Commit | Line | Data |
a0d0e21e |
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 | |
f6b3c421 |
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 | |
4e1d3b43 |
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 |
68dc0745 |
18 | source code, set breakpoints, get stack backtraces, change the values of |
4e1d3b43 |
19 | variables, etc. This is so convenient that you often fire up |
54310121 |
20 | the debugger all by itself just to test out Perl constructs |
4e1d3b43 |
21 | interactively to see what they do. For example: |
22 | |
055fd3a9 |
23 | $ perl -d -e 42 |
4e1d3b43 |
24 | |
055fd3a9 |
25 | In Perl, the debugger is not a separate program the way it usually is in the |
4e1d3b43 |
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 |
055fd3a9 |
30 | preloads a special Perl library file containing the debugger. |
4e1d3b43 |
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 |
055fd3a9 |
39 | (C<eval>'d) as Perl code in the current package. (The debugger |
40 | uses the DB package for keeping its own state information.) |
4e1d3b43 |
41 | |
055fd3a9 |
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. |
4e1d3b43 |
48 | |
49 | =head2 Debugger Commands |
50 | |
51 | The debugger understands the following commands: |
a0d0e21e |
52 | |
53 | =over 12 |
54 | |
492652be |
55 | =item h |
56 | |
57 | Prints out a summary help message |
58 | |
4e1d3b43 |
59 | =item h [command] |
60 | |
492652be |
61 | Prints out a help message for the given debugger command. |
4e1d3b43 |
62 | |
492652be |
63 | =item h h |
4e1d3b43 |
64 | |
492652be |
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 |
055fd3a9 |
68 | past your screen, precede the command with a leading pipe symbol so |
69 | that it's run through your pager, as in |
4e1d3b43 |
70 | |
492652be |
71 | DB> |h h |
72 | |
73 | You may change the pager which is used via C<o pager=...> command. |
4e1d3b43 |
74 | |
e7ea3e70 |
75 | |
4e1d3b43 |
76 | =item p expr |
77 | |
36477c24 |
78 | Same as C<print {$DB::OUT} expr> in the current package. In particular, |
c997b287 |
79 | because this is just Perl's own C<print> function, this means that nested |
4e1d3b43 |
80 | data structures and objects are not dumped, unlike with the C<x> command. |
81 | |
e7ea3e70 |
82 | The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of |
83 | where STDOUT may be redirected to. |
84 | |
3ae893bd |
85 | =item x [maxdepth] expr |
4e1d3b43 |
86 | |
54310121 |
87 | Evaluates its expression in list context and dumps out the result |
4e1d3b43 |
88 | in a pretty-printed fashion. Nested data structures are printed out |
055fd3a9 |
89 | recursively, unlike the real C<print> function in Perl. |
90 | See L<Dumpvalue> if you'd like to do this yourself. |
4e1d3b43 |
91 | |
055fd3a9 |
92 | The output format is governed by multiple options described under |
13a2d996 |
93 | L<"Configurable Options">. |
36477c24 |
94 | |
3ae893bd |
95 | If the C<maxdepth> is included, it must be a numeral I<N>; the value is |
96 | dumped only I<N> levels deep, as if the C<dumpDepth> option had been |
5cc082a2 |
97 | temporarily set to I<N>. |
3ae893bd |
98 | |
4e1d3b43 |
99 | =item V [pkg [vars]] |
100 | |
055fd3a9 |
101 | Display all (or some) variables in package (defaulting to C<main>) |
102 | using a data pretty-printer (hashes show their keys and values so |
103 | you see what's what, control characters are made printable, etc.). |
104 | Make sure you don't put the type specifier (like C<$>) there, just |
105 | the symbol names, like this: |
4e1d3b43 |
106 | |
107 | V DB filename line |
108 | |
055fd3a9 |
109 | Use C<~pattern> and C<!pattern> for positive and negative regexes. |
4e1d3b43 |
110 | |
055fd3a9 |
111 | This is similar to calling the C<x> command on each applicable var. |
36477c24 |
112 | |
4e1d3b43 |
113 | =item X [vars] |
114 | |
115 | Same as C<V currentpackage [vars]>. |
a0d0e21e |
116 | |
d6b7ef86 |
117 | =item y [level [vars]] |
118 | |
119 | Display all (or some) lexical variables (mnemonic: C<mY> variables) |
120 | in the current scope or I<level> scopes higher. You can limit the |
121 | variables that you see with I<vars> which works exactly as it does |
122 | for the C<V> and C<X> commands. Requires the C<PadWalker> module |
123 | version 0.08 or higher; will warn if this isn't installed. Output |
124 | is pretty-printed in the same style as for C<V> and the format is |
125 | controlled by the same options. |
126 | |
a0d0e21e |
127 | =item T |
128 | |
68dc0745 |
129 | Produce a stack backtrace. See below for details on its output. |
a0d0e21e |
130 | |
4e1d3b43 |
131 | =item s [expr] |
a0d0e21e |
132 | |
055fd3a9 |
133 | Single step. Executes until the beginning of another |
4e1d3b43 |
134 | statement, descending into subroutine calls. If an expression is |
135 | supplied that includes function calls, it too will be single-stepped. |
a0d0e21e |
136 | |
e7ea3e70 |
137 | =item n [expr] |
a0d0e21e |
138 | |
055fd3a9 |
139 | Next. Executes over subroutine calls, until the beginning |
774d564b |
140 | of the next statement. If an expression is supplied that includes |
141 | function calls, those functions will be executed with stops before |
142 | each statement. |
a0d0e21e |
143 | |
dce0c882 |
144 | =item r |
145 | |
055fd3a9 |
146 | Continue until the return from the current subroutine. |
147 | Dump the return value if the C<PrintRet> option is set (default). |
dce0c882 |
148 | |
