First of all, have you tried using the B<-w> switch?
+
+If you're new to the Perl debugger, you may prefer to read
+L<perldebtut>, which is a tutorial introduction to the debugger .
+
=head1 The Perl Debugger
If you invoke Perl with the B<-d> switch, your script runs under the
environment, prompting for debugger commands that let you examine
source code, set breakpoints, get stack backtraces, change the values of
variables, etc. This is so convenient that you often fire up
-the debugger all by itself just to test out Perl constructs
+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
-pre-loads 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
=item h [command]
-Prints out a help message.
+Prints out a help message.
If you supply another debugger command as an argument to the C<h> command,
it prints out the description for just that command. The special
argument of C<h h> produces a more compact help listing, designed to fit
together on one screen.
-If the output 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> command (or any command, for that matter) scrolls
+past your screen, precede the command with a leading pipe symbol so
+that it's run through your pager, as in
DB> |h
+You may change the pager which is used via C<O pager=...> command.
+
=item p expr
-Same as C<print DB::OUT expr> in the current package. In particular,
-
since this is just Perl's own B<print> function, this means that nested
+Same as C<print {$DB::OUT} expr> in the current package. In particular,
+
because this is just Perl's own C<print> function, this means that nested
data structures and objects are not dumped, unlike with the C<x> command.
+The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of
+where STDOUT may be redirected to.
+
=item x expr
-Evals its expression in list context and dumps out the result
+Evaluates its expression in list context and dumps out the result
in a pretty-printed fashion. Nested data structures are printed out
-recursively, unlike the C<print> function.
+recursively, unlike the real C<print> function in Perl.
+See L<Dumpvalue> if you'd like to do this yourself.
+
+The output format is governed by multiple options described under
+L<"Configurable Options">.
=item V [pkg [vars]]
-Display all (or some) variables in package (defaulting to the C<main>
-package) using a data pretty-printer (hashes show their keys and values so
-you see what's what, control characters are made printable, etc.). Make
-sure you don't put the type specifier (like C<$>) 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.
+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
+=item n [expr]
+
+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.
-Next. Executes over subroutine calls, until it reaches the beginning
-of the next statement.
+=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 c [line]
+=item c [line|sub]
Continue, optionally inserting a one-time-only breakpoint
-at the specified line.
+at the specified line or subroutine.
=item l
=item l min-max
-List lines C<min> through C<max>.
+List lines C<min> through C<max>. C<l -> is synonymous to C<->.
=item l line
=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.
+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 for the current file.
+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.
+Toggle trace mode (see also the C<AutoTrace> option).
=item t expr
-Trace through execution of expr. For example:
+Trace through execution of C<expr>.
+See L<perldebguts/"Frame Listing Output Examples"> for examples.
- $ perl -de 42
- Stack dump during die enabled outside of evals.
+=item b [line] [condition]
- Loading DB routines from perl5db.pl patch level 0.94
- Emacs support available.
+Set a breakpoint before the given line. If I<line> is omitted, set a
+breakpoint on the line about to be executed. If a condition
+is specified, it's evaluated each time the statement is reached: a
+breakpoint is taken only if the condition is true. Breakpoints may
+only be set on lines that begin an executable statement. Conditions
+don't use C<if>:
- Enter h or `h h' for help.
+ b 237 $x > 30
+ b 237 ++$count237 < 11
+ b 33 /pattern/i
- main::(-e:1): 0
- DB<1> sub foo { 14 }
+=item b subname [condition]
- DB<2> sub bar { 3 }
+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).
- DB<3> t print foo() * bar()
- main::((eval 172):3): print foo() + bar();
- main::foo((eval 168):2):
- main::bar((eval 170):2):
- 42
- DB<4> q
+=item b postpone subname [condition]
-=item b [line] [condition]
+Set a breakpoint at first line of subroutine after it is compiled.
-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 only be set on lines
-that begin an executable statement. Conditions don't use B<if>:
+=item b load filename
- b 237 $x > 30
- b 33 /pattern/i
+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 subname [condition]
+=item b compile subname
-Set a breakpoint at the first line of the named subroutine.
+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
-=over 3
+ 1. check for a breakpoint at this line
+ 2. print the line if necessary (tracing)
+ 3. do any actions associated with that line
+ 4. prompt user if at a breakpoint or in single-step
+ 5. evaluate line
-=item 1
+For example, this will print out $foo every time line
+53 is passed:
-check for a breakpoint at this line
+ a 53 print "DB FOUND $foo\n"
-=item 2
+=item a [line]
-print the line if necessary (tracing)
+Delete an action from the specified line. If I<line> is omitted, delete
+the action on the line that is about to be executed.
