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PERLDEBUG(1)	       Perl Programmers Reference Guide 	  PERLDEBUG(1)

       perldebug - Perl debugging

       First of all, have you tried using the -w switch?

       If youre new to the Perl debugger, you may prefer to read perldebtut,
       which is a tutorial introduction to the debugger .

The Perl Debugger
       If you invoke Perl with the -d switch, your script runs under the Perl
       source debugger.  This works like an interactive Perl environment,
       prompting for debugger commands that let you examine source code, set
       breakpoints, get stack backtraces, change the values of variables, etc.
       This is so convenient that you often fire up the debugger all by itself
       just to test out Perl constructs interactively to see what they do.
       For example:

	   $ perl -d -e 42

       In Perl, the debugger is not a separate program the way it usually is
       in the typical compiled environment.  Instead, the -d flag tells the
       compiler to insert source information into the parse trees its about
       to hand off to the interpreter.	That means your code must first com
       pile correctly for the debugger to work on it.  Then when the inter
       preter starts up, it preloads a special Perl library file containing
       the debugger.

       The program will halt right before the first run-time executable state
       ment (but see below regarding compile-time statements) and ask you to
       enter a debugger command.  Contrary to popular expectations, whenever
       the debugger halts and shows you a line of code, it always displays the
       line its about to execute, rather than the one it has just executed.

       Any command not recognized by the debugger is directly executed
       ("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 "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 pre
       cede the function with something that doesnt look like a debugger com
       mand, such as a leading ";" or perhaps a "+", or by wrapping it with
       parentheses or braces.

       Debugger Commands

       The debugger understands the following commands:

       h	   Prints out a summary help message

       h [command] Prints out a help message for the given debugger command.

       h h	   The special argument of "h h" produces the entire help
		   page, which is quite long.

		   If the output of the "h h" command (or any command, for
		   that matter) scrolls past your screen, precede the command
		   with a leading pipe symbol so that its run through your
		   pager, as in

		       DB> |h h

		   You may change the pager which is used via "o pager=..."

       p expr	   Same as "print {$DB::OUT} expr" in the current package.  In
		   particular, because this is just Perls own "print" func
		   tion, this means that nested data structures and objects
		   are not dumped, unlike with the "x" command.

		   The "DB::OUT" filehandle is opened to /dev/tty, regardless
		   of where STDOUT may be redirected to.

       x [maxdepth] expr
		   Evaluates its expression in list context and dumps out the
		   result in a pretty-printed fashion.	Nested data structures
		   are printed out recursively, unlike the real "print" func
		   tion in Perl.  When dumping hashes, youll probably prefer
		   x \%h rather than x %h.  See Dumpvalue if youd like to
		   do this yourself.

		   The output format is governed by multiple options described
		   under "Configurable Options".

		   If the "maxdepth" is included, it must be a numeral N; the
		   value is dumped only N levels deep, as if the "dumpDepth"
		   option had been temporarily set to N.

       V [pkg [vars]]
		   Display all (or some) variables in package (defaulting to
		   "main") using a data pretty-printer (hashes show their keys
		   and values so you see whats what, control characters are
		   made printable, etc.).  Make sure you dont put the type
		   specifier (like "$") there, just the symbol names, like

		       V DB filename line

		   Use "~pattern" and "!pattern" for positive and negative

		   This is similar to calling the "x" command on each applica
		   ble var.

       X [vars]    Same as "V currentpackage [vars]".

       y [level [vars]]
		   Display all (or some) lexical variables (mnemonic: "mY"
		   variables) in the current scope or level scopes higher.
		   You can limit the variables that you see with vars which
		   works exactly as it does for the "V" and "X" commands.
		   Requires the "PadWalker" module version 0.08 or higher;
		   will warn if this isnt installed.  Output is pretty-
		   printed in the same style as for "V" and the format is con
		   trolled by the same options.

       T	   Produce a stack backtrace.  See below for details on its

       s [expr]    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.

       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.

       r	   Continue until the return from the current subroutine.
		   Dump the return value if the "PrintRet" option is set

       	   Repeat last "n" or "s" command.

       c [line|sub]
		   Continue, optionally inserting a one-time-only breakpoint
		   at the specified line or subroutine.

       l	   List next window of lines.

       l min+incr  List "incr+1" lines starting at "min".

       l min-max   List lines "min" through "max".  "l -" is synonymous to

       l line	   List a single line.

       l subname   List first window of lines from subroutine.	subname may be
		   a variable that contains a code reference.

