First of all, have you tried using the B<-w> switch?
-=head2 Debugging
-
-If you invoke Perl with a B<-d> switch, your script will be run under the
-debugger. However, the Perl debugger is not a separate program as it is
-in a C environment. Instead, the B<-d> flag tells the compiler to insert
-source information into the pseudocode it's about to hand to the
-interpreter. (That means your code must compile correctly for the
-debugger to work on it.) Then when the interpreter starts up, it
-pre-loads a Perl library file containing the debugger itself. The program
-will halt before the first executable statement (but see below) and ask
-you for one of the following commands:
+=head1 The Perl 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."
+
+I< --Maurice Wilkes, 1949>
+
+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
+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:
+
+ perl -d -e 42
+
+In Perl, the debugger is not a separate program as 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.
+
+The program will halt I<right before> the first run-time executable
+statement (but see below regarding compile-time statements) and ask you
+to enter a debugger command. Contrary to popular expectations, whenever
+the debugger halts and shows you a line of code, it always displays the
+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.)
+
+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.
+
+=head2 Debugger Commands
+
+The debugger understands the following commands:
=over 12
-=item h
+=item h [command]
Prints out a help message.
+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.
+
+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
+
+ DB> |h
+
+You may change the pager which is used via C<O pager=...> command.
+
+=item p expr
+
+Same as C<print {$DB::OUT} expr> in the current package. In particular,
+because this is just Perl's own B<print> function, this means that nested
+data structures and objects are not dumped, unlike with the C<x> command.
+
+The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of
+where STDOUT may be redirected to.
+
+=item x expr
+
+Evaluates its expression in list context and dumps out the result
+in a pretty-printed fashion. Nested data structures are printed out
+recursively, unlike the C<print> function.
+
+The details of printout are governed by multiple C<O>ptions.
+
+=item V [pkg [vars]]
+
+Display all (or some) variables in package (defaulting to the C<main>
+package) using a data pretty-printer (hashes show their keys and values so
+you see what's what, control characters are made printable, etc.). Make
+sure you don't put the type specifier (like C<$>) there, just the symbol
+names, like this:
+
+ V DB filename line
+
+Use C<~pattern> and C<!pattern> for positive and negative regexps.
+
+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
-Stack trace.
-If you do bizarre things to your @_ arguments in a subroutine, the stack
-backtrace will not always show the original values.
+Produce a stack backtrace. See below for details on its output.
-=item s
+=item s [expr]
Single step. Executes until it reaches the beginning of another
-statement.
+statement, descending into subroutine calls. If an expression is
+supplied that includes function calls, it too will be single-stepped.
-=item n
+=item n [expr]
Next. Executes over subroutine calls, until it reaches the beginning
-of the next statement.
+of the next statement. If an expression is supplied that includes
+function calls, those functions will be executed with stops before
+each statement.
-=item f
+=item E<lt>CRE<gt>
-Finish. Executes statements until it has finished the current
-subroutine.
+Repeat last C<n> or C<s> command.
-=item c
+=item c [line|sub]
-Continue. Executes until the next breakpoint is reached.
+Continue, optionally inserting a one-time-only breakpoint
+at the specified line or subroutine.
-=item c line
-
-Continue to the specified line. Inserts a one-time-only breakpoint at
-the specified line.
-
-=item <CR>
+=item l
-Repeat last n or s.
+List next window of lines.
=item l min+incr
-List incr+1 lines starting at min. If min is omitted, starts where
-last listing left off. If incr is omitted, previous value of incr is
-used.
+List C<incr+1> lines starting at C<min>.
=item l min-max
-List lines in the indicated range.
+List lines C<min> through C<max>. C<l -> is synonymous to C<->.
=item l line
-List just the indicated line.
+List a single line.
-=item l
+=item l subname
-List next window.
+List first window of lines from subroutine.
=item -
-List previous window.
+List previous window of lines.
-=item w line
+=item w [line]
-List window (a few lines worth of code) around line.
+List window (a few lines) around the current line.
-=item l subname
+=item .
-List subroutine. If it's a long subroutine it just lists the
-beginning. Use "l" to list more.