c47ff5f1 |
149 | =item <CR> |
a0d0e21e |
150 | |
4e1d3b43 |
151 | Repeat last C<n> or C<s> command. |
a0d0e21e |
152 | |
36477c24 |
153 | =item c [line|sub] |
a0d0e21e |
154 | |
4e1d3b43 |
155 | Continue, optionally inserting a one-time-only breakpoint |
36477c24 |
156 | at the specified line or subroutine. |
a0d0e21e |
157 | |
4e1d3b43 |
158 | =item l |
a0d0e21e |
159 | |
4e1d3b43 |
160 | List next window of lines. |
a0d0e21e |
161 | |
162 | =item l min+incr |
163 | |
4e1d3b43 |
164 | List C<incr+1> lines starting at C<min>. |
a0d0e21e |
165 | |
166 | =item l min-max |
167 | |
c47ff5f1 |
168 | List lines C<min> through C<max>. C<l -> is synonymous to C<->. |
a0d0e21e |
169 | |
170 | =item l line |
171 | |
4e1d3b43 |
172 | List a single line. |
a0d0e21e |
173 | |
4e1d3b43 |
174 | =item l subname |
a0d0e21e |
175 | |
83ee9e09 |
176 | List first window of lines from subroutine. I<subname> may |
055fd3a9 |
177 | be a variable that contains a code reference. |
a0d0e21e |
178 | |
179 | =item - |
180 | |
4e1d3b43 |
181 | List previous window of lines. |
a0d0e21e |
182 | |
492652be |
183 | =item v [line] |
a0d0e21e |
184 | |
492652be |
185 | View a few lines of code around the current line. |
a0d0e21e |
186 | |
4e1d3b43 |
187 | =item . |
a0d0e21e |
188 | |
055fd3a9 |
189 | Return the internal debugger pointer to the line last |
190 | executed, and print out that line. |
4e1d3b43 |
191 | |
192 | =item f filename |
193 | |
055fd3a9 |
194 | Switch to viewing a different file or C<eval> statement. If I<filename> |
195 | is not a full pathname found in the values of %INC, it is considered |
196 | a regex. |
a0d0e21e |
197 | |
bee32ff8 |
198 | C<eval>ed strings (when accessible) are considered to be filenames: |
199 | C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string |
055fd3a9 |
200 | (in the order of execution). The bodies of the currently executed C<eval> |
201 | and of C<eval>ed strings that define subroutines are saved and thus |
202 | accessible. |
bee32ff8 |
203 | |
a0d0e21e |
204 | =item /pattern/ |
205 | |
055fd3a9 |
206 | Search forwards for pattern (a Perl regex); final / is optional. |
ae55e07e |
207 | The search is case-insensitive by default. |
a0d0e21e |
208 | |
209 | =item ?pattern? |
210 | |
4e1d3b43 |
211 | Search backwards for pattern; final ? is optional. |
ae55e07e |
212 | The search is case-insensitive by default. |
a0d0e21e |
213 | |
492652be |
214 | =item L [abw] |
a0d0e21e |
215 | |
492652be |
216 | List (default all) actions, breakpoints and watch expressions |
a0d0e21e |
217 | |
055fd3a9 |
218 | =item S [[!]regex] |
a0d0e21e |
219 | |
055fd3a9 |
220 | List subroutine names [not] matching the regex. |
a0d0e21e |
221 | |
222 | =item t |
223 | |
055fd3a9 |
224 | Toggle trace mode (see also the C<AutoTrace> option). |
4e1d3b43 |
225 | |
226 | =item t expr |
227 | |
055fd3a9 |
228 | Trace through execution of C<expr>. |
229 | See L<perldebguts/"Frame Listing Output Examples"> for examples. |
4e1d3b43 |
230 | |
492652be |
231 | =item b |
232 | |
233 | Sets breakpoint on current line |
234 | |
4e1d3b43 |
235 | =item b [line] [condition] |
a0d0e21e |
236 | |
492652be |
237 | Set a breakpoint before the given line. If a condition |
055fd3a9 |
238 | is specified, it's evaluated each time the statement is reached: a |
239 | breakpoint is taken only if the condition is true. Breakpoints may |
240 | only be set on lines that begin an executable statement. Conditions |
c997b287 |
241 | don't use C<if>: |
a0d0e21e |
242 | |
243 | b 237 $x > 30 |
36477c24 |
244 | b 237 ++$count237 < 11 |
a0d0e21e |
245 | b 33 /pattern/i |
246 | |
4e1d3b43 |
247 | =item b subname [condition] |
a0d0e21e |
248 | |
055fd3a9 |
249 | Set a breakpoint before the first line of the named subroutine. I<subname> may |
250 | be a variable containing a code reference (in this case I<condition> |
83ee9e09 |
251 | is not supported). |
a0d0e21e |
252 | |
36477c24 |
253 | =item b postpone subname [condition] |
254 | |
055fd3a9 |
255 | Set a breakpoint at first line of subroutine after it is compiled. |
36477c24 |
256 | |
257 | =item b load filename |
258 | |
055fd3a9 |
259 | Set a breakpoint before the first executed line of the I<filename>, |
260 | which should be a full pathname found amongst the %INC values. |
e7ea3e70 |
261 | |
262 | =item b compile subname |
263 | |
055fd3a9 |
264 | Sets a breakpoint before the first statement executed after the specified |
265 | subroutine is compiled. |
36477c24 |
266 | |
492652be |
267 | =item B line |
a0d0e21e |
268 | |
492652be |
269 | Delete a breakpoint from the specified I<line>. |
a0d0e21e |
270 | |
492652be |
271 | =item B * |
a0d0e21e |
272 | |
4e1d3b43 |
273 | Delete all installed breakpoints. |
274 | |
275 | =item a [line] command |
276 | |
055fd3a9 |
277 | Set an action to be done before the line is executed. If I<line> is |
278 | omitted, set an action on the line about to be executed. |
4e1d3b43 |
279 | The sequence of steps taken by the debugger is |
280 | |
8ebc5c01 |
281 | 1. check for a breakpoint at this line |
282 | 2. print the line if necessary (tracing) |
283 | 3. do any actions associated with that line |
284 | 4. prompt user if at a breakpoint or in single-step |
285 | 5. evaluate line |
a0d0e21e |
286 | |
7b8d334a |
287 | For example, this will print out $foo every time line |
4e1d3b43 |
288 | 53 is passed: |
a0d0e21e |
289 | |
4e1d3b43 |
290 | a 53 print "DB FOUND $foo\n" |
