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1 | =head1 NAME |
2 | ||
3 | perldebug - Perl debugging | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | First of all, have you tried using the B<-w> switch? | |
8 | ||
9 | ||
10 | If you're new to the Perl debugger, you may prefer to read | |
11 | L<perldebtut>, which is a tutorial introduction to the debugger . | |
12 | ||
13 | =head1 The Perl Debugger | |
14 | ||
15 | If you invoke Perl with the B<-d> switch, your script runs under the | |
16 | Perl source debugger. This works like an interactive Perl | |
17 | environment, prompting for debugger commands that let you examine | |
18 | source code, set breakpoints, get stack backtraces, change the values of | |
19 | variables, etc. This is so convenient that you often fire up | |
20 | the debugger all by itself just to test out Perl constructs | |
21 | interactively to see what they do. For example: | |
22 | ||
23 | $ perl -d -e 42 | |
24 | ||
25 | In Perl, the debugger is not a separate program the way it usually is in the | |
26 | typical compiled environment. Instead, the B<-d> flag tells the compiler | |
27 | to insert source information into the parse trees it's about to hand off | |
28 | to the interpreter. That means your code must first compile correctly | |
29 | for the debugger to work on it. Then when the interpreter starts up, it | |
30 | preloads a special Perl library file containing the debugger. | |
31 | ||
32 | The program will halt I<right before> the first run-time executable | |
33 | statement (but see below regarding compile-time statements) and ask you | |
34 | to enter a debugger command. Contrary to popular expectations, whenever | |
35 | the debugger halts and shows you a line of code, it always displays the | |
36 | line it's I<about> to execute, rather than the one it has just executed. | |
37 | ||
38 | Any command not recognized by the debugger is directly executed | |
39 | (C<eval>'d) as Perl code in the current package. (The debugger | |
40 | uses the DB package for keeping its own state information.) | |
41 | ||
42 | For any text entered at the debugger prompt, leading and trailing whitespace | |
43 | is first stripped before further processing. If a debugger command | |
44 | coincides with some function in your own program, merely precede the | |
45 | function with something that doesn't look like a debugger command, such | |
46 | as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses | |
47 | or braces. | |
48 | ||
49 | =head2 Debugger Commands | |
50 | ||
51 | The debugger understands the following commands: | |
52 | ||
53 | =over 12 | |
54 | ||
55 | =item h | |
56 | ||
57 | Prints out a summary help message | |
58 | ||
59 | =item h [command] | |
60 | ||
61 | Prints out a help message for the given debugger command. | |
62 | ||
63 | =item h h | |
64 | ||
65 | The special argument of C<h h> produces the entire help page, which is quite long. | |
66 | ||
67 | If the output of the C<h h> command (or any command, for that matter) scrolls | |
68 | past your screen, precede the command with a leading pipe symbol so | |
69 | that it's run through your pager, as in | |
70 | ||
71 | DB> |h h | |
72 | ||
73 | You may change the pager which is used via C<o pager=...> command. | |
74 | ||
75 | ||
76 | =item p expr | |
77 | ||
78 | Same as C<print {$DB::OUT} expr> in the current package. In particular, | |
79 | because this is just Perl's own C<print> function, this means that nested | |
80 | data structures and objects are not dumped, unlike with the C<x> command. | |
81 | ||
82 | The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of | |
83 | where STDOUT may be redirected to. | |
84 | ||
85 | =item x [maxdepth] expr | |
86 | ||
87 | Evaluates its expression in list context and dumps out the result in a | |
88 | pretty-printed fashion. Nested data structures are printed out | |
89 | recursively, unlike the real C<print> function in Perl. When dumping | |
90 | hashes, you'll probably prefer 'x \%h' rather than 'x %h'. | |
91 | See L<Dumpvalue> if you'd like to do this yourself. | |
92 | ||
93 | The output format is governed by multiple options described under | |
94 | L<"Configurable Options">. | |
95 | ||
96 | If the C<maxdepth> is included, it must be a numeral I<N>; the value is | |
97 | dumped only I<N> levels deep, as if the C<dumpDepth> option had been | |
98 | temporarily set to I<N>. | |
99 | ||
100 | =item V [pkg [vars]] | |
101 | ||
102 | Display all (or some) variables in package (defaulting to C<main>) | |
103 | using a data pretty-printer (hashes show their keys and values so | |
104 | you see what's what, control characters are made printable, etc.). | |
105 | Make sure you don't put the type specifier (like C<$>) there, just | |
106 | the symbol names, like this: | |
107 | ||
108 | V DB filename line | |
109 | ||
110 | Use C<~pattern> and C<!pattern> for positive and negative regexes. | |
111 | ||
112 | This is similar to calling the C<x> command on each applicable var. | |
113 | ||
114 | =item X [vars] | |
115 | ||
116 | Same as C<V currentpackage [vars]>. | |
117 | ||
118 | =item y [level [vars]] | |
119 | ||
120 | Display all (or some) lexical variables (mnemonic: C<mY> variables) | |
