=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>?
If you're new to the Perl debugger, you may prefer to read
-L<perldebtut>, which is a tutorial introduction to the debugger .
+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>.
=head1 The Perl Debugger
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
(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
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
+
+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.
-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.
+=item h h
-If the output of the C<h> command (or any command, for that matter) scrolls
+The special argument of C<h h> produces the entire help page, which is quite long.
+
+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 {$DB::OUT} expr> in the current package. In particular,
because this is just Perl's own C<print> function, this means that nested
The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of
where STDOUT may be redirected to.
-=item x expr
+=item x [maxdepth] expr
+X<debugger command, x>
-Evaluates its expression in list context and dumps out the result
-in a pretty-printed fashion. Nested data structures are printed out
-recursively, unlike the real C<print> function in Perl.
+Evaluates its expression in list context and dumps out the result in a
+pretty-printed fashion. Nested data structures are printed out
+recursively, unlike the real C<print> function in Perl. When dumping
+hashes, you'll probably prefer 'x \%h' rather than 'x %h'.
See L<Dumpvalue> if you'd like to do this yourself.
The output format is governed by multiple options described under
-L<"Configurable Options">.
+L</"Configurable Options">.
+
+If the C<maxdepth> is included, it must be a numeral I<N>; the value is
+dumped only I<N> levels deep, as if the C<dumpDepth> option had been
+temporarily set to I<N>.
=item V [pkg [vars]]
+X<debugger command, V>
-Display all (or some) variables in package (defaulting to C<main>)
+Display all (or some) variables in package (defaulting to C<main>)
using a data pretty-printer (hashes show their keys and values so
you see what's what, control characters are made printable, etc.).
Make sure you don't put the type specifier (like C<$>) there, just
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 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 the beginning
of the next statement. If an expression is supplied that includes
each statement.
=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).
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.
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 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 C<eval> statement. If I<filename>
-is not a full pathname found in the values of %INC, it is considered
+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:
Search backwards for pattern; final ? is optional.
The search is case-insensitive by default.
-=item L
+=item L [abw]
+X<debugger command, L>
-List all breakpoints and actions.
+List (default all) actions, breakpoints and watch expressions
=item S [[!]regex]
+X<debugger command, S>
List subroutine names [not] matching the regex.
-=item t
+=item t [n]
+X<debugger command, t>
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.
-=item t expr
+=item t [n] expr
+X<debugger command, t>
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.
+=item b
+X<breakpoint>
+X<debugger command, b>
+
+Sets breakpoint on current line
+
=item b [line] [condition]
+X<breakpoint>
+X<debugger command, b>
-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
+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
b 237 ++$count237 < 11
b 33 /pattern/i
+If the line number is C<.>, sets a breakpoint on the current line:
+
+ b . $n > 100
+
+=item b [file]:[line] [condition]
+X<breakpoint>
+X<debugger command, b>
+
+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 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 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 a breakpoint at first line of subroutine after it is compiled.
=item b load filename
+X<breakpoint>
+X<debugger command, b>
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 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 from the specified I<line>. If I<line> is omitted, deletes
-the breakpoint from the line 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. If I<line> is
omitted, set an action on the line about to be executed.
a 53 print "DB FOUND $foo\n"
-=item a [line]
+=item A line
+X<debugger command, A>
-Delete an action from the specified line. If I<line> is omitted, delete
-the action on the line that is about to be executed.
+Delete an action from the specified line.
-=item A
+=item A *
+X<debugger command, A>
Delete all installed actions.
+=item w expr
+X<debugger command, w>
+
+Add a global watch-expression. Whenever a watched global changes the
+debugger will stop and display the old and new values.
+
=item W expr
+X<debugger command, W>
-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>.
+Delete watch-expression
-=item W
+=item W *
+X<debugger command, W>
Delete all watch-expressions.
-=item O booloption ...
+=item o
+X<debugger command, o>
+
+Display all options.
+
+=item o booloption ...
+X<debugger command, o>
Set each listed Boolean option to the value C<1>.
-=item O anyoption? ...
+=item o anyoption? ...
+X<debugger command, o>
Print out the value of one or more options.
-=item O option=value ...
+=item o option=value ...