       -	   List previous window of lines.

       v [line]    View a few lines of code around the current line.

       .	   Return the internal debugger pointer to the line last exe
		   cuted, and print out that line.

       f filename  Switch to viewing a different file or "eval" statement.  If
		   filename is not a full pathname found in the values of
		   %INC, it is considered a regex.

		   "eval"ed strings (when accessible) are considered to be
		   filenames: "f (eval 7)" and "f eval 7\b" access the body of
		   the 7th "eval"ed string (in the order of execution).  The
		   bodies of the currently executed "eval" and of "eval"ed
		   strings that define subroutines are saved and thus accessi

       /pattern/   Search forwards for pattern (a Perl regex); final / is
		   optional.  The search is case-insensitive by default.

       ?pattern?   Search backwards for pattern; final ? is optional.  The
		   search is case-insensitive by default.

       L [abw]	   List (default all) actions, breakpoints and watch expres

       S [[!]regex]
		   List subroutine names [not] matching the regex.

       t	   Toggle trace mode (see also the "AutoTrace" option).

       t expr	   Trace through execution of "expr".  See "Frame Listing Out
		   put Examples" in perldebguts for examples.

       b	   Sets breakpoint on current line

       b [line] [condition]
		   Set a breakpoint before the given line.  If a condition is
		   specified, its 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 dont use "if":

		       b 237 $x > 30
		       b 237 ++$count237 < 11
		       b 33 /pattern/i

       b subname [condition]
		   Set a breakpoint before the first line of the named subrou
		   tine.  subname may be a variable containing a code refer
		   ence (in this case condition is not supported).

       b postpone subname [condition]
		   Set a breakpoint at first line of subroutine after it is

       b load filename
		   Set a breakpoint before the first executed line of the
		   filename, which should be a full pathname found amongst the
		   %INC values.

       b compile subname
		   Sets a breakpoint before the first statement executed after
		   the specified subroutine is compiled.

       B line	   Delete a breakpoint from the specified line.

       B *	   Delete all installed breakpoints.

       a [line] command
		   Set an action to be done before the line is executed.  If
		   line is omitted, set an action on the line about to be exe
		   cuted.  The sequence of steps taken by the debugger is

		     1. check for a breakpoint at this line
		     2. print the line if necessary (tracing)
		     3. do any actions associated with that line
		     4. prompt user if at a breakpoint or in single-step
		     5. evaluate line

		   For example, this will print out $foo every time line 53 is

		       a 53 print "DB FOUND $foo\n"

       A line	   Delete an action from the specified line.

       A *	   Delete all installed actions.

       w expr	   Add a global watch-expression.  We hope you know what one
		   of these is, because theyre supposed to be obvious.

       W expr	   Delete watch-expression

       W *	   Delete all watch-expressions.

       o	   Display all options

       o booloption ...
		   Set each listed Boolean option to the value 1.

       o anyoption? ...
		   Print out the value of one or more options.

       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 "o pager="less -MQeicsNfr"" to call less with
		   those specific options.  You may use either single or dou
		   ble 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 irrespec
		   tive of the quote; eg: "o option=this isn\t bad" or "o
		   option="She said, \"Isnt it?\""".

		   For historical reasons, the "=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 "=".	The "option" can be abbrevi
		   ated, but for clarity probably should not be.  Several
		   options can be set together.  See "Configurable Options"
		   for a list of these.

       < ?	   List out all pre-prompt Perl command actions.

       < [ command ]
		   Set an action (Perl command) to happen before every debug
		   ger prompt.	A multi-line command may be entered by back
		   slashing the newlines.

       < *	   Delete all pre-prompt Perl command actions.

       << command  Add an action (Perl command) to happen before every debug
		   ger prompt.	A multi-line command may be entered by back
		   whacking the newlines.

       > ?	   List out post-prompt Perl command actions.

       > command   Set an action (Perl command) to happen after the prompt
		   when youve just given a command to return to executing the
		   script.  A multi-line command may be entered by backslash
		   ing the newlines (we bet you couldntve guessed this by

       > *	   Delete all post-prompt Perl command actions.

