=head1 NAME
+X<debug> X<debugger>
perldebug - Perl debugging
=head1 DESCRIPTION
-First of all, have you tried using the B<-w> switch?
+First of all, have you tried using L<C<use strict;>|strict> and
+L<C<use warnings;>|warnings>?
-=head1 The Perl Debugger
+If you're new to the Perl debugger, you may prefer to read
+L<perldebtut>, which is a tutorial introduction to the debugger.
+
+If you're looking for the nitty gritty details of how the debugger is
+I<implemented>, you may prefer to read L<perldebguts>.
-"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."
---Maurice Wilkes, 1949
+=head1 The Perl Debugger
If you invoke Perl with the B<-d> switch, your script runs under the
Perl source debugger. This works like an interactive Perl
variables, etc. This is so convenient that you often fire up
the debugger all by itself just to test out Perl constructs
interactively to see what they do. For example:
+X<-d>
- perl -d -e 42
+ $ perl -d -e 42
-In Perl, the debugger is not a separate program as it usually is in the
+In Perl, the debugger is not a separate program the way it usually is in the
typical compiled environment. Instead, the B<-d> flag tells the compiler
to insert source information into the parse trees it's about to hand off
to the interpreter. That means your code must first compile correctly
for the debugger to work on it. Then when the interpreter starts up, it
-preloads a Perl library file containing the debugger itself.
+preloads a special Perl library file containing the debugger.
The program will halt I<right before> the first run-time executable
statement (but see below regarding compile-time statements) and ask you
line it's I<about> to execute, rather than the one it has just executed.
Any command not recognized by the debugger is directly executed
-(C<eval>'d) as Perl code in the current package. (The debugger uses the
-DB package for its own state information.)
+(C<eval>'d) as Perl code in the current package. (The debugger
+uses the DB package for keeping its own state information.)
+
+Note that the said C<eval> is bound by an implicit scope. As a
+result any newly introduced lexical variable or any modified
+capture buffer content is lost after the eval. The debugger is a
+nice environment to learn Perl, but if you interactively experiment using
+material which should be in the same scope, stuff it in one line.
+
+For any text entered at the debugger prompt, leading and trailing whitespace
+is first stripped before further processing. If a debugger command
+coincides with some function in your own program, merely precede the
+function with something that doesn't look like a debugger command, such
+as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses
+or braces.
+
+=head2 Calling the Debugger
+
+There are several ways to call the debugger:
+
+=over 4
+
+=item perl -d program_name
-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.
+On the given program identified by C<program_name>.
+
+=item perl -d -e 0
+
+Interactively supply an arbitrary C<expression> using C<-e>.
+
+=item perl -d:ptkdb program_name
+
+Debug a given program via the C<Devel::ptkdb> GUI.
+
+=item perl -dt threaded_program_name
+
+Debug a given program using threads (experimental).
+
+=back
=head2 Debugger Commands
-The debugger understands the following commands:
+The interactive debugger understands the following commands:
=over 12
+=item h
+X<debugger command, h>
+
+Prints out a summary help message
+
=item h [command]
-Prints out a help message.
+Prints out a help message for the given debugger command.
+
+=item h h
-If you supply another debugger command as an argument to the C<h> command,
-it prints out the description for just that command. The special
-argument of C<h h> produces a more compact help listing, designed to fit
-together on one screen.
+The special argument of C<h h> produces the entire help page, which is quite long.
-If the output the C<h> command (or any command, for that matter) scrolls
-past your screen, either precede the command with a leading pipe symbol so
-it's run through your pager, as in
+If the output of the C<h h> command (or any command, for that matter) scrolls
+past your screen, precede the command with a leading pipe symbol so
+that it's run through your pager, as in
- DB> |h
+ DB> |h h
-You may change the pager which is used via C<O pager=...> command.
+You may change the pager which is used via C<o pager=...> command.
=item p expr
+X<debugger command, p>
Same as C<print {$DB::OUT} expr> in the current package. In particular,
-because this is just Perl's own
B<print> function, this means that nested
+because this is just Perl's own
C<print> function, this means that nested
data structures and objects are not dumped, unlike with the C<x> command.
The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of
where STDOUT may be redirected to.
-=item x expr
+=item x [maxdepth] expr
+X<debugger command, x>
+
+Evaluates its expression in list context and dumps out the result in a
+pretty-printed fashion. Nested data structures are printed out
+recursively, unlike the real C<print> function in Perl. When dumping
+hashes, you'll probably prefer 'x \%h' rather than 'x %h'.
+See L<Dumpvalue> if you'd like to do this yourself.
-Evaluates its expression in list context and dumps out the result
-in a pretty-printed fashion. Nested data structures are printed out
-recursively, unlike the C<print> function.
+The output format is governed by multiple options described under
+L</"Configurable Options">.
-The details of printout are governed by multiple C<O>ptions.
+If the C<maxdepth> is included, it must be a numeral I<N>; the value is
+dumped only I<N> levels deep, as if the C<dumpDepth> option had been
+temporarily set to I<N>.
=item V [pkg [vars]]
+X<debugger command, V>
-Display all (or some) variables in package (defaulting to the C<main>
-package) using a data pretty-printer (hashes show their keys and values so
-you see what's what, control characters are made printable, etc.). Make
-sure you don't put the type specifier (like C<$>) there, just the symbol
-names, like this:
+Display all (or some) variables in package (defaulting to C<main>)
+using a data pretty-printer (hashes show their keys and values so
+you see what's what, control characters are made printable, etc.).
+Make sure you don't put the type specifier (like C<$>) there, just
+the symbol names, like this:
V DB filename line
-Use C<~pattern> and C<!pattern> for positive and negative regexps.
