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perldebug ()
  • >> perldebug (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • perldebug (1) ( Разные man: Команды и прикладные программы пользовательского уровня )
  • 
    
    

    NAME

         perldebug - Perl debugging
    
    
    

    DESCRIPTION

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

    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 it's about to hand off to the
         interpreter.  That means your code must first compile
         correctly for the debugger to work on it.  Then when the
         interpreter starts up, it preloads a special Perl library
         file containing the debugger.
    
         The program will halt right before the first run-time
         executable statement (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 it's 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.)
    
         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 `;' or perhaps a `+', or by wrapping it
         with parentheses or braces.
    
         Debugger Commands
    
         The debugger understands the following commands:
    
         h [command] Prints out a help message.
    
                     If you supply another debugger command as an
                     argument to the `h' command, it prints out the
                     description for just that command.  The special
                     argument of `h h' produces a more compact help
                     listing, designed to fit together on one screen.
    
                     If the output of the `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 `O
                     pager=...' command.
    
         p expr      Same as `print {$DB::OUT} expr' in the current
                     package.  In particular, because this is just
                     Perl's own `print' function, 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 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' function in
                     Perl.  See the Dumpvalue manpage if you'd like
                     to do this yourself.
    
                     The output format is governed by multiple
                     options described under the section on
                     "Options".
    
         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 what's what, control characters are made
                     printable, etc.).  Make sure you don't put the
                     type specifier (like `$') there, just the symbol
                     names, like this:
    
                         V DB filename line
    
                     Use `~pattern' and `!pattern' for positive and
                     negative regexes.
                     This is similar to calling the `x' command on
                     each applicable var.
    
         X [vars]    Same as `V currentpackage [vars]'.
    
         T           Produce a stack backtrace.  See below for
                     details on its output.
    
         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 (default).
    
         <CR>        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.
    
         w [line]    List window (a few lines) around the current
                     line.
    
         .           Return the internal debugger pointer to the line
                     last executed, 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 accessible.
    
         /pattern/   Search forwards for pattern (a Perl regex);
                     final / is optional.
    
         ?pattern?   Search backwards for pattern; final ? is
                     optional.
    
         L           List all breakpoints and actions.
    
         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 the
                     Frame Listing Output Examples entry in the
                     perldebguts manpage for examples.
    
         b [line] [condition]
                     Set a breakpoint before the given line.  If 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 `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 subroutine.  subname may be a variable
                     containing a code reference (in this case
                     condition is not supported).
    
         b postpone subname [condition]
                     Set a breakpoint at first line of subroutine
                     after it is compiled.
    
         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.
    
         d [line]    Delete a breakpoint from the specified line.  If
                     line is omitted, deletes the breakpoint from the
                     line about to be executed.
    
         D           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 executed.  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 passed:
    
                         a 53 print "DB FOUND $foo\n"
    
    
         a [line]    Delete an action from the specified line.  If
                     line is omitted, delete the action on the line
                     that is about to be executed.
    
         A           Delete all installed actions.
    
         W expr      Add a global watch-expression.  We hope you know
                     what one of these is, because they're supposed
                     to be obvious.  WARNING: It is far too easy to
                     destroy your watch expressions by accidentally
                     omitting the expr.
    
         W           Delete all watch-expressions.
    
         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
                     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: `O option='this
                     isn\'t bad'' or `O option="She said, \"Isn't
                     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
                     abbreviated, but for clarity probably should not
                     be.  Several options can be set together.  See
                     the section on "Options" for a list of these.
    
         < ?         List out all pre-prompt Perl command actions.
    
         < [ command ]
                     Set an action (Perl command) to happen before
                     every debugger prompt.  A multi-line command may
                     be entered by backslashing the newlines. WARNING
                     If `command' is missing, all actions are wiped
                     out!
    
         << command  Add an action (Perl command) to happen before
                     every debugger prompt.  A multi-line command may
                     be entered by backwhacking the newlines.
    
         > ?         List out post-prompt Perl command actions.
    
         > 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).  WARNING If `command' is missing, all
                     actions are wiped out!
    
         >> command  Adds an action (Perl command) to happen after
                     the prompt when you've just given a command to
                     return to executing the script.  A multi-line
                     command may be entered by slackbashing the
                     newlines.
    
         { ?         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.
                     WARNING If `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 `;{ ... }'
                     or even `do { ... }'.
    
         {{ 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 number'th 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 user's current shell (well, their
                     `$ENV{SHELL}' variable) will be used, which can
                     interfere with proper interpretation of exit
                     status or signal and coredump information.
    
         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" doesn't work for this, unless
                     you've 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 destruction.
    
         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 command-line options -w, -I, and
                     -e.
    
         |dbcmd      Run the debugger command, piping DB::OUT into
                     your current pager.
    
         ||dbcmd     Same as `|dbcmd' but DB::OUT is temporarily
                     `select'ed as well.
    
         = [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 evaluated expression.  The expression may
                     evaluated to a reference to a blessed object, or
                     to a package name.
    
         man [manpage]
                     Despite its name, this calls your system's
                     default documentation 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::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/';
    
    
         Configurable Options
    
         The debugger has numerous options settable using the `O'
         command, either interactively or from the environment or an
         rc file.
    
         `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 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.
    
