X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperldebug.pod;h=bccdcf4f5164772e6b056c701b5bdf2f4443a710;hb=6940069f6d5beebb5f66572e358b4e7d0c3d1c43;hp=17fe25926fe305c5fb8287c28ac5491a47f62230;hpb=a0d0e21ea6ea90a22318550944fe6cb09ae10cda;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perldebug.pod b/pod/perldebug.pod
index 17fe259..bccdcf4 100644
--- a/pod/perldebug.pod
+++ b/pod/perldebug.pod
@@ -6,244 +6,947 @@ perldebug - Perl debugging
 
 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
+
+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 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 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
+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 keeping its own state information.)
+
+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 Debugger Commands
+
+The debugger understands the following commands:
 
 =over 12
 
-=item h
+=item h [command]
 
 Prints out a help message.
 
-=item T
+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, precede the command with a leading pipe symbol so
+that 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 {$DB::OUT} expr> in the current package.  In particular,
+because this is just Perl's own C<print> function, this means that nested
+data structures and objects are not dumped, unlike with the C<x> command.
+
+The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of
+where STDOUT may be redirected to.
+
+=item x expr
+
+Evaluates its expression in list context and dumps out the result
+in a pretty-printed fashion.  Nested data structures are printed out
+recursively, unlike the real C<print> function in Perl.
+See L<Dumpvalue> if you'd like to do this yourself.
+
+The output format is governed by multiple options described under
+L<"Options">.
+
+=item V [pkg [vars]]
+
+Display all (or some) variables in package (defaulting to C<main>) 
+using a data pretty-printer (hashes show their keys and values so
+you see what's what, control characters are made printable, etc.).
+Make sure you don't put the type specifier (like C<$>) there, just
+the symbol names, like this:
+
+    V DB filename line
 
-Stack trace.
-If you do bizarre things to your @_ arguments in a subroutine, the stack
-backtrace will not always show the original values.
+Use C<~pattern> and C<!pattern> for positive and negative regexes.
 
-=item s
+This is similar to calling the C<x> command on each applicable var.
 
-Single step.  Executes until it reaches the beginning of another
-statement.
+=item X [vars]
 
-=item n
+Same as C<V currentpackage [vars]>.
 
-Next.  Executes over subroutine calls, until it reaches the beginning
-of the next statement.
+=item T
+
+Produce a stack backtrace.  See below for details on its output.
 
-=item f
+=item s [expr]
 
-Finish.  Executes statements until it has finished the current
-subroutine.
+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 c
+=item n [expr]
 
-Continue.  Executes until the next breakpoint is reached.
+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 c line
+=item r
 
-Continue to the specified line.  Inserts a one-time-only breakpoint at
-the specified line.
+Continue until the return from the current subroutine.
+Dump the return value if the C<PrintRet> option is set (default).
 
 =item <CR>
 
-Repeat last n or s.
+Repeat last C<n> or C<s> command.
+
+=item c [line|sub]
+
+Continue, optionally inserting a one-time-only breakpoint
+at the specified line or subroutine.
+
+=item l
+
+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.  I<subname> may
+be a variable that contains a code reference.
 
 =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 .
+
+Return the internal debugger pointer to the line last
+executed, and print out that line.
 
-List subroutine.  If it's a long subroutine it just lists the
-beginning.  Use "l" to list more.
+=item f filename
+
+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.
+
+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/
 
-Regular expression search forward in the source code for pattern; the
-final / is optional.
+Search forwards for pattern (a Perl regex); 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 [[!]regex]
 
-Lists the names of all subroutines.
+List subroutine names [not] matching the regex.
 
 =item t
 
-Toggle trace mode on or off.
+Toggle trace mode (see also the C<AutoTrace> option).
+
+=item t expr
 
-=item b line [ condition ]
+Trace through execution of C<expr>.
+See L<perldebguts/"Frame Listing Output Examples"> for examples.
 
-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
-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>:
+=item b [line] [condition]
+
+Set a breakpoint before the given line.  If I<line> is omitted, set a
+breakpoint on the line about to be executed.  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
 
-=item b subname [ condition ]
+=item b subname [condition]
+
+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]
+
+Set a breakpoint at first line of subroutine after it is compiled.
+
+=item b load filename
+
+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
 
-Set breakpoint at first executable line of subroutine.
+Sets a breakpoint before the first statement executed after the specified
+subroutine is compiled.
 
-=item d line
+=item d [line]
 
-Delete breakpoint.  If line is omitted, deletes the breakpoint on the
-line that is about to be executed.
+Delete a breakpoint from the specified I<line>.  If I<line> is omitted, deletes
+the breakpoint from the line about to be executed.
 
