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1 | =head1 NAME |
2 | |
3 | perldebug - Perl debugging |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | First of all, have you tried using the B<-w> switch? |
8 | |
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9 | =head1 The Perl Debugger |
10 | |
11 | If you invoke Perl with the B<-d> switch, your script runs under the |
12 | Perl source debugger. This works like an interactive Perl |
13 | environment, prompting for debugger commands that let you examine |
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14 | source code, set breakpoints, get stack back-traces, change the values of |
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15 | variables, etc. This is so convenient that you often fire up |
16 | the debugger all by itself just to test out Perl constructs |
17 | interactively to see what they do. For example: |
18 | |
19 | perl -d -e 42 |
20 | |
21 | In Perl, the debugger is not a separate program as it usually is in the |
22 | typical compiled environment. Instead, the B<-d> flag tells the compiler |
23 | to insert source information into the parse trees it's about to hand off |
24 | to the interpreter. That means your code must first compile correctly |
25 | for the debugger to work on it. Then when the interpreter starts up, it |
26 | pre-loads a Perl library file containing the debugger itself. |
27 | |
28 | The program will halt I<right before> the first run-time executable |
29 | statement (but see below regarding compile-time statements) and ask you |
30 | to enter a debugger command. Contrary to popular expectations, whenever |
31 | the debugger halts and shows you a line of code, it always displays the |
32 | line it's I<about> to execute, rather than the one it has just executed. |
33 | |
34 | Any command not recognized by the debugger is directly executed |
35 | (C<eval>'d) as Perl code in the current package. (The debugger uses the |
36 | DB package for its own state information.) |
37 | |
38 | Leading white space before a command would cause the debugger to think |
39 | it's I<NOT> a debugger command but for Perl, so be careful not to do |
40 | that. |
41 | |
42 | =head2 Debugger Commands |
43 | |
44 | The debugger understands the following commands: |
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45 | |
46 | =over 12 |
47 | |
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48 | =item h [command] |
49 | |
50 | Prints out a help message. |
51 | |
52 | If you supply another debugger command as an argument to the C<h> command, |
53 | it prints out the description for just that command. The special |
54 | argument of C<h h> produces a more compact help listing, designed to fit |
55 | together on one screen. |
56 | |
57 | If the output the C<h> command (or any command, for that matter) scrolls |
58 | past your screen, either precede the command with a leading pipe symbol so |
59 | it's run through your pager, as in |
60 | |
61 | DB> |h |
62 | |
63 | =item p expr |
64 | |
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65 | Same as C<print {$DB::OUT} expr> in the current package. In particular, |
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66 | because this is just Perl's own B<print> function, this means that nested |
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67 | data structures and objects are not dumped, unlike with the C<x> command. |
68 | |
69 | =item x expr |
70 | |
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71 | Evaluates its expression in list context and dumps out the result |
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72 | in a pretty-printed fashion. Nested data structures are printed out |
73 | recursively, unlike the C<print> function. |
74 | |
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75 | The details of printout are governed by multiple C<O>ptions. |
76 | |
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77 | =item V [pkg [vars]] |
78 | |
79 | Display all (or some) variables in package (defaulting to the C<main> |
80 | package) using a data pretty-printer (hashes show their keys and values so |
81 | you see what's what, control characters are made printable, etc.). Make |
82 | sure you don't put the type specifier (like C<$>) there, just the symbol |
83 | names, like this: |
84 | |
85 | V DB filename line |
86 | |
87 | Use C<~pattern> and C<!pattern> for positive and negative regexps. |
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88 | |
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89 | Nested data structures are printed out in a legible fashion, unlike |
90 | the C<print> function. |
91 | |
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92 | The details of printout are governed by multiple C<O>ptions. |
93 | |
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94 | =item X [vars] |
95 | |
96 | Same as C<V currentpackage [vars]>. |
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97 | |
98 | =item T |
99 | |