         `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 the
                     BUGS manpage 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 `dieLevel' is even 1, then
                     your non-fatal exceptions are also traced and
                     unceremoniously altered if they came from
                     `eval'd' strings or from any kind of `eval'
                     within modules you're attempting to load.  If
                     `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.
    
         `AutoTrace' Trace mode (similar to `t' command, but can be
                     put into `PERLDB_OPTS').
    
         `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.
    
         `inhibit_exit'
                     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 the Term::ReadLine manpage).  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.
    
         `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 interspersed 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
                     subroutine is printed.
    
                     The length at which the argument list is
                     truncated is governed by the next option:
    
    
         `maxTraceLen'
                     Length to truncate the argument list when the
                     `frame' option's bit 4 is set.
    
         The following options affect what happens with `V', `X', and
         `x' commands:
    
         `arrayDepth', `hashDepth'
                     Print only first N elements ('' for all).
    
         `compactDump', `veryCompact'
                     Change the style of array and hash output.  If
                     `compactDump', short array may be printed on one
                     line.
    
         `globPrint' Whether to print contents of globs.
    
         `DumpDBFiles'
                     Dump arrays holding debugged files.
    
         `DumpPackages'
                     Dump symbol tables of packages.
    
         `DumpReused'
                     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 verbatim.
    
         `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.
    
         During startup, options are initialized from
         `$ENV{PERLDB_OPTS}'.  You may place the initialization
         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, you'd 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 choice.
    
                     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
                     `"/tmp/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 $DB::single.
    
         Here's 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 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 "interactive"!)
    
         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 the Debugger Internals entry in the perldebguts manpage
         for details.
    
         Debugger input/output
    
         Prompt  The debugger prompt is something like
    
                     DB<8>
    
                 or even
    
                     DB<<17>>
    
                 where that number is the command number, and which
                 you'd use to access with the built-in csh-like
                 history mechanism.  For example, `!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
                 `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 newline that would normally end
                 the debugger command with a backslash.  Here's an
                 example:
    
                       DB<1> for (1..4) {         \
                       cont:     print "ok\n";   \
                       cont: }
                       ok
                       ok
                       ok
                       ok
    
                 Note that this business of escaping a newline is
                 specific to interactive commands typed into the
                 debugger.
    
         Stack backtrace
                 Here's 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             }
                   105
                   106             next
                   107==>              if(exists $isa{$pack});
                   108
                   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 that's about to be executed is
                 marked by `==>'.
    
         Frame listing
                 When the `frame' option is set, the debugger would
                 print entered (and optionally exited) subroutines in
                 different styles.  See the perldebguts manpage 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 debugger is not running:
    
             $DB::single = 1;
    
         If you set `$DB::single' to 2, it's equivalent to having
         just typed the `n' command, whereas a value of 1 means the
         `s' command.  The `$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 won't ever have to modify it yourself.  You may
         change the behaviour of debugger from within the debugger
         using its `O' command, from the command line via the
         `PERLDB_OPTS' environment variable, and from customization
         files.
    
         You can do some customization by setting up a .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/';
    
         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 processed before processing `PERLDB_OPTS'.  If .perldb
         defines the subroutine `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
         contain arbitrary commands, for security reasons, it must be
         owned by the superuser or the current user, and writable by
         no one but its owner.
    
         If you want to modify the debugger, copy perl5db.pl from the
         Perl library to another name and hack it to your heart's
         content.  You'll 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 debugger by directly setting internal variables or
         calling debugger functions.
    
         Note that any variables and functions that are not
         documented in this document (or in the perldebguts manpage)
         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.
         Unfortunately, the names of lexical variables are not
         available for completion.
    
    
    
         Editor Support for Debugging
    
         If you have the FSF's 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 debuggers.
    
         Perl comes with a start file for making emacs act like a
         syntax-directed editor that understands (some of) Perl's
         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 tool's eventual location in the Perl distribution was
         uncertain.
    
         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
         don't 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 profiler.  Devel::DProf is
         now included with the standard Perl distribution.  To
         profile your Perl program in the file mycode.pl, just type:
    
             $ perl -d:DProf mycode.pl
    
         When the script terminates the profiler will dump the
         profile information 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 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 the Debugging
         regular expressions entry in the perldebguts manpage.
    
    
    

    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 the
         Debugging Perl memory usage entry in the perldebguts manpage
         for the details.
    
    
    

    SEE ALSO

         You did try the -w switch, didn't you?
    
         the perldebguts manpage, the re manpage, the DB manpage, the
         Devel::Dprof manpage, the dprofpp manpage, the Dumpvalue
         manpage, and the perlrun manpage.
    
    
    

    BUGS

         You cannot get stack frame information or in any fashion
         debug functions that were not compiled by Perl, such as
         those from C or C++ extensions.
    
         If you alter your @_ arguments in a subroutine (such as with
         `shift' or `pop', the stack backtrace will not show the
         original values.
    
         The debugger does not currently work in conjunction with the
         -W command-line switch, because it itself is not free of
         warnings.
    
         If you're in a slow syscall (like `wait'ing, `accept'ing, or
         `read'ing from your keyboard or a socket) and haven't set up
         your own `$SIG{INT}' handler, then you won't be able to
         CTRL-C your way back to the debugger, because the debugger's
         own `$SIG{INT}' handler doesn't understand that it needs to
         raise an exception to longjmp(3) out of slow syscalls.
    
    
    
    


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