Commit | Line | Data |
---|---|---|
a0d0e21e | 1 | =head1 NAME |
d74e8afc | 2 | X<debug> X<debugger> |
a0d0e21e LW |
3 | |
4 | perldebug - Perl debugging | |
5 | ||
6 | =head1 DESCRIPTION | |
7 | ||
9095739b LM |
8 | First of all, have you tried using L<C<use strict;>|strict> and |
9 | L<C<use warnings;>|warnings>? | |
a0d0e21e | 10 | |
f6b3c421 | 11 | If you're new to the Perl debugger, you may prefer to read |
5d464584 | 12 | L<perldebtut>, which is a tutorial introduction to the debugger. |
f6b3c421 | 13 | |
d972afbc RS |
14 | If you're looking for the nitty gritty details of how the debugger is |
15 | I<implemented>, you may prefer to read L<perldebguts>. | |
16 | ||
65ac759c DB |
17 | For in-depth technical usage details, see L<perl5db.pl>, the documentation |
18 | of the debugger itself. | |
19 | ||
4e1d3b43 | 20 | =head1 The Perl Debugger |
21 | ||
22 | If you invoke Perl with the B<-d> switch, your script runs under the | |
23 | Perl source debugger. This works like an interactive Perl | |
24 | environment, prompting for debugger commands that let you examine | |
68dc0745 | 25 | source code, set breakpoints, get stack backtraces, change the values of |
4e1d3b43 | 26 | variables, etc. This is so convenient that you often fire up |
54310121 | 27 | the debugger all by itself just to test out Perl constructs |
4e1d3b43 | 28 | interactively to see what they do. For example: |
d74e8afc | 29 | X<-d> |
4e1d3b43 | 30 | |
055fd3a9 | 31 | $ perl -d -e 42 |
4e1d3b43 | 32 | |
055fd3a9 | 33 | In Perl, the debugger is not a separate program the way it usually is in the |
4e1d3b43 | 34 | typical compiled environment. Instead, the B<-d> flag tells the compiler |
35 | to insert source information into the parse trees it's about to hand off | |
36 | to the interpreter. That means your code must first compile correctly | |
37 | for the debugger to work on it. Then when the interpreter starts up, it | |
055fd3a9 | 38 | preloads a special Perl library file containing the debugger. |
4e1d3b43 | 39 | |
40 | The program will halt I<right before> the first run-time executable | |
41 | statement (but see below regarding compile-time statements) and ask you | |
42 | to enter a debugger command. Contrary to popular expectations, whenever | |
43 | the debugger halts and shows you a line of code, it always displays the | |
44 | line it's I<about> to execute, rather than the one it has just executed. | |
45 | ||
46 | Any command not recognized by the debugger is directly executed | |
055fd3a9 GS |
47 | (C<eval>'d) as Perl code in the current package. (The debugger |
48 | uses the DB package for keeping its own state information.) | |
4e1d3b43 | 49 | |
ea5ec306 SP |
50 | Note that the said C<eval> is bound by an implicit scope. As a |
51 | result any newly introduced lexical variable or any modified | |
52 | capture buffer content is lost after the eval. The debugger is a | |
53 | nice environment to learn Perl, but if you interactively experiment using | |
54 | material which should be in the same scope, stuff it in one line. | |
55 | ||
055fd3a9 GS |
56 | For any text entered at the debugger prompt, leading and trailing whitespace |
57 | is first stripped before further processing. If a debugger command | |
58 | coincides with some function in your own program, merely precede the | |
59 | function with something that doesn't look like a debugger command, such | |
60 | as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses | |
61 | or braces. | |
4e1d3b43 | 62 | |
57e8c15d | 63 | =head2 Calling the Debugger |
9311160e RF |
64 | |
65 | There are several ways to call the debugger: | |
66 | ||
67 | =over 4 | |
68 | ||
69 | =item perl -d program_name | |
70 | ||
71 | On the given program identified by C<program_name>. | |
72 | ||
73 | =item perl -d -e 0 | |
74 | ||
75 | Interactively supply an arbitrary C<expression> using C<-e>. | |
76 | ||
bbc1b4cd | 77 | =item perl -d:ptkdb program_name |
9311160e | 78 | |
bbc1b4cd | 79 | Debug a given program via the C<Devel::ptkdb> GUI. |
9311160e RF |
80 | |
81 | =item perl -dt threaded_program_name | |
82 | ||
83 | Debug a given program using threads (experimental). | |
84 | ||
85 | =back | |
86 | ||
4e1d3b43 | 87 | =head2 Debugger Commands |
88 | ||
9311160e | 89 | The interactive debugger understands the following commands: |
a0d0e21e LW |
90 | |
91 | =over 12 | |
92 | ||
492652be | 93 | =item h |
d74e8afc | 94 | X<debugger command, h> |
492652be RF |
95 | |
96 | Prints out a summary help message | |
97 | ||
4e1d3b43 | 98 | =item h [command] |
99 | ||
492652be | 100 | Prints out a help message for the given debugger command. |
4e1d3b43 | 101 | |
492652be | 102 | =item h h |
4e1d3b43 | 103 | |
492652be RF |
104 | The special argument of C<h h> produces the entire help page, which is quite long. |
105 | ||
106 | If the output of the C<h h> command (or any command, for that matter) scrolls | |
055fd3a9 GS |
107 | past your screen, precede the command with a leading pipe symbol so |
108 | that it's run through your pager, as in | |
4e1d3b43 | 109 | |
492652be RF |
110 | DB> |h h |
111 | ||
112 | You may change the pager which is used via C<o pager=...> command. | |
4e1d3b43 | 113 | |
114 | =item p expr | |
d74e8afc | 115 | X<debugger command, p> |
4e1d3b43 | 116 | |
36477c24 | 117 | Same as C<print {$DB::OUT} expr> in the current package. In particular, |
c997b287 | 118 | because this is just Perl's own C<print> function, this means that nested |
4e1d3b43 | 119 | data structures and objects are not dumped, unlike with the C<x> command. |
120 | ||
e7ea3e70 IZ |
121 | The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of |
122 | where STDOUT may be redirected to. | |
123 | ||
3ae893bd | 124 | =item x [maxdepth] expr |
d74e8afc | 125 | X<debugger command, x> |
4e1d3b43 | 126 | |
a991b806 JC |
127 | Evaluates its expression in list context and dumps out the result in a |
128 | pretty-printed fashion. Nested data structures are printed out | |
129 | recursively, unlike the real C<print> function in Perl. When dumping | |
130 | hashes, you'll probably prefer 'x \%h' rather than 'x %h'. | |
055fd3a9 | 131 | See L<Dumpvalue> if you'd like to do this yourself. |
4e1d3b43 | 132 | |
055fd3a9 | 133 | The output format is governed by multiple options described under |
5a0de581 | 134 | L</"Configurable Options">. |
36477c24 | 135 | |
3ae893bd MJD |
136 | If the C<maxdepth> is included, it must be a numeral I<N>; the value is |
137 | dumped only I<N> levels deep, as if the C<dumpDepth> option had been | |
5cc082a2 | 138 | temporarily set to I<N>. |
3ae893bd | 139 | |
4e1d3b43 | 140 | =item V [pkg [vars]] |
d74e8afc | 141 | X<debugger command, V> |
4e1d3b43 | 142 | |
2e8f3c35 | 143 | Display all (or some) variables in package (defaulting to C<main>) |
055fd3a9 GS |
144 | using a data pretty-printer (hashes show their keys and values so |
145 | you see what's what, control characters are made printable, etc.). | |
146 | Make sure you don't put the type specifier (like C<$>) there, just | |
147 | the symbol names, like this: | |
4e1d3b43 | 148 | |
149 | V DB filename line | |
150 | ||
055fd3a9 | 151 | Use C<~pattern> and C<!pattern> for positive and negative regexes. |