121 | in the current scope or I<level> scopes higher. You can limit the | |
122 | variables that you see with I<vars> which works exactly as it does | |
123 | for the C<V> and C<X> commands. Requires the C<PadWalker> module | |
124 | version 0.08 or higher; will warn if this isn't installed. Output | |
125 | is pretty-printed in the same style as for C<V> and the format is | |
126 | controlled by the same options. | |
127 | ||
128 | =item T | |
129 | ||
130 | Produce a stack backtrace. See below for details on its output. | |
131 | ||
132 | =item s [expr] | |
133 | ||
134 | Single step. Executes until the beginning of another | |
135 | statement, descending into subroutine calls. If an expression is | |
136 | supplied that includes function calls, it too will be single-stepped. | |
137 | ||
138 | =item n [expr] | |
139 | ||
140 | Next. Executes over subroutine calls, until the beginning | |
141 | of the next statement. If an expression is supplied that includes | |
142 | function calls, those functions will be executed with stops before | |
143 | each statement. | |
144 | ||
145 | =item r | |
146 | ||
147 | Continue until the return from the current subroutine. | |
148 | Dump the return value if the C<PrintRet> option is set (default). | |
149 | ||
150 | =item <CR> | |
151 | ||
152 | Repeat last C<n> or C<s> command. | |
153 | ||
154 | =item c [line|sub] | |
155 | ||
156 | Continue, optionally inserting a one-time-only breakpoint | |
157 | at the specified line or subroutine. | |
158 | ||
159 | =item l | |
160 | ||
161 | List next window of lines. | |
162 | ||
163 | =item l min+incr | |
164 | ||
165 | List C<incr+1> lines starting at C<min>. | |
166 | ||
167 | =item l min-max | |
168 | ||
169 | List lines C<min> through C<max>. C<l -> is synonymous to C<->. | |
170 | ||
171 | =item l line | |
172 | ||
173 | List a single line. | |
174 | ||
175 | =item l subname | |
176 | ||
177 | List first window of lines from subroutine. I<subname> may | |
178 | be a variable that contains a code reference. | |
179 | ||
180 | =item - | |
181 | ||
182 | List previous window of lines. | |
183 | ||
184 | =item v [line] | |
185 | ||
186 | View a few lines of code around the current line. | |
187 | ||
188 | =item . | |
189 | ||
190 | Return the internal debugger pointer to the line last | |
191 | executed, and print out that line. | |
192 | ||
193 | =item f filename | |
194 | ||
195 | Switch to viewing a different file or C<eval> statement. If I<filename> | |
196 | is not a full pathname found in the values of %INC, it is considered | |
197 | a regex. | |
198 | ||
199 | C<eval>ed strings (when accessible) are considered to be filenames: | |
200 | C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string | |
201 | (in the order of execution). The bodies of the currently executed C<eval> | |
202 | and of C<eval>ed strings that define subroutines are saved and thus | |
203 | accessible. | |
204 | ||
205 | =item /pattern/ | |
206 | ||
207 | Search forwards for pattern (a Perl regex); final / is optional. | |
208 | The search is case-insensitive by default. | |
209 | ||
210 | =item ?pattern? | |
211 | ||
212 | Search backwards for pattern; final ? is optional. | |
213 | The search is case-insensitive by default. | |
214 | ||
215 | =item L [abw] | |
216 | ||
217 | List (default all) actions, breakpoints and watch expressions | |
218 | ||
219 | =item S [[!]regex] | |
220 | ||
221 | List subroutine names [not] matching the regex. | |
222 | ||
223 | =item t | |
224 | ||
225 | Toggle trace mode (see also the C<AutoTrace> option). | |
226 | ||
227 | =item t expr | |
228 | ||
229 | Trace through execution of C<expr>. | |
230 | See L<perldebguts/"Frame Listing Output Examples"> for examples. | |
231 | ||
232 | =item b | |
233 | ||
234 | Sets breakpoint on current line | |
235 | ||
236 | =item b [line] [condition] | |
237 | ||
238 | Set a breakpoint before the given line. If a condition | |
239 | is specified, it's evaluated each time the statement is reached: a | |
240 | breakpoint is taken only if the condition is true. Breakpoints may | |
241 | only be set on lines that begin an executable statement. Conditions | |
242 | don't use C<if>: | |
243 | ||
244 | b 237 $x > 30 | |
245 | b 237 ++$count237 < 11 | |
246 | b 33 /pattern/i | |
247 | ||
248 | =item b subname [condition] | |
249 | ||
250 | Set a breakpoint before the first line of the named subroutine. I<subname> may | |
251 | be a variable containing a code reference (in this case I<condition> | |
252 | is not supported). | |
253 | ||
254 | =item b postpone subname [condition] | |
255 | ||
256 | Set a breakpoint at first line of subroutine after it is compiled. | |
257 | ||
258 | =item b load filename | |
259 | ||
260 | Set a breakpoint before the first executed line of the I<filename>, | |
261 | which should be a full pathname found amongst the %INC values. | |
262 | ||
263 | =item b compile subname | |
264 | ||
265 | Sets a breakpoint before the first statement executed after the specified | |
266 | subroutine is compiled. | |
267 | ||
268 | =item B line | |
269 | ||
270 | Delete a breakpoint from the specified I<line>. | |
271 | ||
272 | =item B * | |
273 | ||
274 | Delete all installed breakpoints. | |
