profile your Perl program in
-the file F<mycode.pl>, just type:
+=over 12
- perl -d:DProf mycode.pl
+=item C<recallCommand>, C<ShellBang>
+X<debugger option, recallCommand>
+X<debugger option, ShellBang>
-When the script terminates the profiler will dump the profile information
-to a file called F<tmon.out>. A tool like B<dprofpp> (also supplied with
-the Devel::DProf package) can be used to interpret the information which is
-in that profile.
+The characters used to recall a command or spawn a shell. By
+default, both are set to C<!>, which is unfortunate.
-=head2 Debugger support in perl
+=item C<pager>
+X<debugger option, pager>
-When you call the B<caller> function (see L<perlfunc/caller>) from the
-package DB, Perl sets the array @DB::args to contain the arguments the
-corresponding stack frame was called with.
+Program to use for output of pager-piped commands (those beginning
+with a C<|> character.) By default, C<$ENV{PAGER}> will be used.
+Because the debugger uses your current terminal characteristics
+for bold and underlining, if the chosen pager does not pass escape
+sequences through unchanged, the output of some debugger commands
+will not be readable when sent through the pager.
-If perl is run with B<-d> option, the following additional features
-are enabled (cf. L<perlvar/$^P>):
+=item C<tkRunning>
+X<debugger option, tkRunning>
-=over
+Run Tk while prompting (with ReadLine).
-=item *
+=item C<signalLevel>, C<warnLevel>, C<dieLevel>
+X<debugger option, signalLevel> X<debugger option, warnLevel>
+X<debugger option, dieLevel>
+
+Level of verbosity. By default, the debugger leaves your exceptions
+and warnings alone, because altering them can break correctly running
+programs. It will attempt to print a message when uncaught INT, BUS, or
+SEGV signals arrive. (But see the mention of signals in L</BUGS> below.)
+
+To disable this default safe mode, set these values to something higher
+than 0. At a level of 1, you get backtraces upon receiving any kind
+of warning (this is often annoying) or exception (this is
+often valuable). Unfortunately, the debugger cannot discern fatal
+exceptions from non-fatal ones. If C<dieLevel> is even 1, then your
+non-fatal exceptions are also traced and unceremoniously altered if they
+came from C<eval'ed> strings or from any kind of C<eval> within modules
+you're attempting to load. If C<dieLevel> is 2, the debugger doesn't
+care where they came from: It usurps your exception handler and prints
+out a trace, then modifies all exceptions with its own embellishments.
+This may perhaps be useful for some tracing purposes, but tends to hopelessly
+destroy any program that takes its exception handling seriously.
-Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require
-'perl5db.pl'}> if not present) before the first line of the
-application.
+=item C<AutoTrace>
+X<debugger option, AutoTrace>
-=item *
+Trace mode (similar to C<t> command, but can be put into
+C<PERLDB_OPTS>).
-The array C<@{"_E<lt>$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)>.
+=item C<LineInfo>
+X<debugger option, LineInfo>
-=item *
+File or pipe to print line number info to. If it is a pipe (say,
+C<|visual_perl_db>), then a short message is used. This is the
+mechanism used to interact with a slave editor or visual debugger,
+such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical
+debugger.
-The hash C<%{"_E<lt>$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.
+=item C<inhibit_exit>
+X<debugger option, inhibit_exit>
-Same for evaluated strings which contain subroutines, or which are
-currently executed. The $filename for C<eval>ed strings looks like
-C<(eval 34)>.
+If 0, allows I<stepping off> the end of the script.
-=item *
+=item C<PrintRet>
+X<debugger option, PrintRet>
-The scalar C<${"_E<lt>$filename"}> contains C<"_E<lt>$filename">. Same for
-evaluated strings which contain subroutines, or which are currently
-executed. The $filename for C<eval>ed strings looks like C<(eval
-34)>.
+Print return value after C<r> command if set (default).
-=item *
+=item C<ornaments>
+X<debugger option, ornaments>
-After each C<require>d file is compiled, but before it is executed,
-C<DB::postponed(*{"_E<lt>$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 %INC).
+Affects screen appearance of the command line (see L<Term::ReadLine>).
+There is currently no way to disable these, which can render
+some output illegible on some displays, or with some pagers.
+This is considered a bug.
-=item *
+=item C<frame>
+X<debugger option, frame>
-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).
+Affects the printing of messages upon entry and exit from subroutines. If
+C<frame & 2> is false, messages are printed on entry only. (Printing
+on exit might be useful if interspersed with other messages.)
-=item *
+If C<frame & 4>, arguments to functions are printed, plus context
+and caller info. If C<frame & 8>, overloaded C<stringify> and
+C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame
+& 16>, the return value from the subroutine is printed.
-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 length at which the argument list is truncated is governed by the
+next option:
-=item *
+=item C<maxTraceLen>
+X<debugger option, maxTraceLen>
-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 & (1E<lt>E<lt>30)>).
+Length to truncate the argument list when the C<frame> option's
+bit 4 is set.
-=item *
+=item C<windowSize>
+X<debugger option, windowSize>
-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>.)