4e1d3b43 | 152 | |
055fd3a9 | 153 | This is similar to calling the C<x> command on each applicable var. |
36477c24 | 154 | |
4e1d3b43 | 155 | =item X [vars] |
d74e8afc | 156 | X<debugger command, X> |
4e1d3b43 | 157 | |
158 | Same as C<V currentpackage [vars]>. | |
a0d0e21e | 159 | |
a7b657ee | 160 | =item y [level [vars]] |
d74e8afc | 161 | X<debugger command, y> |
a7b657ee PS |
162 | |
163 | Display all (or some) lexical variables (mnemonic: C<mY> variables) | |
164 | in the current scope or I<level> scopes higher. You can limit the | |
165 | variables that you see with I<vars> which works exactly as it does | |
166 | for the C<V> and C<X> commands. Requires the C<PadWalker> module | |
167 | version 0.08 or higher; will warn if this isn't installed. Output | |
168 | is pretty-printed in the same style as for C<V> and the format is | |
169 | controlled by the same options. | |
170 | ||
a0d0e21e | 171 | =item T |
d74e8afc | 172 | X<debugger command, T> X<backtrace> X<stack, backtrace> |
a0d0e21e | 173 | |
68dc0745 | 174 | Produce a stack backtrace. See below for details on its output. |
a0d0e21e | 175 | |
4e1d3b43 | 176 | =item s [expr] |
d74e8afc | 177 | X<debugger command, s> X<step> |
a0d0e21e | 178 | |
055fd3a9 | 179 | Single step. Executes until the beginning of another |
4e1d3b43 | 180 | statement, descending into subroutine calls. If an expression is |
181 | supplied that includes function calls, it too will be single-stepped. | |
a0d0e21e | 182 | |
e7ea3e70 | 183 | =item n [expr] |
d74e8afc | 184 | X<debugger command, n> |
a0d0e21e | 185 | |
055fd3a9 | 186 | Next. Executes over subroutine calls, until the beginning |
774d564b | 187 | of the next statement. If an expression is supplied that includes |
188 | function calls, those functions will be executed with stops before | |
189 | each statement. | |
a0d0e21e | 190 | |
dce0c882 | 191 | =item r |
d74e8afc | 192 | X<debugger command, r> |
dce0c882 | 193 | |
055fd3a9 GS |
194 | Continue until the return from the current subroutine. |
195 | Dump the return value if the C<PrintRet> option is set (default). | |
dce0c882 | 196 | |
c47ff5f1 | 197 | =item <CR> |
a0d0e21e | 198 | |
4e1d3b43 | 199 | Repeat last C<n> or C<s> command. |
a0d0e21e | 200 | |
36477c24 | 201 | =item c [line|sub] |
d74e8afc | 202 | X<debugger command, c> |
a0d0e21e | 203 | |
4e1d3b43 | 204 | Continue, optionally inserting a one-time-only breakpoint |
36477c24 | 205 | at the specified line or subroutine. |
a0d0e21e | 206 | |
4e1d3b43 | 207 | =item l |
d74e8afc | 208 | X<debugger command, l> |
a0d0e21e | 209 | |
4e1d3b43 | 210 | List next window of lines. |
a0d0e21e LW |
211 | |
212 | =item l min+incr | |
213 | ||
4e1d3b43 | 214 | List C<incr+1> lines starting at C<min>. |
a0d0e21e LW |
215 | |
216 | =item l min-max | |
217 | ||
c47ff5f1 | 218 | List lines C<min> through C<max>. C<l -> is synonymous to C<->. |
a0d0e21e LW |
219 | |
220 | =item l line | |
221 | ||
4e1d3b43 | 222 | List a single line. |
a0d0e21e | 223 | |
4e1d3b43 | 224 | =item l subname |
a0d0e21e | 225 | |
83ee9e09 | 226 | List first window of lines from subroutine. I<subname> may |
055fd3a9 | 227 | be a variable that contains a code reference. |
a0d0e21e LW |
228 | |
229 | =item - | |
d74e8afc | 230 | X<debugger command, -> |
a0d0e21e | 231 | |
4e1d3b43 | 232 | List previous window of lines. |
a0d0e21e | 233 | |
492652be | 234 | =item v [line] |
d74e8afc | 235 | X<debugger command, v> |
a0d0e21e | 236 | |
492652be | 237 | View a few lines of code around the current line. |
a0d0e21e | 238 | |
4e1d3b43 | 239 | =item . |
d74e8afc | 240 | X<debugger command, .> |
a0d0e21e | 241 | |
055fd3a9 GS |
242 | Return the internal debugger pointer to the line last |
243 | executed, and print out that line. | |
4e1d3b43 | 244 | |
245 | =item f filename | |
d74e8afc | 246 | X<debugger command, f> |
4e1d3b43 | 247 | |
055fd3a9 | 248 | Switch to viewing a different file or C<eval> statement. If I<filename> |
2e8f3c35 | 249 | is not a full pathname found in the values of %INC, it is considered |
055fd3a9 | 250 | a regex. |
a0d0e21e | 251 | |
bee32ff8 GS |
252 | C<eval>ed strings (when accessible) are considered to be filenames: |
253 | C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string | |
055fd3a9 GS |
254 | (in the order of execution). The bodies of the currently executed C<eval> |
255 | and of C<eval>ed strings that define subroutines are saved and thus | |
256 | accessible. | |
bee32ff8 | 257 | |
a0d0e21e LW |
258 | =item /pattern/ |
259 | ||
055fd3a9 | 260 | Search forwards for pattern (a Perl regex); final / is optional. |
ae55e07e | 261 | The search is case-insensitive by default. |
a0d0e21e LW |
262 | |
263 | =item ?pattern? | |
264 | ||
4e1d3b43 | 265 | Search backwards for pattern; final ? is optional. |
ae55e07e | 266 | The search is case-insensitive by default. |
a0d0e21e | 267 | |
492652be | 268 | =item L [abw] |
d74e8afc | 269 | X<debugger command, L> |
a0d0e21e | 270 | |
492652be | 271 | List (default all) actions, breakpoints and watch expressions |
a0d0e21e | 272 | |
055fd3a9 | 273 | =item S [[!]regex] |
d74e8afc | 274 | X<debugger command, S> |
a0d0e21e | 275 | |
055fd3a9 | 276 | List subroutine names [not] matching the regex. |
a0d0e21e | 277 | |
611272bb | 278 | =item t [n] |
d74e8afc | 279 | X<debugger command, t> |
a0d0e21e | 280 | |
055fd3a9 | 281 | Toggle trace mode (see also the C<AutoTrace> option). |
611272bb PS |
282 | Optional argument is the maximum number of levels to trace below |
283 | the current one; anything deeper than that will be silent. | |
4e1d3b43 | 284 | |
611272bb | 285 | =item t [n] expr |
d74e8afc | 286 | X<debugger command, t> |
4e1d3b43 | 287 | |
055fd3a9 | 288 | Trace through execution of C<expr>. |
611272bb PS |
289 | Optional first argument is the maximum number of levels to trace below |
290 | the current one; anything deeper than that will be silent. | |
055fd3a9 | 291 | See L<perldebguts/"Frame Listing Output Examples"> for examples. |
4e1d3b43 | 292 | |
492652be | 293 | =item b |
d74e8afc ITB |
294 | X<breakpoint> |
295 | X<debugger command, b> | |
492652be RF |
296 | |
297 | Sets breakpoint on current line | |
298 | ||
4e1d3b43 | 299 | =item b [line] [condition] |
d74e8afc ITB |
300 | X<breakpoint> |
301 | X<debugger command, b> | |
a0d0e21e | 302 | |
492652be | 303 | Set a breakpoint before the given line. If a condition |
055fd3a9 GS |
304 | is specified, it's evaluated each time the statement is reached: a |
305 | breakpoint is taken only if the condition is true. Breakpoints may | |
306 | only be set on lines that begin an executable statement. Conditions | |
c997b287 | 307 | don't use C<if>: |
a0d0e21e LW |
308 | |
309 | b 237 $x > 30 | |
36477c24 | 310 | b 237 ++$count237 < 11 |
a0d0e21e LW |
311 | b 33 /pattern/i |
312 | ||
5343a617 SF |
313 | If the line number is C<.>, sets a breakpoint on the current line: |
314 | ||
315 | b . $n > 100 | |
316 | ||
076b743f SF |
317 | =item b [file]:[line] [condition] |
318 | X<breakpoint> | |
319 | X<debugger command, b> | |
320 | ||
321 | Set a breakpoint before the given line in a (possibly different) file. If a | |
322 | condition is specified, it's evaluated each time the statement is reached: a | |