-=item 3
+=item A
-do any actions associated with that line
+Delete all installed actions.
-=item 4
+=item W expr
-prompt user if at a breakpoint or in single-step
+Add a global watch-expression. We hope you know what one of these
+is, because they're supposed to be obvious. B<WARNING>: It is far
+too easy to destroy your watch expressions by accidentally omitting
+the I<expr>.
-=item 5
+=item W
-evaluate line
+Delete all watch-expressions.
-=back
+=item O booloption ...
-For example, this will print out C<$foo> every time line
-53 is passed:
+Set each listed Boolean option to the value C<1>.
- a 53 print "DB FOUND $foo\n"
+=item O anyoption? ...
-=item A
+Print out the value of one or more options.
-Delete all installed actions.
+=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<"Configurable 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.
+
+=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 backslashing 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 @ file
+
+Read and execute debugger commands from I<file>. I<file> may itself contain
+C<@> commands.
+
+=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 C<select>ed as well.
+
+=item = [alias value]
+
+Define a command alias, like
+
+ = quit q
+
+or list current aliases.
+
+=item command
+
+Execute command as a Perl statement. A 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 O [opt[=val]] [opt"val"] [opt?]...
+=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:
+
+ $DB::doccmd = 'netscape -remote http://something.here/';
+
+=back
+
+=head2 Configurable Options
+
+The debugger has numerous options settable using the C<O> command,
+either interactively or from the environment or an rc file.
+(./.perldb or ~/.perldb under Unix.)
-Set or query values of options. val defaults to 1. opt can
-be abbreviated. Several options can be listed.
=over 12
-=item recallCommand, ShellBang
+=item C<recallCommand>, C<ShellBang>
The characters used to recall command or spawn shell. By
-default, these are both set to C<!>.
+default, both are set to C<!>, which is unfortunate.
+
+=item C<pager>
+
+Program to use for output of pager-piped commands (those beginning
+with a C<|> character.) By default, C<$ENV{PAGER}> will be used.
+Because the debugger uses your current terminal characteristics
+for bold and underlining, if the chosen pager does not pass escape
+sequences through unchanged, the output of some debugger commands
+will not be readable when sent through the pager.
+
+=item C<tkRunning>
+
+Run Tk while prompting (with ReadLine).
+
+=item C<signalLevel>, C<warnLevel>, C<dieLevel>
+
+Level of verbosity. By default, the debugger leaves your exceptions
+and warnings alone, because altering them can break correctly running
+programs. It will attempt to print a message when uncaught INT, BUS, or
+SEGV signals arrive. (But see the mention of signals in L<BUGS> below.)
+
+To disable this default safe mode, set these values to something higher
+than 0. At a level of 1, you get backtraces upon receiving any kind
+of warning (this is often annoying) or exception (this is
+often valuable). Unfortunately, the debugger cannot discern fatal
+exceptions from non-fatal ones. If C<dieLevel> is even 1, then your
+non-fatal exceptions are also traced and unceremoniously altered if they
+came from C<eval'd> strings or from any kind of C<eval> within modules
+you're attempting to load. If C<dieLevel> is 2, the debugger doesn't
+care where they came from: It usurps your exception handler and prints
+out a trace, then modifies all exceptions with its own embellishments.
+This may perhaps be useful for some tracing purposes, but tends to hopelessly
+destroy any program that takes its exception handling seriously.
+
+=item C<AutoTrace>
+
+Trace mode (similar to C<t> command, but can be put into
+C<PERLDB_OPTS>).
+
+=item C<LineInfo>
+
+File or pipe to print line number info to. If it is a pipe (say,
+C<|visual_perl_db>), then a short message is used. This is the
+mechanism used to interact with a slave editor or visual debugger,
+such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical
+debugger.
+
+=item C<inhibit_exit>
+
+If 0, allows I<stepping off> the end of the script.
+
+=item C<PrintRet>
+
+Print return value after C<r> command if set (default).
+
+=item C<ornaments>
-=item pager
+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.
-Program to use for output of pager-piped commands (those
-beginning with a C<|> character.) By default,
-C<$ENV{PAGER}> will be used.
+=item C<frame>
+
+Affects the printing of messages upon entry and exit from subroutines. If
+C<frame & 2> is false, messages are printed on entry only. (Printing
+on exit might be useful if interspersed with other messages.)
+
+If C<frame & 4>, arguments to functions are printed, plus context
+and caller info. If C<frame & 8>, overloaded C<stringify> and
+C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame
+& 16>, the return value from the subroutine is printed.