a0d0e21e |
291 | |
492652be |
292 | =item A line |
3fbd6552 |
293 | |
492652be |
294 | Delete an action from the specified line. |
3fbd6552 |
295 | |
492652be |
296 | =item A * |
a0d0e21e |
297 | |
4e1d3b43 |
298 | Delete all installed actions. |
299 | |
492652be |
300 | =item w expr |
6ee623d5 |
301 | |
055fd3a9 |
302 | Add a global watch-expression. We hope you know what one of these |
492652be |
303 | is, because they're supposed to be obvious. |
6ee623d5 |
304 | |
492652be |
305 | =item W expr |
306 | |
307 | Delete watch-expression |
308 | |
309 | =item W * |
6ee623d5 |
310 | |
311 | Delete all watch-expressions. |
312 | |
492652be |
313 | =item o |
314 | |
315 | Display all options |
316 | |
317 | =item o booloption ... |
055fd3a9 |
318 | |
319 | Set each listed Boolean option to the value C<1>. |
320 | |
492652be |
321 | =item o anyoption? ... |
055fd3a9 |
322 | |
323 | Print out the value of one or more options. |
324 | |
492652be |
325 | =item o option=value ... |
055fd3a9 |
326 | |
327 | Set the value of one or more options. If the value has internal |
492652be |
328 | whitespace, it should be quoted. For example, you could set C<o |
055fd3a9 |
329 | pager="less -MQeicsNfr"> to call B<less> with those specific options. |
330 | You may use either single or double quotes, but if you do, you must |
331 | escape any embedded instances of same sort of quote you began with, |
332 | as well as any escaping any escapes that immediately precede that |
333 | quote but which are not meant to escape the quote itself. In other |
334 | words, you follow single-quoting rules irrespective of the quote; |
492652be |
335 | eg: C<o option='this isn\'t bad'> or C<o option="She said, \"Isn't |
055fd3a9 |
336 | it?\"">. |
337 | |
338 | For historical reasons, the C<=value> is optional, but defaults to |
339 | 1 only where it is safe to do so--that is, mostly for Boolean |
340 | options. It is always better to assign a specific value using C<=>. |
341 | The C<option> can be abbreviated, but for clarity probably should |
13a2d996 |
342 | not be. Several options can be set together. See L<"Configurable Options"> |
343 | for a list of these. |
055fd3a9 |
344 | |
345 | =item < ? |
346 | |
347 | List out all pre-prompt Perl command actions. |
348 | |
349 | =item < [ command ] |
350 | |
351 | Set an action (Perl command) to happen before every debugger prompt. |
352 | A multi-line command may be entered by backslashing the newlines. |
353 | B<WARNING> If C<command> is missing, all actions are wiped out! |
354 | |
355 | =item << command |
356 | |
357 | Add an action (Perl command) to happen before every debugger prompt. |
358 | A multi-line command may be entered by backwhacking the newlines. |
359 | |
360 | =item > ? |
361 | |
362 | List out post-prompt Perl command actions. |
363 | |
364 | =item > command |
365 | |
366 | Set an action (Perl command) to happen after the prompt when you've |
367 | just given a command to return to executing the script. A multi-line |
368 | command may be entered by backslashing the newlines (we bet you |
369 | couldn't've guessed this by now). B<WARNING> If C<command> is |
370 | missing, all actions are wiped out! |
371 | |
372 | =item >> command |
373 | |
374 | Adds an action (Perl command) to happen after the prompt when you've |
375 | just given a command to return to executing the script. A multi-line |
b1866b2d |
376 | command may be entered by backslashing the newlines. |
055fd3a9 |
377 | |
378 | =item { ? |
379 | |
380 | List out pre-prompt debugger commands. |
381 | |
382 | =item { [ command ] |
383 | |
384 | Set an action (debugger command) to happen before every debugger prompt. |
385 | A multi-line command may be entered in the customary fashion. |
386 | B<WARNING> If C<command> is missing, all actions are wiped out! |
387 | |
388 | Because this command is in some senses new, a warning is issued if |
389 | you appear to have accidentally entered a block instead. If that's |
390 | what you mean to do, write it as with C<;{ ... }> or even |
391 | C<do { ... }>. |
392 | |
393 | =item {{ command |
394 | |
395 | Add an action (debugger command) to happen before every debugger prompt. |
396 | A multi-line command may be entered, if you can guess how: see above. |
397 | |
398 | =item ! number |
399 | |
400 | Redo a previous command (defaults to the previous command). |
401 | |
402 | =item ! -number |
403 | |
404 | Redo number'th previous command. |
405 | |
406 | =item ! pattern |
407 | |
408 | Redo last command that started with pattern. |
492652be |
409 | See C<o recallCommand>, too. |
055fd3a9 |
410 | |
411 | =item !! cmd |
412 | |
413 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See |
492652be |
414 | C<o shellBang>, also. Note that the user's current shell (well, |
055fd3a9 |
415 | their C<$ENV{SHELL}> variable) will be used, which can interfere |
416 | with proper interpretation of exit status or signal and coredump |
417 | information. |
418 | |
5bad0d9e |
419 | =item @ file |
420 | |
421 | Read and execute debugger commands from I<file>. I<file> may itself contain |
422 | C<@> commands. |
423 | |
055fd3a9 |
424 | =item H -number |
425 | |
426 | Display last n commands. Only commands longer than one character are |
427 | listed. If I<number> is omitted, list them all. |
428 | |
429 | =item q or ^D |
430 | |
431 | Quit. ("quit" doesn't work for this, unless you've made an alias) |