323 | breakpoint is taken only if the condition is true. Breakpoints may only be set | |
324 | on lines that begin an executable statement. Conditions don't use C<if>: | |
325 | ||
326 | b lib/MyModule.pm:237 $x > 30 | |
327 | b /usr/lib/perl5/site_perl/CGI.pm:100 ++$count100 < 11 | |
328 | ||
4e1d3b43 | 329 | =item b subname [condition] |
d74e8afc ITB |
330 | X<breakpoint> |
331 | X<debugger command, b> | |
a0d0e21e | 332 | |
055fd3a9 GS |
333 | Set a breakpoint before the first line of the named subroutine. I<subname> may |
334 | be a variable containing a code reference (in this case I<condition> | |
83ee9e09 | 335 | is not supported). |
a0d0e21e | 336 | |
36477c24 | 337 | =item b postpone subname [condition] |
d74e8afc ITB |
338 | X<breakpoint> |
339 | X<debugger command, b> | |
36477c24 | 340 | |
055fd3a9 | 341 | Set a breakpoint at first line of subroutine after it is compiled. |
36477c24 | 342 | |
343 | =item b load filename | |
d74e8afc ITB |
344 | X<breakpoint> |
345 | X<debugger command, b> | |
36477c24 | 346 | |
055fd3a9 GS |
347 | Set a breakpoint before the first executed line of the I<filename>, |
348 | which should be a full pathname found amongst the %INC values. | |
e7ea3e70 IZ |
349 | |
350 | =item b compile subname | |
d74e8afc ITB |
351 | X<breakpoint> |
352 | X<debugger command, b> | |
e7ea3e70 | 353 | |
055fd3a9 GS |
354 | Sets a breakpoint before the first statement executed after the specified |
355 | subroutine is compiled. | |
36477c24 | 356 | |
492652be | 357 | =item B line |
d74e8afc ITB |
358 | X<breakpoint> |
359 | X<debugger command, B> | |
a0d0e21e | 360 | |
2e8f3c35 | 361 | Delete a breakpoint from the specified I<line>. |
a0d0e21e | 362 | |
492652be | 363 | =item B * |
d74e8afc ITB |
364 | X<breakpoint> |
365 | X<debugger command, B> | |
a0d0e21e | 366 | |
4e1d3b43 | 367 | Delete all installed breakpoints. |
368 | ||
e09195af SF |
369 | =item disable [file]:[line] |
370 | X<breakpoint> | |
371 | X<debugger command, disable> | |
372 | X<disable> | |
373 | ||
374 | Disable the breakpoint so it won't stop the execution of the program. | |
375 | Breakpoints are enabled by default and can be re-enabled using the C<enable> | |
376 | command. | |
377 | ||
378 | =item disable [line] | |
379 | X<breakpoint> | |
380 | X<debugger command, disable> | |
381 | X<disable> | |
382 | ||
383 | Disable the breakpoint so it won't stop the execution of the program. | |
384 | Breakpoints are enabled by default and can be re-enabled using the C<enable> | |
385 | command. | |
386 | ||
387 | This is done for a breakpoint in the current file. | |
388 | ||
389 | =item enable [file]:[line] | |
390 | X<breakpoint> | |
391 | X<debugger command, disable> | |
392 | X<disable> | |
393 | ||
394 | Enable the breakpoint so it will stop the execution of the program. | |
395 | ||
396 | =item enable [line] | |
397 | X<breakpoint> | |
398 | X<debugger command, disable> | |
399 | X<disable> | |
400 | ||
401 | Enable the breakpoint so it will stop the execution of the program. | |
402 | ||
403 | This is done for a breakpoint in the current file. | |
404 | ||
4e1d3b43 | 405 | =item a [line] command |
d74e8afc | 406 | X<debugger command, a> |
4e1d3b43 | 407 | |
055fd3a9 GS |
408 | Set an action to be done before the line is executed. If I<line> is |
409 | omitted, set an action on the line about to be executed. | |
4e1d3b43 | 410 | The sequence of steps taken by the debugger is |
411 | ||
8ebc5c01 | 412 | 1. check for a breakpoint at this line |
413 | 2. print the line if necessary (tracing) | |
414 | 3. do any actions associated with that line | |
415 | 4. prompt user if at a breakpoint or in single-step | |
416 | 5. evaluate line | |
a0d0e21e | 417 | |
7b8d334a | 418 | For example, this will print out $foo every time line |
4e1d3b43 | 419 | 53 is passed: |
a0d0e21e | 420 | |
4e1d3b43 | 421 | a 53 print "DB FOUND $foo\n" |
a0d0e21e | 422 | |
492652be | 423 | =item A line |
d74e8afc | 424 | X<debugger command, A> |
3fbd6552 | 425 | |
2e8f3c35 | 426 | Delete an action from the specified line. |
3fbd6552 | 427 | |
492652be | 428 | =item A * |
d74e8afc | 429 | X<debugger command, A> |
a0d0e21e | 430 | |
4e1d3b43 | 431 | Delete all installed actions. |
432 | ||
492652be | 433 | =item w expr |
d74e8afc | 434 | X<debugger command, w> |
6ee623d5 | 435 | |
8a974184 AA |
436 | Add a global watch-expression. Whenever a watched global changes the |
437 | debugger will stop and display the old and new values. | |
6ee623d5 | 438 | |
492652be | 439 | =item W expr |
d74e8afc | 440 | X<debugger command, W> |
492652be RF |
441 | |
442 | Delete watch-expression | |
443 | ||
444 | =item W * | |
d74e8afc | 445 | X<debugger command, W> |
6ee623d5 GS |
446 | |
447 | Delete all watch-expressions. | |
448 | ||
492652be | 449 | =item o |
d74e8afc | 450 | X<debugger command, o> |
492652be | 451 | |
5d464584 | 452 | Display all options. |
492652be RF |
453 | |
454 | =item o booloption ... | |
d74e8afc | 455 | X<debugger command, o> |
055fd3a9 GS |
456 | |
457 | Set each listed Boolean option to the value C<1>. | |
458 | ||
492652be | 459 | =item o anyoption? ... |
d74e8afc | 460 | X<debugger command, o> |
055fd3a9 GS |
461 | |
462 | Print out the value of one or more options. | |
463 | ||
492652be | 464 | =item o option=value ... |
d74e8afc | 465 | X<debugger command, o> |
055fd3a9 GS |
466 | |
467 | Set the value of one or more options. If the value has internal | |
492652be | 468 | whitespace, it should be quoted. For example, you could set C<o |
055fd3a9 GS |
469 | pager="less -MQeicsNfr"> to call B<less> with those specific options. |
470 | You may use either single or double quotes, but if you do, you must | |
471 | escape any embedded instances of same sort of quote you began with, | |
472 | as well as any escaping any escapes that immediately precede that | |
473 | quote but which are not meant to escape the quote itself. In other | |
474 | words, you follow single-quoting rules irrespective of the quote; | |
492652be | 475 | eg: C<o option='this isn\'t bad'> or C<o option="She said, \"Isn't |
055fd3a9 GS |
476 | it?\"">. |
477 | ||
478 | For historical reasons, the C<=value> is optional, but defaults to | |
479 | 1 only where it is safe to do so--that is, mostly for Boolean | |
480 | options. It is always better to assign a specific value using C<=>. | |
481 | The C<option> can be abbreviated, but for clarity probably should | |
5a0de581 | 482 | not be. Several options can be set together. See L</"Configurable Options"> |
13a2d996 | 483 | for a list of these. |
055fd3a9 | 484 | |
2e8f3c35 | 485 | =item < ? |
d74e8afc | 486 | X<< debugger command, < >> |
055fd3a9 GS |
487 | |
488 | List out all pre-prompt Perl command actions. | |
489 | ||
490 | =item < [ command ] | |
d74e8afc | 491 | X<< debugger command, < >> |
055fd3a9 GS |
492 | |
493 | Set an action (Perl command) to happen before every debugger prompt. | |
2e8f3c35 | 494 | A multi-line command may be entered by backslashing the newlines. |
0d6091f7 | 495 | |
2e8f3c35 | 496 | =item < * |
d74e8afc | 497 | X<< debugger command, < >> |
0d6091f7 RF |
498 | |
499 | Delete all pre-prompt Perl command actions. | |
055fd3a9 GS |
500 | |