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100 | Produce a stack back-trace. See below for details on its output. |
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101 | |
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102 | =item s [expr] |
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103 | |
104 | Single step. Executes until it reaches the beginning of another |
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105 | statement, descending into subroutine calls. If an expression is |
106 | supplied that includes function calls, it too will be single-stepped. |
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107 | |
108 | =item n |
109 | |
110 | Next. Executes over subroutine calls, until it reaches the beginning |
111 | of the next statement. |
112 | |
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113 | =item E<lt>CRE<gt> |
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114 | |
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115 | Repeat last C<n> or C<s> command. |
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116 | |
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117 | =item c [line|sub] |
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118 | |
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119 | Continue, optionally inserting a one-time-only breakpoint |
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120 | at the specified line or subroutine. |
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121 | |
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122 | =item l |
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123 | |
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124 | List next window of lines. |
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125 | |
126 | =item l min+incr |
127 | |
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128 | List C<incr+1> lines starting at C<min>. |
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129 | |
130 | =item l min-max |
131 | |
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132 | List lines C<min> through C<max>. |
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133 | |
134 | =item l line |
135 | |
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136 | List a single line. |
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137 | |
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138 | =item l subname |
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139 | |
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140 | List first window of lines from subroutine. |
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141 | |
142 | =item - |
143 | |
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144 | List previous window of lines. |
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145 | |
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146 | =item w [line] |
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147 | |
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148 | List window (a few lines) around the current line. |
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149 | |
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150 | =item . |
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151 | |
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152 | Return debugger pointer to the last-executed line and |
153 | print it out. |
154 | |
155 | =item f filename |
156 | |
157 | Switch to viewing a different file. |
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158 | |
159 | =item /pattern/ |
160 | |
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161 | Search forwards for pattern; final / is optional. |
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162 | |
163 | =item ?pattern? |
164 | |
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165 | Search backwards for pattern; final ? is optional. |
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166 | |
167 | =item L |
168 | |
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169 | List all breakpoints and actions. |
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170 | |
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171 | =item S [[!]pattern] |
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172 | |
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173 | List subroutine names [not] matching pattern. |
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174 | |
175 | =item t |
176 | |
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177 | Toggle trace mode (see also C<AutoTrace> C<O>ption). |
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178 | |
179 | =item t expr |
180 | |
181 | Trace through execution of expr. For example: |
182 | |
183 | $ perl -de 42 |
184 | Stack dump during die enabled outside of evals. |
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185 | |
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186 | Loading DB routines from perl5db.pl patch level 0.94 |
187 | Emacs support available. |
188 | |
189 | Enter h or `h h' for help. |
190 | |
191 | main::(-e:1): 0 |
