IRIX Base Documentation 2002 November

home *** CD-ROM | disk | FTP | other *** search

/ IRIX Base Documentation 2002 November / SGI IRIX Base Documentation 2002 November.iso / usr / share / catman / u_man / cat1 / perldebug.z / perldebug

Wrap

Text File | 2002-10-03 | 51.4 KB | 1,321 lines

PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) NNNNAAAAMMMMEEEE perldebug - Perl debugging DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN First of all, have you tried using the ----wwww switch? TTTThhhheeee PPPPeeeerrrrllll DDDDeeeebbbbuuuuggggggggeeeerrrr "As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs." --_M_a_u_r_i_c_e _W_i_l_k_e_s, _1_9_4_9 If you invoke Perl with the ----dddd 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 as it usually is in the typical compiled environment. Instead, the ----dddd flag tells the compiler to insert source information into the parse trees it's about to hand off to the interpreter. That means your code must first compile correctly for the debugger to work on it. Then when the interpreter starts up, it preloads a Perl library file containing the debugger itself. The program will halt _r_i_g_h_t _b_e_f_o_r_e 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 _a_b_o_u_t 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 its own state information.) Leading white space before a command would cause the debugger to think it's _N_O_T a debugger command but for Perl, so be careful not to do that. DDDDeeeebbbbuuuuggggggggeeeerrrr CCCCoooommmmmmmmaaaannnnddddssss The debugger understands the following commands: h [command] Prints out a help message. If you supply another debugger command as an argument to the PPPPaaaaggggeeee 1111 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) 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, either precede the command with a leading pipe symbol so 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 pppprrrriiiinnnntttt function, this means that nested data structures and objects are not dumped, unlike with the x command. The DB::OUT filehandle is opened to /_d_e_v/_t_t_y, 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 print function. The details of printout are governed by multiple Options. V [pkg [vars]] Display all (or some) variables in package (defaulting to the main package) using a data pretty-printer (hashes show their keys and values so you see what's what, control characters are made printable, etc.). Make sure you don't put the type specifier (like $) there, just the symbol names, like this: V DB filename line Use ~pattern and !pattern for positive and negative regexps. Nested data structures are printed out in a legible fashion, unlike the print function. The details of printout are governed by multiple Options. 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 it reaches the beginning of another statement, descending into subroutine calls. If an expression is supplied that includes function calls, it too PPPPaaaaggggeeee 2222 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) will be single-stepped. n [expr] Next. Executes over subroutine calls, until it reaches 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. <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. - List previous window of lines. w [line] List window (a few lines) around the current line. . Return debugger pointer to the last-executed line and print it out. f filename Switch to viewing a different file or eval statement. If filename is not a full filename as found in values of %INC, it is considered as a regexp. /pattern/ Search forwards for pattern; final / is optional. ?pattern? Search backwards for pattern; final ? is optional. L List all breakpoints and actions. S [[!]pattern] List subroutine names [not] matching pattern. t Toggle trace mode (see also AutoTrace Option). t expr Trace through execution of expr. For example: $ perl -de 42 Stack dump during die enabled outside of evals. Loading DB routines from perl5db.pl patch level 0.94 Emacs support available. PPPPaaaaggggeeee 3333 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) Enter h or `h h' for help. main::(-e:1): 0 DB<1> sub foo { 14 } DB<2> sub bar { 3 } DB<3> t print foo() * bar() main::((eval 172):3): print foo() + bar(); main::foo((eval 168):2): main::bar((eval 170):2): 42 or, with the Option frame=2 set, DB<4> O f=2 frame = '2' DB<5> t print foo() * bar() 3: foo() * bar() entering main::foo 2: sub foo { 14 }; exited main::foo entering main::bar 2: sub bar { 3 }; exited main::bar 42 b [line] [condition] Set a breakpoint. If line is omitted, sets a breakpoint on the line that is about to be executed. If a condition is specified, it's evaluated each time the statement is reached and a breakpoint is taken only if the