+X<debugger command, o>
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
+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
+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">
+not be. Several options can be set together. See L</"Configurable Options">
for a list of these.
-=item < ?
+=item < ?
+X<< debugger command, < >>
List out all pre-prompt Perl command actions.
=item < [ command ]
+X<< debugger 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!
+A multi-line command may be entered by backslashing the newlines.
+
+=item < *
+X<< debugger command, < >>
+
+Delete all pre-prompt Perl command actions.
=item << command
+X<< debugger command, << >>
Add an action (Perl command) to happen before every debugger prompt.
A multi-line command may be entered by backwhacking the newlines.
=item > ?
+X<< debugger command, > >>
List out post-prompt Perl command actions.
=item > command
+X<< debugger 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!
+couldn't have guessed this by now).
+
+=item > *
+X<< debugger command, > >>
+
+Delete all post-prompt Perl command actions.
=item >> command
+X<<< debugger 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 { ?
+X<debugger command, {>
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!
+A multi-line command may be entered in the customary fashion.
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
+what you mean to do, write it as with C<;{ ... }> or even
C<do { ... }>.
+=item { *
+X<debugger command, {>
+
+Delete all pre-prompt debugger commands.
+
=item {{ command
+X<debugger 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
+X<debugger command, !>
Redo a previous command (defaults to the previous command).
=item ! -number
+X<debugger command, !>
Redo number'th previous command.
=item ! pattern
+X<debugger command, !>
Redo last command that started with pattern.
-See C<O recallCommand>, too.
+See C<o recallCommand>, too.
=item !! cmd
+X<debugger command, !!>
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,
+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
+=item source file
+X<debugger command, source>
-Read and execute debugger commands from I<file>. I<file> may itself contain
-C<@> commands.
+Read and execute debugger commands from I<file>.
+I<file> may itself contain C<source> commands.
=item H -number
+X<debugger command, H>
Display last n commands. Only commands longer than one character are
listed. If I<number> is omitted, list them all.
=item q or ^D
+X<debugger command, q>
+X<debugger command, ^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
+off the end the script. You may also need to set $finished to 0
if you want to step through global destruction.
=item R
+X<debugger command, R>
Restart the debugger by C<exec()>ing a new session. We try to maintain
your history across this, but internal settings and command-line options
options B<-w>, B<-I>, and B<-e>.
=item |dbcmd
+X<debugger command, |>
Run the debugger command, piping DB::OUT into your current pager.
=item ||dbcmd
+X<debugger command, ||>
Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well.
=item = [alias value]
+X<debugger command, =>
Define a command alias, like
Perl debugger, use a leading semicolon, too.
=item m expr
+X<debugger command, m>
List which methods may be called on the result of the evaluated
-expression. The expression may evaluated to a reference to a
+expression. The expression may evaluated to a reference to a
blessed object, or to a package name.
+=item M
+X<debugger command, M>
+
+Display all loaded modules and their versions.
+
=item man [manpage]
+X<debugger command, man>
Despite its name, this calls your system's default documentation
viewer on the given page, or on the viewer itself if I<manpage> is
=head2 Configurable Options
-The debugger has numerous options settable using the C<O> command,
+The debugger has numerous options settable using the C<o> command,
either interactively or from the environment or an rc file.
(./.perldb or ~/.perldb under Unix.)
=over 12
=item C<recallCommand>, C<ShellBang>
+X<debugger option, recallCommand>
+X<debugger option, ShellBang>
-The characters used to recall command or spawn shell. By
+The characters used to recall a command or spawn a shell. By
default, both are set to C<!>, which is unfortunate.
=item C<pager>
+X<debugger option, pager>
Program to use for output of pager-piped commands (those beginning
with a C<|> character.) By default, C<$ENV{PAGER}> will be used.
will not be readable when sent through the pager.
=item C<tkRunning>
+X<debugger option, tkRunning>
Run Tk while prompting (with ReadLine).
=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.)
+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
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
+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.
destroy any program that takes its exception handling seriously.
=item C<AutoTrace>
+X<debugger option, AutoTrace>
Trace mode (similar to C<t> command, but can be put into
C<PERLDB_OPTS>).
