=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
the debugger all by itself just to test out Perl constructs
interactively to see what they do. For example:
- perl -d -e 42
+ $ perl -d -e 42
-In Perl, the debugger is not a separate program as it usually is in the
+In Perl, the debugger is not a separate program the way it usually is in the
typical compiled environment. Instead, the B<-d> flag tells the compiler
to insert source information into the parse trees it's about to hand off
to the interpreter. That means your code must first compile correctly
for the debugger to work on it. Then when the interpreter starts up, it
-preloads a Perl library file containing the debugger itself.
+preloads a special Perl library file containing the debugger.
The program will halt I<right before> the first run-time executable
statement (but see below regarding compile-time statements) and ask you
line it's I<about> to execute, rather than the one it has just executed.
Any command not recognized by the debugger is directly executed
-(C<eval>'d) as Perl code in the current package. (The debugger uses the
-DB package for its own state information.)
+(C<eval>'d) as Perl code in the current package. (The debugger
+uses the DB package for keeping its own state information.)
-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.
+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
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
+past your screen, precede the command with a leading pipe symbol so
+that it's run through your pager, as in
DB> |h
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.
+recursively, unlike the real C<print> function in Perl.
+See L<Dumpvalue> if you'd like to do this yourself.
-The details of printout are governed by multiple C<O>ptions.
+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 the C<main>
-package) using a data pretty-printer (hashes show their keys and values so
-you see what's what, control characters are made printable, etc.). Make
-sure you don't put the type specifier (like C<$>) there, just the symbol
-names, like this:
+Display all (or some) variables in package (defaulting to C<main>)
+using a data pretty-printer (hashes show their keys and values so
+you see what's what, control characters are made printable, etc.).
+Make sure you don't put the type specifier (like C<$>) there, just
+the symbol names, like this:
V DB filename line
-Use C<~pattern> and C<!pattern> for positive and negative regexps.
+Use C<~pattern> and C<!pattern> for positive and negative regexes.
-Nested data structures are printed out in a legible fashion, unlike
-the C<print> function.
-
-The details of printout are governed by multiple C<O>ptions.
+This is similar to calling the C<x> command on each applicable var.
=item X [vars]
=item s [expr]
-Single step. Executes until it reaches the beginning of another
+Single step. Executes until the beginning of another
statement, descending into subroutine calls. If an expression is
supplied that includes function calls, it too will be single-stepped.
=item n [expr]
-Next. Executes over subroutine calls, until it reaches the beginning
+Next. Executes over subroutine calls, until the beginning
of the next statement. If an expression is supplied that includes
function calls, those functions will be executed with stops before
each statement.
-=item E<lt>CRE<gt>
+=item r
+
+Continue until the return from the current subroutine.
+Dump the return value if the C<PrintRet> option is set (default).
+
+=item <CR>
Repeat last C<n> or C<s> command.
=item l subname
-List first window of lines from subroutine.
+List first window of lines from subroutine. I<subname> may
+be a variable that contains a code reference.
=item -
=item .
-Return debugger pointer to the last-executed line and
-print it out.
+Return the internal debugger pointer to the line last
+executed, and print out that line.
=item f filename
-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.
+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/
-Search forwards for pattern; final / is optional.
+Search forwards for pattern (a Perl regex); final / is optional.
=item ?pattern?
List all breakpoints and actions.
-=item S [[!]pattern]
+=item S [[!]regex]
-List subroutine names [not] matching pattern.
+List subroutine names [not] matching the regex.
=item t
-Toggle trace mode (see also C<AutoTrace> C<O>ption).
+Toggle trace mode (see also the C<AutoTrace> option).
=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 }
-
- 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
+Trace through execution of C<expr>.
+See L<perldebguts/"Frame Listing Output Examples"> for examples.
=item b [line] [condition]
-Set a breakpoint. If line is omitted, sets a breakpoint on the line
-that is about to be executed. If a condition is specified, it's
-evaluated each time the statement is reached and a breakpoint is taken
-only if the condition is true. Breakpoints may be set on only lines
-that begin an executable statement. Conditions don't use B<if>:
+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 B<if>:
b 237 $x > 30
b 237 ++$count237 < 11
=item b subname [condition]
-Set a breakpoint at the first line of the named subroutine.