275 | ||
276 | =item a [line] command | |
277 | ||
278 | Set an action to be done before the line is executed. If I<line> is | |
279 | omitted, set an action on the line about to be executed. | |
280 | The sequence of steps taken by the debugger is | |
281 | ||
282 | 1. check for a breakpoint at this line | |
283 | 2. print the line if necessary (tracing) | |
284 | 3. do any actions associated with that line | |
285 | 4. prompt user if at a breakpoint or in single-step | |
286 | 5. evaluate line | |
287 | ||
288 | For example, this will print out $foo every time line | |
289 | 53 is passed: | |
290 | ||
291 | a 53 print "DB FOUND $foo\n" | |
292 | ||
293 | =item A line | |
294 | ||
295 | Delete an action from the specified line. | |
296 | ||
297 | =item A * | |
298 | ||
299 | Delete all installed actions. | |
300 | ||
301 | =item w expr | |
302 | ||
303 | Add a global watch-expression. We hope you know what one of these | |
304 | is, because they're supposed to be obvious. | |
305 | ||
306 | =item W expr | |
307 | ||
308 | Delete watch-expression | |
309 | ||
310 | =item W * | |
311 | ||
312 | Delete all watch-expressions. | |
313 | ||
314 | =item o | |
315 | ||
316 | Display all options | |
317 | ||
318 | =item o booloption ... | |
319 | ||
320 | Set each listed Boolean option to the value C<1>. | |
321 | ||
322 | =item o anyoption? ... | |
323 | ||
324 | Print out the value of one or more options. | |
325 | ||
326 | =item o option=value ... | |
327 | ||
328 | Set the value of one or more options. If the value has internal | |
329 | whitespace, it should be quoted. For example, you could set C<o | |
330 | pager="less -MQeicsNfr"> to call B<less> with those specific options. | |
331 | You may use either single or double quotes, but if you do, you must | |
332 | escape any embedded instances of same sort of quote you began with, | |
333 | as well as any escaping any escapes that immediately precede that | |
334 | quote but which are not meant to escape the quote itself. In other | |
335 | words, you follow single-quoting rules irrespective of the quote; | |
336 | eg: C<o option='this isn\'t bad'> or C<o option="She said, \"Isn't | |
337 | it?\"">. | |
338 | ||
339 | For historical reasons, the C<=value> is optional, but defaults to | |
340 | 1 only where it is safe to do so--that is, mostly for Boolean | |
341 | options. It is always better to assign a specific value using C<=>. | |
342 | The C<option> can be abbreviated, but for clarity probably should | |
343 | not be. Several options can be set together. See L<"Configurable Options"> | |
344 | for a list of these. | |
345 | ||
346 | =item < ? | |
347 | ||
348 | List out all pre-prompt Perl command actions. | |
349 | ||
350 | =item < [ command ] | |
351 | ||
352 | Set an action (Perl command) to happen before every debugger prompt. | |
353 | A multi-line command may be entered by backslashing the newlines. | |
354 | B<WARNING> If C<command> is missing, all actions are wiped out! | |
355 | ||
356 | =item << command | |
357 | ||
358 | Add an action (Perl command) to happen before every debugger prompt. | |
359 | A multi-line command may be entered by backwhacking the newlines. | |
360 | ||
361 | =item > ? | |
362 | ||
363 | List out post-prompt Perl command actions. | |
364 | ||
365 | =item > command | |
366 | ||
367 | Set an action (Perl command) to happen after the prompt when you've | |
368 | just given a command to return to executing the script. A multi-line | |
369 | command may be entered by backslashing the newlines (we bet you | |
370 | couldn't've guessed this by now). B<WARNING> If C<command> is | |
371 | missing, all actions are wiped out! | |
372 | ||
373 | =item >> command | |
374 | ||
375 | Adds an action (Perl command) to happen after the prompt when you've | |
376 | just given a command to return to executing the script. A multi-line | |
377 | command may be entered by backslashing the newlines. | |
378 | ||
379 | =item { ? | |
380 | ||
381 | List out pre-prompt debugger commands. | |
382 | ||
383 | =item { [ command ] | |
384 | ||
385 | Set an action (debugger command) to happen before every debugger prompt. | |
386 | A multi-line command may be entered in the customary fashion. | |
387 | B<WARNING> If C<command> is missing, all actions are wiped out! | |
388 | ||
389 | Because this command is in some senses new, a warning is issued if | |
390 | you appear to have accidentally entered a block instead. If that's | |
391 | what you mean to do, write it as with C<;{ ... }> or even | |
392 | C<do { ... }>. | |
393 | ||
394 | =item {{ command | |
395 | ||
396 | Add an action (debugger command) to happen before every debugger prompt. | |
397 | A multi-line command may be entered, if you can guess how: see above. | |
398 | ||
399 | =item ! number | |
400 | ||
401 | Redo a previous command (defaults to the previous command). | |
402 | ||
403 | =item ! -number | |
404 | ||
405 | Redo number'th previous command. | |
406 | ||
407 | =item ! pattern | |
408 | ||
409 | Redo last command that started with pattern. | |
410 | See C<o recallCommand>, too. | |
411 | ||
412 | =item !! cmd | |
413 | ||
414 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See | |