192 | DB<1> sub foo { 14 } |
193 | |
194 | DB<2> sub bar { 3 } |
195 | |
196 | DB<3> t print foo() * bar() |
197 | main::((eval 172):3): print foo() + bar(); |
198 | main::foo((eval 168):2): |
199 | main::bar((eval 170):2): |
200 | 42 |
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201 | |
202 | or, with the C<O>ption C<frame=2> set, |
203 | |
204 | DB<4> O f=2 |
205 | frame = '2' |
206 | DB<5> t print foo() * bar() |
207 | 3: foo() * bar() |
208 | entering main::foo |
209 | 2: sub foo { 14 }; |
210 | exited main::foo |
211 | entering main::bar |
212 | 2: sub bar { 3 }; |
213 | exited main::bar |
214 | 42 |
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215 | |
216 | =item b [line] [condition] |
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217 | |
218 | Set a breakpoint. If line is omitted, sets a breakpoint on the line |
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219 | that is about to be executed. If a condition is specified, it's |
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220 | evaluated each time the statement is reached and a breakpoint is taken |
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221 | only if the condition is true. Breakpoints may be set on only lines |
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222 | that begin an executable statement. Conditions don't use B<if>: |
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223 | |
224 | b 237 $x > 30 |
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225 | b 237 ++$count237 < 11 |
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226 | b 33 /pattern/i |
227 | |
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228 | =item b subname [condition] |
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229 | |
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230 | Set a breakpoint at the first line of the named subroutine. |
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231 | |
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232 | =item b postpone subname [condition] |
233 | |
234 | Set breakpoint at first line of subroutine after it is compiled. |
235 | |
236 | =item b load filename |
237 | |
238 | Set breakpoint at the first executed line of the file. |
239 | |
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240 | =item d [line] |
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241 | |
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242 | Delete a breakpoint at the specified line. If line is omitted, deletes |
243 | the breakpoint on the line that is about to be executed. |
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244 | |
245 | =item D |
246 | |
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247 | Delete all installed breakpoints. |
248 | |
249 | =item a [line] command |
250 | |
251 | Set an action to be done before the line is executed. |
252 | The sequence of steps taken by the debugger is |
253 | |
254 | =over 3 |
255 | |
256 | =item 1 |
257 | |
258 | check for a breakpoint at this line |
259 | |
260 | =item 2 |
261 | |
262 | print the line if necessary (tracing) |
263 | |
264 | =item 3 |
265 | |
266 | do any actions associated with that line |
267 | |
268 | =item 4 |
269 | |
270 | prompt user if at a breakpoint or in single-step |
271 | |
272 | =item 5 |
273 | |
274 | evaluate line |
275 | |
276 | =back |
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277 | |
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278 | For example, this will print out C<$foo> every time line |
279 | 53 is passed: |
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280 | |
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281 | a 53 print "DB FOUND $foo\n" |
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282 | |
283 | =item A |
284 | |
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285 | Delete all installed actions. |
286 | |
287 | =item O [opt[=val]] [opt"val"] [opt?]... |
288 | |
289 | Set or query values of options. val defaults to 1. opt can |
290 | be abbreviated. Several options can be listed. |
291 | |
292 | =over 12 |
293 | |
294 | =item recallCommand, ShellBang |
295 | |
296 | The characters used to recall command or spawn shell. By |
297 | default, these are both set to C<!>. |
298 | |
299 | =item pager |
300 | |
301 | Program to use for output of pager-piped commands (those |
302 | beginning with a C<|> character.) By default, |
303 | C<$ENV{PAGER}> will be used. |
304 | |
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305 | =item tkRunning |
306 | |
307 | Run Tk while prompting (with ReadLine). |
308 | |
309 | =item signalLevel, warnLevel, dieLevel |
310 | |
311 | Level of verbosity. |
312 | |
313 | =item AutoTrace |
314 | |
315 | Where to print all the breakable points in the executed program |
316 | (similar to C<t> command, but can be put into C<PERLDB_OPTS>). |
317 | |
318 | =item LineInfo |
319 | |
320 | File or pipe to print line number info to. If it is a |
321 | pipe, then a short, "emacs like" message is used. |
322 | |
323 | =item C<inhibit_exit> |
324 | |