+
+The length at which the argument list is truncated is governed by the
+next option:
+
+=item C<maxTraceLen>
+
+Length to truncate the argument list when the C<frame> option's
+bit 4 is set.
+
+=item C<windowSize>
+
+Change the size of code list window (default is 10 lines).
=back
=over 12
-=item arrayDepth, hashDepth
+=item C<arrayDepth>, C<hashDepth>
Print only first N elements ('' for all).
-=item compactDump, veryCompact
+=item C<compactDump>, C<veryCompact>
-Change style of array and hash dump.
+Change the style of array and hash output. If C<compactDump>, short array
+may be printed on one line.
-=item globPrint
+=item C<globPrint>
Whether to print contents of globs.
-=item DumpDBFiles
+=item C<DumpDBFiles>
Dump arrays holding debugged files.
-=item DumpPackages
+=item C<DumpPackages>
Dump symbol tables of packages.
-=item quote, HighBit, undefPrint
+=item C<DumpReused>
-Change style of string dump.
+Dump contents of "reused" addresses.
-=item tkRunning
+=item C<quote>, C<HighBit>, C<undefPrint>
-Run Tk while prompting (with ReadLine).
+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 signalLevel, warnLevel. dieLevel
+=item C<UsageOnly>
-Level of verbosity.
+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
-The option C<PrintRet> affects printing of return value after C<r>
-command, The option C<frame> affects printing messages on entry and exit
-from subroutines. If C<frame> is 1, messages are printed on entry only;
-if it's set to more than that, they'll will be printed on exit as well,
-which may be useful if interdispersed with other messages.
-
-During startup options are initialized from $ENV{PERLDB_OPTS}.
-You can put additional initialization options C<TTY>, C<noTTY>,
-C<ReadLine>, and C<NonStop> there. Here's an example of using
-the C<$ENV{PERLDB_OPTS}> variable:
+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.
- $ PERLDB_OPTS="N f=2" perl -d myprogram
+If your rc file contains:
-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.
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace");
-See "Debugger Internals" below for more details.
-
-=item < command
-
-Set an action to happen before every debugger prompt. A multiline
-command may be entered by backslashing the newlines.
+then your script will run without human intervention, putting trace
+information into the file I<db.out>. (If you interrupt it, you'd
+better reset C<LineInfo> to F</dev/tty> if you expect to see anything.)
-=item > command
+=over 12
-Set an action to happen after the prompt when you've just given a
-command to return to executing the script. A multiline command may be
-entered by backslashing the newlines.
+=item C<TTY>
-=item ! number
+The TTY to use for debugging I/O.
-Redo a previous command (default previous command).
+=item C<noTTY>
-=item ! -number
+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 $DB::single from the Perl script), it connects to a TTY
+specified in the C<TTY> option at startup, or to a tty found at
+runtime using the C<Term::Rendezvous> module of your choice.
-Redo number'th-to-last command.
+This module should implement a method named C<new> that returns an object
+with two methods: C<IN> and C<OUT>. These should return filehandles to use
+for debugging input and output correspondingly. The C<new> method should
+inspect an argument containing the value of C<$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 ! pattern
+=item C<ReadLine>
-Redo last command that started with pattern.
-See C<O recallCommand>, too.
+If false, readline support in the debugger is disabled in order
+to debug applications that themselves use ReadLine.
-=item !! cmd
+=item C<NonStop>
-Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT)
-See C<O shellBang> too.
-
-=item H -number
+If set, the debugger goes into non-interactive mode until interrupted, or
+programmatically by setting $DB::signal or $DB::single.
-Display last n commands. Only commands longer than one character are
-listed. If number is omitted, lists them all.
-
-=item q or ^D
+=back
-Quit. ("quit" doesn't work for this.)
+Here's an example of using the C<$ENV{PERLDB_OPTS}> variable:
-=item R
+ $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram
-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.
+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.
-=item |dbcmd
+Other examples include
-Run debugger command, piping DB::OUT to current pager.
+ $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram
-=item ||dbcmd
+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"!)
-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
+Other examples include (using standard shell syntax to show environment
+variable settings):
- |V main
+ $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out"
+ perl -d myprogram )
-=item = [alias value]
+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
-Define a command alias, or list current aliases.
+ $ sleep 1000000
-=item command
+See L<perldebguts/"Debugger Internals"> for details.
-Execute command as a Perl statement. A missing semicolon will be
-supplied.