432 | This is the only supported way to exit the debugger, though typing |
433 | C<exit> twice might work. |
434 | |
435 | Set the C<inhibit_exit> option to 0 if you want to be able to step |
436 | off the end the script. You may also need to set $finished to 0 |
437 | if you want to step through global destruction. |
438 | |
439 | =item R |
440 | |
441 | Restart the debugger by C<exec()>ing a new session. We try to maintain |
442 | your history across this, but internal settings and command-line options |
443 | may be lost. |
444 | |
445 | The following setting are currently preserved: history, breakpoints, |
446 | actions, debugger options, and the Perl command-line |
447 | options B<-w>, B<-I>, and B<-e>. |
448 | |
449 | =item |dbcmd |
450 | |
451 | Run the debugger command, piping DB::OUT into your current pager. |
452 | |
453 | =item ||dbcmd |
454 | |
c997b287 |
455 | Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well. |
055fd3a9 |
456 | |
457 | =item = [alias value] |
458 | |
459 | Define a command alias, like |
460 | |
461 | = quit q |
462 | |
463 | or list current aliases. |
464 | |
465 | =item command |
466 | |
467 | Execute command as a Perl statement. A trailing semicolon will be |
468 | supplied. If the Perl statement would otherwise be confused for a |
469 | Perl debugger, use a leading semicolon, too. |
470 | |
471 | =item m expr |
472 | |
473 | List which methods may be called on the result of the evaluated |
474 | expression. The expression may evaluated to a reference to a |
475 | blessed object, or to a package name. |
476 | |
492652be |
477 | =item M |
478 | |
479 | Displays all loaded modules and their versions |
480 | |
481 | |
055fd3a9 |
482 | =item man [manpage] |
483 | |
484 | Despite its name, this calls your system's default documentation |
485 | viewer on the given page, or on the viewer itself if I<manpage> is |
486 | omitted. If that viewer is B<man>, the current C<Config> information |
487 | is used to invoke B<man> using the proper MANPATH or S<B<-M> |
488 | I<manpath>> option. Failed lookups of the form C<XXX> that match |
489 | known manpages of the form I<perlXXX> will be retried. This lets |
490 | you type C<man debug> or C<man op> from the debugger. |
491 | |
492 | On systems traditionally bereft of a usable B<man> command, the |
493 | debugger invokes B<perldoc>. Occasionally this determination is |
494 | incorrect due to recalcitrant vendors or rather more felicitously, |
495 | to enterprising users. If you fall into either category, just |
496 | manually set the $DB::doccmd variable to whatever viewer to view |
497 | the Perl documentation on your system. This may be set in an rc |
498 | file, or through direct assignment. We're still waiting for a |
499 | working example of something along the lines of: |
4e1d3b43 |
500 | |
055fd3a9 |
501 | $DB::doccmd = 'netscape -remote http://something.here/'; |
502 | |
503 | =back |
504 | |
505 | =head2 Configurable Options |
506 | |
492652be |
507 | The debugger has numerous options settable using the C<o> command, |
055fd3a9 |
508 | either interactively or from the environment or an rc file. |
e00d725b |
509 | (./.perldb or ~/.perldb under Unix.) |
510 | |
4e1d3b43 |
511 | |
512 | =over 12 |
513 | |
e7ea3e70 |
514 | =item C<recallCommand>, C<ShellBang> |
4e1d3b43 |
515 | |
516 | The characters used to recall command or spawn shell. By |
055fd3a9 |
517 | default, both are set to C<!>, which is unfortunate. |
4e1d3b43 |
518 | |
e7ea3e70 |
519 | =item C<pager> |
4e1d3b43 |
520 | |
055fd3a9 |
521 | Program to use for output of pager-piped commands (those beginning |
522 | with a C<|> character.) By default, C<$ENV{PAGER}> will be used. |
523 | Because the debugger uses your current terminal characteristics |
524 | for bold and underlining, if the chosen pager does not pass escape |
525 | sequences through unchanged, the output of some debugger commands |
526 | will not be readable when sent through the pager. |
4e1d3b43 |
527 | |
e7ea3e70 |
528 | =item C<tkRunning> |
36477c24 |
529 | |
530 | Run Tk while prompting (with ReadLine). |
531 | |
e7ea3e70 |
532 | =item C<signalLevel>, C<warnLevel>, C<dieLevel> |
533 | |
4c82ae22 |
534 | Level of verbosity. By default, the debugger leaves your exceptions |
535 | and warnings alone, because altering them can break correctly running |
536 | programs. It will attempt to print a message when uncaught INT, BUS, or |
537 | SEGV signals arrive. (But see the mention of signals in L<BUGS> below.) |
538 | |
539 | To disable this default safe mode, set these values to something higher |
540 | than 0. At a level of 1, you get backtraces upon receiving any kind |
541 | of warning (this is often annoying) or exception (this is |
542 | often valuable). Unfortunately, the debugger cannot discern fatal |
543 | exceptions from non-fatal ones. If C<dieLevel> is even 1, then your |
544 | non-fatal exceptions are also traced and unceremoniously altered if they |
545 | came from C<eval'd> strings or from any kind of C<eval> within modules |
546 | you're attempting to load. If C<dieLevel> is 2, the debugger doesn't |
547 | care where they came from: It usurps your exception handler and prints |
548 | out a trace, then modifies all exceptions with its own embellishments. |
549 | This may perhaps be useful for some tracing purposes, but tends to hopelessly |
550 | destroy any program that takes its exception handling seriously. |