325 | If 0, allows I<stepping off> the end of the script. |
326 | |
327 | =item C<PrintRet> |
328 | |
329 | affects printing of return value after C<r> command. |
330 | |
331 | =item C<frame> |
332 | |
333 | affects printing messages on entry and exit from subroutines. If |
334 | C<frame & 2> is false, messages are printed on entry only. (Printing |
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335 | on exit may be useful if inter(di)spersed with other messages.) |
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336 | |
337 | If C<frame & 4>, arguments to functions are printed as well as the |
338 | context and caller info. |
339 | |
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340 | =back |
341 | |
342 | The following options affect what happens with C<V>, C<X>, and C<x> |
343 | commands: |
344 | |
345 | =over 12 |
346 | |
347 | =item arrayDepth, hashDepth |
348 | |
349 | Print only first N elements ('' for all). |
350 | |
351 | =item compactDump, veryCompact |
352 | |
353 | Change style of array and hash dump. |
354 | |
355 | =item globPrint |
356 | |
357 | Whether to print contents of globs. |
358 | |
359 | =item DumpDBFiles |
360 | |
361 | Dump arrays holding debugged files. |
362 | |
363 | =item DumpPackages |
364 | |
365 | Dump symbol tables of packages. |
366 | |
367 | =item quote, HighBit, undefPrint |
368 | |
369 | Change style of string dump. |
370 | |
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371 | =back |
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372 | |
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373 | During startup options are initialized from C<$ENV{PERLDB_OPTS}>. |
374 | You can put additional initialization options C<TTY>, C<noTTY>, |
375 | C<ReadLine>, and C<NonStop> there. |
376 | |
377 | Example rc file: |
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378 | |
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379 | &parse_options("NonStop=1 LineInfo=db.out AutoTrace"); |
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380 | |
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381 | The script will run without human intervention, putting trace information |
382 | into the file I<db.out>. (If you interrupt it, you would better reset |
383 | C<LineInfo> to something "interactive"!) |
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384 | |
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385 | =over 12 |
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386 | |
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387 | =item C<TTY> |
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388 | |
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389 | The TTY to use for debugging I/O. |
390 | |
391 | =item noTTY |
392 | |
393 | If set, goes in C<NonStop> mode. On interrupt if TTY is not set uses the |
394 | value of C<noTTY> or "/tmp/perldbtty$$" to find TTY using |
395 | C<Term::Rendezvous>. Current variant is to have the name of TTY in this |
396 | file. |
397 | |
398 | =item C<noTTY> |
399 | |
400 | If set, goes in C<NonStop> mode, and would not connect to a TTY. If |
401 | interrupt (or if control goes to debugger via explicit setting of |
402 | $DB::signal or $DB::single from the Perl script), connects to a TTY |
403 | specified by the C<TTY> option at startup, or to a TTY found at |
404 | runtime using C<Term::Rendezvous> module of your choice. |
405 | |
406 | This module should implement a method C<new> which returns an object |
407 | with two methods: C<IN> and C<OUT>, returning two filehandles to use |
408 | for debugging input and output correspondingly. Method C<new> may |
409 | inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at |
410 | startup, or is C<"/tmp/perldbtty$$"> otherwise. |
411 | |
412 | =item C<ReadLine> |
413 | |
414 | If false, readline support in debugger is disabled, so you can debug |
415 | ReadLine applications. |
416 | |
417 | =item C<NonStop> |
418 | |
419 | If set, debugger goes into non-interactive mode until interrupted, or |
420 | programmatically by setting $DB::signal or $DB::single. |
421 | |
422 | =back |
423 | |
424 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: |
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425 | |
426 | $ PERLDB_OPTS="N f=2" perl -d myprogram |
427 | |
428 | will run the script C<myprogram> without human intervention, printing |
429 | out the call tree with entry and exit points. Note that C<N f=2> is |
430 | equivalent to C<NonStop=1 frame=2>. Note also that at the moment when |
431 | this documentation was written all the options to the debugger could |
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432 | be uniquely abbreviated by the first letter (with exception of |
433 | C<Dump*> options). |
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434 | |
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435 | Other examples may include |
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436 | |
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437 | $ PERLDB_OPTS="N f A L=listing" perl -d myprogram |