+=head2 Debugger input/output
-=item p expr
+=over 8
-Same as C<print DB::OUT expr>. The DB::OUT filehandle is opened to
-/dev/tty, regardless of where STDOUT may be redirected to.
-
-=back
+=item Prompt
The debugger prompt is something like
DB<<17>>
-where that number is the command number, which you'd use to access with
-the built-in 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.
+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, you may escape the newline that would
-normally end the debugger command with a backslash. Here's an example:
+definition with several statements or a format, escape the newline
+that would normally end the debugger command with a backslash.
+Here's an example:
DB<1> for (1..4) { \
cont: print "ok\n"; \
Note that this business of escaping a newline is specific to interactive
commands typed into the debugger.
-Here's an example of what a stack backtrace might look like:
+=item Stack backtrace
+
+Here's an example of what a stack backtrace via C<T> command might
+look like:
$ = main::infested called from file `Ambulation.pm' line 10
@ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7
$ = main::pests('bactrian', 4) called from file `camel_flea' line 4
-The left-hand character up there tells whether the function was called
-in a scalar or list context (we bet you can tell which is which). What
-that says is that you were in the function C<main::infested> when you ran
-the stack dump, and that it was called in a scalar context from line 10
-of the file I<Ambulation.pm>, but without any arguments at all, meaning
-it was called as C<&infested>. The next stack frame shows that the
-function C<Ambulation::legs> was called in a list context from the
-I<camel_flea> file with four arguments. The last stack frame shows that
-C<main::pests> was called in a scalar context, also from I<camel_flea>,
-but from line 4.
-
-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. From your own Perl code, however, you can
+The left-hand character up there indicates the context in which the
+function was called, with C<$> and C<@> meaning scalar or list
+contexts respectively, and C<.> meaning void context (which is
+actually a sort of scalar context). The display above says
+that you were in the function C<main::infested> when you ran the
+stack dump, and that it was called in scalar context from line
+10 of the file I<Ambulation.pm>, but without any arguments at all,
+meaning it was called as C<&infested>. The next stack frame shows
+that the function C<Ambulation::legs> was called in list context
+from the I<camel_flea> file with four arguments. The last stack
+frame shows that C<main::pests> was called in scalar context,
+also from I<camel_flea>, but from line 4.
+
+If you execute the C<T> command from inside an active C<use>
+statement, the backtrace will contain both a C<require> frame and
+an C<eval>) frame.
+
+=item Line Listing Format
+
+This shows the sorts of output the C<l> command can produce:
+
+ DB<<13>> l
+ 101: @i{@i} = ();
+ 102:b @isa{@i,$pack} = ()
+ 103 if(exists $i{$prevpack} || exists $isa{$pack});
+ 104 }
+ 105
+ 106 next
+ 107==> if(exists $isa{$pack});
+ 108
+ 109:a if ($extra-- > 0) {
+ 110: %isa = ($pack,1);
+
+Breakable lines are marked with C<:>. Lines with breakpoints are
+marked by C<b> and those with actions by C<a>. The line that's
+about to be executed is marked by C<< ==> >>.
+
+Please be aware that code in debugger listings may not look the same
+as your original source code. Line directives and external source
+filters can alter the code before Perl sees it, causing code to move
+from its original positions or take on entirely different forms.
+
+=item Frame listing
+
+When the C<frame> option is set, the debugger would print entered (and
+optionally exited) subroutines in different styles. See L<perldebguts>
+for incredibly long examples of these.
+
+=back
+
+=head2 Debugging compile-time statements
+
+If you have compile-time executable statements (such as code within
+BEGIN and CHECK blocks or C<use> statements), these will I<not> be
+stopped by debugger, although C<require>s and INIT blocks will, and
+compile-time statements can be traced with C<AutoTrace> option set
+in C<PERLDB_OPTS>). From your own Perl code, however, you can
transfer control back to the debugger using the following statement,
which is harmless if the debugger is not running:
$DB::single = 1;
-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.
-=head2 Debugger Customization
+Another way to debug compile-time code is to start the debugger, set a
+breakpoint on the I<load> of some module:
-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 PERL5DB environment variable to say something like this:
+ DB<7> b load f:/perllib/lib/Carp.pm
+ Will stop on load of `f:/perllib/lib/Carp.pm'.
- BEGIN { require "myperl5db.pl" }
+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
-You can do some customization by setting up a F<.perldb> file which
+The debugger probably contains enough configuration hooks that you
+won't ever have to modify it yourself. You may change the behaviour
+of debugger from within the debugger using its C<O> command, from
+the command line via the C<PERLDB_OPTS> environment variable, and
+from customization files.