       >> command  Adds an action (Perl command) to happen after the prompt
		   when youve just given a command to return to executing the
		   script.  A multi-line command may be entered by backslash
		   ing the newlines.

       { ?	   List out pre-prompt debugger commands.

       { [ command ]
		   Set an action (debugger command) to happen before every
		   debugger prompt.  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 thats what you mean to do, write it as with
		   ";{ ... }" or even "do { ... }".

       { *	   Delete all pre-prompt debugger commands.

       {{ 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.

       ! number    Redo a previous command (defaults to the previous command).

       ! -number   Redo numberth previous command.

       ! pattern   Redo last command that started with pattern.  See "o
		   recallCommand", too.

       !! cmd	   Run cmd in a subprocess (reads from DB::IN, writes to
		   DB::OUT) See "o shellBang", also.  Note that the users
		   current shell (well, their $ENV{SHELL} variable) will be
		   used, which can interfere with proper interpretation of
		   exit status or signal and coredump information.

       source file Read and execute debugger commands from file.  file may
		   itself contain "source" commands.

       H -number   Display last n commands.  Only commands longer than one
		   character are listed.  If number is omitted, list them all.

       q or ^D	   Quit.  ("quit" doesnt work for this, unless youve made an
		   alias) This is the only supported way to exit the debugger,
		   though typing "exit" twice might work.

		   Set the "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 destruc

       R	   Restart the debugger by "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 com
		   mand-line options -w, -I, and -e.

       |dbcmd	   Run the debugger command, piping DB::OUT into your current

       ||dbcmd	   Same as "|dbcmd" but DB::OUT is temporarily "select"ed as

       = [alias value]
		   Define a command alias, like

		       = quit q

		   or list current aliases.

       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.

       m expr	   List which methods may be called on the result of the eval
		   uated expression.  The expression may evaluated to a refer
		   ence to a blessed object, or to a package name.

       M	   Displays all loaded modules and their versions

       man [manpage]
		   Despite its name, this calls your systems default documen
		   tation viewer on the given page, or on the viewer itself if
		   manpage is omitted.	If that viewer is man, the current
		   "Config" information is used to invoke man using the proper
		   MANPATH or -M manpath option.  Failed lookups of the form
		   "XXX" that match known manpages of the form perlXXX will be
		   retried.  This lets you type "man debug" or "man op" from
		   the debugger.

		   On systems traditionally bereft of a usable man command,
		   the debugger invokes 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::doc
		   cmd variable to whatever viewer to view the Perl documenta
		   tion on your system.  This may be set in an rc file, or
		   through direct assignment.  Were still waiting for a work
		   ing example of something along the lines of:

		       $DB::doccmd = netscape -remote http://something.here/;

       Configurable Options

       The debugger has numerous options settable using the "o" command,
       either interactively or from the environment or an rc file.  (./.perldb
       or ~/.perldb under Unix.)

       "recallCommand", "ShellBang"
		   The characters used to recall command or spawn shell.  By
		   default, both are set to "!", which is unfortunate.

       "pager"	   Program to use for output of pager-piped commands (those
		   beginning with a "|" character.)  By default, $ENV{PAGER}
		   will be used.  Because the debugger uses your current ter
		   minal characteristics for bold and underlining, if the cho
		   sen pager does not pass escape sequences through unchanged,
		   the output of some debugger commands will not be readable
		   when sent through the pager.

       "tkRunning" Run Tk while prompting (with ReadLine).

       "signalLevel", "warnLevel", "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 BUGS below.)

		   To disable this default safe mode, set these values to
		   something higher than 0.  At a level of 1, you get back
		   traces upon receiving any kind of warning (this is often
		   annoying) or exception (this is often valuable).  Unfortu
		   nately, the debugger cannot discern fatal exceptions from
		   non-fatal ones.  If "dieLevel" is even 1, then your non-
		   fatal exceptions are also traced and unceremoniously
		   altered if they came from "evald" strings or from any kind
		   of "eval" within modules youre attempting to load.  If
		   "dieLevel" is 2, the debugger doesnt care where they came
		   from:  It usurps your exception handler and prints out a
		   trace, then modifies all exceptions with its own embellish
		   ments.  This may perhaps be useful for some tracing pur
		   poses, but tends to hopelessly destroy any program that
		   takes its exception handling seriously.