condition is true. Breakpoints may be set on only lines that begin an executable statement. Conditions don't use iiiiffff: b 237 $x > 30 b 237 ++$count237 < 11 b 33 /pattern/i b subname [condition] Set a breakpoint at the first line of the named subroutine. b postpone subname [condition] Set breakpoint at first line of subroutine after it is compiled. b load filename Set breakpoint at the first executed line of the file. Filename should be a full name as found in values of %INC. PPPPaaaaggggeeee 4444 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) b compile subname Sets breakpoint at the first statement executed after the subroutine is compiled. d [line] Delete a breakpoint at the specified line. If line is omitted, deletes the breakpoint on the line that is about to be executed. D Delete all installed breakpoints. a [line] command Set an action to be done before the line is 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 Delete all installed actions. O [opt[=val]] [op'val' [opt?]... Set or query values of options. val defaults to 1. opt can be abbreviated. Several options can be listed. recallCommand, ShellBang The characters used to recall command or spawn shell. By default, these are both set to !. pager Program to use for output of pager-piped commands (those beginning with a | character.) By default, $ENV{PAGER} will be used. tkRunning Run Tk while prompting (with ReadLine). signalLevel, warnLevel, dieLevel Level of verbosity. By default the debugger is in a sane verbose mode, thus it will print backtraces on all the warnings and die-messages which are going to be printed out, and will print a message when interesting uncaught signals arrive. To disable this behaviour, set these values to 0. If dieLevel is 2, then the messages which will be PPPPaaaaggggeeee 5555 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) caught by surrounding eval are also printed. 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, "emacs like" message is used. inhibit_exit If 0, allows _s_t_e_p_p_i_n_g _o_f_f the end of the script. PrintRet affects printing of return value after r command. ornaments affects screen appearance of the command line (see the _T_e_r_m::_R_e_a_d_L_i_n_e manpage). frame affects printing messages on entry and exit from subroutines. If frame & 2 is false, messages are printed on entry only. (Printing on exit may be useful if _i_n_t_e_r(di)spersed with other messages.) If frame & 4, arguments to functions are printed as well as the context and caller info. If frame & 8, overloaded stringify and tied FETCH are enabled on the printed arguments. If frame & 16, the return value from the subroutine is printed as well. The length at which the argument list is truncated is governed by the next option: maxTraceLen length at which the argument list is truncated when 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 style of array and hash dump. 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. PPPPaaaaggggeeee 6666 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) quote, HighBit, undefPrint Change style of string dump. Default value of quote is auto, one can enable either double- quotish dump, or single-quotish by setting it to " or '. By default, characters with high bit set are printed _a_s _i_s. UsageOnly _v_e_r_y rudimentally per-package memory usage dump. Calculates total size of strings in variables in the package. During startup options are initialized from $ENV{PERLDB_OPTS}. You can put additional initialization options TTY, noTTY, ReadLine, and NonStop there. Example rc file: &parse_options("NonStop=1 LineInfo=db.out AutoTrace"); The script will run without human intervention, putting trace information into the file _d_b._o_u_t. (If you interrupt it, you would better reset LineInfo to something "interactive"!) TTY The TTY to use for debugging I/O. noTTY If set, goes in NonStop mode, and would not connect to a TTY. If interrupt (or if control goes to debugger via explicit setting of $DB::signal or $DB::single from the Perl script), connects to a TTY specified by the TTY option at startup, or to a TTY found at runtime using Term::Rendezvous module of your choice. This module should implement a method new which returns an object with two methods: IN and OUT, returning two filehandles to use for debugging input and output correspondingly. Method new may inspect an argument which is a value of $ENV{PERLDB_NOTTY} at startup, or is "/tmp/perldbtty$$" otherwise. ReadLine If false, readline support in debugger is disabled, so you can debug ReadLine applications. NonStop If set, debugger goes into noninteractive mode until interrupted, or programmatically by setting $DB::signal or $DB::single. Here's an example of using the $ENV{PERLDB_OPTS} variable: PPPPaaaaggggeeee 