 =item D
 
-Delete all breakpoints.
+Delete all installed breakpoints.
 
-=item a line command
+=item a [line] command
 
-Set an action for line.  A multiline command may be entered by
-backslashing the newlines.  This command is Perl code, not another
-debugger command.
+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
+
+  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 [line]
+
+Delete an action from the specified line.  If I<line> is omitted, delete
+the action on the line that is about to be executed.
 
 =item A
 
-Delete all line actions.
+Delete all installed actions.
+
+=item W expr
+
+Add a global watch-expression.  We hope you know what one of these
+is, because they're supposed to be obvious.  B<WARNING>: It is far
+too easy to destroy your watch expressions by accidentally omitting
+the I<expr>.
+
+=item W
+
+Delete all watch-expressions.
+
+=item O booloption ...
+
+Set each listed Boolean option to the value C<1>.
+
+=item O anyoption? ...
+
+Print out the value of one or more options.
+
+=item O option=value ...
+
+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?\"">.
+
+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<"Options"> for
+a list of these.
+
+=item < ? 
+
+List out all pre-prompt Perl command actions.
+
+=item < [ command ]
+
+Set an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines.  
+B<WARNING> If C<command> is missing, all actions are wiped out!
 
-=item < command
+=item << command
 
-Set an action to happen before every debugger prompt.  A multiline
-command may be entered by backslashing the newlines.
+Add an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backwhacking the newlines.
+
+=item > ?
+
+List out post-prompt Perl command actions.
 
 =item > command
 
-Set an action to happen after the prompt when you've just given a
-command to return to executing the script.  A multiline command may be
-entered by backslashing the newlines.
+Set an action (Perl command) to happen after the prompt when you've
+just given a command to return to executing the script.  A multi-line
+command may be entered by backslashing the newlines (we bet you
+couldn't've guessed this by now).  B<WARNING> If C<command> is
+missing, all actions are wiped out!
+
+=item >> 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 slackbashing the newlines.
 
-=item V package [symbols]
+=item { ?
 
-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:
+List out pre-prompt debugger commands.
 
-    V DB filename line 
+=item { [ command ]
 
-=item X [symbols] 
+Set an action (debugger command) to happen before every debugger prompt.
+A multi-line command may be entered in the customary fashion.  
+B<WARNING> If C<command> is missing, all actions are wiped out!
 
-Same as as "V" command, but within the current package.  
+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 {{ command
+
+Add an action (debugger command) to happen before every debugger prompt.
+A multi-line command may be entered, if you can guess how: see above.
 
 =item ! number
 
-Redo a debugging command.  If number is omitted, redoes the previous
-command.
+Redo a previous command (defaults to the previous command).
 
 =item ! -number
 
-Redo the command that was that many commands ago.
+Redo number'th previous 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>, 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.
 
 =item H -number
 
 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
 
-Quit.  ("quit" doesn't work for this.)
+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 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
+
+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.
+
+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
+
+Run the debugger command, piping DB::OUT into your current pager.
+
+=item ||dbcmd
+
+Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well.
+
+=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.
+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 p expr
+=item m expr
+
+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.
+
+=item man [manpage]
+
+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.
+
+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:
 
-Same as C<print DB::OUT expr>.  The DB::OUT filehandle is opened to
-/dev/tty, regardless of where STDOUT may be redirected to.
+    $DB::doccmd = 'netscape -remote http://something.here/';
 
 =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 Configurable Options
+
+The debugger has numerous options settable using the C<O> command,
+either interactively or from the environment or an rc file.
+
+=over 12
+
+=item C<recallCommand>, C<ShellBang>
+
+The characters used to recall command or spawn shell.  By
+default, both are set to C<!>, which is unfortunate.
+
+=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.
+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.
+
+=item C<tkRunning>
+
+Run Tk while prompting (with ReadLine).
+
+=item C<signalLevel>, C<warnLevel>, C<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'd> 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.
+
+=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 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.
+
+=item C<inhibit_exit>
+
+If 0, allows I<stepping off> the end of the script.
+
+=item C<PrintRet>
+
+Print return value after C<r> command if set (default).
+
+=item C<ornaments>
+
+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 C<frame>
+
+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.)
+
+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.
+
+The length at which the argument list is truncated is governed by the
+next option:
+
+=item C<maxTraceLen>
 