=item C<LineInfo>
+X<debugger option, 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
debugger.
=item C<inhibit_exit>
+X<debugger option, inhibit_exit>
If 0, allows I<stepping off> the end of the script.
=item C<PrintRet>
+X<debugger option, PrintRet>
Print return value after C<r> command if set (default).
=item C<ornaments>
+X<debugger option, ornaments>
Affects screen appearance of the command line (see L<Term::ReadLine>).
There is currently no way to disable these, which can render
This is considered a bug.
=item C<frame>
+X<debugger option, 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
next option:
=item C<maxTraceLen>
+X<debugger option, maxTraceLen>
Length to truncate the argument list when the C<frame> option's
bit 4 is set.
=item C<windowSize>
+X<debugger option, windowSize>
Change the size of code list window (default is 10 lines).
=over 12
=item C<arrayDepth>, C<hashDepth>
+X<debugger option, arrayDepth> X<debugger option, hashDepth>
Print only first N elements ('' for all).
+=item C<dumpDepth>
+X<debugger option, dumpDepth>
+
+Limit recursion depth to N levels when dumping structures.
+Negative values are interpreted as infinity. Default: infinity.
+
=item C<compactDump>, C<veryCompact>
+X<debugger option, compactDump> X<debugger option, veryCompact>
Change the style of array and hash output. If C<compactDump>, short array
may be printed on one line.
=item C<globPrint>
+X<debugger option, globPrint>
Whether to print contents of globs.
=item C<DumpDBFiles>
+X<debugger option, DumpDBFiles>
Dump arrays holding debugged files.
=item C<DumpPackages>
+X<debugger option, DumpPackages>
Dump symbol tables of packages.
=item C<DumpReused>
+X<debugger option, DumpReused>
Dump contents of "reused" addresses.
=item C<quote>, C<HighBit>, C<undefPrint>
+X<debugger option, quote> X<debugger option, HighBit>
+X<debugger option, undefPrint>
Change the style of string dump. The default value for C<quote>
is C<auto>; one can enable double-quotish or single-quotish format
with their high bit set are printed verbatim.
=item C<UsageOnly>
+X<debugger option, UsageOnly>
Rudimentary per-package memory usage dump. Calculates total
size of strings found in variables in the package. This does not
include lexicals in a module's file scope, or lost in closures.
+=item C<HistFile>
+X<debugger option, history, HistFile>
+
+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.
+
+=item C<HistSize>
+X<debugger option, history, HistSize>
+
+The count of the saved lines in the history (assuming C<HistFile> above).
+
=back
After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}>
-environment variable and parses this as the remainder of a `O ...'
+environment variable and parses this as the remainder of a "O ..."
line as one might enter at the debugger prompt. You may place the
initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop>
there.
=over 12
=item C<TTY>
+X<debugger option, TTY>
The TTY to use for debugging I/O.
=item C<noTTY>
+X<debugger option, noTTY>
If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If
interrupted (or if control goes to the debugger via explicit setting of
with two methods: C<IN> and C<OUT>. These should return filehandles to use
for debugging input and output correspondingly. The C<new> method should
inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at
-startup, or C<"/tmp/perldbtty$$"> otherwise. This file is not
+startup, or C<"$ENV{HOME}/.perldbtty$$"> otherwise. This file is not
inspected for proper ownership, so security hazards are theoretically
possible.
=item C<ReadLine>
+X<debugger option, ReadLine>
If false, readline support in the debugger is disabled in order
to debug applications that themselves use ReadLine.
=item C<NonStop>
+X<debugger option, NonStop>
If set, the debugger goes into non-interactive mode until interrupted, or
programmatically by setting $DB::signal or $DB::single.
See L<perldebguts/"Debugger Internals"> for details.
-=head2 Debugger input/output
+=head2 Debugger Input/Output
=over 8
commands typed into the debugger.
=item Stack backtrace
+X<backtrace> X<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
+ $ = 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<$> and C<@> meaning scalar or list
If you execute the C<T> command from inside an active C<use>
statement, the backtrace will contain both a C<require> frame and
-an C<eval>) frame.
+an C<eval> frame.