+Set a breakpoint before the first line of the named subroutine. I<subname> may
+be a variable containing a code reference (in this case I<condition>
+is not supported).
=item b postpone subname [condition]
-Set breakpoint at first line of subroutine after it is compiled.
+Set a breakpoint at first line of subroutine after it is compiled.
=item b load filename
-Set breakpoint at the first executed line of the file. Filename should
-be a full name as found in values of %INC.
+Set a breakpoint before the first executed line of the I<filename>,
+which should be a full pathname found amongst the %INC values.
=item b compile subname
-Sets breakpoint at the first statement executed after the subroutine
-is compiled.
+Sets a breakpoint before the first statement executed after the specified
+subroutine is compiled.
=item d [line]
-Delete a breakpoint at the specified line. If line is omitted, deletes
-the breakpoint on the line that is about to be executed.
+Delete a breakpoint from the specified I<line>. If I<line> is omitted, deletes
+the breakpoint from the line about to be executed.
=item D
=item a [line] command
-Set an action to be done before the line is executed.
+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
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 installed actions.
-=item W [expr]
+=item W expr
-Add a global watch-expression.
+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 [opt[=val]] [opt"val"] [opt?]...
+=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
+
+Add an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backwhacking the newlines.
-Set or query values of options. val defaults to 1. opt can
-be abbreviated. Several options can be listed.
+=item > ?
+
+List out post-prompt Perl command actions.
+
+=item > 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 (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 { ?
+
+List out pre-prompt debugger commands.
+
+=item { [ command ]
+
+Set an action (debugger command) to happen before every debugger prompt.
+A multi-line command may be entered in the customary fashion.
+B<WARNING> If C<command> is missing, all actions are wiped out!
+
+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 previous command (defaults to the previous command).
+
+=item ! -number
+
+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 I<number> is omitted, list them all.
+
+=item q or ^D
+
+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 B<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 trailing semicolon will be
+supplied. If the Perl statement would otherwise be confused for a
+Perl debugger, use a leading semicolon, too.
+
+=item m expr
+
+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:
+
+ $DB::doccmd = 'netscape -remote http://something.here/';
+
+=back
+
+=head2 Configurable Options
+
+The debugger has numerous options settable using the C<O> command,
+either interactively or from the environment or an rc file.
=over 12
=item C<recallCommand>, C<ShellBang>
The characters used to recall command or spawn shell. By
-default, these are both set to C<!>.
+default, both are set to C<!>, which is unfortunate.
=item C<pager>
-Program to use for output of pager-piped commands (those
-beginning with a C<|> character.) By default,
-C<$ENV{PAGER}> will be used.
+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>
=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.
+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>
=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.
+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>
=item C<PrintRet>
-affects printing of return value after C<r> command.
+Print return value after C<r> command if set (default).
=item C<ornaments>
-affects screen appearance of the command line (see L<Term::ReadLine>).
+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 printing messages on entry and exit from subroutines. If
+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 may be useful if inter(di)spersed with other messages.)
+on exit might be useful if interspersed 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.
+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>
-length at which the argument list is truncated when C<frame> option's
+Length to truncate the argument list when the C<frame> option's
bit 4 is set.
=back
=item C<compactDump>, C<veryCompact>
-Change style of array and hash dump. If C<compactDump>, short array
+Change the style of array and hash output. If C<compactDump>, short array
may be printed on one line.
=item C<globPrint>
=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>.
+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>
-I<very> rudimentally per-package memory usage dump. Calculates total
-size of strings in variables in the package.
+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 can put additional initialization options C<TTY>, C<noTTY>,
+During startup, options are initialized from C<$ENV{PERLDB_OPTS}>.
+You may place the initialization options C<TTY>, C<noTTY>,
C<ReadLine>, and C<NonStop> there.
-Example rc file:
+If your rc file contains:
- &parse_options("NonStop=1 LineInfo=db.out AutoTrace");
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace");
-The script will run without human intervention, putting trace information
-into the file I<db.out>. (If you interrupt it, you would better reset
-C<LineInfo> to something "interactive"!)
+then your script will run without human intervention, putting trace
+information into the file I<db.out>. (If you interrupt it, you'd
+better reset C<LineInfo> to F</dev/tty> if you expect to see anything.)