+Use C<~pattern> and C<!pattern> for positive and negative regexes.
-Nested data structures are printed out in a legible fashion, unlike
-the C<print> function.
-
-The details of printout are governed by multiple C<O>ptions.
+This is similar to calling the C<x> command on each applicable var.
=item X [vars]
+X<debugger command, X>
Same as C<V currentpackage [vars]>.
+=item y [level [vars]]
+X<debugger command, y>
+
+Display all (or some) lexical variables (mnemonic: C<mY> variables)
+in the current scope or I<level> scopes higher. You can limit the
+variables that you see with I<vars> which works exactly as it does
+for the C<V> and C<X> commands. Requires the C<PadWalker> module
+version 0.08 or higher; will warn if this isn't installed. Output
+is pretty-printed in the same style as for C<V> and the format is
+controlled by the same options.
+
=item T
+X<debugger command, T> X<backtrace> X<stack, backtrace>
Produce a stack backtrace. See below for details on its output.
=item s [expr]
+X<debugger command, s> X<step>
-Single step. Executes until it reaches the beginning of another
+Single step. Executes until the beginning of another
statement, descending into subroutine calls. If an expression is
supplied that includes function calls, it too will be single-stepped.
=item n [expr]
+X<debugger command, n>
-Next. Executes over subroutine calls, until it reaches the beginning
+Next. Executes over subroutine calls, until the beginning
of the next statement. If an expression is supplied that includes
function calls, those functions will be executed with stops before
each statement.
-=item E<lt>CRE<gt>
+=item r
+X<debugger command, r>
+
+Continue until the return from the current subroutine.
+Dump the return value if the C<PrintRet> option is set (default).
+
+=item <CR>
Repeat last C<n> or C<s> command.
=item c [line|sub]
+X<debugger command, c>
Continue, optionally inserting a one-time-only breakpoint
at the specified line or subroutine.
=item l
+X<debugger command, l>
List next window of lines.
=item l subname
-List first window of lines from subroutine.
+List first window of lines from subroutine. I<subname> may
+be a variable that contains a code reference.
=item -
+X<debugger command, ->
List previous window of lines.
-=item w [line]
+=item v [line]
+X<debugger command, v>
-List window (a few lines) around the current line.
+View a few lines of code around the current line.
=item .
+X<debugger command, .>
-Return debugger pointer to the last-executed line and
-print it out.
+Return the internal debugger pointer to the line last
+executed, and print out that line.
=item f filename
+X<debugger command, f>
-Switch to viewing a different file or 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.
+The search is case-insensitive by default.
=item ?pattern?
Search backwards for pattern; final ? is optional.
+The search is case-insensitive by default.
-=item L
-
-List all breakpoints and actions.
+=item L [abw]
+X<debugger command, L>
-=item S [[!]pattern]
+List (default all) actions, breakpoints and watch expressions
-List subroutine names [not] matching pattern.
+=item S [[!]regex]
+X<debugger command, S>
-=item t
+List subroutine names [not] matching the regex.
-Toggle trace mode (see also C<AutoTrace> C<O>ption).
+=item t [n]
+X<debugger command, t>
-=item t expr
+Toggle trace mode (see also the C<AutoTrace> option).
+Optional argument is the maximum number of levels to trace below
+the current one; anything deeper than that will be silent.
-Trace through execution of expr. For example:
+=item t [n] expr
+X<debugger command, t>
- $ perl -de 42
- Stack dump during die enabled outside of evals.
+Trace through execution of C<expr>.
+Optional first argument is the maximum number of levels to trace below
+the current one; anything deeper than that will be silent.
+See L<perldebguts/"Frame Listing Output Examples"> for examples.
- Loading DB routines from perl5db.pl patch level 0.94
- Emacs support available.
+=item b
+X<breakpoint>
+X<debugger command, b>
- Enter h or `h h' for help.
+Sets breakpoint on current line
- main::(-e:1): 0
- DB<1> sub foo { 14 }
+=item b [line] [condition]
+X<breakpoint>
+X<debugger command, b>
- DB<2> sub bar { 3 }
+Set a breakpoint before the given line. If a condition
+is specified, it's evaluated each time the statement is reached: a
+breakpoint is taken only if the condition is true. Breakpoints may
+only be set on lines that begin an executable statement. Conditions
+don't use C<if>:
- DB<3> t print foo() * bar()
- main::((eval 172):3): print foo() + bar();
- main::foo((eval 168):2):
- main::bar((eval 170):2):
- 42
+ b 237 $x > 30
+ b 237 ++$count237 < 11
+ b 33 /pattern/i
-or, with the C<O>ption C<frame=2> set,
+If the line number is C<.>, sets a breakpoint on the current line:
- DB<4> O f=2
- frame = '2'
- DB<5> t print foo() * bar()
- 3: foo() * bar()
- entering main::foo
- 2: sub foo { 14 };
- exited main::foo
- entering main::bar
- 2: sub bar { 3 };
- exited main::bar
- 42
+ b . $n > 100
-=item b [line] [condition]
+=item b [file]:[line] [condition]
+X<breakpoint>
+X<debugger command, b>
-Set a breakpoint. If line is omitted, sets a breakpoint on the line
-that is about to be executed. If a condition is specified, it's
-evaluated each time the statement is reached and a breakpoint is taken
-only if the condition is true. Breakpoints may be set on only lines
-that begin an executable statement. Conditions don't use B<if>:
+Set a breakpoint before the given line in a (possibly different) file. If a
+condition is specified, it's evaluated each time the statement is reached: a
+breakpoint is taken only if the condition is true. Breakpoints may only be set
+on lines that begin an executable statement. Conditions don't use C<if>:
- b 237 $x > 30
- b 237 ++$count237 < 11
- b 33 /pattern/i
+ b lib/MyModule.pm:237 $x > 30
+ b /usr/lib/perl5/site_perl/CGI.pm:100 ++$count100 < 11
=item b subname [condition]
+X<breakpoint>
+X<debugger command, b>
-Set a breakpoint at the first line of the named subroutine.