+Return debugger pointer to the last-executed line and
+print it out.
+
+=item f filename
+
+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.
=item /pattern/
-Regular expression search forward in the source code for pattern; the
-final / is optional.
+Search forwards for pattern; final / is optional.
=item ?pattern?
-Regular expression search backward in the source code for pattern; the
-final ? is optional.
+Search backwards for pattern; final ? is optional.
=item L
-List lines that have breakpoints or actions.
+List all breakpoints and actions.
-=item S
+=item S [[!]pattern]
-Lists the names of all subroutines.
+List subroutine names [not] matching pattern.
=item t
-Toggle trace mode on or off.
+Toggle trace mode (see also C<AutoTrace> C<O>ption).
+
+=item t expr
+
+Trace through execution of expr. For example:
+
+ $ perl -de 42
+ Stack dump during die enabled outside of evals.
+
+ Loading DB routines from perl5db.pl patch level 0.94
+ Emacs support available.
+
+ Enter h or `h h' for help.
+
+ main::(-e:1): 0
+ DB<1> sub foo { 14 }
+
+ DB<2> sub bar { 3 }
-=item b line [ condition ]
+ DB<3> t print foo() * bar()
+ main::((eval 172):3): print foo() + bar();
+ main::foo((eval 168):2):
+ main::bar((eval 170):2):
+ 42
+
+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 is
+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
-that begin an executable statement. Conditions don't use C<if>:
+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 ]
+=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.
-Set breakpoint at first executable line of subroutine.
+=item b load filename
-=item d line
+Set breakpoint at the first executed line of the file. Filename should
+be a full name as found in values of %INC.
-Delete breakpoint. If line is omitted, deletes the breakpoint on the
-line that is about to be executed.
+=item b compile subname
+
+Sets breakpoint at the first statement executed after the subroutine
+is compiled.
+
+=item d [line]
+
+Delete a breakpoint at the specified line. If line is omitted, deletes
+the breakpoint on the line that is about to be executed.
=item D
-Delete all breakpoints.
+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
-=item a line command
+For example, this will print out $foo every time line
+53 is passed:
-Set an action for line. A multiline command may be entered by
-backslashing the newlines. This command is Perl code, not another
-debugger command.
+ a 53 print "DB FOUND $foo\n"
=item A
-Delete all line actions.
+Delete all installed actions.
-=item < command
+=item W [expr]
-Set an action to happen before every debugger prompt. A multiline
-command may be entered by backslashing the newlines.
+Add a global watch-expression.
-=item > command
+=item W
-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.
+Delete all watch-expressions.
-=item V package [symbols]
+=item O [opt[=val]] [opt"val"] [opt?]...
-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 $) there, just the symbol
-names, like this:
+Set or query values of options. val defaults to 1. opt can
+be abbreviated. Several options can be listed.
+
+=over 12
+
+=item C<recallCommand>, C<ShellBang>
+
+The characters used to recall command or spawn shell. By
+default, these are both set to C<!>.
+
+=item C<pager>
+
+Program to use for output of pager-piped commands (those
+beginning with a C<|> character.) By default,
+C<$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:
- V DB filename line
+=over 12
+
+=item C<arrayDepth>, C<hashDepth>
+
+Print only first N elements ('' for all).
+
+=item C<compactDump>, C<veryCompact>
+
+Change style of array and hash dump. If C<compactDump>, short array
+may be printed on one line.
+
+=item C<globPrint>
+
+Whether to print contents of globs.
+
+=item C<DumpDBFiles>
+
+Dump arrays holding debugged files.
+
+=item C<DumpPackages>
+
+Dump symbol tables of packages.
+
+=item C<DumpReused>
+
+Dump contents of "reused" addresses.
+
+=item C<quote>, C<HighBit>, C<undefPrint>
+
+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 C<UsageOnly>
+
+I<very> rudimentally per-package memory usage dump. Calculates total
+size of strings in variables in the package.
+
+=back
+
+During startup options are initialized from C<$ENV{PERLDB_OPTS}>.