+Change the size of code list window (default is 10 lines).
=back
-Note that if C<&DB::sub> needs some external data to be setup for it
-to work, no subroutine call is possible until this is done. For the
-standard debugger C<$DB::deep> (how many levels of recursion deep into
-the debugger you can go before a mandatory break) gives an example of
-such a dependency.
-
-The minimal working debugger consists of one line
-
- sub DB::DB {}
-
-which is quite handy as contents of C<PERL5DB> environment
-variable:
-
- env "PERL5DB=sub DB::DB {}" perl -d your-script
-
-Another (a little bit more useful) minimal debugger can be created
-with the only line being
-
- sub DB::DB {print ++$i; scalar <STDIN>}
-
-This debugger would print the sequential number of encountered
-statement, and would wait for your C<CR> to continue.
-
-The following debugger is quite functional:
-
- {
- package DB;
- sub DB {}
- sub sub {print ++$i, " $sub\n"; &$sub}
- }
-
-It prints the sequential number of subroutine call and the name of the
-called subroutine. Note that C<&DB::sub> should be compiled into the
-package C<DB>.
-
-=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 a list 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?
-
-=head2 BUGS
+The following options affect what happens with C<V>, C<X>, and C<x>
+commands:
-You cannot get the stack frame information or otherwise debug functions
-that were not compiled by Perl, such as C or C++ extensions.
+=over 12
-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.
+=item C<arrayDepth>, C<hashDepth>
+X<debugger option, arrayDepth> X<debugger option, hashDepth>
-=head1 Debugging Perl memory usage
+Print only first N elements ('' for all).
-Perl is I<very> frivolous with memory. There is a saying that to
-estimate memory usage of Perl, assume a reasonable algorithm of
-allocation, and multiply your estimates by 10. This is not absolutely
-true, but may give you a good grasp of what happens.
+=item C<dumpDepth>
+X<debugger option, dumpDepth>
-Say, an integer cannot take less than 20 bytes of memory, a float
-cannot take less than 24 bytes, a string cannot take less than 32
-bytes (all these examples assume 32-bit architectures, the result are
-much worse on 64-bit architectures). If a variable is accessed in two
-of three different ways (which require an integer, a float, or a
-string), the memory footprint may increase by another 20 bytes. A
-sloppy malloc() implementation will make these numbers yet more.
+Limit recursion depth to N levels when dumping structures.
+Negative values are interpreted as infinity. Default: infinity.
-On the opposite end of the scale, a declaration like
+=item C<compactDump>, C<veryCompact>
+X<debugger option, compactDump> X<debugger option, veryCompact>
- sub foo;
+Change the style of array and hash output. If C<compactDump>, short array
+may be printed on one line.
-may take (on some versions of perl) up to 500 bytes of memory.
+=item C<globPrint>
+X<debugger option, globPrint>
-Off-the-cuff anecdotal estimates of a code bloat give a factor around
-8. This means that the compiled form of reasonable (commented
-indented etc.) code will take approximately 8 times more than the
-disk space the code takes.
+Whether to print contents of globs.
-There are two Perl-specific ways to analyze the memory usage:
-$ENV{PERL_DEBUG_MSTATS} and B<-DL> switch. First one is available
-only if perl is compiled with Perl's malloc(), the second one only if
-Perl compiled with C<-DDEBUGGING> (as with giving C<-D optimise=-g>
-option to F<Configure>).
+=item C<DumpDBFiles>
+X<debugger option, DumpDBFiles>
-=head2 Using C<$ENV{PERL_DEBUG_MSTATS}>
+Dump arrays holding debugged files.
-If your perl is using Perl's malloc(), and compiled with correct
-switches (this is the default), then it will print memory usage
-statistics after compiling your code (if C<$ENV{PERL_DEBUG_MSTATS}> >
-1), and before termination of the script (if
-C<$ENV{PERL_DEBUG_MSTATS}> >= 1). The report format is similar to one
-in the following example:
+=item C<DumpPackages>
+X<debugger option, DumpPackages>
- env PERL_DEBUG_MSTATS=2 perl -e "require Carp"
- Memory allocation statistics after compilation: (buckets 4(4)..8188(8192)
- 14216 free: 130 117 28 7 9 0 2 2 1 0 0
- 437 61 36 0 5
- 60924 used: 125 137 161 55 7 8 6 16 2 0 1
- 74 109 304 84 20
- Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048.
- Memory allocation statistics after execution: (buckets 4(4)..8188(8192)
- 30888 free: 245 78 85 13 6 2 1 3 2 0 1
- 315 162 39 42 11
- 175816 used: 265 176 1112 111 26 22 11 27 2 1 1
- 196 178 1066 798 39
- Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144.
+Dump symbol tables of packages.
-It is possible to ask for such a statistic at arbitrary moment by
-using Devel::Peek::mstats() (module Devel::Peek is available on CPAN).
+=item C<DumpReused>
+X<debugger option, DumpReused>
-Here is the explanation of different parts of the format:
+Dump contents of "reused" addresses.