+Set a breakpoint before the first line of the named subroutine. I<subname> may
+be a variable containing a code reference (in this case I<condition>
+is not supported).
=item b postpone subname [condition]
+X<breakpoint>
+X<debugger command, b>
-Set breakpoint at first line of subroutine after it is compiled.
+Set a breakpoint at first line of subroutine after it is compiled.
=item b load filename
+X<breakpoint>
+X<debugger command, b>
-Set breakpoint at the first executed line of the file. Filename should
-be a full name as found in values of %INC.
+Set a breakpoint before the first executed line of the I<filename>,
+which should be a full pathname found amongst the %INC values.
=item b compile subname
+X<breakpoint>
+X<debugger command, b>
-Sets breakpoint at the first statement executed after the subroutine
-is compiled.
+Sets a breakpoint before the first statement executed after the specified
+subroutine is compiled.
-=item d [line]
+=item B line
+X<breakpoint>
+X<debugger command, B>
-Delete a breakpoint at the specified line. If line is omitted, deletes
-the breakpoint on the line that is about to be executed.
+Delete a breakpoint from the specified I<line>.
-=item D
+=item B *
+X<breakpoint>
+X<debugger command, B>
Delete all installed breakpoints.
+=item disable [file]:[line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
+
+Disable the breakpoint so it won't stop the execution of the program.
+Breakpoints are enabled by default and can be re-enabled using the C<enable>
+command.
+
+=item disable [line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
+
+Disable the breakpoint so it won't stop the execution of the program.
+Breakpoints are enabled by default and can be re-enabled using the C<enable>
+command.
+
+This is done for a breakpoint in the current file.
+
+=item enable [file]:[line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
+
+Enable the breakpoint so it will stop the execution of the program.
+
+=item enable [line]
+X<breakpoint>
+X<debugger command, disable>
+X<disable>
+
+Enable the breakpoint so it will stop the execution of the program.
+
+This is done for a breakpoint in the current file.
+
=item a [line] command
+X<debugger command, a>
-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
4. prompt user if at a breakpoint or in single-step
5. evaluate line
-For example, this will print out C<$foo> every time line
+For example, this will print out $foo every time line
53 is passed:
a 53 print "DB FOUND $foo\n"
-=item A
+=item A line
+X<debugger command, A>
+
+Delete an action from the specified line.
+
+=item A *
+X<debugger command, A>
Delete all installed actions.
-=item O [opt[=val]] [opt"val"] [opt?]...
+=item w expr
+X<debugger command, w>
-Set or query values of options. val defaults to 1. opt can
-be abbreviated. Several options can be listed.
+Add a global watch-expression. Whenever a watched global changes the
+debugger will stop and display the old and new values.
-=over 12
+=item W expr
+X<debugger command, W>
-=item C<recallCommand>, C<ShellBang>
+Delete watch-expression
-The characters used to recall command or spawn shell. By
-default, these are both set to C<!>.
+=item W *
+X<debugger command, W>
-=item C<pager>
+Delete all watch-expressions.
-Program to use for output of pager-piped commands (those
-beginning with a C<|> character.) By default,
-C<$ENV{PAGER}> will be used.
+=item o
+X<debugger command, o>
-=item C<tkRunning>
+Display all options.
-Run Tk while prompting (with ReadLine).
+=item o booloption ...
+X<debugger command, o>
-=item C<signalLevel>, C<warnLevel>, C<dieLevel>
+Set each listed Boolean option to the value C<1>.
-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.
+=item o anyoption? ...
+X<debugger command, o>
-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.
+Print out the value of one or more options.
-=item C<AutoTrace>
+=item o option=value ...
+X<debugger command, o>
-Trace mode (similar to C<t> command, but can be put into
-C<PERLDB_OPTS>).
+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?\"">.
-=item C<LineInfo>
+For historical reasons, the C<=value> is optional, but defaults to
+1 only where it is safe to do so--that is, mostly for Boolean
+options. It is always better to assign a specific value using C<=>.
+The C<option> can be abbreviated, but for clarity probably should
+not be. Several options can be set together. See L</"Configurable Options">
+for a list of these.
-File or pipe to print line number info to. If it is a pipe (say,
-C<|visual_perl_db>), then a short, "emacs like" message is used.
+=item < ?
+X<< debugger command, < >>
-=item C<inhibit_exit>
+List out all pre-prompt Perl command actions.
-If 0, allows I<stepping off> the end of the script.
+=item < [ command ]
+X<< debugger command, < >>
-=item C<PrintRet>
+Set an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backslashing the newlines.
-affects printing of return value after C<r> command.
+=item < *
+X<< debugger command, < >>
-=item C<ornaments>
+Delete all pre-prompt Perl command actions.
-affects screen appearance of the command line (see L<Term::ReadLine>).
+=item << command
+X<< debugger command, << >>
-=item C<frame>
+Add an action (Perl command) to happen before every debugger prompt.
+A multi-line command may be entered by backwhacking the newlines.
-affects printing messages on entry and exit from subroutines. If
-C<frame & 2> is false, messages are printed on entry only. (Printing
-on exit may be useful if inter(di)spersed with other messages.)
+=item > ?