+You can put additional initialization options C<TTY>, C<noTTY>,
+C<ReadLine>, and C<NonStop> there.
+
+Example rc file:
+
+ &parse_options("NonStop=1 LineInfo=db.out AutoTrace");
+
+The script will run without human intervention, putting trace information
+into the file I<db.out>. (If you interrupt it, you would better reset
+C<LineInfo> to something "interactive"!)
+
+=over 12
+
+=item C<TTY>
+
+The TTY to use for debugging I/O.
+
+=item C<noTTY>
+
+If set, goes in C<NonStop> mode, and would not connect to a TTY. If
+interrupt (or if control goes to debugger via explicit setting of
+$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 noninteractive 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
+
+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).
+
+Other examples may include
+
+ $ PERLDB_OPTS="N f A L=listing" perl -d myprogram
+
+- 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"!)
+
+
+ $ 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.
+
+=item E<lt> [ command ]
-=item X [symbols]
+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.
-Same as as "V" command, but within the current package.
+=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 (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
-Redo a debugging command. If number is omitted, redoes the previous
-command.
+Redo a previous command (default previous command).
=item ! -number
-Redo the command that was that many commands ago.
+Redo number'th-to-last command.
+
+=item ! pattern
+
+Redo last command that started with pattern.
+See C<O recallCommand>, too.
+
+=item !! cmd
+
+Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT)
+See C<O shellBang> too.
=item H -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 $finished to 0 at
+some moment if you want to step through global destruction.
+
+=item 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
+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.
+
+=item ||dbcmd
+
+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
+
+=item = [alias value]
+
+Define a command alias, like
+
+ = quit q
+
+or list current aliases.
=item command
Execute command as a Perl statement. A missing semicolon will be
supplied.
-=item p expr
+=item m expr
+
+The expression is evaluated, and the methods which may be applied to
+the result are listed.
+
+=item m package
-Same as C<print DB::OUT expr>. The DB::OUT filehandle is opened to
-/dev/tty, regardless of where STDOUT may be redirected to.
+The methods which may be applied to objects in the C<package> are listed.
=back
-Any command you type in that isn't recognized by the debugger will be
-directly executed (C<eval>'d) as Perl code. Leading white space will
-cause the debugger to think it's C<NOT> a debugger command.
+=head2 Debugger input/output
+
+=over 8
+
+=item Prompt
+
+The debugger prompt is something like
+
+ DB<8>
+
+or even
+
+ DB<<17>>
-If you have any compile-time executable statements (code within a BEGIN
-block or a C<use> statement), these will I<NOT> be stopped by debugger,
-although C<require>s will. From your own code, however, you can transfer
-control back to the debugger using the following statement, which is harmless
-if the debugger is not running:
+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.
+
+=item Multiline commands
+
+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), 'PERL_VERSION') from lib/Config.pm:574
+ in $=Config::FETCH(ref(Config), 'PERL_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), 'PERL_VERSION') from lib/Config.pm:574
+ out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
+ in $=Config::FETCH(ref(Config), 'PERL_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.
+
+=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:
$DB::single = 1;
-=head2 Customization
+If you set C<$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.
-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 environment variable PERL5DB to say something like this:
+Another way to debug compile-time code is to start debugger, set a
+breakpoint on I<load> of some module thusly
- BEGIN { require "myperl5db.pl" }
+ 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 in particular most people seem to expect to
-be there):
+like these (the last one is one people expect to be there):
- $DB::alias{'len'} = 's/^len(.*)/p length($1)/';
+ $DB::alias{'len'} = 's/^len(.*)/p length($1)/';
$DB::alias{'stop'} = 's/^stop (at|in)/b/';
- $DB::alias{'.'} = 's/^\./p '
- . '"\$DB::sub(\$DB::filename:\$DB::line):\t"'
- . ',\$DB::dbline[\$DB::line]/' ;
+ $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.
+
+(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.)
+
+=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:
+
+ perl -d:DProf mycode.pl
+
+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.
+
+=head2 Debugger support in perl
+
+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.
+
+If perl is run with B<-d> option, the following additional features
+are enabled (cf. L<perlvar/$^P>):
+
+=over
+
+=item *
+
+Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require
+'perl5db.pl'}> if not present) before the first line of the
+application.