7777 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) $ PERLDB_OPTS="N f=2" perl -d myprogram will run the script myprogram without human intervention, printing out the call tree with entry and exit points. Note that N f=2 is equivalent to NonStop=1 frame=2. Note also that at the moment when this documentation was written all the options to the debugger could be uniquely abbreviated by the first letter (with exception of Dump* options). Other examples may include $ PERLDB_OPTS="N f A L=listing" perl -d myprogram - runs script noninteractively, printing info on each entry into a subroutine and each executed line into the file _l_i_s_t_i_n_g. (If you interrupt it, you would better reset LineInfo to something "interactive"!) $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram may be useful for debugging a program which uses Term::ReadLine itself. Do not forget detach shell from the TTY in the window which corresponds to /_d_e_v/_t_t_y_c, say, by issuing a command like $ sleep 1000000 See the section on _D_e_b_u_g_g_e_r _I_n_t_e_r_n_a_l_s below for more details. < [ command ] Set an action (Perl command) to happen before every debugger prompt. A multi-line command may be entered by backslashing the newlines. If command is missing, resets the list of actions. << command Add an action (Perl command) to happen before every debugger prompt. A multi-line command may be entered by backslashing the newlines. > 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. If command is missing, resets the list of actions. PPPPaaaaggggeeee 8888 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) >> 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. { [ command ] Set an action (debugger command) to happen before every debugger prompt. A multi-line command may be entered by backslashing the newlines. If command is missing, resets the list of actions. {{ command Add an action (debugger command) to happen before every debugger prompt. A multi-line command may be entered by backslashing the newlines. ! number Redo a previous command (default previous command). ! -number Redo number'th-to-last 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 too. H -number Display last n commands. Only commands longer than one character are listed. If number is omitted, lists them all. q or ^D Quit. ("quit" doesn't work for this.) This is the only supported way to exit the debugger, though typing exit twice may do it too. Set an Option inhibit_exit to 0 if you want to be able to _s_t_e_p _o_f_f the end the script. You may also need to set $finished to 0 at some moment if you want to step through global destruction. R Restart the debugger by eeeexxxxeeeeccccing a new session. It tries to maintain your history across this, but internal settings and command line options may be lost. Currently the following setting are preserved: history, breakpoints, actions, debugger Options, and the following command line options: ----wwww, ----IIII, and ----eeee. |dbcmd Run debugger command, piping DB::OUT to current pager. ||dbcmd Same as |dbcmd but DB::OUT is temporarily sssseeeelllleeeecccctttted as well. Often used with commands that would otherwise produce long output, such as |V main PPPPaaaaggggeeee 9999 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) = [alias value] Define a command alias, like = quit q or list current aliases. command Execute command as a Perl statement. A missing semicolon will be supplied. m expr The expression is evaluated, and the methods which may be applied to the result are listed. m package The methods which may be applied to objects in the package are listed. DDDDeeeebbbbuuuuggggggggeeeerrrr iiiinnnnppppuuuutttt////oooouuuuttttppppuuuutttt Prompt The debugger prompt is something like DB<8> or even DB<<17>> where that number is the command number, which you'd use to access with the builtin ccccsssshhhh-like history mechanism, e.g., !17 would repeat command number 17. The number of angle brackets indicates the depth of the debugger. You could get more than one set of brackets, for example, if you'd already at a breakpoint and then printed out the result of a function call that itself also has a breakpoint, or you step into an expression via 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, you may 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. PPPPaaaaggggeeee 11110000 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) 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 tells whether the function was called in a scalar or list context (we bet you can tell which is which). What that says is that you were in the function main::infested when you ran the stack dump, and that it was called in a scalar context from line 10 of the file _A_m_b_u_l_a_t_i_o_n._p_m, 