501 | =item << command | |
d74e8afc | 502 | X<< debugger command, << >> |
055fd3a9 GS |
503 | |
504 | Add an action (Perl command) to happen before every debugger prompt. | |
505 | A multi-line command may be entered by backwhacking the newlines. | |
506 | ||
507 | =item > ? | |
d74e8afc | 508 | X<< debugger command, > >> |
055fd3a9 GS |
509 | |
510 | List out post-prompt Perl command actions. | |
511 | ||
512 | =item > command | |
d74e8afc | 513 | X<< debugger command, > >> |
055fd3a9 GS |
514 | |
515 | Set an action (Perl command) to happen after the prompt when you've | |
516 | just given a command to return to executing the script. A multi-line | |
517 | command may be entered by backslashing the newlines (we bet you | |
353c6505 | 518 | couldn't have guessed this by now). |
0d6091f7 | 519 | |
2e8f3c35 | 520 | =item > * |
d74e8afc | 521 | X<< debugger command, > >> |
0d6091f7 RF |
522 | |
523 | Delete all post-prompt Perl command actions. | |
055fd3a9 GS |
524 | |
525 | =item >> command | |
d74e8afc | 526 | X<<< debugger command, >> >>> |
055fd3a9 GS |
527 | |
528 | Adds an action (Perl command) to happen after the prompt when you've | |
529 | just given a command to return to executing the script. A multi-line | |
b1866b2d | 530 | command may be entered by backslashing the newlines. |
055fd3a9 GS |
531 | |
532 | =item { ? | |
d74e8afc | 533 | X<debugger command, {> |
055fd3a9 GS |
534 | |
535 | List out pre-prompt debugger commands. | |
536 | ||
537 | =item { [ command ] | |
538 | ||
539 | Set an action (debugger command) to happen before every debugger prompt. | |
2e8f3c35 | 540 | A multi-line command may be entered in the customary fashion. |
055fd3a9 GS |
541 | |
542 | Because this command is in some senses new, a warning is issued if | |
543 | you appear to have accidentally entered a block instead. If that's | |
2e8f3c35 | 544 | what you mean to do, write it as with C<;{ ... }> or even |
055fd3a9 GS |
545 | C<do { ... }>. |
546 | ||
2e8f3c35 | 547 | =item { * |
d74e8afc | 548 | X<debugger command, {> |
0d6091f7 RF |
549 | |
550 | Delete all pre-prompt debugger commands. | |
551 | ||
055fd3a9 | 552 | =item {{ command |
d74e8afc | 553 | X<debugger command, {{> |
055fd3a9 GS |
554 | |
555 | Add an action (debugger command) to happen before every debugger prompt. | |
556 | A multi-line command may be entered, if you can guess how: see above. | |
557 | ||
558 | =item ! number | |
d74e8afc | 559 | X<debugger command, !> |
055fd3a9 GS |
560 | |
561 | Redo a previous command (defaults to the previous command). | |
562 | ||
563 | =item ! -number | |
d74e8afc | 564 | X<debugger command, !> |
055fd3a9 GS |
565 | |
566 | Redo number'th previous command. | |
567 | ||
568 | =item ! pattern | |
d74e8afc | 569 | X<debugger command, !> |
055fd3a9 GS |
570 | |
571 | Redo last command that started with pattern. | |
492652be | 572 | See C<o recallCommand>, too. |
055fd3a9 GS |
573 | |
574 | =item !! cmd | |
d74e8afc | 575 | X<debugger command, !!> |
055fd3a9 GS |
576 | |
577 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See | |
492652be | 578 | C<o shellBang>, also. Note that the user's current shell (well, |
055fd3a9 GS |
579 | their C<$ENV{SHELL}> variable) will be used, which can interfere |
580 | with proper interpretation of exit status or signal and coredump | |
581 | information. | |
582 | ||
947cb114 | 583 | =item source file |
d74e8afc | 584 | X<debugger command, source> |
5bad0d9e | 585 | |
947cb114 PS |
586 | Read and execute debugger commands from I<file>. |
587 | I<file> may itself contain C<source> commands. | |
5bad0d9e | 588 | |
055fd3a9 | 589 | =item H -number |
d74e8afc | 590 | X<debugger command, H> |
055fd3a9 GS |
591 | |
592 | Display last n commands. Only commands longer than one character are | |
593 | listed. If I<number> is omitted, list them all. | |
594 | ||
595 | =item q or ^D | |
d74e8afc ITB |
596 | X<debugger command, q> |
597 | X<debugger command, ^D> | |
055fd3a9 GS |
598 | |
599 | Quit. ("quit" doesn't work for this, unless you've made an alias) | |
600 | This is the only supported way to exit the debugger, though typing | |
601 | C<exit> twice might work. | |
602 | ||
603 | Set the C<inhibit_exit> option to 0 if you want to be able to step | |
2e8f3c35 | 604 | off the end the script. You may also need to set $finished to 0 |
055fd3a9 GS |
605 | if you want to step through global destruction. |
606 | ||
607 | =item R | |
d74e8afc | 608 | X<debugger command, R> |
055fd3a9 GS |
609 | |
610 | Restart the debugger by C<exec()>ing a new session. We try to maintain | |
611 | your history across this, but internal settings and command-line options | |
612 | may be lost. | |
613 | ||
614 | The following setting are currently preserved: history, breakpoints, | |
615 | actions, debugger options, and the Perl command-line | |
616 | options B<-w>, B<-I>, and B<-e>. | |
617 | ||
618 | =item |dbcmd | |
d74e8afc | 619 | X<debugger command, |> |
055fd3a9 GS |
620 | |
621 | Run the debugger command, piping DB::OUT into your current pager. | |
622 | ||
623 | =item ||dbcmd | |
d74e8afc | 624 | X<debugger command, ||> |
055fd3a9 | 625 | |
c997b287 | 626 | Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well. |
055fd3a9 GS |
627 | |
628 | =item = [alias value] | |
d74e8afc | 629 | X<debugger command, => |
055fd3a9 GS |
630 | |
631 | Define a command alias, like | |
632 | ||
633 | = quit q | |
634 | ||
635 | or list current aliases. | |
636 | ||
637 | =item command | |
638 | ||
639 | Execute command as a Perl statement. A trailing semicolon will be | |
640 | supplied. If the Perl statement would otherwise be confused for a | |
641 | Perl debugger, use a leading semicolon, too. | |
642 | ||
643 | =item m expr | |
d74e8afc | 644 | X<debugger command, m> |
055fd3a9 GS |
645 | |
646 | List which methods may be called on the result of the evaluated | |
2e8f3c35 | 647 | expression. The expression may evaluated to a reference to a |
055fd3a9 GS |
648 | blessed object, or to a package name. |
649 | ||
492652be | 650 | =item M |
d74e8afc | 651 | X<debugger command, M> |
492652be | 652 | |
5d464584 | 653 | Display all loaded modules and their versions. |
492652be | 654 | |
055fd3a9 | 655 | =item man [manpage] |
d74e8afc | 656 | X<debugger command, man> |
055fd3a9 GS |
657 | |
658 | Despite its name, this calls your system's default documentation | |
659 | viewer on the given page, or on the viewer itself if I<manpage> is | |
660 | omitted. If that viewer is B<man>, the current C<Config> information | |
661 | is used to invoke B<man> using the proper MANPATH or S<B<-M> | |
662 | I<manpath>> option. Failed lookups of the form C<XXX> that match | |
663 | known manpages of the form I<perlXXX> will be retried. This lets | |
664 | you type C<man debug> or C<man op> from the debugger. | |
665 | ||
666 | On systems traditionally bereft of a usable B<man> command, the | |
667 | debugger invokes B<perldoc>. Occasionally this determination is | |
668 | incorrect due to recalcitrant vendors or rather more felicitously, | |
669 | to enterprising users. If you fall into either category, just | |
670 | manually set the $DB::doccmd variable to whatever viewer to view | |