-=over
+=item C<quote>, C<HighBit>, C<undefPrint>
+X<debugger option, quote> X<debugger option, HighBit>
+X<debugger option, undefPrint>
-=item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)>
+Change the style of string dump. The default value for C<quote>
+is C<auto>; one can enable double-quotish or single-quotish format
+by setting it to C<"> or C<'>, respectively. By default, characters
+with their high bit set are printed verbatim.
-Perl's malloc() uses bucketed allocations. Every request is rounded
-up to the closest bucket size available, and a bucket of these size is
-taken from the pool of the buckets of this size.
+=item C<UsageOnly>
+X<debugger option, UsageOnly>
-The above line describes limits of buckets currently in use. Each
-bucket has two sizes: memory footprint, and the maximal size of user
-data which may be put into this bucket. Say, in the above example the
-smallest bucket is both sizes 4. The biggest bucket has usable size
-8188, and the memory footprint 8192.
+Rudimentary per-package memory usage dump. Calculates total
+size of strings found in variables in the package. This does not
+include lexicals in a module's file scope, or lost in closures.
-With debugging Perl some buckets may have negative usable size. This
-means that these buckets cannot (and will not) be used. For greater
-buckets the memory footprint may be one page greater than a power of
-2. In such a case the corresponding power of two is printed instead
-in the C<APPROX> field above.
+=item C<HistFile>
+X<debugger option, history, HistFile>
-=item Free/Used
+The path of the file from which the history (assuming a usable
+Term::ReadLine backend) will be read on the debugger's startup, and to which
+it will be saved on shutdown (for persistence across sessions). Similar in
+concept to Bash's C<.bash_history> file.
-The following 1 or 2 rows of numbers correspond to the number of
-buckets of each size between C<SMALLEST> and C<GREATEST>. In the
-first row the sizes (memory footprints) of buckets are powers of two
-(or possibly one page greater). In the second row (if present) the
-memory footprints of the buckets are between memory footprints of two
-buckets "above".
+=item C<HistSize>
+X<debugger option, history, HistSize>
-Say, with the above example the memory footprints are (with current
-algorithm)
+The count of the saved lines in the history (assuming C<HistFile> above).
- free: 8 16 32 64 128 256 512 1024 2048 4096 8192
- 4 12 24 48 80
+=back
-With non-C<DEBUGGING> perl the buckets starting from C<128>-long ones
-have 4-byte overhead, thus 8192-long bucket may take up to
-8188-byte-long allocations.
+After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}>
+environment variable and parses this as the remainder of a "O ..."
+line as one might enter at the debugger prompt. You may place the
+initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop>
+there.
-=item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS>
+If your rc file contains:
-The first two fields give the total amount of memory perl sbrk()ed,
-and number of sbrk()s used. The third number is what perl thinks
-about continuity of returned chunks. As far as this number is
-positive, malloc() will assume that it is probable that sbrk() will
-provide continuous memory.
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace");
-The amounts sbrk()ed by external libraries is not counted.
+then your script will run without human intervention, putting trace
+information into the file I<db.out>. (If you interrupt it, you'd
+better reset C<LineInfo> to F</dev/tty> if you expect to see anything.)
-=item C<pad: 0>
+=over 12
-The amount of sbrk()ed memory needed to keep buckets aligned.
+=item C<TTY>
+X<debugger option, TTY>
-=item C<heads: 2192>
+The TTY to use for debugging I/O.
-While memory overhead of bigger buckets is kept inside the bucket, for
-smaller buckets it is kept in separate areas. This field gives the
-total size of these areas.
+=item C<noTTY>
+X<debugger option, noTTY>
+
+If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If
+interrupted (or if control goes to the debugger via explicit setting of
+$DB::signal or $DB::single from the Perl script), it connects to a TTY
+specified in the C<TTY> option at startup, or to a tty found at
+runtime using the C<Term::Rendezvous> module of your choice.
+
+This module should implement a method named C<new> that returns an object
+with two methods: C<IN> and C<OUT>. These should return filehandles to use
+for debugging input and output correspondingly. The C<new> method should
+inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at
+startup, or C<"$ENV{HOME}/.perldbtty$$"> otherwise. This file is not
+inspected for proper ownership, so security hazards are theoretically
+possible.
-=item C<chain: 0>
+=item C<ReadLine>
+X<debugger option, ReadLine>
-malloc() may want to subdivide a bigger bucket into smaller buckets.
-If only a part of the deceased-bucket is left non-subdivided, the rest
-is kept as an element of a linked list. This field gives the total
-size of these chunks.
+If false, readline support in the debugger is disabled in order
+to debug applications that themselves use ReadLine.
-=item C<tail: 6144>
+=item C<NonStop>
+X<debugger option, NonStop>
-To minimize amount of sbrk()s malloc() asks for more memory. This
-field gives the size of the yet-unused part, which is sbrk()ed, but
-never touched.
+If set, the debugger goes into non-interactive mode until interrupted, or
+programmatically by setting $DB::signal or $DB::single.