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 a list context from the _c_a_m_e_l__f_l_e_a file with four arguments. The last stack frame shows that main::pests was called in a scalar context, also from _c_a_m_e_l__f_l_e_a, but from line 4. Note that if you execute T command from inside an active use statement, the backtrace will contain both require frame and an eval) frame. Listing Listing given via different flavors of l command looks like this: DB<<13>> l 101: @i{@i} = (); 102:b @isa{@i,$pack} = () 103 if(exists $i{$prevpack} || exists $isa{$pack}); 104 } 105 106 next 107==> if(exists $isa{$pack}); 108 109:a if ($extra-- > 0) { 110: %isa = ($pack,1); Note that the breakable lines are marked with :, lines with breakpoints are marked by b, with actions by a, and the next executed line is marked by ==>. Frame listing When frame option is set, debugger would print entered (and optionally exited) subroutines in different styles. What follows is the start of the listing of env "PERLDB_OPTS=f=n N" perl -d -V for different values of n: PPPPaaaaggggeeee 11111111 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) 1 entering main::BEGIN entering Config::BEGIN Package lib/Exporter.pm. Package lib/Carp.pm. Package lib/Config.pm. entering Config::TIEHASH entering Exporter::import entering Exporter::export entering Config::myconfig entering Config::FETCH entering Config::FETCH entering Config::FETCH entering Config::FETCH 2 entering main::BEGIN entering Config::BEGIN Package lib/Exporter.pm. Package lib/Carp.pm. exited Config::BEGIN Package lib/Config.pm. entering Config::TIEHASH exited Config::TIEHASH entering Exporter::import entering Exporter::export exited Exporter::export exited Exporter::import exited main::BEGIN entering Config::myconfig entering Config::FETCH exited Config::FETCH entering Config::FETCH exited Config::FETCH entering Config::FETCH 4 PPPPaaaaggggeeee 11112222 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) in $=main::BEGIN() from /dev/nul:0 in $=Config::BEGIN() from lib/Config.pm:2 Package lib/Exporter.pm. Package lib/Carp.pm. Package lib/Config.pm. in $=Config::TIEHASH('Config') from lib/Config.pm:644 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li in @=Config::myconfig() from /dev/nul:0 in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'SUBVERSION') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574 6 in $=main::BEGIN() from /dev/nul:0 in $=Config::BEGIN() from lib/Config.pm:2 Package lib/Exporter.pm. Package lib/Carp.pm. out $=Config::BEGIN() from lib/Config.pm:0 Package lib/Config.pm. in $=Config::TIEHASH('Config') from lib/Config.pm:644 out $=Config::TIEHASH('Config') from lib/Config.pm:644 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 out $=main::BEGIN() from /dev/nul:0 in @=Config::myconfig() from /dev/nul:0 in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574 out $=Config::FETCH(ref(Config), 'PATCHLEVEL') from lib/Config.pm:574 in $=Config::FETCH(ref(Config), 'SUBVERSION') from lib/Config.pm:574 14 PPPPaaaaggggeeee 11113333 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) in $=main::BEGIN() from /dev/nul:0 in $=Config::BEGIN() from lib/Config.pm:2 Package lib/Exporter.pm. Package lib/Carp.pm. out $=Config::BEGIN() from lib/Config.pm:0 Package lib/Config.pm. in $=Config::TIEHASH('Config') from lib/Config.pm:644 out $=Config::TIEHASH('Config') from lib/Config.pm:644 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 out $=main::BEGIN() from /dev/nul:0 in @=Config::myconfig() from /dev/nul:0 in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 30 in $=CODE(0x15eca4)() from /dev/null:0 in $=CODE(0x182528)() from lib/Config.pm:2 Package lib/Exporter.pm. out $=CODE(0x182528)() from lib/Config.pm:0 scalar context return from CODE(0x182528): undef Package lib/Config.pm. in $=Config::TIEHASH('Config') from lib/Config.pm:628 out $=Config::TIEHASH('Config') from lib/Config.pm:628 scalar context return from Config::TIEHASH: empty hash in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 scalar context return from Exporter::export: '' out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 scalar context return from Exporter::import: '' In all the cases indentation of lines shows the call tree, if bit 2 of frame is set, then a line is printed on exit from a subroutine as well, if bit 4 is set, then the arguments are printed as well as the caller info, if bit 8 is set, the arguments are printed even if they are tied or references, if bit 16 is set, the return value is printed as well. When a package is compiled, a line like this Package lib/Carp.pm. is printed with proper indentation. PPPPaaaaggggeeee 11114444 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) DDDDeeeebbbbuuuuggggggggiiiinnnngggg ccccoooommmmppppiiiilllleeee----ttttiiiimmmmeeee