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438 | |
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439 | - runs script non-interactively, printing info on each entry into a |
440 | subroutine and each executed line into the file F<listing>. (If you |
441 | interrupt it, you would better reset C<LineInfo> to something |
442 | "interactive"!) |
443 | |
444 | |
445 | $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram |
446 | |
447 | may be useful for debugging a program which uses C<Term::ReadLine> |
448 | itself. Do not forget detach shell from the TTY in the window which |
449 | corresponds to F</dev/ttyc>, say, by issuing a command like |
450 | |
451 | $ sleep 1000000 |
452 | |
453 | See L<"Debugger Internals"> below for more details. |
454 | |
455 | =item E<lt> [ command ] |
456 | |
457 | Set an action (Perl command) to happen before every debugger prompt. |
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458 | A multi-line command may be entered by backslashing the newlines. If |
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459 | C<command> is missing, resets the list of actions. |
460 | |
461 | =item E<lt>E<lt> command |
462 | |
463 | Add an action (Perl command) to happen before every debugger prompt. |
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464 | A multi-line command may be entered by backslashing the newlines. |
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465 | |
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466 | =item E<gt> command |
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467 | |
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468 | Set an action (Perl command) to happen after the prompt when you've |
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469 | just given a command to return to executing the script. A multi-line |
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470 | command may be entered by backslashing the newlines. If C<command> is |
471 | missing, resets the list of actions. |
472 | |
473 | =item E<gt>E<gt> command |
474 | |
475 | Adds an action (Perl command) to happen after the prompt when you've |
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476 | just given a command to return to executing the script. A multi-line |
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477 | command may be entered by backslashing the newlines. |
478 | |
479 | =item { [ command ] |
480 | |
481 | Set an action (debugger command) to happen before every debugger prompt. |
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482 | A multi-line command may be entered by backslashing the newlines. If |
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483 | C<command> is missing, resets the list of actions. |
484 | |
485 | =item {{ command |
486 | |
487 | Add an action (debugger command) to happen before every debugger prompt. |
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488 | A multi-line command may be entered by backslashing the newlines. |
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489 | |
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490 | =item ! number |
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491 | |
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492 | Redo a previous command (default previous command). |
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493 | |
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494 | =item ! -number |
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495 | |
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496 | Redo number'th-to-last command. |
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497 | |
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498 | =item ! pattern |
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499 | |
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500 | Redo last command that started with pattern. |
501 | See C<O recallCommand>, too. |
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502 | |
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503 | =item !! cmd |
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504 | |
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505 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) |
506 | See C<O shellBang> too. |
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507 | |
508 | =item H -number |
509 | |
510 | Display last n commands. Only commands longer than one character are |
511 | listed. If number is omitted, lists them all. |
512 | |
513 | =item q or ^D |
514 | |
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515 | Quit. ("quit" doesn't work for this.) This is the only supported way |
516 | to exit the debugger, though typing C<exit> twice may do it too. |
517 | |
518 | Set an C<O>ption C<inhibit_exit> to 0 if you want to be able to I<step |
519 | off> the end the script. You may also need to set C<$finished> to 0 at |
520 | some moment if you want to step through global destruction. |