=back
-=head2 Example of using B<-DL> switch
-
-Below we show how to analyse memory usage by
-
- do 'lib/auto/POSIX/autosplit.ix';
-
-The file in question contains a header and 146 lines similar to
-
- sub getcwd ;
+Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
-B<Note:> I<the discussion below supposes 32-bit architecture. In the
-newer versions of perl the memory usage of the constructs discussed
-here is much improved, but the story discussed below is a real-life
-story. This story is very terse, and assumes more than cursory
-knowledge of Perl internals.>
+ $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram
-Here is the itemized list of Perl allocations performed during parsing
-of this file:
+That will run the script B<myprogram> without human intervention,
+printing out the call tree with entry and exit points. Note that
+C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally,
+options could be uniquely abbreviated by the first letter (modulo
+the C<Dump*> options). It is nevertheless recommended that you
+always spell them out in full for legibility and future compatibility.
- !!! "after" at test.pl line 3.
- Id subtot 4 8 12 16 20 24 28 32 36 40 48 56 64 72 80 80+
- 0 02 13752 . . . . 294 . . . . . . . . . . 4
- 0 54 5545 . . 8 124 16 . . . 1 1 . . . . . 3
- 5 05 32 . . . . . . . 1 . . . . . . . .
- 6 02 7152 . . . . . . . . . . 149 . . . . .
- 7 02 3600 . . . . . 150 . . . . . . . . . .
- 7 03 64 . -1 . 1 . . 2 . . . . . . . . .
- 7 04 7056 . . . . . . . . . . . . . . . 7
- 7 17 38404 . . . . . . . 1 . . 442 149 . . 147 .
- 9 03 2078 17 249 32 . . . . 2 . . . . . . . .
+Other examples include
+ $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram
-To see this list insert two C<warn('!...')> statements around the call:
+which runs script non-interactively, printing info on each entry
+into a subroutine and each executed line into the file named F<listing>.
+(If you interrupt it, you would better reset C<LineInfo> to something
+"interactive"!)
- warn('!');
- do 'lib/auto/POSIX/autosplit.ix';
- warn('!!! "after"');
+Other examples include (using standard shell syntax to show environment
+variable settings):
-and run it with B<-DL> option. The first warn() will print memory
-allocation info before the parsing of the file, and will memorize the
-statistics at this point (we ignore what it prints). The second warn()
-will print increments w.r.t. this memorized statistics. This is the
-above printout.
+ $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out"
+ perl -d myprogram )
-Different I<Id>s on the left correspond to different subsystems of
-perl interpreter, they are just first argument given to perl memory
-allocation API New(). To find what C<9 03> means C<grep> the perl
-source for C<903>. You will see that it is F<util.c>, function
-savepvn(). This function is used to store a copy of existing chunk of
-memory. Using C debugger, one can see that it is called either
-directly from gv_init(), or via sv_magic(), and gv_init() is called
-from gv_fetchpv() - which is called from newSUB().
+which may be useful for debugging a program that uses C<Term::ReadLine>
+itself. Do not forget to detach your shell from the TTY in the window that
+corresponds to F</dev/ttyXX>, say, by issuing a command like
-B<Note:> to reach this place in debugger and skip all the calls to
-savepvn during the compilation of the main script, set a C breakpoint
-in Perl_warn(), C<continue> this point is reached, I<then> set
-breakpoint in Perl_savepvn(). Note that you may need to skip a
-handful of Perl_savepvn() which do not correspond to mass production
-of CVs (there are more C<903> allocations than 146 similar lines of
-F<lib/auto/POSIX/autosplit.ix>). Note also that C<Perl_> prefixes are
-added by macroization code in perl header files to avoid conflicts
-with external libraries.
+ $ sleep 1000000
-Anyway, we see that C<903> ids correspond to creation of globs, twice
-per glob - for glob name, and glob stringification magic.
+See L<perldebguts/"Debugger Internals"> for details.
-Here are explanations for other I<Id>s above:
+=head2 Debugger Input/Output
-=over
+=over 8
-=item C<717>
+=item Prompt
-is for creation of bigger C<XPV*> structures. In the above case it
-creates 3 C<AV> per subroutine, one for a list of lexical variable
-names, one for a scratchpad (which contains lexical variables and
-C<targets>), and one for the array of scratchpads needed for
-recursion.
+The debugger prompt is something like
-It also creates a C<GV> and a C<CV> per subroutine (all called from
-start_subparse()).
+ DB<8>
-=item C<002>
+or even
-Creates C array corresponding to the C<AV> of scratchpads, and the
-scratchpad itself (the first fake entry of this scratchpad is created
-though the subroutine itself is not defined yet).
+ DB<<17>>
-It also creates C arrays to keep data for the stash (this is one HV,
-but it grows, thus there are 4 big allocations: the big chunks are not
-freed, but are kept as additional arenas for C<SV> allocations).
+where that number is the command number, and which you'd use to
+access with the built-in B<csh>-like history mechanism. For example,
+C<!17> would repeat command number 17. The depth of the angle
+brackets indicates the nesting 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 the result of a function call that
+itself has a breakpoint, or you step into an expression via C<s/n/t
+expression> command.
-=item C<054>
+=item Multiline commands
-creates a C<HEK> for the name of the glob for the subroutine (this
-name is a key in a I<stash>).