+X<< debugger command, > >>
-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.
+List out post-prompt Perl command actions.
-The length at which the argument list is truncated is governed by the
-next option:
+=item > command
+X<< debugger command, > >>
-=item C<maxTraceLen>
+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 have guessed this by now).
-length at which the argument list is truncated when C<frame> option's
-bit 4 is set.
+=item > *
+X<< debugger command, > >>
-=back
+Delete all post-prompt Perl command actions.
-The following options affect what happens with C<V>, C<X>, and C<x>
-commands:
+=item >> command
+X<<< debugger command, >> >>>
-=over 12
+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 C<arrayDepth>, C<hashDepth>
+=item { ?
+X<debugger command, {>
-Print only first N elements ('' for all).
+List out pre-prompt debugger commands.
-=item C<compactDump>, C<veryCompact>
+=item { [ command ]
-Change style of array and hash dump. If C<compactDump>, short array
-may be printed on one line.
+Set an action (debugger command) to happen before every debugger prompt.
+A multi-line command may be entered in the customary fashion.
-=item C<globPrint>
+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 { ... }>.
-Whether to print contents of globs.
+=item { *
+X<debugger command, {>
-=item C<DumpDBFiles>
+Delete all pre-prompt debugger commands.
-Dump arrays holding debugged files.
+=item {{ command
+X<debugger command, {{>
-=item C<DumpPackages>
+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.
-Dump symbol tables of packages.
+=item ! number
+X<debugger command, !>
-=item C<quote>, C<HighBit>, C<undefPrint>
+Redo a previous command (defaults to the previous command).
-Change style of string dump. Default value of C<quote> is C<auto>, one
-can enable either double-quotish dump, or single-quotish by setting it
-to C<"> or C<'>. By default, characters with high bit set are printed
-I<as is>.
+=item ! -number
+X<debugger command, !>
-=item C<UsageOnly>
+Redo number'th previous command.
-I<very> rudimentally per-package memory usage dump. Calculates total
-size of strings in variables in the package.
+=item ! pattern
+X<debugger command, !>
-=back
+Redo last command that started with pattern.
+See C<o recallCommand>, too.
-During startup options are initialized from C<$ENV{PERLDB_OPTS}>.
-You can put additional initialization options C<TTY>, C<noTTY>,
-C<ReadLine>, and C<NonStop> there.
+=item !! cmd
+X<debugger command, !!>
-Example rc file:
+Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See
+C<o shellBang>, also. Note that the user's current shell (well,
+their C<$ENV{SHELL}> variable) will be used, which can interfere
+with proper interpretation of exit status or signal and coredump
+information.
- &parse_options("NonStop=1 LineInfo=db.out AutoTrace");
+=item source file
+X<debugger command, source>
-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"!)
+Read and execute debugger commands from I<file>.
+I<file> may itself contain C<source> commands.
-=over 12
+=item H -number
+X<debugger command, H>
-=item C<TTY>
+Display last n commands. Only commands longer than one character are
+listed. If I<number> is omitted, list them all.
-The TTY to use for debugging I/O.
+=item q or ^D
+X<debugger command, q>
+X<debugger command, ^D>
-=item C<noTTY>
+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.
-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.
+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 $finished to 0
+if you want to step through global destruction.
-This module should implement a method C<new> which returns an object
-with two methods: C<IN> and C<OUT>, returning two filehandles to use
-for debugging input and output correspondingly. Method C<new> may
-inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at
-startup, or is C<"/tmp/perldbtty$$"> otherwise.
+=item R
+X<debugger command, R>
-=item C<ReadLine>
+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.
-If false, readline support in debugger is disabled, so you can debug
-ReadLine applications.
+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 C<NonStop>
+=item |dbcmd
+X<debugger command, |>
-If set, debugger goes into noninteractive mode until interrupted, or
-programmatically by setting $DB::signal or $DB::single.
+Run the debugger command, piping DB::OUT into your current pager.
-=back
+=item ||dbcmd
+X<debugger command, ||>
-Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
+Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well.
- $ PERLDB_OPTS="N f=2" perl -d myprogram
+=item = [alias value]
+X<debugger command, =>
-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).
+Define a command alias, like
-Other examples may include
+ = quit q
- $ PERLDB_OPTS="N f A L=listing" perl -d myprogram
+or list current aliases.
-- runs script noninteractively, printing info on each entry into a
-subroutine and each executed line into the file F<listing>. (If you
-interrupt it, you would better reset C<LineInfo> to something
-"interactive"!)
+=item 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.
- $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram
+=item m expr
+X<debugger command, m>
-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
+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.
- $ sleep 1000000
+=item M
+X<debugger command, M>
-See L<"Debugger Internals"> below for more details.
+Display all loaded modules and their versions.
-=item E<lt> [ command ]
+=item man [manpage]
+X<debugger command, man>
-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.
+Despite its name, this calls your system's default documentation
+viewer on the given page, or on the viewer itself if I<manpage> is
+omitted. If that viewer is B<man>, the current C<Config> information
+is used to invoke B<man> using the proper MANPATH or S<B<-M>
+I<manpath>> option. Failed lookups of the form C<XXX> that match
+known manpages of the form I<perlXXX> will be retried. This lets
+you type C<man debug> or C<man op> from the debugger.
-=item E<lt>E<lt> command
+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:
-Add an action (Perl command) to happen before every debugger prompt.
-A multi-line command may be entered by backslashing the newlines.
+ $DB::doccmd = 'netscape -remote http://something.here/';
-=item E<gt> command
+=back
-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.
+=head2 Configurable Options
-=item E<gt>E<gt> command
+The debugger has numerous options settable using the C<o> command,
+either interactively or from the environment or an rc file.