36477c24 |
551 | |
e7ea3e70 |
552 | =item C<AutoTrace> |
36477c24 |
553 | |
e7ea3e70 |
554 | Trace mode (similar to C<t> command, but can be put into |
555 | C<PERLDB_OPTS>). |
36477c24 |
556 | |
e7ea3e70 |
557 | =item C<LineInfo> |
36477c24 |
558 | |
e7ea3e70 |
559 | File or pipe to print line number info to. If it is a pipe (say, |
055fd3a9 |
560 | C<|visual_perl_db>), then a short message is used. This is the |
561 | mechanism used to interact with a slave editor or visual debugger, |
562 | such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical |
563 | debugger. |
36477c24 |
564 | |
565 | =item C<inhibit_exit> |
566 | |
567 | If 0, allows I<stepping off> the end of the script. |
568 | |
54310121 |
569 | =item C<PrintRet> |
36477c24 |
570 | |
04cf9722 |
571 | Print return value after C<r> command if set (default). |
36477c24 |
572 | |
28d1fb14 |
573 | =item C<ornaments> |
574 | |
055fd3a9 |
575 | Affects screen appearance of the command line (see L<Term::ReadLine>). |
576 | There is currently no way to disable these, which can render |
577 | some output illegible on some displays, or with some pagers. |
578 | This is considered a bug. |
28d1fb14 |
579 | |
54310121 |
580 | =item C<frame> |
36477c24 |
581 | |
055fd3a9 |
582 | Affects the printing of messages upon entry and exit from subroutines. If |
36477c24 |
583 | C<frame & 2> is false, messages are printed on entry only. (Printing |
055fd3a9 |
584 | on exit might be useful if interspersed with other messages.) |
36477c24 |
585 | |
055fd3a9 |
586 | If C<frame & 4>, arguments to functions are printed, plus context |
587 | and caller info. If C<frame & 8>, overloaded C<stringify> and |
588 | C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame |
589 | & 16>, the return value from the subroutine is printed. |
28d1fb14 |
590 | |
591 | The length at which the argument list is truncated is governed by the |
592 | next option: |
e7ea3e70 |
593 | |
594 | =item C<maxTraceLen> |
595 | |
055fd3a9 |
596 | Length to truncate the argument list when the C<frame> option's |
e7ea3e70 |
597 | bit 4 is set. |
36477c24 |
598 | |
6f891d7d |
599 | =item C<windowSize> |
600 | |
601 | Change the size of code list window (default is 10 lines). |
602 | |
4e1d3b43 |
603 | =back |
604 | |
605 | The following options affect what happens with C<V>, C<X>, and C<x> |
606 | commands: |
607 | |
608 | =over 12 |
609 | |
e7ea3e70 |
610 | =item C<arrayDepth>, C<hashDepth> |
4e1d3b43 |
611 | |
612 | Print only first N elements ('' for all). |
613 | |
d03c2a1b |
614 | =item C<dumpDepth> |
615 | |
616 | Limit recursion depth to N levels when dumping structures. |
617 | Negative values are interpreted as infinity. Default: infinity. |
618 | |
e7ea3e70 |
619 | =item C<compactDump>, C<veryCompact> |
4e1d3b43 |
620 | |
055fd3a9 |
621 | Change the style of array and hash output. If C<compactDump>, short array |
e7ea3e70 |
622 | may be printed on one line. |
4e1d3b43 |
623 | |
e7ea3e70 |
624 | =item C<globPrint> |
4e1d3b43 |
625 | |
626 | Whether to print contents of globs. |
627 | |
e7ea3e70 |
628 | =item C<DumpDBFiles> |
4e1d3b43 |
629 | |
630 | Dump arrays holding debugged files. |
631 | |
e7ea3e70 |
632 | =item C<DumpPackages> |
4e1d3b43 |
633 | |
634 | Dump symbol tables of packages. |
635 | |
6ee623d5 |
636 | =item C<DumpReused> |
637 | |
638 | Dump contents of "reused" addresses. |
639 | |
e7ea3e70 |
640 | =item C<quote>, C<HighBit>, C<undefPrint> |
641 | |
055fd3a9 |
642 | Change the style of string dump. The default value for C<quote> |
643 | is C<auto>; one can enable double-quotish or single-quotish format |
644 | by setting it to C<"> or C<'>, respectively. By default, characters |
645 | with their high bit set are printed verbatim. |
e7ea3e70 |
646 | |
54310121 |
647 | =item C<UsageOnly> |
4e1d3b43 |
648 | |
055fd3a9 |
649 | Rudimentary per-package memory usage dump. Calculates total |
650 | size of strings found in variables in the package. This does not |
651 | include lexicals in a module's file scope, or lost in closures. |
4e1d3b43 |
652 | |
36477c24 |
653 | =back |
4e1d3b43 |
654 | |
e00d725b |
655 | After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}> |
656 | environment variable and parses this as the remainder of a `O ...' |
657 | line as one might enter at the debugger prompt. You may place the |
658 | initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop> |
659 | there. |
36477c24 |
660 | |
055fd3a9 |
661 | If your rc file contains: |
4e1d3b43 |
662 | |
055fd3a9 |
663 | parse_options("NonStop=1 LineInfo=db.out AutoTrace"); |
4e1d3b43 |
664 | |
055fd3a9 |
665 | then your script will run without human intervention, putting trace |
666 | information into the file I<db.out>. (If you interrupt it, you'd |
667 | better reset C<LineInfo> to F</dev/tty> if you expect to see anything.) |
4e1d3b43 |
668 | |
36477c24 |
669 | =over 12 |
4e1d3b43 |
670 | |
36477c24 |
671 | =item C<TTY> |
4e1d3b43 |
672 | |
36477c24 |
673 | The TTY to use for debugging I/O. |
674 | |
36477c24 |
675 | =item C<noTTY> |
676 | |
055fd3a9 |
677 | If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If |
678 | interrupted (or if control goes to the debugger via explicit setting of |
679 | $DB::signal or $DB::single from the Perl script), it connects to a TTY |
680 | specified in the C<TTY> option at startup, or to a tty found at |