671 | the Perl documentation on your system. This may be set in an rc | |
672 | file, or through direct assignment. We're still waiting for a | |
673 | working example of something along the lines of: | |
4e1d3b43 | 674 | |
055fd3a9 GS |
675 | $DB::doccmd = 'netscape -remote http://something.here/'; |
676 | ||
677 | =back | |
678 | ||
679 | =head2 Configurable Options | |
680 | ||
492652be | 681 | The debugger has numerous options settable using the C<o> command, |
bf8d11e4 S |
682 | either interactively or from the environment or an rc file. The file |
683 | is named F<./.perldb> or F<~/.perldb> under Unix with F</dev/tty>, | |
684 | F<perldb.ini> otherwise. | |
4e1d3b43 | 685 | |
686 | =over 12 | |
687 | ||
e7ea3e70 | 688 | =item C<recallCommand>, C<ShellBang> |
d74e8afc ITB |
689 | X<debugger option, recallCommand> |
690 | X<debugger option, ShellBang> | |
4e1d3b43 | 691 | |
228c5779 | 692 | The characters used to recall a command or spawn a shell. By |
055fd3a9 | 693 | default, both are set to C<!>, which is unfortunate. |
4e1d3b43 | 694 | |
e7ea3e70 | 695 | =item C<pager> |
d74e8afc | 696 | X<debugger option, pager> |
4e1d3b43 | 697 | |
055fd3a9 GS |
698 | Program to use for output of pager-piped commands (those beginning |
699 | with a C<|> character.) By default, C<$ENV{PAGER}> will be used. | |
700 | Because the debugger uses your current terminal characteristics | |
701 | for bold and underlining, if the chosen pager does not pass escape | |
702 | sequences through unchanged, the output of some debugger commands | |
703 | will not be readable when sent through the pager. | |
4e1d3b43 | 704 | |
e7ea3e70 | 705 | =item C<tkRunning> |
d74e8afc | 706 | X<debugger option, tkRunning> |
36477c24 | 707 | |
708 | Run Tk while prompting (with ReadLine). | |
709 | ||
e7ea3e70 | 710 | =item C<signalLevel>, C<warnLevel>, C<dieLevel> |
d74e8afc ITB |
711 | X<debugger option, signalLevel> X<debugger option, warnLevel> |
712 | X<debugger option, dieLevel> | |
e7ea3e70 | 713 | |
4c82ae22 GS |
714 | Level of verbosity. By default, the debugger leaves your exceptions |
715 | and warnings alone, because altering them can break correctly running | |
716 | programs. It will attempt to print a message when uncaught INT, BUS, or | |
96090e4f | 717 | SEGV signals arrive. (But see the mention of signals in L</BUGS> below.) |
4c82ae22 GS |
718 | |
719 | To disable this default safe mode, set these values to something higher | |
720 | than 0. At a level of 1, you get backtraces upon receiving any kind | |
721 | of warning (this is often annoying) or exception (this is | |
722 | often valuable). Unfortunately, the debugger cannot discern fatal | |
723 | exceptions from non-fatal ones. If C<dieLevel> is even 1, then your | |
724 | non-fatal exceptions are also traced and unceremoniously altered if they | |
353c6505 | 725 | came from C<eval'ed> strings or from any kind of C<eval> within modules |
4c82ae22 GS |
726 | you're attempting to load. If C<dieLevel> is 2, the debugger doesn't |
727 | care where they came from: It usurps your exception handler and prints | |
728 | out a trace, then modifies all exceptions with its own embellishments. | |
729 | This may perhaps be useful for some tracing purposes, but tends to hopelessly | |
730 | destroy any program that takes its exception handling seriously. | |
36477c24 | 731 | |
e7ea3e70 | 732 | =item C<AutoTrace> |
d74e8afc | 733 | X<debugger option, AutoTrace> |
36477c24 | 734 | |
e7ea3e70 IZ |
735 | Trace mode (similar to C<t> command, but can be put into |
736 | C<PERLDB_OPTS>). | |
36477c24 | 737 | |
e7ea3e70 | 738 | =item C<LineInfo> |
d74e8afc | 739 | X<debugger option, LineInfo> |
36477c24 | 740 | |
e7ea3e70 | 741 | File or pipe to print line number info to. If it is a pipe (say, |
055fd3a9 | 742 | C<|visual_perl_db>), then a short message is used. This is the |
3a99f1de | 743 | mechanism used to interact with a client editor or visual debugger, |
055fd3a9 GS |
744 | such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical |
745 | debugger. | |
36477c24 | 746 | |
747 | =item C<inhibit_exit> | |
d74e8afc | 748 | X<debugger option, inhibit_exit> |
36477c24 | 749 | |
750 | If 0, allows I<stepping off> the end of the script. | |
751 | ||
54310121 | 752 | =item C<PrintRet> |
d74e8afc | 753 | X<debugger option, PrintRet> |
36477c24 | 754 | |
04cf9722 | 755 | Print return value after C<r> command if set (default). |
36477c24 | 756 | |
28d1fb14 | 757 | =item C<ornaments> |
d74e8afc | 758 | X<debugger option, ornaments> |
28d1fb14 | 759 | |
055fd3a9 GS |
760 | Affects screen appearance of the command line (see L<Term::ReadLine>). |
761 | There is currently no way to disable these, which can render | |
762 | some output illegible on some displays, or with some pagers. | |
763 | This is considered a bug. | |
28d1fb14 | 764 | |
54310121 | 765 | =item C<frame> |
d74e8afc | 766 | X<debugger option, frame> |
36477c24 | 767 | |
055fd3a9 | 768 | Affects the printing of messages upon entry and exit from subroutines. If |
36477c24 | 769 | C<frame & 2> is false, messages are printed on entry only. (Printing |
055fd3a9 | 770 | on exit might be useful if interspersed with other messages.) |
36477c24 | 771 | |
055fd3a9 GS |
772 | If C<frame & 4>, arguments to functions are printed, plus context |
773 | and caller info. If C<frame & 8>, overloaded C<stringify> and | |
774 | C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame | |
775 | & 16>, the return value from the subroutine is printed. | |
28d1fb14 IZ |
776 | |
777 | The length at which the argument list is truncated is governed by the | |
778 | next option: | |
e7ea3e70 IZ |
779 | |
780 | =item C<maxTraceLen> | |
d74e8afc | 781 | X<debugger option, maxTraceLen> |
e7ea3e70 | 782 | |
055fd3a9 | 783 | Length to truncate the argument list when the C<frame> option's |
e7ea3e70 | 784 | bit 4 is set. |
36477c24 | 785 | |
6f891d7d | 786 | =item C<windowSize> |
d74e8afc | 787 | X<debugger option, windowSize> |
6f891d7d SM |
788 | |
789 | Change the size of code list window (default is 10 lines). | |
790 | ||
4e1d3b43 | 791 | =back |
792 | ||
793 | The following options affect what happens with C<V>, C<X>, and C<x> | |
794 | commands: | |
795 | ||
796 | =over 12 | |
797 | ||
e7ea3e70 | 798 | =item C<arrayDepth>, C<hashDepth> |
d74e8afc | 799 | X<debugger option, arrayDepth> X<debugger option, hashDepth> |
4e1d3b43 | 800 | |
801 | Print only first N elements ('' for all). | |
802 | ||
d03c2a1b | 803 | =item C<dumpDepth> |
d74e8afc | 804 | X<debugger option, dumpDepth> |
d03c2a1b MJD |
805 | |
806 | Limit recursion depth to N levels when dumping structures. | |
807 | Negative values are interpreted as infinity. Default: infinity. | |
808 | ||
e7ea3e70 | 809 | =item C<compactDump>, C<veryCompact> |
d74e8afc | 810 | X<debugger option, compactDump> X<debugger option, veryCompact> |
4e1d3b43 | 811 | |
055fd3a9 | 812 | Change the style of array and hash output. If C<compactDump>, short array |
e7ea3e70 | 813 | may be printed on one line. |
4e1d3b43 | 814 | |
e7ea3e70 | 815 | =item C<globPrint> |
d74e8afc | 816 | X<debugger option, globPrint> |
4e1d3b43 | 817 | |
818 | Whether to print contents of globs. | |
819 | ||