+
+=item *
+
+The array C<@{"_E<lt>$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 $filename
+for C<eval>ed strings looks like C<(eval 34)>.
+
+=item *
+
+The hash C<%{"_E<lt>$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.
+
+Same for evaluated strings which contain subroutines, or which are
+currently executed. The $filename for C<eval>ed strings looks like
+C<(eval 34)>.
+
+=item *
+
+The scalar C<${"_E<lt>$filename"}> contains C<"_E<lt>$filename">. Same for
+evaluated strings which contain subroutines, or which are currently
+executed. The $filename for C<eval>ed strings looks like C<(eval
+34)>.
+
+=item *
+
+After each C<require>d file is compiled, but before it is executed,
+C<DB::postponed(*{"_E<lt>$filename"})> is called (if subroutine
+C<DB::postponed> exists). Here the $filename is the expanded name of
+the C<require>d file (as found in values of %INC).
+
+=item *
+
+After each subroutine C<subname> is compiled existence of
+C<$DB::postponed{subname}> is checked. If this key exists,
+C<DB::postponed(subname)> is called (if subroutine C<DB::postponed>
+exists).
+
+=item *
+
+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.
+=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 & (1E<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<$DB::sub> being
+the name of the called subroutine. (Unless the subroutine is compiled
+in the package C<DB>.)
+
+=back
+
+Note that if C<&DB::sub> needs some external data to be setup for it
+to work, no subroutine call is possible until this is done. For the
+standard debugger C<$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<$> or C<@>), C<sub> (subroutine name, or info about
+eval), C<args> (C<undef> or a reference to an array), C<file>, and
+C<line>.
+
+The function C<DB::print_trace(FH, skip[, count[, short]])> prints
+formatted info about caller frames. The last two functions may be
+convenient as arguments to C<E<lt>>, C<E<lt>E<lt>> commands.
=head2 Other resources
You did try the B<-w> switch, didn't you?
-=head1 BUGS
+=head2 BUGS
+
+You cannot get the stack frame information or otherwise debug functions
+that were not compiled by Perl, such as C or C++ extensions.
+
+If you alter your @_ arguments in a subroutine (such as with B<shift>
+or B<pop>, the stack backtrace will not show the original values.
+
+=head1 Debugging Perl memory usage
+
+Perl is I<very> frivolous with memory. There is a saying that to
+estimate memory usage of Perl, assume a reasonable algorithm of
+allocation, and multiply your estimates by 10. This is not absolutely
+true, but may give you a good grasp of what happens.
+
+Say, an integer cannot take less than 20 bytes of memory, a float
+cannot take less than 24 bytes, a string cannot take less than 32
+bytes (all these examples assume 32-bit architectures, the result are
+much worse on 64-bit architectures). If a variable is accessed in two
+of three different ways (which require an integer, a float, or a
+string), the memory footprint may increase by another 20 bytes. A
+sloppy malloc() implementation will make these numbers yet more.
+
+On the opposite end of the scale, a declaration like
+
+ sub foo;
+
+may take (on some versions of perl) up to 500 bytes of memory.
+
+Off-the-cuff anecdotal estimates of a code bloat give a factor around
+8. This means that the compiled form of reasonable (commented
+indented etc.) code will take approximately 8 times more than the
+disk space the code takes.
+
+There are two Perl-specific ways to analyze the memory usage:
+$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>).
+
+=head2 Using C<$ENV{PERL_DEBUG_MSTATS}>
+
+If your perl is using Perl's malloc(), and compiled with correct
+switches (this is the default), then it will print memory usage
+statistics after compiling your code (if C<$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:
+
+ 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.
+
+It is possible to ask for such a statistic at arbitrary moment by
+using Devel::Peek::mstats() (module Devel::Peek is available on CPAN).
+
+Here is the explanation of different parts of the format:
+
+=over
+
+=item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)>
+
+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.
+
+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.
+
+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 Free/Used
+
+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".