681 | runtime using the C<Term::Rendezvous> module of your choice. |
36477c24 |
682 | |
055fd3a9 |
683 | This module should implement a method named C<new> that returns an object |
200f06d0 |
684 | with two methods: C<IN> and C<OUT>. These should return filehandles to use |
055fd3a9 |
685 | for debugging input and output correspondingly. The C<new> method should |
686 | inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at |
687 | startup, or C<"/tmp/perldbtty$$"> otherwise. This file is not |
688 | inspected for proper ownership, so security hazards are theoretically |
689 | possible. |
36477c24 |
690 | |
691 | =item C<ReadLine> |
692 | |
055fd3a9 |
693 | If false, readline support in the debugger is disabled in order |
694 | to debug applications that themselves use ReadLine. |
36477c24 |
695 | |
696 | =item C<NonStop> |
697 | |
055fd3a9 |
698 | If set, the debugger goes into non-interactive mode until interrupted, or |
36477c24 |
699 | programmatically by setting $DB::signal or $DB::single. |
700 | |
701 | =back |
702 | |
703 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: |
4e1d3b43 |
704 | |
055fd3a9 |
705 | $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram |
4e1d3b43 |
706 | |
055fd3a9 |
707 | That will run the script B<myprogram> without human intervention, |
708 | printing out the call tree with entry and exit points. Note that |
709 | C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally, |
710 | options could be uniquely abbreviated by the first letter (modulo |
711 | the C<Dump*> options). It is nevertheless recommended that you |
712 | always spell them out in full for legibility and future compatibility. |
4e1d3b43 |
713 | |
055fd3a9 |
714 | Other examples include |
a0d0e21e |
715 | |
1472e7de |
716 | $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram |
a0d0e21e |
717 | |
055fd3a9 |
718 | which runs script non-interactively, printing info on each entry |
719 | into a subroutine and each executed line into the file named F<listing>. |
720 | (If you interrupt it, you would better reset C<LineInfo> to something |
36477c24 |
721 | "interactive"!) |
722 | |
055fd3a9 |
723 | Other examples include (using standard shell syntax to show environment |
724 | variable settings): |
36477c24 |
725 | |
055fd3a9 |
726 | $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out" |
727 | perl -d myprogram ) |
36477c24 |
728 | |
055fd3a9 |
729 | which may be useful for debugging a program that uses C<Term::ReadLine> |
730 | itself. Do not forget to detach your shell from the TTY in the window that |
731 | corresponds to F</dev/ttyXX>, say, by issuing a command like |
36477c24 |
732 | |
e7ea3e70 |
733 | $ sleep 1000000 |
36477c24 |
734 | |
055fd3a9 |
735 | See L<perldebguts/"Debugger Internals"> for details. |
a0d0e21e |
736 | |
e7ea3e70 |
737 | =head2 Debugger input/output |
738 | |
739 | =over 8 |
740 | |
741 | =item Prompt |
742 | |
4e1d3b43 |
743 | The debugger prompt is something like |
744 | |
745 | DB<8> |
746 | |
747 | or even |
748 | |
749 | DB<<17>> |
750 | |
055fd3a9 |
751 | where that number is the command number, and which you'd use to |
752 | access with the built-in B<csh>-like history mechanism. For example, |
753 | C<!17> would repeat command number 17. The depth of the angle |
754 | brackets indicates the nesting depth of the debugger. You could |
755 | get more than one set of brackets, for example, if you'd already |
756 | at a breakpoint and then printed the result of a function call that |
757 | itself has a breakpoint, or you step into an expression via C<s/n/t |
758 | expression> command. |
4e1d3b43 |
759 | |
54310121 |
760 | =item Multiline commands |
e7ea3e70 |
761 | |
4a6725af |
762 | If you want to enter a multi-line command, such as a subroutine |
055fd3a9 |
763 | definition with several statements or a format, escape the newline |
764 | that would normally end the debugger command with a backslash. |
e7ea3e70 |
765 | Here's an example: |
a0d0e21e |
766 | |
4e1d3b43 |
767 | DB<1> for (1..4) { \ |
768 | cont: print "ok\n"; \ |
769 | cont: } |
770 | ok |
771 | ok |
772 | ok |
773 | ok |
774 | |
775 | Note that this business of escaping a newline is specific to interactive |
776 | commands typed into the debugger. |
777 | |
e7ea3e70 |
778 | =item Stack backtrace |
779 | |
68dc0745 |
780 | Here's an example of what a stack backtrace via C<T> command might |
e7ea3e70 |
781 | look like: |
4e1d3b43 |
782 | |
783 | $ = main::infested called from file `Ambulation.pm' line 10 |
784 | @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7 |
785 | $ = main::pests('bactrian', 4) called from file `camel_flea' line 4 |
786 | |
055fd3a9 |
787 | The left-hand character up there indicates the context in which the |
788 | function was called, with C<$> and C<@> meaning scalar or list |
789 | contexts respectively, and C<.> meaning void context (which is |
790 | actually a sort of scalar context). The display above says |
791 | that you were in the function C<main::infested> when you ran the |
792 | stack dump, and that it was called in scalar context from line |
793 | 10 of the file I<Ambulation.pm>, but without any arguments at all, |
794 | meaning it was called as C<&infested>. The next stack frame shows |
795 | that the function C<Ambulation::legs> was called in list context |
796 | from the I<camel_flea> file with four arguments. The last stack |
797 | frame shows that C<main::pests> was called in scalar context, |