+(./.perldb or ~/.perldb under Unix.)
-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 ]
+=over 12
-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 C<recallCommand>, C<ShellBang>
+X<debugger option, recallCommand>
+X<debugger option, ShellBang>
-=item {{ command
+The characters used to recall a command or spawn a shell. By
+default, both are set to C<!>, which is unfortunate.
-Add an action (debugger command) to happen before every debugger prompt.
-A multi-line command may be entered by backslashing the newlines.
+=item C<pager>
+X<debugger option, pager>
-=item ! number
+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.
-Redo a previous command (default previous command).
+=item C<tkRunning>
+X<debugger option, tkRunning>
-=item ! -number
+Run Tk while prompting (with ReadLine).
-Redo number'th-to-last command.
+=item C<signalLevel>, C<warnLevel>, C<dieLevel>
+X<debugger option, signalLevel> X<debugger option, warnLevel>
+X<debugger option, dieLevel>
+
+Level of verbosity. By default, the debugger leaves your exceptions
+and warnings alone, because altering them can break correctly running
+programs. It will attempt to print a message when uncaught INT, BUS, or
+SEGV signals arrive. (But see the mention of signals in L</BUGS> below.)
+
+To disable this default safe mode, set these values to something higher
+than 0. At a level of 1, you get backtraces upon receiving any kind
+of warning (this is often annoying) or exception (this is
+often valuable). Unfortunately, the debugger cannot discern fatal
+exceptions from non-fatal ones. If C<dieLevel> is even 1, then your
+non-fatal exceptions are also traced and unceremoniously altered if they
+came from C<eval'ed> strings or from any kind of C<eval> within modules
+you're attempting to load. If C<dieLevel> is 2, the debugger doesn't
+care where they came from: It usurps your exception handler and prints
+out a trace, then modifies all exceptions with its own embellishments.
+This may perhaps be useful for some tracing purposes, but tends to hopelessly
+destroy any program that takes its exception handling seriously.
-=item ! pattern
+=item C<AutoTrace>
+X<debugger option, AutoTrace>
-Redo last command that started with pattern.
-See C<O recallCommand>, too.
+Trace mode (similar to C<t> command, but can be put into
+C<PERLDB_OPTS>).
-=item !! cmd
+=item C<LineInfo>
+X<debugger option, LineInfo>
-Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT)
-See C<O shellBang> too.
+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 H -number
+=item C<inhibit_exit>
+X<debugger option, inhibit_exit>
-Display last n commands. Only commands longer than one character are
-listed. If number is omitted, lists them all.
+If 0, allows I<stepping off> the end of the script.
-=item q or ^D
+=item C<PrintRet>
+X<debugger option, PrintRet>
-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.
+Print return value after C<r> command if set (default).
-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 C<ornaments>
+X<debugger option, ornaments>
-=item R
+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.
-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.
+=item C<frame>
+X<debugger option, frame>
-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>.
+Affects the printing of messages upon entry and exit from subroutines. If
+C<frame & 2> is false, messages are printed on entry only. (Printing
+on exit might be useful if interspersed with other messages.)
-=item |dbcmd
+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.
-Run debugger command, piping DB::OUT to current pager.
+The length at which the argument list is truncated is governed by the
+next option:
-=item ||dbcmd
+=item C<maxTraceLen>
+X<debugger option, maxTraceLen>
-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
+Length to truncate the argument list when the C<frame> option's
+bit 4 is set.
- |V main
+=item C<windowSize>
+X<debugger option, windowSize>
-=item = [alias value]
+Change the size of code list window (default is 10 lines).
-Define a command alias, like
+=back
- = quit q
+The following options affect what happens with C<V>, C<X>, and C<x>
+commands:
-or list current aliases.
+=over 12
-=item command
+=item C<arrayDepth>, C<hashDepth>
+X<debugger option, arrayDepth> X<debugger option, hashDepth>
-Execute command as a Perl statement. A missing semicolon will be
-supplied.
+Print only first N elements ('' for all).
-=item m expr
+=item C<dumpDepth>
+X<debugger option, dumpDepth>
-The expression is evaluated, and the methods which may be applied to
-the result are listed.
+Limit recursion depth to N levels when dumping structures.
+Negative values are interpreted as infinity. Default: infinity.
-=item m package
+=item C<compactDump>, C<veryCompact>
+X<debugger option, compactDump> X<debugger option, veryCompact>
-The methods which may be applied to objects in the C<package> are listed.
+Change the style of array and hash output. If C<compactDump>, short array
+may be printed on one line.
-=back
+=item C<globPrint>
+X<debugger option, globPrint>
-=head2 Debugger input/output
+Whether to print contents of globs.
-=over 8
+=item C<DumpDBFiles>
+X<debugger option, DumpDBFiles>
-=item Prompt
+Dump arrays holding debugged files.
-The debugger prompt is something like
+=item C<DumpPackages>
+X<debugger option, DumpPackages>
- DB<8>
+Dump symbol tables of packages.
-or even
+=item C<DumpReused>
+X<debugger option, DumpReused>
- DB<<17>>
+Dump contents of "reused" addresses.
-where that number is the command number, which you'd use to access with
-the builtin B<csh>-like history mechanism, e.g., C<!17> would repeat
-command number 17. The number of angle brackets indicates the depth of
-the debugger. You could get more than one set of brackets, for example, if
-you'd already at a breakpoint and then printed out the result of a
-function call that itself also has a breakpoint, or you step into an
-expression via C<s/n/t expression> command.
+=item C<quote>, C<HighBit>, C<undefPrint>
+X<debugger option, quote> X<debugger option, HighBit>
+X<debugger option, undefPrint>
-=item Multiline commands
+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.