e7ea3e70 | 820 | =item C<DumpDBFiles> |
d74e8afc | 821 | X<debugger option, DumpDBFiles> |
4e1d3b43 | 822 | |
823 | Dump arrays holding debugged files. | |
824 | ||
e7ea3e70 | 825 | =item C<DumpPackages> |
d74e8afc | 826 | X<debugger option, DumpPackages> |
4e1d3b43 | 827 | |
828 | Dump symbol tables of packages. | |
829 | ||
6ee623d5 | 830 | =item C<DumpReused> |
d74e8afc | 831 | X<debugger option, DumpReused> |
6ee623d5 GS |
832 | |
833 | Dump contents of "reused" addresses. | |
834 | ||
e7ea3e70 | 835 | =item C<quote>, C<HighBit>, C<undefPrint> |
d74e8afc ITB |
836 | X<debugger option, quote> X<debugger option, HighBit> |
837 | X<debugger option, undefPrint> | |
e7ea3e70 | 838 | |
055fd3a9 GS |
839 | Change the style of string dump. The default value for C<quote> |
840 | is C<auto>; one can enable double-quotish or single-quotish format | |
841 | by setting it to C<"> or C<'>, respectively. By default, characters | |
842 | with their high bit set are printed verbatim. | |
e7ea3e70 | 843 | |
54310121 | 844 | =item C<UsageOnly> |
d74e8afc | 845 | X<debugger option, UsageOnly> |
4e1d3b43 | 846 | |
055fd3a9 GS |
847 | Rudimentary per-package memory usage dump. Calculates total |
848 | size of strings found in variables in the package. This does not | |
849 | include lexicals in a module's file scope, or lost in closures. | |
4e1d3b43 | 850 | |
5c112a16 SF |
851 | =item C<HistFile> |
852 | X<debugger option, history, HistFile> | |
853 | ||
854 | The path of the file from which the history (assuming a usable | |
855 | Term::ReadLine backend) will be read on the debugger's startup, and to which | |
856 | it will be saved on shutdown (for persistence across sessions). Similar in | |
857 | concept to Bash's C<.bash_history> file. | |
858 | ||
859 | =item C<HistSize> | |
860 | X<debugger option, history, HistSize> | |
861 | ||
862 | The count of the saved lines in the history (assuming C<HistFile> above). | |
863 | ||
36477c24 | 864 | =back |
4e1d3b43 | 865 | |
e00d725b | 866 | After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}> |
66a1b24b | 867 | environment variable and parses this as the remainder of a "O ..." |
e00d725b MJD |
868 | line as one might enter at the debugger prompt. You may place the |
869 | initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop> | |
870 | there. | |
36477c24 | 871 | |
055fd3a9 | 872 | If your rc file contains: |
4e1d3b43 | 873 | |
055fd3a9 | 874 | parse_options("NonStop=1 LineInfo=db.out AutoTrace"); |
4e1d3b43 | 875 | |
055fd3a9 GS |
876 | then your script will run without human intervention, putting trace |
877 | information into the file I<db.out>. (If you interrupt it, you'd | |
878 | better reset C<LineInfo> to F</dev/tty> if you expect to see anything.) | |
4e1d3b43 | 879 | |
36477c24 | 880 | =over 12 |
4e1d3b43 | 881 | |
36477c24 | 882 | =item C<TTY> |
d74e8afc | 883 | X<debugger option, TTY> |
4e1d3b43 | 884 | |
36477c24 | 885 | The TTY to use for debugging I/O. |
886 | ||
36477c24 | 887 | =item C<noTTY> |
d74e8afc | 888 | X<debugger option, noTTY> |
36477c24 | 889 | |
055fd3a9 GS |
890 | If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If |
891 | interrupted (or if control goes to the debugger via explicit setting of | |
892 | $DB::signal or $DB::single from the Perl script), it connects to a TTY | |
893 | specified in the C<TTY> option at startup, or to a tty found at | |
894 | runtime using the C<Term::Rendezvous> module of your choice. | |
36477c24 | 895 | |
055fd3a9 | 896 | This module should implement a method named C<new> that returns an object |
200f06d0 | 897 | with two methods: C<IN> and C<OUT>. These should return filehandles to use |
055fd3a9 GS |
898 | for debugging input and output correspondingly. The C<new> method should |
899 | inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at | |
2e8f3c35 | 900 | startup, or C<"$ENV{HOME}/.perldbtty$$"> otherwise. This file is not |
055fd3a9 GS |
901 | inspected for proper ownership, so security hazards are theoretically |
902 | possible. | |
36477c24 | 903 | |
904 | =item C<ReadLine> | |
d74e8afc | 905 | X<debugger option, ReadLine> |
36477c24 | 906 | |
055fd3a9 GS |
907 | If false, readline support in the debugger is disabled in order |
908 | to debug applications that themselves use ReadLine. | |
36477c24 | 909 | |
910 | =item C<NonStop> | |
d74e8afc | 911 | X<debugger option, NonStop> |
36477c24 | 912 | |
055fd3a9 | 913 | If set, the debugger goes into non-interactive mode until interrupted, or |
36477c24 | 914 | programmatically by setting $DB::signal or $DB::single. |
915 | ||
916 | =back | |
917 | ||
918 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: | |
4e1d3b43 | 919 | |
055fd3a9 | 920 | $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram |
4e1d3b43 | 921 | |
055fd3a9 GS |
922 | That will run the script B<myprogram> without human intervention, |
923 | printing out the call tree with entry and exit points. Note that | |
924 | C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally, | |
925 | options could be uniquely abbreviated by the first letter (modulo | |
926 | the C<Dump*> options). It is nevertheless recommended that you | |
927 | always spell them out in full for legibility and future compatibility. | |
4e1d3b43 | 928 | |
055fd3a9 | 929 | Other examples include |
a0d0e21e | 930 | |
1472e7de | 931 | $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram |
a0d0e21e | 932 | |
055fd3a9 GS |
933 | which runs script non-interactively, printing info on each entry |
934 | into a subroutine and each executed line into the file named F<listing>. | |
935 | (If you interrupt it, you would better reset C<LineInfo> to something | |
36477c24 | 936 | "interactive"!) |
937 | ||
055fd3a9 GS |
938 | Other examples include (using standard shell syntax to show environment |
939 | variable settings): | |
36477c24 | 940 | |
055fd3a9 GS |
941 | $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out" |
942 | perl -d myprogram ) | |
36477c24 | 943 | |
055fd3a9 GS |
944 | which may be useful for debugging a program that uses C<Term::ReadLine> |
945 | itself. Do not forget to detach your shell from the TTY in the window that | |
946 | corresponds to F</dev/ttyXX>, say, by issuing a command like | |
36477c24 | 947 | |
e7ea3e70 | 948 | $ sleep 1000000 |
36477c24 | 949 | |
055fd3a9 | 950 | See L<perldebguts/"Debugger Internals"> for details. |
a0d0e21e | 951 | |
57e8c15d | 952 | =head2 Debugger Input/Output |
e7ea3e70 IZ |
953 | |
954 | =over 8 | |
955 | ||
956 | =item Prompt | |
957 | ||
4e1d3b43 | 958 | The debugger prompt is something like |
959 | ||
960 | DB<8> | |
961 | ||
962 | or even | |
963 | ||
964 | DB<<17>> | |
965 | ||
055fd3a9 GS |
966 | where that number is the command number, and which you'd use to |
967 | access with the built-in B<csh>-like history mechanism. For example, | |
968 | C<!17> would repeat command number 17. The depth of the angle | |
969 | brackets indicates the nesting depth of the debugger. You could | |
970 | get more than one set of brackets, for example, if you'd already | |
971 | at a breakpoint and then printed the result of a function call that | |
972 | itself has a breakpoint, or you step into an expression via C<s/n/t | |