-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:
+Length to truncate the argument list when the 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>
+
+Change the style of array and hash output.  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 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.
+
+=item C<UsageOnly>
+
+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.
+
+=back
+
+During startup, options are initialized from C<$ENV{PERLDB_OPTS}>.
+You may place the initialization options C<TTY>, C<noTTY>,
+C<ReadLine>, and C<NonStop> there.
+
+If your rc file contains:
+
+  parse_options("NonStop=1 LineInfo=db.out AutoTrace");
+
+then your script will run without human intervention, putting trace
+information into the file I<db.out>.  (If you interrupt it, you'd
+better reset C<LineInfo> to F</dev/tty> if you expect to see anything.)
+
+=over 12
+
+=item C<TTY>
+
+The TTY to use for debugging I/O.
+
+=item C<noTTY>
+
+If set, the debugger goes into C<NonStop> mode and will not connect to a TTY.  If
+interrupted (or if control goes to the debugger via explicit setting of
+$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<"/tmp/perldbtty$$"> otherwise.  This file is not 
+inspected for proper ownership, so security hazards are theoretically
+possible.
+
+=item C<ReadLine>
+
+If false, readline support in the debugger is disabled in order
+to debug applications that themselves use ReadLine.
+
+=item C<NonStop>
+
+If set, the debugger goes into non-interactive mode until interrupted, or
+programmatically by setting $DB::signal or $DB::single.
+
+=back
+
+Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
+
+    $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram
+
+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.
+
+Other examples include
+
+    $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram
+
+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"!)
+
+Other examples include (using standard shell syntax to show environment
+variable settings):
+
+  $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out"
+      perl -d myprogram )
+
+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
+
+  $ sleep 1000000
+
+See L<perldebguts/"Debugger Internals"> for details.
+
+=head2 Debugger input/output
+
+=over 8
+
+=item Prompt
+
+The debugger prompt is something like
+
+    DB<8>
+
+or even
+
+    DB<<17>>
+
+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 Multiline commands
+
+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:
+
+      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 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 Frame listing
+
+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 Debugging compile-time statements
+
+If you have compile-time executable statements (such as code within
+BEGIN 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 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<$DB::single> to 2, it's equivalent to having
+just typed the C<n> command, whereas a value of 1 means the C<s>
+command.  The C<$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 the debugger, set a
+breakpoint on the I<load> of some module:
 
-    BEGIN { require "myperl5db.pl" }
+    DB<7> b load f:/perllib/lib/Carp.pm
+  Will stop on load of `f:/perllib/lib/Carp.pm'.
+
+and then restart the debugger using the C<R> command (if possible).  One can use C<b
+compile subname> for the same purpose.
 
-You can do some customization by setting up a F<.perldb> file which
+=head2 Debugger Customization
+
+The debugger probably contains enough configuration hooks that you
+won't ever have to modify it yourself.  You may change the behaviour
+of 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.
+
+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/';
+
+You can change options from F<.perldb> by using 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>, 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 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:
+
+    BEGIN { require "myperl5db.pl" }
+
+As a last resort, you could also use C<PERL5DB> to customize the debugger
+by directly setting internal variables or calling debugger functions.
+
+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.
+
+=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.
+These do not support normal B<vi> command-line editing, however.
+
+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 the FSF'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.
 
-=head2 Other resources
+Perl comes 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.
+
+A similar setup by Tom Christiansen for interacting with any
+vendor-shipped B<vi> and the X11 window system is also available.
+This works similarly to the integrated multiwindow support that
+B<emacs> provides, where the debugger drives the editor.  At the
+time of this writing, however, that tool's eventual location in the
+Perl distribution was uncertain.
+
+Users of B<vi> should also look into B<vim> and B<gvim>, the mousey
+and windy version, for coloring of Perl keywords.  
+
+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.
+
+=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.  The most popular alternative debuggers for Perl is the
+Perl profiler.  Devel::DProf is now included with the standard Perl
+distribution.  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 standard Perl distribution, can be used to
+interpret the information in that profile.
+
+=head1 Debugging regular expressions
+
+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
+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">.
+
+=head1 Debugging memory usage
+
+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.
+
+=head1 SEE ALSO
 
 You did try the B<-w> switch, didn't you?
 
+L<perldebguts>,
+L<re>,
+L<DB>,
+L<Devel::Dprof>,
+L<dprofpp>,
+L<Dumpvalue>,
+and
+L<perlrun>.
+
 =head1 BUGS
 
-If your program exit()s or die()s, so does the debugger.
+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.
 
-There's no builtin way to restart the debugger without exiting and coming back
-into it.  You could use an alias like this:
+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.
 
-    $DB::alias{'rerun'} = 'exec "perl -d $DB::filename"';
+The debugger does not currently work in conjunction with the B<-W>
+command-line switch, because it itself is not free of warnings.
 
-But you'd lose any pending breakpoint information, and that might not
-be the right path, etc.
+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.