-If you want to enter a multi-line command, such as a subroutine
-definition with several statements, or a format, you may escape the
-newline that would normally end the debugger command with a backslash.
-Here's an example:
+=item C<UsageOnly>
+X<debugger option, UsageOnly>
- DB<1> for (1..4) { \
- cont: print "ok\n"; \
- cont: }
- ok
- ok
- ok
- ok
+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.
-Note that this business of escaping a newline is specific to interactive
-commands typed into the debugger.
+=item C<HistFile>
+X<debugger option, history, HistFile>
-=item Stack backtrace
+The path of the file from which the history (assuming a usable
+Term::ReadLine backend) will be read on the debugger's startup, and to which
+it will be saved on shutdown (for persistence across sessions). Similar in
+concept to Bash's C<.bash_history> file.
-Here's an example of what a stack backtrace via C<T> command might
-look like:
+=item C<HistSize>
+X<debugger option, history, HistSize>
- $ = main::infested called from file `Ambulation.pm' line 10
- @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7
- $ = main::pests('bactrian', 4) called from file `camel_flea' line 4
-
-The left-hand character up there tells whether the function was called
-in a scalar or list context (we bet you can tell which is which). What
-that says is that you were in the function C<main::infested> when you ran
-the stack dump, and that it was called in a scalar context from line 10
-of the file I<Ambulation.pm>, but without any arguments at all, meaning
-it was called as C<&infested>. The next stack frame shows that the
-function C<Ambulation::legs> was called in a list context from the
-I<camel_flea> file with four arguments. The last stack frame shows that
-C<main::pests> was called in a scalar context, also from I<camel_flea>,
-but from line 4.
-
-Note that if you execute C<T> command from inside an active C<use>
-statement, the backtrace will contain both C<L<perlfunc/require>>
-frame and an C<L<perlfunc/eval EXPR>>) frame.
-
-=item Listing
-
-Listing given via different flavors of C<l> command looks like this:
-
- DB<<13>> l
- 101: @i{@i} = ();
- 102:b @isa{@i,$pack} = ()
- 103 if(exists $i{$prevpack} || exists $isa{$pack});
- 104 }
- 105
- 106 next
- 107==> if(exists $isa{$pack});
- 108
- 109:a if ($extra-- > 0) {
- 110: %isa = ($pack,1);
-
-Note that the breakable lines are marked with C<:>, lines with
-breakpoints are marked by C<b>, with actions by C<a>, and the
-next executed line is marked by C<==E<gt>>.
+The count of the saved lines in the history (assuming C<HistFile> above).
-=item Frame listing
+=back
-When C<frame> option is set, debugger would print entered (and
-optionally exited) subroutines in different styles.
+After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}>
+environment variable and parses this as the remainder of a "O ..."
+line as one might enter at the debugger prompt. You may place the
+initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop>
+there.
-What follows is the start of the listing of
+If your rc file contains:
- env "PERLDB_OPTS=f=n N" perl -d -V
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace");
-for different values of C<n>:
+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 4
+=over 12
-=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: ''
+=item C<TTY>
+X<debugger option, TTY>
+The TTY to use for debugging I/O.
-=back
+=item C<noTTY>
+X<debugger option, noTTY>
+
+If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If
+interrupted (or if control goes to the debugger via explicit setting of
+$DB::signal or $DB::single from the Perl script), it connects to a TTY
+specified in the C<TTY> option at startup, or to a tty found at
+runtime using the C<Term::Rendezvous> module of your choice.
+
+This module should implement a method named C<new> that returns an object
+with two methods: C<IN> and C<OUT>. These should return filehandles to use
+for debugging input and output correspondingly. The C<new> method should
+inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at
+startup, or C<"$ENV{HOME}/.perldbtty$$"> otherwise. This file is not
+inspected for proper ownership, so security hazards are theoretically
+possible.
-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.
+=item C<ReadLine>
+X<debugger option, ReadLine>
-When a package is compiled, a line like this
+If false, readline support in the debugger is disabled in order
+to debug applications that themselves use ReadLine.
- Package lib/Carp.pm.
+=item C<NonStop>
+X<debugger option, NonStop>
-is printed with proper indentation.
+If set, the debugger goes into non-interactive mode until interrupted, or
+programmatically by setting $DB::signal or $DB::single.
=back
-=head2 Debugging compile-time statements
+Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
-If you have any compile-time executable statements (code within a BEGIN
-block or a C<use> statement), these will C<NOT> be stopped by debugger,
-although C<require>s will (and compile-time statements can be traced
-with C<AutoTrace> option set in C<PERLDB_OPTS>). From your own Perl
-code, however, you can
-transfer control back to the debugger using the following statement,
-which is harmless if the debugger is not running:
+ $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram
- $DB::single = 1;
+That will run the script B<myprogram> without human intervention,
+printing out the call tree with entry and exit points. Note that
+C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally,
+options could be uniquely abbreviated by the first letter (modulo
+the C<Dump*> options). It is nevertheless recommended that you
+always spell them out in full for legibility and future compatibility.
-If you set C<$DB::single> to the value 2, it's equivalent to having
-just typed the C<n> command, whereas a value of 1 means the C<s>
-command. The C<$DB::trace> variable should be set to 1 to simulate
-having typed the C<t> command.
+Other examples include
-Another way to debug compile-time code is to start debugger, set a
-breakpoint on I<load> of some module thusly
+ $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram
- DB<7> b load f:/perllib/lib/Carp.pm
- Will stop on load of `f:/perllib/lib/Carp.pm'.
+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"!)