+If you want to enter a multi-line command, such as a subroutine
+definition with several statements or a format, escape the newline
+that would normally end the debugger command with a backslash.
+Here's an example:
-Big allocations with this I<Id> correspond to allocations of new
-arenas to keep C<HE>.
+ DB<1> for (1..4) { \
+ cont: print "ok\n"; \
+ cont: }
+ ok
+ ok
+ ok
+ ok
-=item C<602>
+Note that this business of escaping a newline is specific to interactive
+commands typed into the debugger.
-creates a C<GP> for the glob for the subroutine.
+=item Stack backtrace
+X<backtrace> X<stack, backtrace>
-=item C<702>
+Here's an example of what a stack backtrace via C<T> command might
+look like:
-creates the C<MAGIC> for the glob for the subroutine.
+ $ = main::infested called from file 'Ambulation.pm' line 10
+ @ = Ambulation::legs(1, 2, 3, 4) called from file 'camel_flea'
+ line 7
+ $ = main::pests('bactrian', 4) called from file 'camel_flea'
+ line 4
+
+The left-hand character up there indicates the context in which the
+function was called, with C<$> and C<@> meaning scalar or list
+contexts respectively, and C<.> meaning void context (which is
+actually a sort of scalar context). The display above says
+that you were in the function C<main::infested> when you ran the
+stack dump, and that it was called in scalar context from line
+10 of the file I<Ambulation.pm>, but without any arguments at all,
+meaning it was called as C<&infested>. The next stack frame shows
+that the function C<Ambulation::legs> was called in list context
+from the I<camel_flea> file with four arguments. The last stack
+frame shows that C<main::pests> was called in scalar context,
+also from I<camel_flea>, but from line 4.
+
+If you execute the C<T> command from inside an active C<use>
+statement, the backtrace will contain both a C<require> frame and
+an C<eval> frame.
+
+=item Line Listing Format
+
+This shows the sorts of output the C<l> command can produce:
+
+ DB<<13>> l
+ 101: @i{@i} = ();
+ 102:b @isa{@i,$pack} = ()
+ 103 if(exists $i{$prevpack} || exists $isa{$pack});
+ 104 }
+ 105
+ 106 next
+ 107==> if(exists $isa{$pack});
+ 108
+ 109:a if ($extra-- > 0) {
+ 110: %isa = ($pack,1);
+
+Breakable lines are marked with C<:>. Lines with breakpoints are
+marked by C<b> and those with actions by C<a>. The line that's
+about to be executed is marked by C<< ==> >>.
+
+Please be aware that code in debugger listings may not look the same
+as your original source code. Line directives and external source
+filters can alter the code before Perl sees it, causing code to move
+from its original positions or take on entirely different forms.
-=item C<704>
+=item Frame listing
-creates I<arenas> which keep SVs.
+When the C<frame> option is set, the debugger would print entered (and
+optionally exited) subroutines in different styles. See L<perldebguts>
+for incredibly long examples of these.
=back
-=head2 B<-DL> details
+=head2 Debugging Compile-Time Statements
-If Perl is run with B<-DL> option, then warn()s which start with `!'
-behave specially. They print a list of I<categories> of memory
-allocations, and statistics of allocations of different sizes for
-these categories.
+If you have compile-time executable statements (such as code within
+BEGIN, UNITCHECK and CHECK blocks or C<use> statements), these will
+I<not> be stopped by debugger, although C<require>s and INIT blocks
+will, and compile-time statements can be traced with the 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:
-If warn() string starts with
-
-=over
+ $DB::single = 1;
-=item C<!!!>
+If you set C<$DB::single> to 2, it's equivalent to having
+just typed the C<n> command, whereas a value of 1 means the C<s>
+command. The C<$DB::trace> variable should be set to 1 to simulate
+having typed the C<t> command.
-print changed categories only, print the differences in counts of allocations;
+Another way to debug compile-time code is to start the debugger, set a
+breakpoint on the I<load> of some module:
-=item C<!!>
+ DB<7> b load f:/perllib/lib/Carp.pm
+ Will stop on load of 'f:/perllib/lib/Carp.pm'.
-print grown categories only; print the absolute values of counts, and totals;
+and then restart the debugger using the C<R> command (if possible). One can use C<b
+compile subname> for the same purpose.
-=item C<!>
+=head2 Debugger Customization
-print nonempty categories, print the absolute values of counts and totals.
+The debugger probably contains enough configuration hooks that you
+won't ever have to modify it yourself. You may change the behaviour
+of the debugger from within the debugger using its C<o> command, from
+the command line via the C<PERLDB_OPTS> environment variable, and
+from customization files.
-=back
+You can do some customization by setting up a F<.perldb> file, which
+contains initialization code. For instance, you could make aliases
+like these (the last one is one people expect to be there):
-=head2 Limitations of B<-DL> statistic
+ $DB::alias{'len'} = 's/^len(.*)/p length($1)/';
+ $DB::alias{'stop'} = 's/^stop (at|in)/b/';
+ $DB::alias{'ps'} = 's/^ps\b/p scalar /';
+ $DB::alias{'quit'} = 's/^quit(\s*)/exit/';
-If an extension or an external library does not use Perl API to
-allocate memory, these allocations are not counted.