       "AutoTrace" Trace mode (similar to "t" command, but can be put into

       "LineInfo"  File or pipe to print line number info to.  If it is a pipe
		   (say, "|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 "vi" or "emacs"
		   hooks, or the "ddd" graphical debugger.

		   If 0, allows stepping off the end of the script.

       "PrintRet"  Print return value after "r" command if set (default).

       "ornaments" Affects screen appearance of the command line (see
		   Term::ReadLine).  There is currently no way to disable
		   these, which can render some output illegible on some dis
		   plays, or with some pagers.	This is considered a bug.

       "frame"	   Affects the printing of messages upon entry and exit from
		   subroutines.  If "frame & 2" is false, messages are printed
		   on entry only. (Printing on exit might be useful if inter
		   spersed with other messages.)

		   If "frame & 4", arguments to functions are printed, plus
		   context and caller info.  If "frame & 8", overloaded
		   "stringify" and "tie"d "FETCH" is enabled on the printed
		   arguments.  If "frame & 16", the return value from the sub
		   routine is printed.

		   The length at which the argument list is truncated is gov
		   erned by the next option:

		   Length to truncate the argument list when the "frame"
		   options bit 4 is set.

		   Change the size of code list window (default is 10 lines).

       The following options affect what happens with "V", "X", and "x" com

       "arrayDepth", "hashDepth"
		   Print only first N elements ( for all).

       "dumpDepth" Limit recursion depth to N levels when dumping structures.
		   Negative values are interpreted as infinity.  Default:

       "compactDump", "veryCompact"
		   Change the style of array and hash output.  If "compact
		   Dump", short array may be printed on one line.

       "globPrint" Whether to print contents of globs.

		   Dump arrays holding debugged files.

		   Dump symbol tables of packages.

		   Dump contents of "reused" addresses.

       "quote", "HighBit", "undefPrint"
		   Change the style of string dump.  The default value for
		   "quote" is "auto"; one can enable double-quotish or single-
		   quotish format by setting it to """ or "", respectively.
		   By default, characters with their high bit set are printed

       "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 modules file scope, or
		   lost in closures.

       After the rc file is read, the debugger reads the $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 ini
       tialization options "TTY", "noTTY", "ReadLine", and "NonStop" there.

       If your rc file contains:

	 parse_options("NonStop=1 LineInfo=db.out AutoTrace");

       then your script will run without human intervention, putting trace
       information into the file db.out.  (If you interrupt it, youd better
       reset "LineInfo" to /dev/tty if you expect to see anything.)

       "TTY"	   The TTY to use for debugging I/O.

       "noTTY"	   If set, the debugger goes into "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 "TTY" option at startup, or to a tty found
		   at runtime using the "Term::Rendezvous" module of your

		   This module should implement a method named "new" that
		   returns an object with two methods: "IN" and "OUT".	These
		   should return filehandles to use for debugging input and
		   output correspondingly.  The "new" method should inspect an
		   argument containing the value of $ENV{PERLDB_NOTTY} at
		   startup, or "$ENV{HOME}/.perldbtty$$" otherwise.  This file
		   is not inspected for proper ownership, so security hazards
		   are theoretically possible.

       "ReadLine"  If false, readline support in the debugger is disabled in
		   order to debug applications that themselves use ReadLine.

       "NonStop"   If set, the debugger goes into non-interactive mode until
		   interrupted, or programmatically by setting $DB::signal or

       Heres an example of using the $ENV{PERLDB_OPTS} variable:

	   $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram

       That will run the script myprogram without human intervention, printing
       out the call tree with entry and exit points.  Note that "NonStop=1
       frame=2" is equivalent to "N f=2", and that originally, options could
       be uniquely abbreviated by the first letter (modulo the "Dump*"
       options).  It is nevertheless recommended that you always spell them
       out in full for legibility and future compatibility.