-and restart debugger by C<R> command (if possible). One can use C<b
-compile subname> for the same purpose.
+Other examples include (using standard shell syntax to show environment
+variable settings):
-=head2 Debugger Customization
+ $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out"
+ perl -d myprogram )
-Most probably you not want to modify the debugger, it contains enough
-hooks to satisfy most needs. You may change the behaviour of debugger
-from the debugger itself, using C<O>ptions, from the command line via
-C<PERLDB_OPTS> environment variable, and from I<customization files>.
+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
-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\$/';
+ $ sleep 1000000
-One changes options from F<.perldb> file via calls like this one;
+See L<perldebguts/"Debugger Internals"> for details.
- parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2");
+=head2 Debugger Input/Output
-(the code is executed in the package C<DB>). Note that F<.perldb> is
-processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the
-subroutine C<afterinit>, it is called after all the debugger
-initialization ends. F<.perldb> may be contained in the current
-directory, or in the C<LOGDIR>/C<HOME> directory.
+=over 8
-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:
+=item Prompt
- BEGIN { require "myperl5db.pl" }
+The debugger prompt is something like
-As the last resort, one can use C<PERL5DB> to customize debugger by
-directly setting internal variables or calling debugger functions.
+ DB<8>
-=head2 Readline Support
+or even
-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.
+ DB<<17>>
-A rudimentary command line completion is also available.
-Unfortunately, the names of lexical variables are not available for
-completion.
+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.
-=head2 Editor Support for Debugging
+=item Multiline commands
-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.
+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:
-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.
+ DB<1> for (1..4) { \
+ cont: print "ok\n"; \
+ cont: }
+ ok
+ ok
+ ok
+ ok
-(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.)
+Note that this business of escaping a newline is specific to interactive
+commands typed into the debugger.
-=head2 The Perl Profiler
+=item Stack backtrace
+X<backtrace> X<stack, backtrace>
-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".
+Here's an example of what a stack backtrace via C<T> command might
+look like:
-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:
+ $ = 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.
- perl -d:DProf mycode.pl
+=item Frame listing
-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.
+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.
-=head2 Debugger support in perl
+=back
-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.
+=head2 Debugging Compile-Time Statements
-If perl is run with B<-d> option, the following additional features
-are enabled:
+If you have compile-time executable statements (such as code within
+BEGIN, UNITCHECK and CHECK blocks or C<use> statements), these will
+I<not> be stopped by debugger, although C<require>s and INIT blocks
+will, and compile-time statements can be traced with the C<AutoTrace>
+option set in C<PERLDB_OPTS>). From your own Perl code, however, you
+can transfer control back to the debugger using the following
+statement, which is harmless if the debugger is not running:
-=over
+ $DB::single = 1;
-=item *
+If you set C<$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<$DB::trace> variable should be set to 1 to simulate
+having typed the C<t> command.
-Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require
-'perl5db.pl'}> if not present) before the first line of the
-application.
+Another way to debug compile-time code is to start the debugger, set a
+breakpoint on the I<load> of some module:
-=item *
+ DB<7> b load f:/perllib/lib/Carp.pm
+ Will stop on load of 'f:/perllib/lib/Carp.pm'.
-The array C<@{"_<$filename"}> is the line-by-line contents of
-$filename for all the compiled files. Same for C<eval>ed strings which
-contain subroutines, or which are currently executed. The C<$filename>
-for C<eval>ed strings looks like C<(eval 34)>.
+and then restart the debugger using the C<R> command (if possible). One can use C<b
+compile subname> for the same purpose.
-=item *
+=head2 Debugger Customization
-The hash C<%{"_<$filename"}> contains breakpoints and action (it is
-keyed by line number), and individual entries are settable (as opposed
-to the whole hash). Only true/false is important to Perl, though the
-values used by F<perl5db.pl> have the form
-C<"$break_condition\0$action">. Values are magical in numeric context:
-they are zeros if the line is not breakable.
+The debugger probably contains enough configuration hooks that you
+won't ever have to modify it yourself. You may change the behaviour
+of the debugger from within the debugger using its C<o> command, from
+the command line via the C<PERLDB_OPTS> environment variable, and
+from customization files.
-Same for evaluated strings which contain subroutines, or which are
-currently executed. The C<$filename> for C<eval>ed strings looks like
-C<(eval 34)>.
+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):
-=item *
+ $DB::alias{'len'} = 's/^len(.*)/p length($1)/';
+ $DB::alias{'stop'} = 's/^stop (at|in)/b/';
+ $DB::alias{'ps'} = 's/^ps\b/p scalar /';
+ $DB::alias{'quit'} = 's/^quit(\s*)/exit/';
-The scalar C<${"_<$filename"}> contains C<"_<$filename">. Same for
-evaluated strings which contain subroutines, or which are currently
-executed. The C<$filename> for C<eval>ed strings looks like C<(eval
-34)>.
+You can change options from F<.perldb> by using calls like this one;
-=item *
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2");
-After each C<require>d file is compiled, but before it is executed,
-C<DB::postponed(*{"_<$filename"})> is called (if subroutine
-C<DB::postponed> exists). Here the $filename is the expanded name of
-the C<require>d file (as found in values of C<%INC>).
+The code is executed in the package C<DB>. Note that F<.perldb> is
+processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the
+subroutine C<afterinit>, that function is called after debugger
+initialization ends. F<.perldb> may be contained in the current
+directory, or in the home directory. Because this file is sourced
+in by Perl and may contain arbitrary commands, for security reasons,
+it must be owned by the superuser or the current user, and writable
+by no one but its owner.