=over 12
=item C<noTTY>
-If set, goes in C<NonStop> mode, and would not connect to a TTY. If
-interrupt (or if control goes to debugger via explicit setting of
-$DB::signal or $DB::single from the Perl script), connects to a TTY
-specified by the C<TTY> option at startup, or to a TTY found at
-runtime using C<Term::Rendezvous> module of your choice.
+If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If
+interrupted (or if control goes to the debugger via explicit setting of
+$DB::signal or $DB::single from the Perl script), it connects to a TTY
+specified in the C<TTY> option at startup, or to a tty found at
+runtime using the C<Term::Rendezvous> module of your choice.
-This module should implement a method C<new> which returns an object
-with two methods: C<IN> and C<OUT>, returning two filehandles to use
-for debugging input and output correspondingly. Method C<new> may
-inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at
-startup, or is C<"/tmp/perldbtty$$"> otherwise.
+This module should implement a method named C<new> that returns an object
+with two methods: C<IN> and C<OUT>. These should return filehandles to use
+for debugging input and output correspondingly. The C<new> method should
+inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at
+startup, or C<"/tmp/perldbtty$$"> otherwise. This file is not
+inspected for proper ownership, so security hazards are theoretically
+possible.
=item C<ReadLine>
-If false, readline support in debugger is disabled, so you can debug
-ReadLine applications.
+If false, readline support in the debugger is disabled in order
+to debug applications that themselves use ReadLine.
=item C<NonStop>
-If set, debugger goes into noninteractive mode until interrupted, or
+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="N f=2" perl -d myprogram
+ $ PERLDB_OPTS="NonStop frame=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).
+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 may include
+Other examples include
- $ PERLDB_OPTS="N f A L=listing" perl -d myprogram
+ $ PERLDB_OPTS="NonStop frame=2" 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
+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):
- $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram
+ $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out"
+ 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
+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<"Debugger Internals"> below for more details.
-
-=item E<lt> [ command ]
-
-Set an action (Perl command) to happen before every debugger prompt.
-A multi-line command may be entered by backslashing the newlines. If
-C<command> is missing, resets the list of actions.
-
-=item E<lt>E<lt> command
-
-Add an action (Perl command) to happen before every debugger prompt.
-A multi-line command may be entered by backslashing the newlines.
-
-=item E<gt> command
-
-Set an action (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 previous command (default previous command).
-
-=item ! -number
-
-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
-
-Display last n commands. Only commands longer than one character are
-listed. If number is omitted, lists them all.
-
-=item q or ^D
-
-Quit. ("quit" doesn't work for this.) This is the only supported way
-to exit the debugger, though typing C<exit> twice may do it too.
-
-Set an C<O>ption C<inhibit_exit> to 0 if you want to be able to I<step
-off> the end the script. You may also need to set C<$finished> to 0 at
-some moment if you want to step through global destruction.
-
-=item R
-
-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 m expr
-
-The expression is evaluated, and the methods which may be applied to
-the result are listed.
-
-=item m package
-
-The methods which may be applied to objects in the C<package> are listed.
-
-=back
+See L<perldebguts/"Debugger Internals"> for details.
=head2 Debugger input/output
DB<<17>>
-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.
+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, you may escape the
-newline that would normally end the debugger command with a backslash.
+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) { \
@ = 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.
+The left-hand character up there indicates the context in which the
+function was called, with C<$> and C<@> meaning scalar or list
+contexts respectively, and C<.> meaning void context (which is
+actually a sort of scalar context). The display above says
+that you were in the function C<main::infested> when you ran the
+stack dump, and that it was called in scalar context from line
+10 of the file I<Ambulation.pm>, but without any arguments at all,
+meaning it was called as C<&infested>. The next stack frame shows
+that the function C<Ambulation::legs> was called in list context
+from the I<camel_flea> file with four arguments. The last stack
+frame shows that C<main::pests> was called in scalar context,
+also from I<camel_flea>, but from line 4.
-Note that if you execute C<T> command from inside an active C<use>
-statement, the backtrace will contain both C<require>
-frame and an C<eval>) frame.
+If you execute the C<T> command from inside an active C<use>
+statement, the backtrace will contain both a C<require> frame and
+an C<eval>) frame.