       Other examples include

	   $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram

       which runs script non-interactively, printing info on each entry into a
       subroutine and each executed line into the file named listing.  (If you
       interrupt it, you would better reset "LineInfo" to something "interac

       Other examples include (using standard shell syntax to show environment
       variable settings):

	 $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out"
	     perl -d myprogram )

       which may be useful for debugging a program that uses "Term::ReadLine"
       itself.	Do not forget to detach your shell from the TTY in the window
       that corresponds to /dev/ttyXX, say, by issuing a command like

	 $ sleep 1000000

       See "Debugger Internals" in perldebguts for details.

       Debugger input/output

       Prompt  The debugger prompt is something like


	       or even


	       where that number is the command number, and which youd use to
	       access with the built-in csh-like history mechanism.  For exam
	       ple, "!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
	       youd 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 "s/n/t expression" command.

       Multiline commands
	       If you want to enter a multi-line command, such as a subroutine
	       definition with several statements or a format, escape the new
	       line that would normally end the debugger command with a back
	       slash.  Heres an example:

		     DB<1> for (1..4) { 	\
		     cont:     print "ok\n";   \
		     cont: }

	       Note that this business of escaping a newline is specific to
	       interactive commands typed into the debugger.

       Stack backtrace
	       Heres an example of what a stack backtrace via "T" command
	       might look like:

		   $ = main::infested called from file Ambulation.pm line 10
		   @ = Ambulation::legs(1, 2, 3, 4) called from file camel_flea line 7
		   $ = main::pests(bactrian, 4) called from file camel_flea line 4

	       The left-hand character up there indicates the context in which
	       the function was called, with "$" and "@" meaning scalar or
	       list contexts respectively, and "." meaning void context (which
	       is actually a sort of scalar context).  The display above says
	       that you were in the function "main::infested" when you ran the
	       stack dump, and that it was called in scalar context from line
	       10 of the file Ambulation.pm, but without any arguments at all,
	       meaning it was called as &infested.  The next stack frame shows
	       that the function "Ambulation::legs" was called in list context
	       from the camel_flea file with four arguments.  The last stack
	       frame shows that "main::pests" was called in scalar context,
	       also from camel_flea, but from line 4.

	       If you execute the "T" command from inside an active "use"
	       statement, the backtrace will contain both a "require" frame
	       and an "eval") frame.

       Line Listing Format
	       This shows the sorts of output the "l" command can produce:

		   DB<<13>> l
		 101:		     @i{@i} = ();
		 102:b		     @isa{@i,$pack} = ()
		 103			 if(exists $i{$prevpack} || exists $isa{$pack});
		 104		 }
		 106		 next
		 107==> 	     if(exists $isa{$pack});
		 109:a		 if ($extra-- > 0) {
		 110:		     %isa = ($pack,1);

	       Breakable lines are marked with ":".  Lines with breakpoints
	       are marked by "b" and those with actions by "a".  The line
	       thats about to be executed is marked by "==>".

	       Please be aware that code in debugger listings may not look the
	       same as your original source code.  Line directives and exter
	       nal source filters can alter the code before Perl sees it,
	       causing code to move from its original positions or take on
	       entirely different forms.

       Frame listing
	       When the "frame" option is set, the debugger would print
	       entered (and optionally exited) subroutines in different
	       styles.	See perldebguts for incredibly long examples of these.

       Debugging compile-time statements

       If you have compile-time executable statements (such as code within
       BEGIN and CHECK blocks or "use" statements), these will not be stopped
       by debugger, although "require"s and INIT blocks will, and compile-time
       statements can be traced with "AutoTrace" option set in "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 debug
       ger is not running:

	   $DB::single = 1;

       If you set $DB::single to 2, its equivalent to having just typed the
       "n" command, whereas a value of 1 means the "s" command.  The
       $DB::trace  variable should be set to 1 to simulate having typed the
       "t" command.

       Another way to debug compile-time code is to start the debugger, set a
       breakpoint on the load of some module:

	   DB<7> b load f:/perllib/lib/Carp.pm
	 Will stop on load of f:/perllib/lib/Carp.pm.

       and then restart the debugger using the "R" command (if possible).  One
       can use "b compile subname" for the same purpose.

       Debugger Customization

       The debugger probably contains enough configuration hooks that you
       wont ever have to modify it yourself.  You may change the behaviour of
       debugger from within the debugger using its "o" command, from the com
       mand line via the "PERLDB_OPTS" environment variable, and from cus
       tomization files.