+
+Say, with the above example the memory footprints are (with current
+algorithm)
+
+ free: 8 16 32 64 128 256 512 1024 2048 4096 8192
+ 4 12 24 48 80
+
+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.
-If your program exit()s or die()s, so does the debugger.
+=item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS>
-There's no builtin way to restart the debugger without exiting and coming back
-into it. You could use an alias like this:
+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.
- $DB::alias{'rerun'} = 'exec "perl -d $DB::filename"';
+The amounts sbrk()ed by external libraries is not counted.
+
+=item C<pad: 0>
+
+The amount of sbrk()ed memory needed to keep buckets aligned.
+
+=item C<heads: 2192>
+
+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<chain: 0>
+
+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.
+
+=item C<tail: 6144>
+
+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.
+
+=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 ;
+
+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.>
+
+Here is the itemized list of Perl allocations performed during parsing
+of this file:
+
+ !!! "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 . . . . . . . .
+
+
+To see this list insert two C<warn('!...')> statements around the call:
+
+ warn('!');
+ do 'lib/auto/POSIX/autosplit.ix';
+ warn('!!! "after"');
+
+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.
+
+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().
+
+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.
+
+Anyway, we see that C<903> ids correspond to creation of globs, twice
+per glob - for glob name, and glob stringification magic.
+
+Here are explanations for other I<Id>s above:
+
+=over
+
+=item C<717>
+
+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.
+
+It also creates a C<GV> and a C<CV> per subroutine (all called from
+start_subparse()).
+
+=item C<002>
+
+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).
+
+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).
+
+=item C<054>
+
+creates a C<HEK> for the name of the glob for the subroutine (this
+name is a key in a I<stash>).
+
+Big allocations with this I<Id> correspond to allocations of new
+arenas to keep C<HE>.
+
+=item C<602>
+
+creates a C<GP> for the glob for the subroutine.
+
+=item C<702>
+
+creates the C<MAGIC> for the glob for the subroutine.
+
+=item C<704>
+
+creates I<arenas> which keep SVs.
+
+=back
+
+=head2 B<-DL> details
+
+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 warn() string starts with
+
+=over
+
+=item C<!!!>
+
+print changed categories only, print the differences in counts of allocations;
+
+=item C<!!>
+
+print grown categories only; print the absolute values of counts, and totals;
+
+=item C<!>
+
+print nonempty categories, print the absolute values of counts and totals.
+
+=back
+
+=head2 Limitations of B<-DL> statistic
+
+If an extension or an external library does not use Perl API to
+allocate memory, these allocations are not counted.
+
+=head1 Debugging regular expressions
+
+There are two ways to enable debugging output for regular expressions.
+
+If your perl is compiled with C<-DDEBUGGING>, you may use the
+B<-Dr> flag on the command line.
+
+Otherwise, one can C<use re 'debug'>, which has effects both at
+compile time, and at run time (and is I<not> lexically scoped).
+
+=head2 Compile-time output
+
+The debugging output for the compile time looks 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
+
+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.
+
+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.
+
+The fields of interest which may appear in the last line are
+
+=over
+
+=item C<anchored> I<STRING> C<at> I<POS>
+
+=item C<floating> I<STRING> C<at> I<POS1..POS2>
+
+see above;
+
+=item C<matching floating/anchored>
+
+which substring to check first;
+
+=item C<minlen>
+
+the minimal length of the match;
+
+=item C<stclass> I<TYPE>
+
+The type of the first matching node.
+
+=item C<noscan>
+
+which advises to not scan for the found substrings;
+
+=item C<isall>
+
+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);
+
+=item C<GPOS>
+
+if the pattern contains C<\G>;
+
+=item C<plus>
+
+if the pattern starts with a repeated char (as in C<x+y>);
+
+=item C<implicit>
+
+if the pattern starts with C<.*>;
+
+=item C<with eval>
+
+if the pattern contain eval-groups (see L<perlre/(?{ code })>);
+
+=item C<anchored(TYPE)>
+
+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).
+
+=back
-But you'd lose any pending breakpoint information, and that might not
-be the right path, etc.
+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
https://perl5.git.perl.org / perl5.git / blobdiff