415 | C<o shellBang>, also. Note that the user's current shell (well, | |
416 | their C<$ENV{SHELL}> variable) will be used, which can interfere | |
417 | with proper interpretation of exit status or signal and coredump | |
418 | information. | |
419 | ||
420 | =item source file | |
421 | ||
422 | Read and execute debugger commands from I<file>. | |
423 | I<file> may itself contain C<source> commands. | |
424 | ||
425 | =item H -number | |
426 | ||
427 | Display last n commands. Only commands longer than one character are | |
428 | listed. If I<number> is omitted, list them all. | |
429 | ||
430 | =item q or ^D | |
431 | ||
432 | Quit. ("quit" doesn't work for this, unless you've made an alias) | |
433 | This is the only supported way to exit the debugger, though typing | |
434 | C<exit> twice might work. | |
435 | ||
436 | Set the C<inhibit_exit> option to 0 if you want to be able to step | |
437 | off the end the script. You may also need to set $finished to 0 | |
438 | if you want to step through global destruction. | |
439 | ||
440 | =item R | |
441 | ||
442 | Restart the debugger by C<exec()>ing a new session. We try to maintain | |
443 | your history across this, but internal settings and command-line options | |
444 | may be lost. | |
445 | ||
446 | The following setting are currently preserved: history, breakpoints, | |
447 | actions, debugger options, and the Perl command-line | |
448 | options B<-w>, B<-I>, and B<-e>. | |
449 | ||
450 | =item |dbcmd | |
451 | ||
452 | Run the debugger command, piping DB::OUT into your current pager. | |
453 | ||
454 | =item ||dbcmd | |
455 | ||
456 | Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well. | |
457 | ||
458 | =item = [alias value] | |
459 | ||
460 | Define a command alias, like | |
461 | ||
462 | = quit q | |
463 | ||
464 | or list current aliases. | |
465 | ||
466 | =item command | |
467 | ||
468 | Execute command as a Perl statement. A trailing semicolon will be | |
469 | supplied. If the Perl statement would otherwise be confused for a | |
470 | Perl debugger, use a leading semicolon, too. | |
471 | ||
472 | =item m expr | |
473 | ||
474 | List which methods may be called on the result of the evaluated | |
475 | expression. The expression may evaluated to a reference to a | |
476 | blessed object, or to a package name. | |
477 | ||
478 | =item M | |
479 | ||
480 | Displays all loaded modules and their versions | |
481 | ||
482 | ||
483 | =item man [manpage] | |
484 | ||
485 | Despite its name, this calls your system's default documentation | |
486 | viewer on the given page, or on the viewer itself if I<manpage> is | |
487 | omitted. If that viewer is B<man>, the current C<Config> information | |
488 | is used to invoke B<man> using the proper MANPATH or S<B<-M> | |
489 | I<manpath>> option. Failed lookups of the form C<XXX> that match | |
490 | known manpages of the form I<perlXXX> will be retried. This lets | |
491 | you type C<man debug> or C<man op> from the debugger. | |
492 | ||
493 | On systems traditionally bereft of a usable B<man> command, the | |
494 | debugger invokes B<perldoc>. Occasionally this determination is | |
495 | incorrect due to recalcitrant vendors or rather more felicitously, | |
496 | to enterprising users. If you fall into either category, just | |
497 | manually set the $DB::doccmd variable to whatever viewer to view | |
498 | the Perl documentation on your system. This may be set in an rc | |
499 | file, or through direct assignment. We're still waiting for a | |
500 | working example of something along the lines of: | |
501 | ||
502 | $DB::doccmd = 'netscape -remote http://something.here/'; | |
503 | ||
504 | =back | |
505 | ||
506 | =head2 Configurable Options | |
507 | ||
508 | The debugger has numerous options settable using the C<o> command, | |
509 | either interactively or from the environment or an rc file. | |
510 | (./.perldb or ~/.perldb under Unix.) | |
511 | ||
512 | ||
513 | =over 12 | |
514 | ||
515 | =item C<recallCommand>, C<ShellBang> | |
516 | ||
517 | The characters used to recall command or spawn shell. By | |
518 | default, both are set to C<!>, which is unfortunate. | |
519 | ||
520 | =item C<pager> | |
521 | ||
522 | Program to use for output of pager-piped commands (those beginning | |
523 | with a C<|> character.) By default, C<$ENV{PAGER}> will be used. | |
524 | Because the debugger uses your current terminal characteristics | |
525 | for bold and underlining, if the chosen pager does not pass escape | |
526 | sequences through unchanged, the output of some debugger commands | |
527 | will not be readable when sent through the pager. | |
528 | ||
529 | =item C<tkRunning> | |
530 | ||
531 | Run Tk while prompting (with ReadLine). | |
532 | ||
533 | =item C<signalLevel>, C<warnLevel>, C<dieLevel> | |
534 | ||
535 | Level of verbosity. By default, the debugger leaves your exceptions | |
536 | and warnings alone, because altering them can break correctly running | |
537 | programs. It will attempt to print a message when uncaught INT, BUS, or | |
538 | SEGV signals arrive. (But see the mention of signals in L<BUGS> below.) | |
539 | ||
540 | To disable this default safe mode, set these values to something higher | |