-=item Listing
+=item Line Listing Format
-Listing given via different flavors of C<l> command looks like this:
+This shows the sorts of output the C<l> command can produce:
DB<<13>> l
101: @i{@i} = ();
109:a if ($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>>.
+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<< ==> >>.
=item Frame listing
-When C<frame> option is set, debugger would print entered (and
-optionally exited) subroutines in different styles.
-
-What follows is the start of the listing of
-
- env "PERLDB_OPTS=f=n N" perl -d -V
-
-for different values of C<n>:
-
-=over 4
-
-=item 1
-
- entering main::BEGIN
- entering Config::BEGIN
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- Package lib/Config.pm.
- entering Config::TIEHASH
- entering Exporter::import
- entering Exporter::export
- entering Config::myconfig
- entering Config::FETCH
- entering Config::FETCH
- entering Config::FETCH
- entering Config::FETCH
-
-=item 2
-
- entering main::BEGIN
- entering Config::BEGIN
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- exited Config::BEGIN
- Package lib/Config.pm.
- entering Config::TIEHASH
- exited Config::TIEHASH
- entering Exporter::import
- entering Exporter::export
- exited Exporter::export
- exited Exporter::import
- exited main::BEGIN
- entering Config::myconfig
- entering Config::FETCH
- exited Config::FETCH
- entering Config::FETCH
- exited Config::FETCH
- entering Config::FETCH
-
-=item 4
-
- in $=main::BEGIN() from /dev/nul:0
- in $=Config::BEGIN() from lib/Config.pm:2
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:644
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li
- in @=Config::myconfig() from /dev/nul:0
- in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'SUBVERSION') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574
-
-=item 6
-
- in $=main::BEGIN() from /dev/nul:0
- in $=Config::BEGIN() from lib/Config.pm:2
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- out $=Config::BEGIN() from lib/Config.pm:0
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:644
- out $=Config::TIEHASH('Config') from lib/Config.pm:644
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
- out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
- out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- out $=main::BEGIN() from /dev/nul:0
- in @=Config::myconfig() from /dev/nul:0
- in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
- out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
- out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574
- out $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574
- in $=Config::FETCH(ref(Config), 'SUBVERSION') from lib/Config.pm:574
-
-=item 14
-
- in $=main::BEGIN() from /dev/nul:0
- in $=Config::BEGIN() from lib/Config.pm:2
- Package lib/Exporter.pm.
- Package lib/Carp.pm.
- out $=Config::BEGIN() from lib/Config.pm:0
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:644
- out $=Config::TIEHASH('Config') from lib/Config.pm:644
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
- out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
- out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0
- out $=main::BEGIN() from /dev/nul:0
- in @=Config::myconfig() from /dev/nul:0
- in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
- out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
- in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
- out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
-
-=item 30
-
- in $=CODE(0x15eca4)() from /dev/null:0
- in $=CODE(0x182528)() from lib/Config.pm:2
- Package lib/Exporter.pm.
- out $=CODE(0x182528)() from lib/Config.pm:0
- scalar context return from CODE(0x182528): undef
- Package lib/Config.pm.
- in $=Config::TIEHASH('Config') from lib/Config.pm:628
- out $=Config::TIEHASH('Config') from lib/Config.pm:628
- scalar context return from Config::TIEHASH: empty hash
- in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
- in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
- out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
- scalar context return from Exporter::export: ''
- out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
- scalar context return from Exporter::import: ''
-
-
-=back
-
-In all the cases indentation of lines shows the call tree, if bit 2 of
-C<frame> is set, then a line is printed on exit from a subroutine as
-well, if bit 4 is set, then the arguments are printed as well as the
-caller info, if bit 8 is set, the arguments are printed even if they
-are tied or references, if bit 16 is set, the return value is printed
-as well.
-
-When a package is compiled, a line like this
-
- Package lib/Carp.pm.
-
-is printed with proper indentation.
+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 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
+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:
$DB::single = 1;
-If you set C<$DB::single> to the value 2, it's equivalent to having
+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.
-Another way to debug compile-time code is to start debugger, set a
-breakpoint on I<load> of some module thusly
+Another way to debug compile-time code is to start the debugger, set a
+breakpoint on the I<load> of some module:
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
+and then restart the debugger using the 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>.