=item Line Listing Format
This shows the sorts of output the C<l> command can produce:
- DB<<13>> l
- 101: @i{@i} = ();
- 102:b @isa{@i,$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);
+ 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
=back
-=head2 Debugging compile-time statements
+=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:
+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:
$DB::single = 1;
breakpoint on the I<load> of some module:
DB<7> b load f:/perllib/lib/Carp.pm
- Will stop on load of `f:/perllib/lib/Carp.pm'.
+ Will stop on load of 'f:/perllib/lib/Carp.pm'.
and then restart the debugger using the C<R> command (if possible). One can use C<b
compile subname> for the same purpose.
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
+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.
it must be owned by the superuser or the current user, and writable
by no one but its owner.
+You can mock TTY input to debugger by adding arbitrary commands to
+@DB::typeahead. For example, your F<.perldb> file might contain:
+
+ sub afterinit { push @DB::typeahead, "b 4", "b 6"; }
+
+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.
+
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
this document (or in L<perldebguts>) are considered for internal
use only, and as such are subject to change without notice.
-=head2 Readline Support
+=head2 Readline Support / History in the Debugger
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.
+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.
-A rudimentary command-line completion is also available.
-Unfortunately, the names of lexical variables are not available for
-completion.
+A rudimentary command-line completion is also available, including
+lexical variables in the current scope if the C<PadWalker> module
+is installed.
+
+Without Readline support you may see the symbols "^[[A", "^[[C", "^[[B",
+"^[[D"", "^H", ... when using the arrow keys and/or the backspace key.
=head2 Editor Support for Debugging
-If you have the FSF's version of B<emacs> installed on your system,
+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.
-Perl comes with a start file for making B<emacs> act like a
+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.
-Look in the I<emacs> directory of the Perl source distribution.
-
-A similar setup by Tom Christiansen for interacting with any
-vendor-shipped B<vi> and the X11 window system is also available.
-This works similarly to the integrated multiwindow support that
-B<emacs> provides, where the debugger drives the editor. At the
-time of this writing, however, that tool's eventual location in the
-Perl distribution was uncertain.
+See L<perlfaq3>.
Users of B<vi> should also look into B<vim> and B<gvim>, the mousey
-and windy version, for coloring of Perl keywords.
+and windy version, for coloring of Perl keywords.
Note that only perl can truly parse Perl, so all such CASE tools
fall somewhat short of the mark, especially if you don't program
your Perl as a C programmer might.
=head2 The Perl Profiler
+X<profile> X<profiling> X<profiler>
-If you wish to supply an alternative debugger for Perl to run, just
+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. The most popular alternative debuggers for Perl is the
-Perl profiler. Devel::DProf is now included with the standard Perl
+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:
- $ perl -d:DProf mycode.pl
+ $ perl -d:NYTProf mycode.pl
-When the script terminates the profiler will dump the profile
-information to a file called F<tmon.out>. A tool like B<dprofpp>,
-also supplied with the standard Perl distribution, can be used to
-interpret the information in that profile.
+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.
-=head1 Debugging regular expressions
+=head1 Debugging Regular Expressions
+X<regular expression, debugging>
+X<regex, debugging> X<regexp, debugging>
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
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">.
+L<perldebguts/"Debugging Regular Expressions">.
-=head1 Debugging memory usage
+=head1 Debugging Memory Usage
+X<memory usage>
Perl contains internal support for reporting its own memory usage,
but this is a fairly advanced concept that requires some understanding
of how memory allocation works.
-See L<perldebguts/"Debugging Perl memory usage"> for the details.
+See L<perldebguts/"Debugging Perl Memory Usage"> for the details.
=head1 SEE ALSO
-You did try the B<-w> switch, didn't you?
+You do have C<use strict> and C<use warnings> enabled, don't you?
L<perldebtut>,
L<perldebguts>,
L<re>,
L<DB>,
-L<Devel::DProf>,
-L<dprofpp>,
+L<Devel::NYTProf>,
L<Dumpvalue>,
and
L<perlrun>.
+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>.
+
+ $ perl -Sd foo.pl
+
=head1 BUGS
You cannot get stack frame information or in any fashion debug functions
https://perl5.git.perl.org / perl5.git / blobdiff