541 | than 0. At a level of 1, you get backtraces upon receiving any kind | |
542 | of warning (this is often annoying) or exception (this is | |
543 | often valuable). Unfortunately, the debugger cannot discern fatal | |
544 | exceptions from non-fatal ones. If C<dieLevel> is even 1, then your | |
545 | non-fatal exceptions are also traced and unceremoniously altered if they | |
546 | came from C<eval'd> strings or from any kind of C<eval> within modules | |
547 | you're attempting to load. If C<dieLevel> is 2, the debugger doesn't | |
548 | care where they came from: It usurps your exception handler and prints | |
549 | out a trace, then modifies all exceptions with its own embellishments. | |
550 | This may perhaps be useful for some tracing purposes, but tends to hopelessly | |
551 | destroy any program that takes its exception handling seriously. | |
552 | ||
553 | =item C<AutoTrace> | |
554 | ||
555 | Trace mode (similar to C<t> command, but can be put into | |
556 | C<PERLDB_OPTS>). | |
557 | ||
558 | =item C<LineInfo> | |
559 | ||
560 | File or pipe to print line number info to. If it is a pipe (say, | |
561 | C<|visual_perl_db>), then a short message is used. This is the | |
562 | mechanism used to interact with a slave editor or visual debugger, | |
563 | such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical | |
564 | debugger. | |
565 | ||
566 | =item C<inhibit_exit> | |
567 | ||
568 | If 0, allows I<stepping off> the end of the script. | |
569 | ||
570 | =item C<PrintRet> | |
571 | ||
572 | Print return value after C<r> command if set (default). | |
573 | ||
574 | =item C<ornaments> | |
575 | ||
576 | Affects screen appearance of the command line (see L<Term::ReadLine>). | |
577 | There is currently no way to disable these, which can render | |
578 | some output illegible on some displays, or with some pagers. | |
579 | This is considered a bug. | |
580 | ||
581 | =item C<frame> | |
582 | ||
583 | Affects the printing of messages upon entry and exit from subroutines. If | |
584 | C<frame & 2> is false, messages are printed on entry only. (Printing | |
585 | on exit might be useful if interspersed with other messages.) | |
586 | ||
587 | If C<frame & 4>, arguments to functions are printed, plus context | |
588 | and caller info. If C<frame & 8>, overloaded C<stringify> and | |
589 | C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame | |
590 | & 16>, the return value from the subroutine is printed. | |
591 | ||
592 | The length at which the argument list is truncated is governed by the | |
593 | next option: | |
594 | ||
595 | =item C<maxTraceLen> | |
596 | ||
597 | Length to truncate the argument list when the C<frame> option's | |
598 | bit 4 is set. | |
599 | ||
600 | =item C<windowSize> | |
601 | ||
602 | Change the size of code list window (default is 10 lines). | |
603 | ||
604 | =back | |
605 | ||
606 | The following options affect what happens with C<V>, C<X>, and C<x> | |
607 | commands: | |
608 | ||
609 | =over 12 | |
610 | ||
611 | =item C<arrayDepth>, C<hashDepth> | |
612 | ||
613 | Print only first N elements ('' for all). | |
614 | ||
615 | =item C<dumpDepth> | |
616 | ||
617 | Limit recursion depth to N levels when dumping structures. | |
618 | Negative values are interpreted as infinity. Default: infinity. | |
619 | ||
620 | =item C<compactDump>, C<veryCompact> | |
621 | ||
622 | Change the style of array and hash output. If C<compactDump>, short array | |
623 | may be printed on one line. | |
624 | ||
625 | =item C<globPrint> | |
626 | ||
627 | Whether to print contents of globs. | |
628 | ||
629 | =item C<DumpDBFiles> | |
630 | ||
631 | Dump arrays holding debugged files. | |
632 | ||
633 | =item C<DumpPackages> | |
634 | ||
635 | Dump symbol tables of packages. | |
636 | ||
637 | =item C<DumpReused> | |
638 | ||
639 | Dump contents of "reused" addresses. | |
640 | ||
641 | =item C<quote>, C<HighBit>, C<undefPrint> | |
642 | ||
643 | Change the style of string dump. The default value for C<quote> | |
644 | is C<auto>; one can enable double-quotish or single-quotish format | |
645 | by setting it to C<"> or C<'>, respectively. By default, characters | |
646 | with their high bit set are printed verbatim. | |
647 | ||
648 | =item C<UsageOnly> | |
649 | ||
650 | Rudimentary per-package memory usage dump. Calculates total | |
651 | size of strings found in variables in the package. This does not | |
652 | include lexicals in a module's file scope, or lost in closures. | |
653 | ||
654 | =back | |
655 | ||
656 | After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}> | |
657 | environment variable and parses this as the remainder of a `O ...' | |
658 | line as one might enter at the debugger prompt. You may place the | |
659 | initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop> | |
660 | there. | |
661 | ||
662 | If your rc file contains: | |
663 | ||
664 | parse_options("NonStop=1 LineInfo=db.out AutoTrace"); | |
665 | ||
666 | then your script will run without human intervention, putting trace | |
667 | information into the file I<db.out>. (If you interrupt it, you'd | |
668 | better reset C<LineInfo> to F</dev/tty> if you expect to see anything.) | |
669 | ||
670 | =over 12 | |