973 | expression> command. | |
4e1d3b43 | 974 | |
54310121 | 975 | =item Multiline commands |
e7ea3e70 | 976 | |
4a6725af | 977 | If you want to enter a multi-line command, such as a subroutine |
055fd3a9 GS |
978 | definition with several statements or a format, escape the newline |
979 | that would normally end the debugger command with a backslash. | |
e7ea3e70 | 980 | Here's an example: |
a0d0e21e | 981 | |
4e1d3b43 | 982 | DB<1> for (1..4) { \ |
983 | cont: print "ok\n"; \ | |
984 | cont: } | |
985 | ok | |
986 | ok | |
987 | ok | |
988 | ok | |
989 | ||
990 | Note that this business of escaping a newline is specific to interactive | |
991 | commands typed into the debugger. | |
992 | ||
e7ea3e70 | 993 | =item Stack backtrace |
d74e8afc | 994 | X<backtrace> X<stack, backtrace> |
e7ea3e70 | 995 | |
68dc0745 | 996 | Here's an example of what a stack backtrace via C<T> command might |
e7ea3e70 | 997 | look like: |
4e1d3b43 | 998 | |
f185f654 KW |
999 | $ = main::infested called from file 'Ambulation.pm' line 10 |
1000 | @ = Ambulation::legs(1, 2, 3, 4) called from file 'camel_flea' | |
1001 | line 7 | |
1002 | $ = main::pests('bactrian', 4) called from file 'camel_flea' | |
1003 | line 4 | |
4e1d3b43 | 1004 | |
055fd3a9 GS |
1005 | The left-hand character up there indicates the context in which the |
1006 | function was called, with C<$> and C<@> meaning scalar or list | |
1007 | contexts respectively, and C<.> meaning void context (which is | |
1008 | actually a sort of scalar context). The display above says | |
1009 | that you were in the function C<main::infested> when you ran the | |
1010 | stack dump, and that it was called in scalar context from line | |
1011 | 10 of the file I<Ambulation.pm>, but without any arguments at all, | |
1012 | meaning it was called as C<&infested>. The next stack frame shows | |
1013 | that the function C<Ambulation::legs> was called in list context | |
1014 | from the I<camel_flea> file with four arguments. The last stack | |
1015 | frame shows that C<main::pests> was called in scalar context, | |
1016 | also from I<camel_flea>, but from line 4. | |
4e1d3b43 | 1017 | |
055fd3a9 GS |
1018 | If you execute the C<T> command from inside an active C<use> |
1019 | statement, the backtrace will contain both a C<require> frame and | |
5d464584 | 1020 | an C<eval> frame. |
e7ea3e70 | 1021 | |
055fd3a9 | 1022 | =item Line Listing Format |
e7ea3e70 | 1023 | |
055fd3a9 | 1024 | This shows the sorts of output the C<l> command can produce: |
e7ea3e70 | 1025 | |
f185f654 KW |
1026 | DB<<13>> l |
1027 | 101: @i{@i} = (); | |
1028 | 102:b @isa{@i,$pack} = () | |
1029 | 103 if(exists $i{$prevpack} || exists $isa{$pack}); | |
1030 | 104 } | |
1031 | 105 | |
1032 | 106 next | |
1033 | 107==> if(exists $isa{$pack}); | |
1034 | 108 | |
1035 | 109:a if ($extra-- > 0) { | |
1036 | 110: %isa = ($pack,1); | |
e7ea3e70 | 1037 | |
055fd3a9 GS |
1038 | Breakable lines are marked with C<:>. Lines with breakpoints are |
1039 | marked by C<b> and those with actions by C<a>. The line that's | |
1040 | about to be executed is marked by C<< ==> >>. | |
e7ea3e70 | 1041 | |
003183f2 GS |
1042 | Please be aware that code in debugger listings may not look the same |
1043 | as your original source code. Line directives and external source | |
1044 | filters can alter the code before Perl sees it, causing code to move | |
1045 | from its original positions or take on entirely different forms. | |
1046 | ||
e7ea3e70 IZ |
1047 | =item Frame listing |
1048 | ||
055fd3a9 GS |
1049 | When the C<frame> option is set, the debugger would print entered (and |
1050 | optionally exited) subroutines in different styles. See L<perldebguts> | |
1051 | for incredibly long examples of these. | |
e7ea3e70 IZ |
1052 | |
1053 | =back | |
1054 | ||
57e8c15d | 1055 | =head2 Debugging Compile-Time Statements |
e7ea3e70 | 1056 | |
055fd3a9 | 1057 | If you have compile-time executable statements (such as code within |
3c10abe3 AG |
1058 | BEGIN, UNITCHECK and CHECK blocks or C<use> statements), these will |
1059 | I<not> be stopped by debugger, although C<require>s and INIT blocks | |
5d464584 | 1060 | will, and compile-time statements can be traced with the C<AutoTrace> |
3c10abe3 AG |
1061 | option set in C<PERLDB_OPTS>). From your own Perl code, however, you |
1062 | can transfer control back to the debugger using the following | |
1063 | statement, which is harmless if the debugger is not running: | |
a0d0e21e LW |
1064 | |
1065 | $DB::single = 1; | |
1066 | ||
055fd3a9 | 1067 | If you set C<$DB::single> to 2, it's equivalent to having |
4e1d3b43 | 1068 | just typed the C<n> command, whereas a value of 1 means the C<s> |
1069 | command. The C<$DB::trace> variable should be set to 1 to simulate | |
1070 | having typed the C<t> command. | |
1071 | ||
055fd3a9 GS |
1072 | Another way to debug compile-time code is to start the debugger, set a |
1073 | breakpoint on the I<load> of some module: | |
e7ea3e70 IZ |
1074 | |
1075 | DB<7> b load f:/perllib/lib/Carp.pm | |
ccf3535a | 1076 | Will stop on load of 'f:/perllib/lib/Carp.pm'. |
e7ea3e70 | 1077 | |
055fd3a9 | 1078 | and then restart the debugger using the C<R> command (if possible). One can use C<b |
e7ea3e70 IZ |
1079 | compile subname> for the same purpose. |
1080 | ||
4e1d3b43 | 1081 | =head2 Debugger Customization |
a0d0e21e | 1082 | |
055fd3a9 GS |
1083 | The debugger probably contains enough configuration hooks that you |
1084 | won't ever have to modify it yourself. You may change the behaviour | |
5d464584 | 1085 | of the debugger from within the debugger using its C<o> command, from |
055fd3a9 GS |
1086 | the command line via the C<PERLDB_OPTS> environment variable, and |
1087 | from customization files. | |
a0d0e21e | 1088 | |
055fd3a9 | 1089 | You can do some customization by setting up a F<.perldb> file, which |
a0d0e21e | 1090 | contains initialization code. For instance, you could make aliases |
4e1d3b43 | 1091 | like these (the last one is one people expect to be there): |
a0d0e21e | 1092 | |
4e1d3b43 | 1093 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; |
a0d0e21e | 1094 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; |
4e1d3b43 | 1095 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; |
055fd3a9 | 1096 | $DB::alias{'quit'} = 's/^quit(\s*)/exit/'; |
4e1d3b43 | 1097 | |
055fd3a9 | 1098 | You can change options from F<.perldb> by using calls like this one; |
36477c24 | 1099 | |
1100 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); | |
1101 | ||
055fd3a9 | 1102 | The code is executed in the package C<DB>. Note that F<.perldb> is |
774d564b | 1103 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the |
055fd3a9 | 1104 | subroutine C<afterinit>, that function is called after debugger |
774d564b | 1105 | initialization ends. F<.perldb> may be contained in the current |
055fd3a9 GS |
1106 | directory, or in the home directory. Because this file is sourced |
1107 | in by Perl and may contain arbitrary commands, for security reasons, | |
1108 | it must be owned by the superuser or the current user, and writable | |
1109 | by no one but its owner. | |
36477c24 | 1110 | |
bea98532 JH |
