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