671 | ||
672 | =item C<TTY> | |
673 | ||
674 | The TTY to use for debugging I/O. | |
675 | ||
676 | =item C<noTTY> | |
677 | ||
678 | If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If | |
679 | interrupted (or if control goes to the debugger via explicit setting of | |
680 | $DB::signal or $DB::single from the Perl script), it connects to a TTY | |
681 | specified in the C<TTY> option at startup, or to a tty found at | |
682 | runtime using the C<Term::Rendezvous> module of your choice. | |
683 | ||
684 | This module should implement a method named C<new> that returns an object | |
685 | with two methods: C<IN> and C<OUT>. These should return filehandles to use | |
686 | for debugging input and output correspondingly. The C<new> method should | |
687 | inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at | |
688 | startup, or C<"/tmp/perldbtty$$"> otherwise. This file is not | |
689 | inspected for proper ownership, so security hazards are theoretically | |
690 | possible. | |
691 | ||
692 | =item C<ReadLine> | |
693 | ||
694 | If false, readline support in the debugger is disabled in order | |
695 | to debug applications that themselves use ReadLine. | |
696 | ||
697 | =item C<NonStop> | |
698 | ||
699 | If set, the debugger goes into non-interactive mode until interrupted, or | |
700 | programmatically by setting $DB::signal or $DB::single. | |
701 | ||
702 | =back | |
703 | ||
704 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: | |
705 | ||
706 | $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram | |
707 | ||
708 | That will run the script B<myprogram> without human intervention, | |
709 | printing out the call tree with entry and exit points. Note that | |
710 | C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally, | |
711 | options could be uniquely abbreviated by the first letter (modulo | |
712 | the C<Dump*> options). It is nevertheless recommended that you | |
713 | always spell them out in full for legibility and future compatibility. | |
714 | ||
715 | Other examples include | |
716 | ||
717 | $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram | |
718 | ||
719 | which runs script non-interactively, printing info on each entry | |
720 | into a subroutine and each executed line into the file named F<listing>. | |
721 | (If you interrupt it, you would better reset C<LineInfo> to something | |
722 | "interactive"!) | |
723 | ||
724 | Other examples include (using standard shell syntax to show environment | |
725 | variable settings): | |
726 | ||
727 | $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out" | |
728 | perl -d myprogram ) | |
729 | ||
730 | which may be useful for debugging a program that uses C<Term::ReadLine> | |
731 | itself. Do not forget to detach your shell from the TTY in the window that | |
732 | corresponds to F</dev/ttyXX>, say, by issuing a command like | |
733 | ||
734 | $ sleep 1000000 | |
735 | ||
736 | See L<perldebguts/"Debugger Internals"> for details. | |
737 | ||
738 | =head2 Debugger input/output | |
739 | ||
740 | =over 8 | |
741 | ||
742 | =item Prompt | |
743 | ||
744 | The debugger prompt is something like | |
745 | ||
746 | DB<8> | |
747 | ||
748 | or even | |
749 | ||
750 | DB<<17>> | |
751 | ||
752 | where that number is the command number, and which you'd use to | |
753 | access with the built-in B<csh>-like history mechanism. For example, | |
754 | C<!17> would repeat command number 17. The depth of the angle | |
755 | brackets indicates the nesting depth of the debugger. You could | |
756 | get more than one set of brackets, for example, if you'd already | |
757 | at a breakpoint and then printed the result of a function call that | |
758 | itself has a breakpoint, or you step into an expression via C<s/n/t | |
759 | expression> command. | |
760 | ||
761 | =item Multiline commands | |
762 | ||
763 | If you want to enter a multi-line command, such as a subroutine | |
764 | definition with several statements or a format, escape the newline | |
765 | that would normally end the debugger command with a backslash. | |
766 | Here's an example: | |
767 | ||
768 | DB<1> for (1..4) { \ | |
769 | cont: print "ok\n"; \ | |
770 | cont: } | |
771 | ok | |
772 | ok | |
773 | ok | |
774 | ok | |
775 | ||
776 | Note that this business of escaping a newline is specific to interactive | |
777 | commands typed into the debugger. | |
778 | ||
779 | =item Stack backtrace | |
780 | ||
781 | Here's an example of what a stack backtrace via C<T> command might | |
782 | look like: | |
783 | ||
784 | $ = main::infested called from file `Ambulation.pm' line 10 | |
785 | @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7 | |
786 | $ = main::pests('bactrian', 4) called from file `camel_flea' line 4 | |
787 | ||
788 | The left-hand character up there indicates the context in which the | |
789 | function was called, with C<$> and C<@> meaning scalar or list | |
790 | contexts respectively, and C<.> meaning void context (which is | |
791 | actually a sort of scalar context). The display above says | |
792 | that you were in the function C<main::infested> when you ran the | |
793 | stack dump, and that it was called in scalar context from line | |