+You can change options from F<.perldb> by using calls like this one;
-=head1 Debugging regular expressions
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2");
-There are two ways to enable debugging output for regular expressions.
+The code is executed in the package C<DB>. Note that F<.perldb> is
+processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the
+subroutine C<afterinit>, that function is called after debugger
+initialization ends. F<.perldb> may be contained in the current
+directory, or in the home directory. Because this file is sourced
+in by Perl and may contain arbitrary commands, for security reasons,
+it must be owned by the superuser or the current user, and writable
+by no one but its owner.
-If your perl is compiled with C<-DDEBUGGING>, you may use the
-B<-Dr> flag on the command line.
+You can mock TTY input to debugger by adding arbitrary commands to
+@DB::typeahead. For example, your F<.perldb> file might contain:
-Otherwise, one can C<use re 'debug'>, which has effects both at
-compile time, and at run time (and is I<not> lexically scoped).
+ sub afterinit { push @DB::typeahead, "b 4", "b 6"; }
-=head2 Compile-time output
+Which would attempt to set breakpoints on lines 4 and 6 immediately
+after debugger initialization. Note that @DB::typeahead is not a supported
+interface and is subject to change in future releases.
-The debugging output for the compile time looks like this:
+If you want to modify the debugger, copy F<perl5db.pl> from the
+Perl library to another name and hack it to your heart's content.
+You'll then want to set your C<PERL5DB> environment variable to say
+something like this:
- compiling RE `[bc]d(ef*g)+h[ij]k$'
- size 43 first at 1
- 1: ANYOF(11)
- 11: EXACT <d>(13)
- 13: CURLYX {1,32767}(27)
- 15: OPEN1(17)
- 17: EXACT <e>(19)
- 19: STAR(22)
- 20: EXACT <f>(0)
- 22: EXACT <g>(24)
- 24: CLOSE1(26)
- 26: WHILEM(0)
- 27: NOTHING(28)
- 28: EXACT <h>(30)
- 30: ANYOF(40)
- 40: EXACT <k>(42)
- 42: EOL(43)
- 43: END(0)
- anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating)
- stclass `ANYOF' minlen 7
+ BEGIN { require "myperl5db.pl" }
-The first line shows the pre-compiled form of the regexp, and the
-second shows the size of the compiled form (in arbitrary units,
-usually 4-byte words) and the label I<id> of the first node which
-does a match.
+As a last resort, you could also use C<PERL5DB> to customize the debugger
+by directly setting internal variables or calling debugger functions.
-The last line (split into two lines in the above) contains the optimizer
-info. In the example shown, the optimizer found that the match
-should contain a substring C<de> at the offset 1, and substring C<gh>
-at some offset between 3 and infinity. Moreover, when checking for
-these substrings (to abandon impossible matches quickly) it will check
-for the substring C<gh> before checking for the substring C<de>. The
-optimizer may also use the knowledge that the match starts (at the
-C<first> I<id>) with a character class, and the match cannot be
-shorter than 7 chars.
+Note that any variables and functions that are not documented in
+this document (or in L<perldebguts>) are considered for internal
+use only, and as such are subject to change without notice.
-The fields of interest which may appear in the last line are
+=head2 Readline Support / History in the Debugger
-=over
+As shipped, the only command-line history supplied is a simplistic one
+that checks for leading exclamation points. However, if you install
+the Term::ReadKey and Term::ReadLine modules from CPAN (such as
+Term::ReadLine::Gnu, Term::ReadLine::Perl, ...) you will
+have full editing capabilities much like those GNU I<readline>(3) provides.
+Look for these in the F<modules/by-module/Term> directory on CPAN.
+These do not support normal B<vi> command-line editing, however.
-=item C<anchored> I<STRING> C<at> I<POS>
+A rudimentary command-line completion is also available, including
+lexical variables in the current scope if the C<PadWalker> module
+is installed.
-=item C<floating> I<STRING> C<at> I<POS1..POS2>
+Without Readline support you may see the symbols "^[[A", "^[[C", "^[[B",
+"^[[D"", "^H", ... when using the arrow keys and/or the backspace key.
-see above;
+=head2 Editor Support for Debugging
-=item C<matching floating/anchored>
+If you have the GNU's version of B<emacs> installed on your system,
+it can interact with the Perl debugger to provide an integrated
+software development environment reminiscent of its interactions
+with C debuggers.
-which substring to check first;
+Recent versions of Emacs come with a
+start file for making B<emacs> act like a
+syntax-directed editor that understands (some of) Perl's syntax.
+See L<perlfaq3>.
-=item C<minlen>
+Users of B<vi> should also look into B<vim> and B<gvim>, the mousey
+and windy version, for coloring of Perl keywords.
-the minimal length of the match;
+Note that only perl can truly parse Perl, so all such CASE tools
+fall somewhat short of the mark, especially if you don't program
+your Perl as a C programmer might.
-=item C<stclass> I<TYPE>
+=head2 The Perl Profiler
+X<profile> X<profiling> X<profiler>
-The type of the first matching node.