-=item *
+You can mock TTY input to debugger by adding arbitrary commands to
+@DB::typeahead. For example, your F<.perldb> file might contain:
-After each subroutine C<subname> is compiled existence of
-C<$DB::postponed{subname}> is checked. If this key exists,
-C<DB::postponed(subname)> is called (if subroutine C<DB::postponed>
-exists).
+ sub afterinit { push @DB::typeahead, "b 4", "b 6"; }
-=item *
+Which would attempt to set breakpoints on lines 4 and 6 immediately
+after debugger initialization. Note that @DB::typeahead is not a supported
+interface and is subject to change in future releases.
-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.
+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:
-=item *
+ BEGIN { require "myperl5db.pl" }
-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)>).
+As a last resort, you could also use C<PERL5DB> to customize the debugger
+by directly setting internal variables or calling debugger functions.
-=item *
+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.
-When execution of the application reaches a subroutine call, a call
-to C<&DB::sub>(I<args>) is performed instead, with C<$DB::sub> being
-the name of the called subroutine. (Unless the subroutine is compiled
-in the package C<DB>.)
+=head2 Readline Support / History in the Debugger
-=back
+As shipped, the only command-line history supplied is a simplistic one
+that checks for leading exclamation points. However, if you install
+the Term::ReadKey and Term::ReadLine modules from CPAN (such as
+Term::ReadLine::Gnu, Term::ReadLine::Perl, ...) you will
+have full editing capabilities much like those GNU I<readline>(3) provides.
+Look for these in the F<modules/by-module/Term> directory on CPAN.
+These do not support normal B<vi> command-line editing, however.
-Note that no subroutine call is possible until C<&DB::sub> is defined
-(for subroutines outside of package C<DB>). (This restriction is
-recently lifted.)
+A rudimentary command-line completion is also available, including
+lexical variables in the current scope if the C<PadWalker> module
+is installed.
-(In fact, for the standard debugger the same is true if C<$DB::deep>
-(how many levels of recursion deep into the debugger you can go before
-a mandatory break) is not defined.)
+Without Readline support you may see the symbols "^[[A", "^[[C", "^[[B",
+"^[[D"", "^H", ... when using the arrow keys and/or the backspace key.
-With the recent updates the minimal possible debugger consists of one
-line
+=head2 Editor Support for Debugging
- sub DB::DB {}
+If you have the GNU's version of B<emacs> installed on your system,
+it can interact with the Perl debugger to provide an integrated
+software development environment reminiscent of its interactions
+with C debuggers.
-which is quite handy as contents of C<PERL5DB> environment
-variable:
+Recent versions of Emacs come with a
+start file for making B<emacs> act like a
+syntax-directed editor that understands (some of) Perl's syntax.
+See L<perlfaq3>.
- env "PERL5DB=sub DB::DB {}" perl -d your-script
+Users of B<vi> should also look into B<vim> and B<gvim>, the mousey
+and windy version, for coloring of Perl keywords.
-Another (a little bit more useful) minimal debugger can be created
-with the only line being
+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.
- sub DB::DB {print ++$i; scalar <STDIN>}
+=head2 The Perl Profiler
+X<profile> X<profiling> X<profiler>
-This debugger would print the sequential number of encountered
-statement, and would wait for your C<CR> to continue.
+If you wish to supply an alternative debugger for Perl to run,
+invoke your script with a colon and a package argument given to the
+B<-d> flag. Perl's alternative debuggers include a Perl profiler,
+L<Devel::NYTProf>, which is available separately as a CPAN
+distribution. To profile your Perl program in the file F<mycode.pl>,
+just type:
-The following debugger is quite functional:
+ $ perl -d:NYTProf mycode.pl
- {
- package DB;
- sub DB {}
- sub sub {print ++$i, " $sub\n"; &$sub}
- }
+When the script terminates the profiler will create a database of the
+profile information that you can turn into reports using the profiler's
+tools. See <perlperf> for details.
-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>.
+=head1 Debugging Regular Expressions
+X<regular expression, debugging>
+X<regex, debugging> X<regexp, debugging>
-=head2 Debugger Internals
+C<use re 'debug'> enables you to see the gory details of how the Perl
+regular expression engine works. In order to understand this typically
+voluminous output, one must not only have some idea about how regular
+expression matching works in general, but also know how Perl's regular
+expressions are internally compiled into an automaton. These matters
+are explored in some detail in
+L<perldebguts/"Debugging Regular Expressions">.
-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.
+=head1 Debugging Memory Usage
+X<memory usage>
-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.
+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.
-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.
+=head1 SEE ALSO
-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<$> or C<@>), C<sub> (subroutine name, or info about
-eval), C<args> (C<undef> or a reference to an array), C<file>, and
-C<line>.
+You do have C<use strict> and C<use warnings> enabled, don't you?
-The function C<DB::print_trace(FH, skip[, count[, short]])> prints
-formatted info about caller frames. The last two functions may be
-convenient as arguments to C<E<lt>>, C<E<lt>E<lt>> commands.
+L<perldebtut>,
+L<perldebguts>,
+L<re>,
+L<DB>,
+L<Devel::NYTProf>,
+L<Dumpvalue>,
+and
+L<perlrun>.
-=head2 Other resources
+When debugging a script that uses #! and is thus normally found in
+$PATH, the -S option causes perl to search $PATH for it, so you don't
+have to type the path or C<which $scriptname>.
-You did try the B<-w> switch, didn't you?
+ $ perl -Sd foo.pl
=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 C<shift>
+or C<pop>), the stack backtrace will not show the original values.
+
+The debugger does not currently work in conjunction with the B<-W>
+command-line switch, because it itself is not free of warnings.
-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.
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