794 | 10 of the file I<Ambulation.pm>, but without any arguments at all, | |
795 | meaning it was called as C<&infested>. The next stack frame shows | |
796 | that the function C<Ambulation::legs> was called in list context | |
797 | from the I<camel_flea> file with four arguments. The last stack | |
798 | frame shows that C<main::pests> was called in scalar context, | |
799 | also from I<camel_flea>, but from line 4. | |
800 | ||
801 | If you execute the C<T> command from inside an active C<use> | |
802 | statement, the backtrace will contain both a C<require> frame and | |
803 | an C<eval>) frame. | |
804 | ||
805 | =item Line Listing Format | |
806 | ||
807 | This shows the sorts of output the C<l> command can produce: | |
808 | ||
809 | DB<<13>> l | |
810 | 101: @i{@i} = (); | |
811 | 102:b @isa{@i,$pack} = () | |
812 | 103 if(exists $i{$prevpack} || exists $isa{$pack}); | |
813 | 104 } | |
814 | 105 | |
815 | 106 next | |
816 | 107==> if(exists $isa{$pack}); | |
817 | 108 | |
818 | 109:a if ($extra-- > 0) { | |
819 | 110: %isa = ($pack,1); | |
820 | ||
821 | Breakable lines are marked with C<:>. Lines with breakpoints are | |
822 | marked by C<b> and those with actions by C<a>. The line that's | |
823 | about to be executed is marked by C<< ==> >>. | |
824 | ||
825 | Please be aware that code in debugger listings may not look the same | |
826 | as your original source code. Line directives and external source | |
827 | filters can alter the code before Perl sees it, causing code to move | |
828 | from its original positions or take on entirely different forms. | |
829 | ||
830 | =item Frame listing | |
831 | ||
832 | When the C<frame> option is set, the debugger would print entered (and | |
833 | optionally exited) subroutines in different styles. See L<perldebguts> | |
834 | for incredibly long examples of these. | |
835 | ||
836 | =back | |
837 | ||
838 | =head2 Debugging compile-time statements | |
839 | ||
840 | If you have compile-time executable statements (such as code within | |
841 | BEGIN and CHECK blocks or C<use> statements), these will I<not> be | |
842 | stopped by debugger, although C<require>s and INIT blocks will, and | |
843 | compile-time statements can be traced with C<AutoTrace> option set | |
844 | in C<PERLDB_OPTS>). From your own Perl code, however, you can | |
845 | transfer control back to the debugger using the following statement, | |
846 | which is harmless if the debugger is not running: | |
847 | ||
848 | $DB::single = 1; | |
849 | ||
850 | If you set C<$DB::single> to 2, it's equivalent to having | |
851 | just typed the C<n> command, whereas a value of 1 means the C<s> | |
852 | command. The C<$DB::trace> variable should be set to 1 to simulate | |
853 | having typed the C<t> command. | |
854 | ||
855 | Another way to debug compile-time code is to start the debugger, set a | |
856 | breakpoint on the I<load> of some module: | |
857 | ||
858 | DB<7> b load f:/perllib/lib/Carp.pm | |
859 | Will stop on load of `f:/perllib/lib/Carp.pm'. | |
860 | ||
861 | and then restart the debugger using the C<R> command (if possible). One can use C<b | |
862 | compile subname> for the same purpose. | |
863 | ||
864 | =head2 Debugger Customization | |
865 | ||
866 | The debugger probably contains enough configuration hooks that you | |
867 | won't ever have to modify it yourself. You may change the behaviour | |
868 | of debugger from within the debugger using its C<o> command, from | |
869 | the command line via the C<PERLDB_OPTS> environment variable, and | |
870 | from customization files. | |
871 | ||
872 | You can do some customization by setting up a F<.perldb> file, which | |
873 | contains initialization code. For instance, you could make aliases | |
874 | like these (the last one is one people expect to be there): | |
875 | ||
876 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; | |
877 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; | |
878 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; | |
879 | $DB::alias{'quit'} = 's/^quit(\s*)/exit/'; | |
880 | ||
881 | You can change options from F<.perldb> by using calls like this one; | |
882 | ||
883 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); | |
884 | ||
885 | The code is executed in the package C<DB>. Note that F<.perldb> is | |
886 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the | |
887 | subroutine C<afterinit>, that function is called after debugger | |
888 | initialization ends. F<.perldb> may be contained in the current | |
889 | directory, or in the home directory. Because this file is sourced | |
890 | in by Perl and may contain arbitrary commands, for security reasons, | |
891 | it must be owned by the superuser or the current user, and writable | |
892 | by no one but its owner. | |
893 | ||
894 | If you want to modify the debugger, copy F<perl5db.pl> from the | |
895 | Perl library to another name and hack it to your heart's content. | |
896 | You'll then want to set your C<PERL5DB> environment variable to say | |
897 | something like this: | |
898 | ||
899 | BEGIN { require "myperl5db.pl" } | |
900 | ||
901 | As a last resort, you could also use C<PERL5DB> to customize the debugger | |