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521 | |
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522 | =item R |
523 | |
524 | Restart the debugger by B<exec>ing a new session. It tries to maintain |
525 | your history across this, but internal settings and command line options |
526 | may be lost. |
527 | |
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528 | Currently the following setting are preserved: history, breakpoints, |
529 | actions, debugger C<O>ptions, and the following command-line |
530 | options: B<-w>, B<-I>, and B<-e>. |
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531 | |
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532 | =item |dbcmd |
533 | |
534 | Run debugger command, piping DB::OUT to current pager. |
535 | |
536 | =item ||dbcmd |
537 | |
538 | Same as C<|dbcmd> but DB::OUT is temporarily B<select>ed as well. |
539 | Often used with commands that would otherwise produce long |
540 | output, such as |
541 | |
542 | |V main |
543 | |
544 | =item = [alias value] |
545 | |
546 | Define a command alias, or list current aliases. |
547 | |
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548 | =item command |
549 | |
550 | Execute command as a Perl statement. A missing semicolon will be |
551 | supplied. |
552 | |
553 | =item p expr |
554 | |
555 | Same as C<print DB::OUT expr>. The DB::OUT filehandle is opened to |
556 | /dev/tty, regardless of where STDOUT may be redirected to. |
557 | |
558 | =back |
559 | |
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560 | The debugger prompt is something like |
561 | |
562 | DB<8> |
563 | |
564 | or even |
565 | |
566 | DB<<17>> |
567 | |
568 | where that number is the command number, which you'd use to access with |
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569 | the built-in B<csh>-like history mechanism, e.g., C<!17> would repeat |
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570 | command number 17. The number of angle brackets indicates the depth of |
571 | the debugger. You could get more than one set of brackets, for example, if |
572 | you'd already at a breakpoint and then printed out the result of a |
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573 | function call that itself also has a breakpoint, or you step into an |
574 | expression via C<s/n/t expression> command. |
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575 | |
576 | If you want to enter a multi-line command, such as a subroutine |
577 | definition with several statements, you may escape the newline that would |
578 | normally end the debugger command with a backslash. Here's an example: |
a0d0e21e |
579 | |
4e1d3b43 |
580 | DB<1> for (1..4) { \ |
581 | cont: print "ok\n"; \ |
582 | cont: } |
583 | ok |
584 | ok |
585 | ok |
586 | ok |
587 | |
588 | Note that this business of escaping a newline is specific to interactive |
589 | commands typed into the debugger. |
590 | |
5f05dabc |
591 | Here's an example of what a stack back-trace might look like: |
4e1d3b43 |
592 | |
593 | $ = main::infested called from file `Ambulation.pm' line 10 |
594 | @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7 |
595 | $ = main::pests('bactrian', 4) called from file `camel_flea' line 4 |
596 | |
597 | The left-hand character up there tells whether the function was called |
598 | in a scalar or list context (we bet you can tell which is which). What |
599 | that says is that you were in the function C<main::infested> when you ran |
600 | the stack dump, and that it was called in a scalar context from line 10 |
601 | of the file I<Ambulation.pm>, but without any arguments at all, meaning |
602 | it was called as C<&infested>. The next stack frame shows that the |
603 | function C<Ambulation::legs> was called in a list context from the |
604 | I<camel_flea> file with four arguments. The last stack frame shows that |
605 | C<main::pests> was called in a scalar context, also from I<camel_flea>, |
606 | but from line 4. |
607 | |
608 | If you have any compile-time executable statements (code within a BEGIN |
609 | block or a C<use> statement), these will C<NOT> be stopped by debugger, |
36477c24 |
610 | although C<require>s will (and compile-time statements can be traced |
611 | with C<AutoTrace> option set in C<PERLDB_OPTS>). From your own Perl |
612 | code, however, you can |
4e1d3b43 |
613 | transfer control back to the debugger using the following statement, |
614 | which is harmless if the debugger is not running: |
a0d0e21e |
615 | |
616 | $DB::single = 1; |
617 | |
4e1d3b43 |
618 | If you set C<$DB::single> to the value 2, it's equivalent to having |
619 | just typed the C<n> command, whereas a value of 1 means the C<s> |
620 | command. The C<$DB::trace> variable should be set to 1 to simulate |
621 | having typed the C<t> command. |
622 | |
623 | =head2 Debugger Customization |
a0d0e21e |
624 | |
36477c24 |
625 | Most probably you not want to modify the debugger, it contains enough |
626 | hooks to satisfy most needs. You may change the behaviour of debugger |