798 | also from I<camel_flea>, but from line 4. |
4e1d3b43 |
799 | |
055fd3a9 |
800 | If you execute the C<T> command from inside an active C<use> |
801 | statement, the backtrace will contain both a C<require> frame and |
802 | an C<eval>) frame. |
e7ea3e70 |
803 | |
055fd3a9 |
804 | =item Line Listing Format |
e7ea3e70 |
805 | |
055fd3a9 |
806 | This shows the sorts of output the C<l> command can produce: |
e7ea3e70 |
807 | |
808 | DB<<13>> l |
809 | 101: @i{@i} = (); |
810 | 102:b @isa{@i,$pack} = () |
811 | 103 if(exists $i{$prevpack} || exists $isa{$pack}); |
812 | 104 } |
813 | 105 |
814 | 106 next |
815 | 107==> if(exists $isa{$pack}); |
816 | 108 |
817 | 109:a if ($extra-- > 0) { |
818 | 110: %isa = ($pack,1); |
819 | |
055fd3a9 |
820 | Breakable lines are marked with C<:>. Lines with breakpoints are |
821 | marked by C<b> and those with actions by C<a>. The line that's |
822 | about to be executed is marked by C<< ==> >>. |
e7ea3e70 |
823 | |
003183f2 |
824 | Please be aware that code in debugger listings may not look the same |
825 | as your original source code. Line directives and external source |
826 | filters can alter the code before Perl sees it, causing code to move |
827 | from its original positions or take on entirely different forms. |
828 | |
e7ea3e70 |
829 | =item Frame listing |
830 | |
055fd3a9 |
831 | When the C<frame> option is set, the debugger would print entered (and |
832 | optionally exited) subroutines in different styles. See L<perldebguts> |
833 | for incredibly long examples of these. |
e7ea3e70 |
834 | |
835 | =back |
836 | |
837 | =head2 Debugging compile-time statements |
838 | |
055fd3a9 |
839 | If you have compile-time executable statements (such as code within |
840 | BEGIN and CHECK blocks or C<use> statements), these will I<not> be |
841 | stopped by debugger, although C<require>s and INIT blocks will, and |
842 | compile-time statements can be traced with C<AutoTrace> option set |
843 | in C<PERLDB_OPTS>). From your own Perl code, however, you can |
4e1d3b43 |
844 | transfer control back to the debugger using the following statement, |
845 | which is harmless if the debugger is not running: |
a0d0e21e |
846 | |
847 | $DB::single = 1; |
848 | |
055fd3a9 |
849 | If you set C<$DB::single> to 2, it's equivalent to having |
4e1d3b43 |
850 | just typed the C<n> command, whereas a value of 1 means the C<s> |
851 | command. The C<$DB::trace> variable should be set to 1 to simulate |
852 | having typed the C<t> command. |
853 | |
055fd3a9 |
854 | Another way to debug compile-time code is to start the debugger, set a |
855 | breakpoint on the I<load> of some module: |
e7ea3e70 |
856 | |
857 | DB<7> b load f:/perllib/lib/Carp.pm |
858 | Will stop on load of `f:/perllib/lib/Carp.pm'. |
859 | |
055fd3a9 |
860 | and then restart the debugger using the C<R> command (if possible). One can use C<b |
e7ea3e70 |
861 | compile subname> for the same purpose. |
862 | |
4e1d3b43 |
863 | =head2 Debugger Customization |
a0d0e21e |
864 | |
055fd3a9 |
865 | The debugger probably contains enough configuration hooks that you |
866 | won't ever have to modify it yourself. You may change the behaviour |
492652be |
867 | of debugger from within the debugger using its C<o> command, from |
055fd3a9 |
868 | the command line via the C<PERLDB_OPTS> environment variable, and |
869 | from customization files. |
a0d0e21e |
870 | |
055fd3a9 |
871 | You can do some customization by setting up a F<.perldb> file, which |
a0d0e21e |
872 | contains initialization code. For instance, you could make aliases |
4e1d3b43 |
873 | like these (the last one is one people expect to be there): |
a0d0e21e |
874 | |
4e1d3b43 |
875 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; |
a0d0e21e |
876 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; |
4e1d3b43 |
877 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; |
055fd3a9 |
878 | $DB::alias{'quit'} = 's/^quit(\s*)/exit/'; |
4e1d3b43 |
879 | |
055fd3a9 |
880 | You can change options from F<.perldb> by using calls like this one; |
36477c24 |
881 | |
882 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); |
883 | |
055fd3a9 |
884 | The code is executed in the package C<DB>. Note that F<.perldb> is |
774d564b |
885 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the |
055fd3a9 |
886 | subroutine C<afterinit>, that function is called after debugger |
774d564b |
887 | initialization ends. F<.perldb> may be contained in the current |
055fd3a9 |
888 | directory, or in the home directory. Because this file is sourced |
889 | in by Perl and may contain arbitrary commands, for security reasons, |
890 | it must be owned by the superuser or the current user, and writable |
891 | by no one but its owner. |
36477c24 |
892 | |
055fd3a9 |
893 | If you want to modify the debugger, copy F<perl5db.pl> from the |
894 | Perl library to another name and hack it to your heart's content. |
895 | You'll then want to set your C<PERL5DB> environment variable to say |
896 | something like this: |
36477c24 |
897 | |
898 | BEGIN { require "myperl5db.pl" } |
899 | |
055fd3a9 |
900 | As a last resort, you could also use C<PERL5DB> to customize the debugger |
901 | by directly setting internal variables or calling debugger functions. |
902 | |
903 | Note that any variables and functions that are not documented in |
904 | this document (or in L<perldebguts>) are considered for internal |