+If you wish to supply an alternative debugger for Perl to run,
+invoke your script with a colon and a package argument given to the
+B<-d> flag. Perl's alternative debuggers include a Perl profiler,
+L<Devel::NYTProf>, which is available separately as a CPAN
+distribution. To profile your Perl program in the file F<mycode.pl>,
+just type:
-=item C<noscan>
+ $ perl -d:NYTProf mycode.pl
-which advises to not scan for the found substrings;
+When the script terminates the profiler will create a database of the
+profile information that you can turn into reports using the profiler's
+tools. See <perlperf> for details.
-=item C<isall>
+=head1 Debugging Regular Expressions
+X<regular expression, debugging>
+X<regex, debugging> X<regexp, debugging>
-which says that the optimizer info is in fact all that the regular
-expression contains (thus one does not need to enter the RE engine at
-all);
+C<use re 'debug'> enables you to see the gory details of how the Perl
+regular expression engine works. In order to understand this typically
+voluminous output, one must not only have some idea about how regular
+expression matching works in general, but also know how Perl's regular
+expressions are internally compiled into an automaton. These matters
+are explored in some detail in
+L<perldebguts/"Debugging Regular Expressions">.
-=item C<GPOS>
+=head1 Debugging Memory Usage
+X<memory usage>
-if the pattern contains C<\G>;
+Perl contains internal support for reporting its own memory usage,
+but this is a fairly advanced concept that requires some understanding
+of how memory allocation works.
+See L<perldebguts/"Debugging Perl Memory Usage"> for the details.
-=item C<plus>
+=head1 SEE ALSO
-if the pattern starts with a repeated char (as in C<x+y>);
+You do have C<use strict> and C<use warnings> enabled, don't you?
-=item C<implicit>
+L<perldebtut>,
+L<perldebguts>,
+L<re>,
+L<DB>,
+L<Devel::NYTProf>,
+L<Dumpvalue>,
+and
+L<perlrun>.
-if the pattern starts with C<.*>;
+When debugging a script that uses #! and is thus normally found in
+$PATH, the -S option causes perl to search $PATH for it, so you don't
+have to type the path or C<which $scriptname>.
-=item C<with eval>
+ $ perl -Sd foo.pl
-if the pattern contain eval-groups (see L<perlre/(?{ code })>);
+=head1 BUGS
-=item C<anchored(TYPE)>
+You cannot get stack frame information or in any fashion debug functions
+that were not compiled by Perl, such as those from C or C++ extensions.
-if the pattern may
-match only at a handful of places (with C<TYPE> being
-C<BOL>, C<MBOL>, or C<GPOS>, see the table below).
+If you alter your @_ arguments in a subroutine (such as with C<shift>
+or C<pop>), the stack backtrace will not show the original values.
-=back
+The debugger does not currently work in conjunction with the B<-W>
+command-line switch, because it itself is not free of warnings.
-If a substring is known to match at end-of-line only, it may be
-followed by C<$>, as in C<floating `k'$>.
-
-The optimizer-specific info is used to avoid entering (a slow) RE
-engine on strings which will definitely not match. If C<isall> flag
-is set, a call to the RE engine may be avoided even when optimizer
-found an appropriate place for the match.
-
-The rest of the output contains the list of I<nodes> of the compiled
-form of the RE. Each line has format
-
-C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>)
-
-=head2 Types of nodes
-
-Here is the list of possible types with short descriptions:
-
- # TYPE arg-description [num-args] [longjump-len] DESCRIPTION
-
- # Exit points
- END no End of program.
- SUCCEED no Return from a subroutine, basically.
-
- # Anchors:
- BOL no Match "" at beginning of line.
- MBOL no Same, assuming multiline.
- SBOL no Same, assuming singleline.
- EOS no Match "" at end of string.
- EOL no Match "" at end of line.
- MEOL no Same, assuming multiline.
- SEOL no Same, assuming singleline.
- BOUND no Match "" at any word boundary
- BOUNDL no Match "" at any word boundary
- NBOUND no Match "" at any word non-boundary
- NBOUNDL no Match "" at any word non-boundary
- GPOS no Matches where last m//g left off.
-
- # [Special] alternatives
- ANY no Match any one character (except newline).
- SANY no Match any one character.
- ANYOF sv Match character in (or not in) this class.
- ALNUM no Match any alphanumeric character
- ALNUML no Match any alphanumeric char in locale
- NALNUM no Match any non-alphanumeric character
- NALNUML no Match any non-alphanumeric char in locale
- SPACE no Match any whitespace character
- SPACEL no Match any whitespace char in locale
- NSPACE no Match any non-whitespace character
- NSPACEL no Match any non-whitespace char in locale
- DIGIT no Match any numeric character
- NDIGIT no Match any non-numeric character
-
- # BRANCH The set of branches constituting a single choice are hooked
- # together with their "next" pointers, since precedence prevents
- # anything being concatenated to any individual branch. The
- # "next" pointer of the last BRANCH in a choice points to the
- # thing following the whole choice. This is also where the
- # final "next" pointer of each individual branch points; each
- # branch starts with the operand node of a BRANCH node.