627 | from the debugger itself, using C<O>ptions, from the command line via |
628 | C<PERLDB_OPTS> environment variable, and from I<customization files>. |
a0d0e21e |
629 | |
630 | You can do some customization by setting up a F<.perldb> file which |
631 | contains initialization code. For instance, you could make aliases |
4e1d3b43 |
632 | like these (the last one is one people expect to be there): |
a0d0e21e |
633 | |
4e1d3b43 |
634 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; |
a0d0e21e |
635 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; |
4e1d3b43 |
636 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; |
637 | $DB::alias{'quit'} = 's/^quit(\s*)/exit\$/'; |
638 | |
36477c24 |
639 | One changes options from F<.perldb> file via calls like this one; |
640 | |
641 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); |
642 | |
643 | (the code is executed in the package C<DB>). Note that F<.perldb> is |
644 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the |
645 | subroutine C<afterinit>, it is called after all the debugger |
646 | initialization ends. F<.perldb> may be contained in the current |
647 | directory, or in the C<LOGDIR>/C<HOME> directory. |
648 | |
649 | If you want to modify the debugger, copy F<perl5db.pl> from the Perl |
650 | library to another name and modify it as necessary. You'll also want |
651 | to set your C<PERL5DB> environment variable to say something like this: |
652 | |
653 | BEGIN { require "myperl5db.pl" } |
654 | |
655 | As the last resort, one can use C<PERL5DB> to customize debugger by |
656 | directly setting internal variables or calling debugger functions. |
657 | |
4e1d3b43 |
658 | =head2 Readline Support |
659 | |
660 | As shipped, the only command line history supplied is a simplistic one |
661 | that checks for leading exclamation points. However, if you install |
662 | the Term::ReadKey and Term::ReadLine modules from CPAN, you will |
663 | have full editing capabilities much like GNU I<readline>(3) provides. |
664 | Look for these in the F<modules/by-module/Term> directory on CPAN. |
665 | |
666 | =head2 Editor Support for Debugging |
667 | |
668 | If you have GNU B<emacs> installed on your system, it can interact with |
669 | the Perl debugger to provide an integrated software development |
670 | environment reminiscent of its interactions with C debuggers. |
671 | |
672 | Perl is also delivered with a start file for making B<emacs> act like a |
673 | syntax-directed editor that understands (some of) Perl's syntax. Look in |
674 | the I<emacs> directory of the Perl source distribution. |
675 | |
676 | (Historically, a similar setup for interacting with B<vi> and the |
677 | X11 window system had also been available, but at the time of this |
678 | writing, no debugger support for B<vi> currently exists.) |
679 | |
680 | =head2 The Perl Profiler |
681 | |
682 | If you wish to supply an alternative debugger for Perl to run, just |
683 | invoke your script with a colon and a package argument given to the B<-d> |
684 | flag. One of the most popular alternative debuggers for Perl is |
685 | B<DProf>, the Perl profiler. As of this writing, B<DProf> is not |
686 | included with the standard Perl distribution, but it is expected to |
687 | be included soon, for certain values of "soon". |
688 | |
689 | Meanwhile, you can fetch the Devel::Dprof module from CPAN. Assuming |
690 | it's properly installed on your system, to profile your Perl program in |
691 | the file F<mycode.pl>, just type: |
692 | |
693 | perl -d:DProf mycode.pl |
694 | |
695 | When the script terminates the profiler will dump the profile information |
696 | to a file called F<tmon.out>. A tool like B<dprofpp> (also supplied with |
697 | the Devel::DProf package) can be used to interpret the information which is |
698 | in that profile. |
699 | |
36477c24 |
700 | =head2 Debugger support in perl |
4e1d3b43 |
701 | |
702 | When you call the B<caller> function from package DB, Perl sets the |
703 | C<@DB::args> array to contain the arguments that stack frame was called |
36477c24 |
704 | with. |
4e1d3b43 |
705 | |
36477c24 |
706 | If perl is run with B<-d> option, the following additional features |
707 | are enabled: |
a0d0e21e |
708 | |
36477c24 |
709 | =over |
4e1d3b43 |
710 | |
36477c24 |
711 | =item * |
4e1d3b43 |
712 | |
36477c24 |
713 | Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require |
714 | 'perl5db.pl'}> if not present) before the first line of the |
715 | application. |
4e1d3b43 |
716 | |
36477c24 |
717 | =item * |
4e1d3b43 |
718 | |
36477c24 |
719 | The array C<@{"_<$filename"}> is the line-by-line contents of |
720 | $filename for all the compiled files. Same for C<eval>ed strings which |
721 | contain subroutines, or which are currently executed. The C<$filename> |
722 | for C<eval>ed strings looks like C<(eval 34)>. |
4e1d3b43 |
723 | |
36477c24 |
724 | =item * |
4e1d3b43 |
725 | |
36477c24 |
726 | The hash C<%{"_<$filename"}> contains breakpoints and action (it is |
727 | keyed by line number), and individual entries are settable (as opposed |