905 | use only, and as such are subject to change without notice. |
36477c24 |
906 | |
4e1d3b43 |
907 | =head2 Readline Support |
908 | |
055fd3a9 |
909 | As shipped, the only command-line history supplied is a simplistic one |
4e1d3b43 |
910 | that checks for leading exclamation points. However, if you install |
911 | the Term::ReadKey and Term::ReadLine modules from CPAN, you will |
912 | have full editing capabilities much like GNU I<readline>(3) provides. |
913 | Look for these in the F<modules/by-module/Term> directory on CPAN. |
055fd3a9 |
914 | These do not support normal B<vi> command-line editing, however. |
4e1d3b43 |
915 | |
055fd3a9 |
916 | A rudimentary command-line completion is also available. |
e7ea3e70 |
917 | Unfortunately, the names of lexical variables are not available for |
918 | completion. |
919 | |
4e1d3b43 |
920 | =head2 Editor Support for Debugging |
921 | |
055fd3a9 |
922 | If you have the FSF's version of B<emacs> installed on your system, |
923 | it can interact with the Perl debugger to provide an integrated |
924 | software development environment reminiscent of its interactions |
925 | with C debuggers. |
4e1d3b43 |
926 | |
055fd3a9 |
927 | Perl comes with a start file for making B<emacs> act like a |
928 | syntax-directed editor that understands (some of) Perl's syntax. |
929 | Look in the I<emacs> directory of the Perl source distribution. |
4e1d3b43 |
930 | |
055fd3a9 |
931 | A similar setup by Tom Christiansen for interacting with any |
932 | vendor-shipped B<vi> and the X11 window system is also available. |
933 | This works similarly to the integrated multiwindow support that |
934 | B<emacs> provides, where the debugger drives the editor. At the |
935 | time of this writing, however, that tool's eventual location in the |
936 | Perl distribution was uncertain. |
4e1d3b43 |
937 | |
055fd3a9 |
938 | Users of B<vi> should also look into B<vim> and B<gvim>, the mousey |
939 | and windy version, for coloring of Perl keywords. |
a0d0e21e |
940 | |
055fd3a9 |
941 | Note that only perl can truly parse Perl, so all such CASE tools |
942 | fall somewhat short of the mark, especially if you don't program |
943 | your Perl as a C programmer might. |
e7ea3e70 |
944 | |
055fd3a9 |
945 | =head2 The Perl Profiler |
e7ea3e70 |
946 | |
055fd3a9 |
947 | If you wish to supply an alternative debugger for Perl to run, just |
948 | invoke your script with a colon and a package argument given to the |
949 | B<-d> flag. The most popular alternative debuggers for Perl is the |
950 | Perl profiler. Devel::DProf is now included with the standard Perl |
951 | distribution. To profile your Perl program in the file F<mycode.pl>, |
952 | just type: |
36477c24 |
953 | |
055fd3a9 |
954 | $ perl -d:DProf mycode.pl |
36477c24 |
955 | |
055fd3a9 |
956 | When the script terminates the profiler will dump the profile |
957 | information to a file called F<tmon.out>. A tool like B<dprofpp>, |
958 | also supplied with the standard Perl distribution, can be used to |
959 | interpret the information in that profile. |
36477c24 |
960 | |
055fd3a9 |
961 | =head1 Debugging regular expressions |
36477c24 |
962 | |
3d555cb8 |
963 | C<use re 'debug'> enables you to see the gory details of how the Perl |
964 | regular expression engine works. In order to understand this typically |
965 | voluminous output, one must not only have some idea about how regular |
966 | expression matching works in general, but also know how Perl's regular |
967 | expressions are internally compiled into an automaton. These matters |
968 | are explored in some detail in |
055fd3a9 |
969 | L<perldebguts/"Debugging regular expressions">. |
36477c24 |
970 | |
055fd3a9 |
971 | =head1 Debugging memory usage |
36477c24 |
972 | |
055fd3a9 |
973 | Perl contains internal support for reporting its own memory usage, |
974 | but this is a fairly advanced concept that requires some understanding |
975 | of how memory allocation works. |
976 | See L<perldebguts/"Debugging Perl memory usage"> for the details. |
36477c24 |
977 | |
055fd3a9 |
978 | =head1 SEE ALSO |
a0d0e21e |
979 | |
980 | You did try the B<-w> switch, didn't you? |
981 | |
f6b3c421 |
982 | L<perldebtut>, |
055fd3a9 |
983 | L<perldebguts>, |
984 | L<re>, |
985 | L<DB>, |
fe854a6f |
986 | L<Devel::DProf>, |
055fd3a9 |
987 | L<dprofpp>, |
988 | L<Dumpvalue>, |
989 | and |
990 | L<perlrun>. |
a0d0e21e |
991 | |
055fd3a9 |
992 | =head1 BUGS |
993 | |
994 | You cannot get stack frame information or in any fashion debug functions |
995 | that were not compiled by Perl, such as those from C or C++ extensions. |
a0d0e21e |
996 | |
c997b287 |
997 | If you alter your @_ arguments in a subroutine (such as with C<shift> |
6edf2346 |
998 | or C<pop>), the stack backtrace will not show the original values. |
c997b287 |
999 | |
1000 | The debugger does not currently work in conjunction with the B<-W> |
1001 | command-line switch, because it itself is not free of warnings. |
4c82ae22 |
1002 | |
1003 | If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing |
1004 | from your keyboard or a socket) and haven't set up your own C<$SIG{INT}> |
1005 | handler, then you won't be able to CTRL-C your way back to the debugger, |
1006 | because the debugger's own C<$SIG{INT}> handler doesn't understand that |
1007 | it needs to raise an exception to longjmp(3) out of slow syscalls. |