ssssttttaaaatttteeeemmmmeeeennnnttttssss If you have any compile-time executable statements (code within a BEGIN block or a use statement), these will NOT be stopped by debugger, although requires 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 the value 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 debugger, set a breakpoint on _l_o_a_d of some module thusly DB<7> b load f:/perllib/lib/Carp.pm Will stop on load of `f:/perllib/lib/Carp.pm'. and restart debugger by R command (if possible). One can use b compile subname for the same purpose. DDDDeeeebbbbuuuuggggggggeeeerrrr CCCCuuuussssttttoooommmmiiiizzzzaaaattttiiiioooonnnn Most probably you do not want to modify the debugger, it contains enough hooks to satisfy most needs. You may change the behaviour of debugger from the debugger itself, using Options, from the command line via PERLDB_OPTS environment variable, and from _c_u_s_t_o_m_i_z_a_t_i_o_n _f_i_l_e_s. You can do some customization by setting up a ._p_e_r_l_d_b 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\$/'; One changes options from ._p_e_r_l_d_b file via 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 ._p_e_r_l_d_b is processed before processing PERLDB_OPTS. If ._p_e_r_l_d_b defines the subroutine afterinit, it is called after all the debugger initialization ends. ._p_e_r_l_d_b may be contained in the current directory, or in the LOGDIR/HOME directory. PPPPaaaaggggeeee 11115555 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) If you want to modify the debugger, copy _p_e_r_l_5_d_b._p_l from the Perl library to another name and modify it as necessary. You'll also want to set your PERL5DB environment variable to say something like this: BEGIN { require "myperl5db.pl" } As the last resort, one can use PERL5DB to customize debugger by directly setting internal variables or calling debugger functions. RRRReeeeaaaaddddlllliiiinnnneeee SSSSuuuuppppppppoooorrrrtttt 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 _r_e_a_d_l_i_n_e(3) provides. Look for these in the _m_o_d_u_l_e_s/_b_y-_m_o_d_u_l_e/_T_e_r_m directory on CPAN. A rudimentary command line completion is also available. Unfortunately, the names of lexical variables are not available for completion. EEEEddddiiiittttoooorrrr SSSSuuuuppppppppoooorrrrtttt ffffoooorrrr DDDDeeeebbbbuuuuggggggggiiiinnnngggg If you have GNU eeeemmmmaaaaccccssss 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 is also delivered with a start file for making eeeemmmmaaaaccccssss act like a syntax-directed editor that understands (some of) Perl's syntax. Look in the _e_m_a_c_s directory of the Perl source distribution. (Historically, a similar setup for interacting with vvvviiii and the X11 window system had also been available, but at the time of this writing, no debugger support for vvvviiii currently exists.) TTTThhhheeee PPPPeeeerrrrllll PPPPrrrrooooffffiiiilllleeeerrrr 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 ----dddd flag. One of the most popular alternative debuggers for Perl is DDDDPPPPrrrrooooffff, the Perl profiler. As of this writing, DDDDPPPPrrrrooooffff is not included with the standard Perl distribution, but it is expected to be included soon, for certain values of "soon". Meanwhile, you can fetch the Devel::Dprof module from CPAN. Assuming it's properly installed on your system, to profile your Perl program in the file _m_y_c_o_d_e._p_l, just type: perl -d:DProf mycode.pl When the script terminates the profiler will dump the profile information to a file called _t_m_o_n._o_u_t. A tool like ddddpppprrrrooooffffpppppppp (also supplied with the Devel::DProf package) can be used to interpret the information which is PPPPaaaaggggeeee 11116666 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) in that profile. DDDDeeeebbbbuuuuggggggggeeeerrrr ssssuuuuppppppppoooorrrrtttt iiiinnnn ppppeeeerrrrllll When you call the ccccaaaalllllllleeeerrrr function (see the caller entry in the _p_e_r_l_f_u_n_c manpage) from the package DB, Perl sets the array @DB::args to contain the arguments the corresponding stack frame was called with. If perl is run with ----dddd option, the following additional features are enabled (cf. the section on $^_P in the _p_e_r_l_v_a_r manpage): +o Perl inserts the contents of $ENV{PERL5DB} (or BEGIN {require 'perl5db.pl'} if not present) before the first line of the application. +o The array @{"_<$filename"} is the line-by-line contents of $filename for all the compiled files. Same for evaled strings which contain subroutines, or which are currently executed. The $filename for evaled strings looks like (eval 34). +o The hash %{"_<$filename"} contains breakpoints and action (it is keyed by line number), and individual entries are settable (as opposed to the