728 | to the whole hash). Only true/false is important to Perl, though the |
729 | values used by F<perl5db.pl> have the form |
730 | C<"$break_condition\0$action">. Values are magical in numeric context: |
731 | they are zeros if the line is not breakable. |
4e1d3b43 |
732 | |
36477c24 |
733 | Same for evaluated strings which contain subroutines, or which are |
734 | currently executed. The C<$filename> for C<eval>ed strings looks like |
735 | C<(eval 34)>. |
4e1d3b43 |
736 | |
36477c24 |
737 | =item * |
4e1d3b43 |
738 | |
36477c24 |
739 | The scalar C<${"_<$filename"}> contains C<"_<$filename">. Same for |
740 | evaluated strings which contain subroutines, or which are currently |
741 | executed. The C<$filename> for C<eval>ed strings looks like C<(eval |
742 | 34)>. |
4e1d3b43 |
743 | |
36477c24 |
744 | =item * |
4e1d3b43 |
745 | |
36477c24 |
746 | After each C<require>d file is compiled, but before it is executed, |
747 | C<DB::postponed(*{"_<$filename"})> is called (if subroutine |
748 | C<DB::postponed> exists). Here the $filename is the expanded name of |
749 | the C<require>d file (as found in values of C<%INC>). |
4e1d3b43 |
750 | |
36477c24 |
751 | =item * |
4e1d3b43 |
752 | |
36477c24 |
753 | After each subroutine C<subname> is compiled existence of |
754 | C<$DB::postponed{subname}> is checked. If this key exists, |
755 | C<DB::postponed(subname)> is called (if subroutine C<DB::postponed> |
756 | exists). |
4e1d3b43 |
757 | |
36477c24 |
758 | =item * |
4e1d3b43 |
759 | |
36477c24 |
760 | A hash C<%DB::sub> is maintained, with keys being subroutine names, |
761 | values having the form C<filename:startline-endline>. C<filename> has |
762 | the form C<(eval 31)> for subroutines defined inside C<eval>s. |
4e1d3b43 |
763 | |
36477c24 |
764 | =item * |
765 | |
5f05dabc |
766 | When execution of the application reaches a place that can have |
767 | a breakpoint, a call to C<DB::DB()> is performed if any one of |
768 | variables $DB::trace, $DB::single, or $DB::signal is true. (Note that |
36477c24 |
769 | these variables are not C<local>izable.) This feature is disabled when |
770 | the control is inside C<DB::DB()> or functions called from it (unless |
771 | C<$^D & 1 E<lt>E<lt> 30>). |
772 | |
773 | =item * |
774 | |
5f05dabc |
775 | When execution of the application reaches a subroutine call, a call |
36477c24 |
776 | to C<&DB::sub>(I<args>) is performed instead, with C<$DB::sub> being |
777 | the name of the called subroutine. (Unless the subroutine is compiled |
778 | in the package C<DB>.) |
4e1d3b43 |
779 | |
780 | =back |
a0d0e21e |
781 | |
36477c24 |
782 | Note that no subroutine call is possible until C<&DB::sub> is defined |
783 | (for subroutines outside of package C<DB>). (In fact, for the |
784 | standard debugger the same is true if C<$DB::deep> (how many levels of |
785 | recursion deep into the debugger you can go before a mandatory break) |
786 | is not defined.) |
787 | |
788 | =head2 Debugger Internals |
789 | |
790 | At the start, the debugger reads your rc file (F<./.perldb> or |
791 | F<~/.perldb> under UNIX), which can set important options. This file may |
792 | define a subroutine C<&afterinit> to be executed after the debugger is |
793 | initialized. |
794 | |
5f05dabc |
795 | After the rc file is read, the debugger reads environment variable |
36477c24 |
796 | PERLDB_OPTS and parses it as a rest of C<O ...> line in debugger prompt. |
797 | |
798 | It also maintains magical internal variables, such as C<@DB::dbline>, |
799 | C<%DB::dbline>, which are aliases for C<@{"::_<current_file"}> |
800 | C<%{"::_<current_file"}>. Here C<current_file> is the currently |
801 | selected (with the debugger's C<f> command, or by flow of execution) |
802 | file. |
803 | |
804 | Some functions are provided to simplify customization. See L<"Debugger |
805 | Customization"> for description of C<DB::parse_options(string)>. The |
806 | function C<DB::dump_trace(skip[, count])> skips the specified number |
807 | of frames, and returns an array containing info about the caller |
808 | frames (all if C<count> is missing). Each entry is a hash with keys |
809 | C<context> (C<$> or C<@>), C<sub> (subroutine name, or info about |
5f05dabc |
810 | eval), C<args> (C<undef> or a reference to an array), C<file>, and |
36477c24 |
811 | C<line>. |
812 | |
813 | The function C<DB::print_trace(FH, skip[, count[, short]])> prints |
814 | formatted info about caller frames. The last two functions may be |
815 | convenient as arguments to C<E<lt>>, C<E<lt>E<lt>> commands. |
816 | |
a0d0e21e |
817 | =head2 Other resources |
818 | |
819 | You did try the B<-w> switch, didn't you? |
820 | |
821 | =head1 BUGS |
822 | |
4e1d3b43 |
823 | You cannot get the stack frame information or otherwise debug functions |
824 | that were not compiled by Perl, such as C or C++ extensions. |
a0d0e21e |
825 | |
4e1d3b43 |
826 | If you alter your @_ arguments in a subroutine (such as with B<shift> |
5f05dabc |
827 | or B<pop>, the stack back-trace will not show the original values. |