- #
- BRANCH node Match this alternative, or the next...
-
- # BACK Normal "next" pointers all implicitly point forward; BACK
- # exists to make loop structures possible.
- # not used
- BACK no Match "", "next" ptr points backward.
-
- # Literals
- EXACT sv Match this string (preceded by length).
- EXACTF sv Match this string, folded (prec. by length).
- EXACTFL sv Match this string, folded in locale (w/len).
-
- # Do nothing
- NOTHING no Match empty string.
- # A variant of above which delimits a group, thus stops optimizations
- TAIL no Match empty string. Can jump here from outside.
-
- # STAR,PLUS '?', and complex '*' and '+', are implemented as circular
- # BRANCH structures using BACK. Simple cases (one character
- # per match) are implemented with STAR and PLUS for speed
- # and to minimize recursive plunges.
- #
- STAR node Match this (simple) thing 0 or more times.
- PLUS node Match this (simple) thing 1 or more times.
-
- CURLY sv 2 Match this simple thing {n,m} times.
- CURLYN no 2 Match next-after-this simple thing
- # {n,m} times, set parenths.
- CURLYM no 2 Match this medium-complex thing {n,m} times.
- CURLYX sv 2 Match this complex thing {n,m} times.
-
- # This terminator creates a loop structure for CURLYX
- WHILEM no Do curly processing and see if rest matches.
-
- # OPEN,CLOSE,GROUPP ...are numbered at compile time.
- OPEN num 1 Mark this point in input as start of #n.
- CLOSE num 1 Analogous to OPEN.
-
- REF num 1 Match some already matched string
- REFF num 1 Match already matched string, folded
- REFFL num 1 Match already matched string, folded in loc.
-
- # grouping assertions
- IFMATCH off 1 2 Succeeds if the following matches.
- UNLESSM off 1 2 Fails if the following matches.
- SUSPEND off 1 1 "Independent" sub-RE.
- IFTHEN off 1 1 Switch, should be preceeded by switcher .
- GROUPP num 1 Whether the group matched.
-
- # Support for long RE
- LONGJMP off 1 1 Jump far away.
- BRANCHJ off 1 1 BRANCH with long offset.
-
- # The heavy worker
- EVAL evl 1 Execute some Perl code.
-
- # Modifiers
- MINMOD no Next operator is not greedy.
- LOGICAL no Next opcode should set the flag only.
-
- # This is not used yet
- RENUM off 1 1 Group with independently numbered parens.
-
- # This is not really a node, but an optimized away piece of a "long" node.
- # To simplify debugging output, we mark it as if it were a node
- OPTIMIZED off Placeholder for dump.
-
-=head2 Run-time output
-
-First of all, when doing a match, one may get no run-time output even
-if debugging is enabled. this means that the RE engine was never
-entered, all of the job was done by the optimizer.
-
-If RE engine was entered, the output may look like this:
-
- Matching `[bc]d(ef*g)+h[ij]k$' against `abcdefg__gh__'
- Setting an EVAL scope, savestack=3
- 2 <ab> <cdefg__gh_> | 1: ANYOF
- 3 <abc> <defg__gh_> | 11: EXACT <d>
- 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767}
- 4 <abcd> <efg__gh_> | 26: WHILEM
- 0 out of 1..32767 cc=effff31c
- 4 <abcd> <efg__gh_> | 15: OPEN1
- 4 <abcd> <efg__gh_> | 17: EXACT <e>
- 5 <abcde> <fg__gh_> | 19: STAR
- EXACT <f> can match 1 times out of 32767...
- Setting an EVAL scope, savestack=3
- 6 <bcdef> <g__gh__> | 22: EXACT <g>
- 7 <bcdefg> <__gh__> | 24: CLOSE1
- 7 <bcdefg> <__gh__> | 26: WHILEM
- 1 out of 1..32767 cc=effff31c
- Setting an EVAL scope, savestack=12
- 7 <bcdefg> <__gh__> | 15: OPEN1
- 7 <bcdefg> <__gh__> | 17: EXACT <e>
- restoring \1 to 4(4)..7
- failed, try continuation...
- 7 <bcdefg> <__gh__> | 27: NOTHING
- 7 <bcdefg> <__gh__> | 28: EXACT <h>
- failed...
- failed...
-
-The most significant information in the output is about the particular I<node>
-of the compiled RE which is currently being tested against the target string.
-The format of these lines is
-
-C< >I<STRING-OFFSET> <I<PRE-STRING>> <I<POST-STRING>> |I<ID>: I<TYPE>
-
-The I<TYPE> info is indented with respect to the backtracking level.
-Other incidental information appears interspersed within.
-
-=cut
+If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing
+from your keyboard or a socket) and haven't set up your own C<$SIG{INT}>
+handler, then you won't be able to CTRL-C your way back to the debugger,
+because the debugger's own C<$SIG{INT}> handler doesn't understand that
+it needs to raise an exception to longjmp(3) out of slow syscalls.
https://perl5.git.perl.org / perl5.git / blobdiff