902 | by directly setting internal variables or calling debugger functions. | |
903 | ||
904 | Note that any variables and functions that are not documented in | |
905 | this document (or in L<perldebguts>) are considered for internal | |
906 | use only, and as such are subject to change without notice. | |
907 | ||
908 | =head2 Readline Support | |
909 | ||
910 | As shipped, the only command-line history supplied is a simplistic one | |
911 | that checks for leading exclamation points. However, if you install | |
912 | the Term::ReadKey and Term::ReadLine modules from CPAN, you will | |
913 | have full editing capabilities much like GNU I<readline>(3) provides. | |
914 | Look for these in the F<modules/by-module/Term> directory on CPAN. | |
915 | These do not support normal B<vi> command-line editing, however. | |
916 | ||
917 | A rudimentary command-line completion is also available. | |
918 | Unfortunately, the names of lexical variables are not available for | |
919 | completion. | |
920 | ||
921 | =head2 Editor Support for Debugging | |
922 | ||
923 | If you have the FSF's version of B<emacs> installed on your system, | |
924 | it can interact with the Perl debugger to provide an integrated | |
925 | software development environment reminiscent of its interactions | |
926 | with C debuggers. | |
927 | ||
928 | Perl comes with a start file for making B<emacs> act like a | |
929 | syntax-directed editor that understands (some of) Perl's syntax. | |
930 | Look in the I<emacs> directory of the Perl source distribution. | |
931 | ||
932 | A similar setup by Tom Christiansen for interacting with any | |
933 | vendor-shipped B<vi> and the X11 window system is also available. | |
934 | This works similarly to the integrated multiwindow support that | |
935 | B<emacs> provides, where the debugger drives the editor. At the | |
936 | time of this writing, however, that tool's eventual location in the | |
937 | Perl distribution was uncertain. | |
938 | ||
939 | Users of B<vi> should also look into B<vim> and B<gvim>, the mousey | |
940 | and windy version, for coloring of Perl keywords. | |
941 | ||
942 | Note that only perl can truly parse Perl, so all such CASE tools | |
943 | fall somewhat short of the mark, especially if you don't program | |
944 | your Perl as a C programmer might. | |
945 | ||
946 | =head2 The Perl Profiler | |
947 | ||
948 | If you wish to supply an alternative debugger for Perl to run, just | |
949 | invoke your script with a colon and a package argument given to the | |
950 | B<-d> flag. The most popular alternative debuggers for Perl is the | |
951 | Perl profiler. Devel::DProf is now included with the standard Perl | |
952 | distribution. To profile your Perl program in the file F<mycode.pl>, | |
953 | just type: | |
954 | ||
955 | $ perl -d:DProf mycode.pl | |
956 | ||
957 | When the script terminates the profiler will dump the profile | |
958 | information to a file called F<tmon.out>. A tool like B<dprofpp>, | |
959 | also supplied with the standard Perl distribution, can be used to | |
960 | interpret the information in that profile. | |
961 | ||
962 | =head1 Debugging regular expressions | |
963 | ||
964 | C<use re 'debug'> enables you to see the gory details of how the Perl | |
965 | regular expression engine works. In order to understand this typically | |
966 | voluminous output, one must not only have some idea about how regular | |
967 | expression matching works in general, but also know how Perl's regular | |
968 | expressions are internally compiled into an automaton. These matters | |
969 | are explored in some detail in | |
970 | L<perldebguts/"Debugging regular expressions">. | |
971 | ||
972 | =head1 Debugging memory usage | |
973 | ||
974 | Perl contains internal support for reporting its own memory usage, | |
975 | but this is a fairly advanced concept that requires some understanding | |
976 | of how memory allocation works. | |
977 | See L<perldebguts/"Debugging Perl memory usage"> for the details. | |
978 | ||
979 | =head1 SEE ALSO | |
980 | ||
981 | You did try the B<-w> switch, didn't you? | |
982 | ||
983 | L<perldebtut>, | |
984 | L<perldebguts>, | |
985 | L<re>, | |
986 | L<DB>, | |
987 | L<Devel::DProf>, | |
988 | L<dprofpp>, | |
989 | L<Dumpvalue>, | |
990 | and | |
991 | L<perlrun>. | |
992 | ||
993 | =head1 BUGS | |
994 | ||
995 | You cannot get stack frame information or in any fashion debug functions | |
996 | that were not compiled by Perl, such as those from C or C++ extensions. | |
997 | ||
998 | If you alter your @_ arguments in a subroutine (such as with C<shift> | |
999 | or C<pop>), the stack backtrace will not show the original values. | |
1000 | ||
1001 | The debugger does not currently work in conjunction with the B<-W> | |
1002 | command-line switch, because it itself is not free of warnings. | |
1003 | ||
1004 | If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing | |
1005 | from your keyboard or a socket) and haven't set up your own C<$SIG{INT}> | |
1006 | handler, then you won't be able to CTRL-C your way back to the debugger, | |
1007 | because the debugger's own C<$SIG{INT}> handler doesn't understand that | |
1008 | it needs to raise an exception to longjmp(3) out of slow syscalls. |