+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
+You can do some customization by setting up a F<.perldb> file, which
contains initialization code. For instance, you could make aliases
like these (the last one is one people expect to be there):
$DB::alias{'len'} = 's/^len(.*)/p length($1)/';
$DB::alias{'stop'} = 's/^stop (at|in)/b/';
$DB::alias{'ps'} = 's/^ps\b/p scalar /';
- $DB::alias{'quit'} = 's/^quit(\s*)/exit\$/';
+ $DB::alias{'quit'} = 's/^quit(\s*)/exit/';
-One changes options from F<.perldb> file via calls like this one;
+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
+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
+subroutine C<afterinit>, that function is called after debugger
initialization ends. F<.perldb> may be contained in the current
-directory, or in the C<LOGDIR>/C<HOME> directory.
+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 modify it as necessary. You'll also want
-to set your C<PERL5DB> environment variable to say something like this:
+If you want to modify the debugger, copy F<perl5db.pl> from the
+Perl library to another name and hack it to your heart's content.
+You'll then want to set your C<PERL5DB> environment variable to say
+something like this:
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.
+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
+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.
+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 *
+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.
-Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require
-'perl5db.pl'}> if not present) before the first line of the
-application.
+Perl comes with a start file for making B<emacs> act like a
+syntax-directed editor that understands (some of) Perl's syntax.
+Look in the I<emacs> directory of the Perl source distribution.
-=item *
+A similar setup by Tom Christiansen for interacting with any
+vendor-shipped B<vi> and the X11 window system is also available.
+This works similarly to the integrated multiwindow support that
+B<emacs> provides, where the debugger drives the editor. At the
+time of this writing, however, that tool's eventual location in the
+Perl distribution was uncertain.
-The array C<@{"_E<lt>$filename"}> is the line-by-line contents of
-$filename for all the compiled files. Same for C<eval>ed strings which
-contain subroutines, or which are currently executed. The C<$filename>
-for C<eval>ed strings looks like C<(eval 34)>.
+Users of B<vi> should also look into B<vim> and B<gvim>, the mousey
+and windy version, for coloring of Perl keywords.
-=item *
+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.
-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}
- }
+=head2 The Perl Profiler
-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>.
+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:
-=head2 Debugger Internals
+ $ perl -d:DProf mycode.pl
-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.
+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.
-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.
+=head1 Debugging regular expressions
-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.
+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">.
-Some functions are provided to simplify customization. See L<"Debugger
-Customization"> for description of C<DB::parse_options(string)>. The
-function C<DB::dump_trace(skip[, count])> skips the specified number
-of frames, and returns an array containing info about the caller
-frames (all if C<count> is missing). Each entry is a hash with keys
-C<context> (C<$> or C<@>), C<sub> (subroutine name, or info about
-eval), C<args> (C<undef> or a reference to an array), C<file>, and
-C<line>.
+=head1 Debugging memory usage
-The function C<DB::print_trace(FH, skip[, count[, short]])> prints
-formatted info about caller frames. The last two functions may be
-convenient as arguments to C<E<lt>>, C<E<lt>E<lt>> commands.
+Perl contains internal support for reporting its own memory usage,
+but this is a fairly advanced concept that requires some understanding
+of how memory allocation works.
+See L<perldebguts/"Debugging Perl memory usage"> for the details.
-=head2 Other resources
+=head1 SEE ALSO
You did try the B<-w> switch, didn't you?
+L<perldebguts>,
+L<re>,
+L<DB>,
+L<Devel::Dprof>,
+L<dprofpp>,
+L<Dumpvalue>,
+and
+L<perlrun>.
+
=head1 BUGS
-You cannot get the stack frame information or otherwise debug functions
-that were not compiled by Perl, such as C or C++ extensions.
+You cannot get stack frame information or in any fashion debug functions
+that were not compiled by Perl, such as those from C or C++ extensions.
If you alter your @_ arguments in a subroutine (such as with B<shift>
or B<pop>, the stack backtrace will not show the original values.
+
+If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing
+from your keyboard or a socket) and haven't set up your own C<$SIG{INT}>
+handler, then you won't be able to CTRL-C your way back to the debugger,
+because the debugger's own C<$SIG{INT}> handler doesn't understand that
+it needs to raise an exception to longjmp(3) out of slow syscalls.
https://perl5.git.perl.org / perl5.git / blobdiff