       You can do some customization by setting up a .perldb file, which con
       tains 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/;

       You can change options from .perldb by using calls like this one;

	   parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2");

       The code is executed in the package "DB".  Note that .perldb is pro
       cessed before processing "PERLDB_OPTS".	If .perldb defines the subrou
       tine "afterinit", that function is called after debugger initialization
       ends.  .perldb may be contained in the current directory, or in the
       home directory.	Because this file is sourced in by Perl and may con
       tain arbitrary commands, for security reasons, 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 .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 sup
       ported interface and is subject to change in future releases.

       If you want to modify the debugger, copy perl5db.pl from the Perl
       library to another name and hack it to your hearts content.  Youll
       then want to set your "PERL5DB" environment variable to say something
       like this:

	   BEGIN { require "myperl5db.pl" }

       As a last resort, you could also use "PERL5DB" to customize the debug
       ger by directly setting internal variables or calling debugger func

       Note that any variables and functions that are not documented in this
       document (or in perldebguts) are considered for internal use only, and
       as such are subject to change without notice.

       Readline Support

       As shipped, the only command-line history supplied is a simplistic one
       that checks for leading exclamation points.  However, if you install
       the Term::ReadKey and Term::ReadLine modules from CPAN, you will have
       full editing capabilities much like GNU readline(3) provides.  Look for
       these in the modules/by-module/Term directory on CPAN.  These do not
       support normal vi command-line editing, however.

       A rudimentary command-line completion is also available.  Unfortu
       nately, the names of lexical variables are not available for comple

       Editor Support for Debugging

       If you have the FSFs version of 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 debug

       Perl comes with a start file for making emacs act like a syntax-
       directed editor that understands (some of) Perls syntax.  Look in the
       emacs directory of the Perl source distribution.

       A similar setup by Tom Christiansen for interacting with any vendor-
       shipped vi and the X11 window system is also available.	This works
       similarly to the integrated multiwindow support that emacs provides,
       where the debugger drives the editor.  At the time of this writing,
       however, that tools eventual location in the Perl distribution was

       Users of vi should also look into vim and gvim, the mousey and windy
       version, for coloring of Perl keywords.

       Note that only perl can truly parse Perl, so all such CASE tools fall
       somewhat short of the mark, especially if you dont program your Perl
       as a C programmer might.

       The Perl Profiler

       If you wish to supply an alternative debugger for Perl to run, just
       invoke your script with a colon and a package argument given to the -d
       flag.  The most popular alternative debuggers for Perl is the Perl pro
       filer.  Devel::DProf is now included with the standard Perl
       distribution.  To profile your Perl program in the file mycode.pl, just

	   $ perl -d:DProf mycode.pl

       When the script terminates the profiler will dump the profile informa
       tion to a file called tmon.out.	A tool like dprofpp, also supplied
       with the standard Perl distribution, can be used to interpret the
       information in that profile.

Debugging regular expressions
       "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 Perls regular
       expressions are internally compiled into an automaton. These matters
       are explored in some detail in "Debugging regular expressions" in

Debugging memory usage
       Perl contains internal support for reporting its own memory usage, but
       this is a fairly advanced concept that requires some understanding of
       how memory allocation works.  See "Debugging Perl memory usage" in
       perldebguts for the details.

       You did try the -w switch, didnt you?

       perldebtut, perldebguts, re, DB, Devel::DProf, dprofpp, Dumpvalue, and

       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 dont
       have to type the path or "which $scriptname".

	 $ perl -Sd foo.pl

       You cannot get stack frame information or in any fashion debug func
       tions that were not compiled by Perl, such as those from C or C++

       If you alter your @_ arguments in a subroutine (such as with "shift" or
       "pop"), the stack backtrace will not show the original values.

       The debugger does not currently work in conjunction with the -W com
       mand-line switch, because it itself is not free of warnings.

       If youre in a slow syscall (like "wait"ing, "accept"ing, or "read"ing
       from your keyboard or a socket) and havent set up your own $SIG{INT}
       handler, then you wont be able to CTRL-C your way back to the debug
       ger, because the debuggers own $SIG{INT} handler doesnt understand
       that it needs to raise an exception to longjmp(3) out of slow syscalls.

perl v5.8.8			  2008-04-25			  PERLDEBUG(1)

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