1111 | You can mock TTY input to debugger by adding arbitrary commands to |
1112 | @DB::typeahead. For example, your F<.perldb> file might contain: | |
1113 | ||
1114 | sub afterinit { push @DB::typeahead, "b 4", "b 6"; } | |
1115 | ||
1116 | Which would attempt to set breakpoints on lines 4 and 6 immediately | |
d7f8936a | 1117 | after debugger initialization. Note that @DB::typeahead is not a supported |
bea98532 JH |
1118 | interface and is subject to change in future releases. |
1119 | ||
055fd3a9 GS |
1120 | If you want to modify the debugger, copy F<perl5db.pl> from the |
1121 | Perl library to another name and hack it to your heart's content. | |
1122 | You'll then want to set your C<PERL5DB> environment variable to say | |
1123 | something like this: | |
36477c24 | 1124 | |
1125 | BEGIN { require "myperl5db.pl" } | |
1126 | ||
055fd3a9 GS |
1127 | As a last resort, you could also use C<PERL5DB> to customize the debugger |
1128 | by directly setting internal variables or calling debugger functions. | |
1129 | ||
1130 | Note that any variables and functions that are not documented in | |
1131 | this document (or in L<perldebguts>) are considered for internal | |
1132 | use only, and as such are subject to change without notice. | |
36477c24 | 1133 | |
57e8c15d | 1134 | =head2 Readline Support / History in the Debugger |
4e1d3b43 | 1135 | |
055fd3a9 | 1136 | As shipped, the only command-line history supplied is a simplistic one |
4e1d3b43 | 1137 | that checks for leading exclamation points. However, if you install |
3244086b B |
1138 | the Term::ReadKey and Term::ReadLine modules from CPAN (such as |
1139 | Term::ReadLine::Gnu, Term::ReadLine::Perl, ...) you will | |
5d464584 | 1140 | have full editing capabilities much like those GNU I<readline>(3) provides. |
4e1d3b43 | 1141 | Look for these in the F<modules/by-module/Term> directory on CPAN. |
055fd3a9 | 1142 | These do not support normal B<vi> command-line editing, however. |
4e1d3b43 | 1143 | |
d2286278 S |
1144 | A rudimentary command-line completion is also available, including |
1145 | lexical variables in the current scope if the C<PadWalker> module | |
1146 | is installed. | |
e7ea3e70 | 1147 | |
3244086b B |
1148 | Without Readline support you may see the symbols "^[[A", "^[[C", "^[[B", |
1149 | "^[[D"", "^H", ... when using the arrow keys and/or the backspace key. | |
1150 | ||
4e1d3b43 | 1151 | =head2 Editor Support for Debugging |
1152 | ||
c5cd7eb8 | 1153 | If you have the GNU's version of B<emacs> installed on your system, |
055fd3a9 GS |
1154 | it can interact with the Perl debugger to provide an integrated |
1155 | software development environment reminiscent of its interactions | |
1156 | with C debuggers. | |
4e1d3b43 | 1157 | |
7d0d50dd FC |
1158 | Recent versions of Emacs come with a |
1159 | start file for making B<emacs> act like a | |
055fd3a9 | 1160 | syntax-directed editor that understands (some of) Perl's syntax. |
7d0d50dd | 1161 | See L<perlfaq3>. |
4e1d3b43 | 1162 | |
055fd3a9 | 1163 | Users of B<vi> should also look into B<vim> and B<gvim>, the mousey |
2e8f3c35 | 1164 | and windy version, for coloring of Perl keywords. |
a0d0e21e | 1165 | |
055fd3a9 GS |
1166 | Note that only perl can truly parse Perl, so all such CASE tools |
1167 | fall somewhat short of the mark, especially if you don't program | |
1168 | your Perl as a C programmer might. | |
e7ea3e70 | 1169 | |
055fd3a9 | 1170 | =head2 The Perl Profiler |
d74e8afc | 1171 | X<profile> X<profiling> X<profiler> |
e7ea3e70 | 1172 | |
e8b1531a | 1173 | If you wish to supply an alternative debugger for Perl to run, |
055fd3a9 | 1174 | invoke your script with a colon and a package argument given to the |
c9dab4e9 FR |
1175 | B<-d> flag. Perl's alternative debuggers include a Perl profiler, |
1176 | L<Devel::NYTProf>, which is available separately as a CPAN | |
055fd3a9 GS |
1177 | distribution. To profile your Perl program in the file F<mycode.pl>, |
1178 | just type: | |
36477c24 | 1179 | |
c9dab4e9 | 1180 | $ perl -d:NYTProf mycode.pl |
36477c24 | 1181 | |
c9dab4e9 FR |
1182 | When the script terminates the profiler will create a database of the |
1183 | profile information that you can turn into reports using the profiler's | |
1184 | tools. See <perlperf> for details. | |
36477c24 | 1185 | |
57e8c15d | 1186 | =head1 Debugging Regular Expressions |
d74e8afc ITB |
1187 | X<regular expression, debugging> |
1188 | X<regex, debugging> X<regexp, debugging> | |
36477c24 | 1189 | |
3d555cb8 WL |
1190 | C<use re 'debug'> enables you to see the gory details of how the Perl |
1191 | regular expression engine works. In order to understand this typically | |
1192 | voluminous output, one must not only have some idea about how regular | |
1193 | expression matching works in general, but also know how Perl's regular | |
1194 | expressions are internally compiled into an automaton. These matters | |
1195 | are explored in some detail in | |
d9f2b251 | 1196 | L<perldebguts/"Debugging Regular Expressions">. |
36477c24 | 1197 | |
57e8c15d | 1198 | =head1 Debugging Memory Usage |
d74e8afc | 1199 | X<memory usage> |
36477c24 | 1200 | |
055fd3a9 GS |
1201 | Perl contains internal support for reporting its own memory usage, |
1202 | but this is a fairly advanced concept that requires some understanding | |
1203 | of how memory allocation works. | |
d9f2b251 | 1204 | See L<perldebguts/"Debugging Perl Memory Usage"> for the details. |
36477c24 | 1205 | |
055fd3a9 | 1206 | =head1 SEE ALSO |
a0d0e21e | 1207 | |
9095739b | 1208 | You do have C<use strict> and C<use warnings> enabled, don't you? |
a0d0e21e | 1209 | |
f6b3c421 | 1210 | L<perldebtut>, |
055fd3a9 | 1211 | L<perldebguts>, |
65ac759c | 1212 | L<perl5db.pl>, |
055fd3a9 GS |
1213 | L<re>, |
1214 | L<DB>, | |
c9dab4e9 | 1215 | L<Devel::NYTProf>, |
055fd3a9 GS |
1216 | L<Dumpvalue>, |
1217 | and | |
1218 | L<perlrun>. | |
a0d0e21e | 1219 | |
fa3aa65a JC |
1220 | When debugging a script that uses #! and is thus normally found in |
1221 | $PATH, the -S option causes perl to search $PATH for it, so you don't | |
66a1b24b | 1222 | have to type the path or C<which $scriptname>. |
fa3aa65a JC |
1223 | |
1224 | $ perl -Sd foo.pl | |
1225 | ||
055fd3a9 GS |
1226 | =head1 BUGS |
1227 | ||
1228 | You cannot get stack frame information or in any fashion debug functions | |
1229 | that were not compiled by Perl, such as those from C or C++ extensions. | |
a0d0e21e | 1230 | |
c997b287 | 1231 | If you alter your @_ arguments in a subroutine (such as with C<shift> |
6edf2346 | 1232 | or C<pop>), the stack backtrace will not show the original values. |
c997b287 GS |
1233 | |
1234 | The debugger does not currently work in conjunction with the B<-W> | |
1235 | command-line switch, because it itself is not free of warnings. | |
4c82ae22 GS |
1236 | |
1237 | If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing | |
1238 | from your keyboard or a socket) and haven't set up your own C<$SIG{INT}> | |
1239 | handler, then you won't be able to CTRL-C your way back to the debugger, | |
1240 | because the debugger's own C<$SIG{INT}> handler doesn't understand that | |
1241 | it needs to raise an exception to longjmp(3) out of slow syscalls. |