whole hash). Only true/false is important to Perl, though the values used by _p_e_r_l_5_d_b._p_l have the form "$break_condition\0$action". Values are magical in numeric context: they are zeros if the line is not breakable. Same for evaluated strings which contain subroutines, or which are currently executed. The $filename for evaled strings looks like (eval 34). +o The scalar ${"_<$filename"} contains "_<$filename". Same for evaluated strings which contain subroutines, or which are currently executed. The $filename for evaled strings looks like (eval 34). +o After each required file is compiled, but before it is executed, DB::postponed(*{"_<$filename"}) is called (if subroutine DB::postponed exists). Here the $filename is the expanded name of the required file (as found in values of %INC). +o After each subroutine subname is compiled existence of $DB::postponed{subname} is checked. If this key exists, DB::postponed(subname) is called (if subroutine DB::postponed exists). +o A hash %DB::sub is maintained, with keys being subroutine names, values having the form filename:startline-endline. filename has the form (eval 31) for subroutines defined inside evals. +o When execution of the application reaches a place that can have a breakpoint, a call to DB::DB() is performed if any one of variables $DB::trace, $DB::single, or $DB::signal is true. (Note that these PPPPaaaaggggeeee 11117777 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) variables are not localizable.) This feature is disabled when the control is inside DB::DB() or functions called from it (unless $^D & (1<<30)). +o When execution of the application reaches a subroutine call, a call to &DB::sub(_a_r_g_s) is performed instead, with $DB::sub being the name of the called subroutine. (Unless the subroutine is compiled in the package DB.) Note that if &DB::sub needs some external data to be setup for it to work, no subroutine call is possible until this is done. For the standard debugger $DB::deep (how many levels of recursion deep into the debugger you can go before a mandatory break) gives an example of such a dependency. The minimal working debugger consists of one line sub DB::DB {} which is quite handy as contents of PERL5DB environment variable: env "PERL5DB=sub DB::DB {}" perl -d your-script Another (a little bit more useful) minimal debugger can be created with the only line being sub DB::DB {print ++$i; scalar <STDIN>} This debugger would print the sequential number of encountered statement, and would wait for your CR to continue. The following debugger is quite functional: { package DB; sub DB {} sub sub {print ++$i, " $sub\n"; &$sub} } It prints the sequential number of subroutine call and the name of the called subroutine. Note that &DB::sub should be compiled into the package DB. DDDDeeeebbbbuuuuggggggggeeeerrrr IIIInnnntttteeeerrrrnnnnaaaallllssss At the start, the debugger reads your rc file (./._p_e_r_l_d_b or ~/._p_e_r_l_d_b under Unix), which can set important options. This file may define a subroutine &afterinit to be executed after the debugger is initialized. After the rc file is read, the debugger reads environment variable PERLDB_OPTS and parses it as a rest of O ... line in debugger prompt. PPPPaaaaggggeeee 11118888 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) It also maintains magical internal variables, such as @DB::dbline, %DB::dbline, which are aliases for @{"::_<current_file"} %{"::_<current_file"}. Here current_file is the currently selected (with the debugger's f command, or by flow of execution) file. Some functions are provided to simplify customization. See the section on _D_e_b_u_g_g_e_r _C_u_s_t_o_m_i_z_a_t_i_o_n for description of DB::parse_options(string). The function DB::dump_trace(skip[, count]) skips the specified number of frames, and returns a list containing info about the caller frames (all if count is missing). Each entry is a hash with keys context ($ or @), sub (subroutine name, or info about eval), args (undef or a reference to an array), file, and line. The function DB::print_trace(FH, skip[, count[, short]]) prints formatted info about caller frames. The last two functions may be convenient as arguments to <, << commands. OOOOtttthhhheeeerrrr rrrreeeessssoooouuuurrrrcccceeeessss You did try the ----wwww switch, didn't you? BBBBUUUUGGGGSSSS You cannot get the stack frame information or otherwise debug functions that were not compiled by Perl, such as C or C++ extensions. If you alter your @_ arguments in a subroutine (such as with sssshhhhiiiifffftttt or ppppoooopppp, the stack backtrace will not show the original values. PPPPaaaaggggeeee 11119999 PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPEEEERRRRLLLLDDDDEEEEBBBBUUUUGGGG((((1111)))) PPPPaaaaggggeeee 22220000