+
+You can do some customization by setting up a F<.perldb> file, which
contains initialization code. For instance, you could make aliases
like these (the last one 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/';
-=head2 Readline Support
+You can change options from F<.perldb> by using calls like this 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.
+ parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2");
-=head2 Editor Support for Debugging
+The code is executed in the package C<DB>. Note that F<.perldb> is
+processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the
+subroutine C<afterinit>, that function is called after debugger
+initialization ends. F<.perldb> may be contained in the current
+directory, or in the home directory. Because this file is sourced
+in by Perl and may contain arbitrary commands, for security reasons,
+it must be owned by the superuser or the current user, and writable
+by no one but its owner.
-If you 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 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:
-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.
+ BEGIN { require "myperl5db.pl" }
-(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.)
+As a last resort, you could also use C<PERL5DB> to customize the debugger
+by directly setting internal variables or calling debugger functions.
-=head2 The Perl Profiler
+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.
-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 Internals
-
-When you call the B<caller> function from package DB, Perl sets the
-C<@DB::args> array to contain the arguments that stack frame was called
-with. It also maintains other magical internal variables, such as
-C<@DB::dbline>, an array of the source code lines for the currently
-selected (with the debugger's C<f> command) file. Perl effectively
-inserts a call to the function C<DB::DB>(I<linenum>) in front of every
-place that can have a breakpoint. Instead of a subroutine call it calls
-C<DB::sub> setting C<$DB::sub> being the called subroutine. It also
-inserts a C<BEGIN {require 'perl5db.pl'}> before the first line.
-
-Note that no subroutine call is possible until C<&DB::sub> is defined
-(for subroutines defined outside this file). In fact, the same is
-true if C<$DB::deep> (how many levels of recursion deep into the
-debugger you are) is not defined.
-
-At the start, the debugger reads your rc file (F<./.perldb> or
-F<~/.perldb> under UNIX), which can set important options. This file may
-define a subroutine C<&afterinit> to be executed after the debugger is
-initialized.
-
-After the rc file is read, the debugger reads environment variable
-PERLDB_OPTS and parses it as a rest of C<O ...> line in debugger prompt.
-
-The following options can only be specified at startup. To set them in
-your rc file, call C<&parse_options("optionName=new_value")>.
+=head2 Readline Support
-=over 12
+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.
-=item TTY
+A rudimentary command-line completion is also available.
+Unfortunately, the names of lexical variables are not available for
+completion.
-The TTY to use for debugging I/O.
+=head2 Editor Support for Debugging
-=item noTTY
+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.
-If set, goes in C<NonStop> mode. On interrupt if TTY is not set uses the
-value of C<noTTY> or "/tmp/perldbtty$$" to find TTY using
-C<Term::Rendezvous>. Current variant is to have the name of TTY in this
-file.
+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 ReadLine
+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.
-If false, dummy ReadLine is used, so you can debug
-ReadLine applications.
+Users of B<vi> should also look into B<vim> and B<gvim>, the mousey
+and windy version, for coloring of Perl keywords.
-=item NonStop
+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.
-If true, no I/O is performed until an interrupt.
+=head2 The Perl Profiler
-=item LineInfo
+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:
-File or pipe to print line number info to. If it'sis a
-pipe, then a short, "emacs like" message is used.
+ $ perl -d:DProf mycode.pl
-Example rc file:
+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.
- &parse_options("NonStop=1 LineInfo=db.out");
- sub afterinit { $trace = 1; }
+=head1 Debugging regular expressions
-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"!)
+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">.
-=back
+=head1 Debugging memory usage
-=head2 Other resources
+Perl contains internal support for reporting its own memory usage,
+but this is a fairly advanced concept that requires some understanding
+of how memory allocation works.
+See L<perldebguts/"Debugging Perl memory usage"> for the details.
+
+=head1 SEE ALSO
You did try the B<-w> switch, didn't you?
+L<perldebtut>,
+L<perldebguts>,
+L<re>,
+L<DB>,
+L<Devel::Dprof>,
+L<dprofpp>,
+L<Dumpvalue>,
+and
+L<perlrun>.
+
=head1 BUGS
-If your program exit()s or die()s, so too does the debugger.
+You cannot get stack frame information or in any fashion debug functions
+that were not compiled by Perl, such as those from C or C++ extensions.
-You cannot get the stack frame information or otherwise debug functions
-that were not compiled by Perl, such as C or C++ extensions.
+If you alter your @_ arguments in a subroutine (such as with C<shift>
+or C<pop>), the stack backtrace will not show the original values.
-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.
+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'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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