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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 | |
26f28346 |
11 | "As soon as we started programming, we found to our |
12 | surprise that it wasn't as easy to get programs right |
13 | as we had thought. Debugging had to be discovered. |
14 | I can remember the exact instant when I realized that |
15 | a large part of my life from then on was going to be |
16 | spent in finding mistakes in my own programs." |
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17 | |
18 | I< --Maurice Wilkes, 1949> |
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19 | |
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20 | If you invoke Perl with the B<-d> switch, your script runs under the |
21 | Perl source debugger. This works like an interactive Perl |
22 | environment, prompting for debugger commands that let you examine |
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23 | source code, set breakpoints, get stack backtraces, change the values of |
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24 | variables, etc. This is so convenient that you often fire up |
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25 | the debugger all by itself just to test out Perl constructs |
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26 | interactively to see what they do. For example: |
27 | |
28 | perl -d -e 42 |
29 | |
30 | In Perl, the debugger is not a separate program as it usually is in the |
31 | typical compiled environment. Instead, the B<-d> flag tells the compiler |
32 | to insert source information into the parse trees it's about to hand off |
33 | to the interpreter. That means your code must first compile correctly |
34 | for the debugger to work on it. Then when the interpreter starts up, it |
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35 | preloads a Perl library file containing the debugger itself. |
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36 | |
37 | The program will halt I<right before> the first run-time executable |
38 | statement (but see below regarding compile-time statements) and ask you |
39 | to enter a debugger command. Contrary to popular expectations, whenever |
40 | the debugger halts and shows you a line of code, it always displays the |
41 | line it's I<about> to execute, rather than the one it has just executed. |
42 | |
43 | Any command not recognized by the debugger is directly executed |
44 | (C<eval>'d) as Perl code in the current package. (The debugger uses the |
45 | DB package for its own state information.) |
46 | |
47 | Leading white space before a command would cause the debugger to think |
48 | it's I<NOT> a debugger command but for Perl, so be careful not to do |
49 | that. |
50 | |
51 | =head2 Debugger Commands |
52 | |
53 | The debugger understands the following commands: |
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54 | |
55 | =over 12 |
56 | |
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57 | =item h [command] |
58 | |
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59 | Prints out a help message. |
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60 | |
61 | If you supply another debugger command as an argument to the C<h> command, |
62 | it prints out the description for just that command. The special |
63 | argument of C<h h> produces a more compact help listing, designed to fit |
64 | together on one screen. |
65 | |
7b8d334a |
66 | If the output of the C<h> command (or any command, for that matter) scrolls |
4e1d3b43 |
67 | past your screen, either precede the command with a leading pipe symbol so |
68 | it's run through your pager, as in |
69 | |
70 | DB> |h |
71 | |
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72 | You may change the pager which is used via C<O pager=...> command. |
73 | |
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74 | =item p expr |
75 | |
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76 | Same as C<print {$DB::OUT} expr> in the current package. In particular, |
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77 | because this is just Perl's own B<print> function, this means that nested |
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78 | data structures and objects are not dumped, unlike with the C<x> command. |
79 | |
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80 | The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of |
81 | where STDOUT may be redirected to. |
82 | |
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83 | =item x expr |
84 | |
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85 | Evaluates its expression in list context and dumps out the result |
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86 | in a pretty-printed fashion. Nested data structures are printed out |
87 | recursively, unlike the C<print> function. |
88 | |
36477c24 |
89 | The details of printout are governed by multiple C<O>ptions. |
90 | |
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91 | =item V [pkg [vars]] |
92 | |
93 | Display all (or some) variables in package (defaulting to the C<main> |
94 | package) using a data pretty-printer (hashes show their keys and values so |
95 | you see what's what, control characters are made printable, etc.). Make |
96 | sure you don't put the type specifier (like C<$>) there, just the symbol |
97 | names, like this: |
98 | |
99 | V DB filename line |
100 | |
101 | Use C<~pattern> and C<!pattern> for positive and negative regexps. |
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102 | |
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103 | Nested data structures are printed out in a legible fashion, unlike |
104 | the C<print> function. |
105 | |
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106 | The details of printout are governed by multiple C<O>ptions. |
107 | |
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108 | =item X [vars] |
109 | |
110 | Same as C<V currentpackage [vars]>. |
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111 | |
112 | =item T |
113 | |
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114 | Produce a stack backtrace. See below for details on its output. |
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115 | |
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116 | =item s [expr] |
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117 | |
118 | Single step. Executes until it reaches the beginning of another |
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119 | statement, descending into subroutine calls. If an expression is |
120 | supplied that includes function calls, it too will be single-stepped. |
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121 | |
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122 | =item n [expr] |
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123 | |
124 | Next. Executes over subroutine calls, until it reaches the beginning |
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125 | of the next statement. If an expression is supplied that includes |
126 | function calls, those functions will be executed with stops before |
127 | each statement. |
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128 | |
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129 | =item E<lt>CRE<gt> |
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130 | |
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131 | Repeat last C<n> or C<s> command. |
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132 | |
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133 | =item c [line|sub] |
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134 | |
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135 | Continue, optionally inserting a one-time-only breakpoint |
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136 | at the specified line or subroutine. |
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137 | |
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138 | =item l |
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139 | |
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140 | List next window of lines. |
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141 | |
142 | =item l min+incr |
143 | |
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144 | List C<incr+1> lines starting at C<min>. |
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145 | |
146 | =item l min-max |
147 | |
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148 | List lines C<min> through C<max>. C<l E<45>> is synonymous to C<E<45>>. |
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149 | |
150 | =item l line |
151 | |
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152 | List a single line. |
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153 | |
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154 | =item l subname |
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155 | |
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156 | List first window of lines from subroutine. I<subname> may |
157 | be a variable which contains a code reference. |
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158 | |
159 | =item - |
160 | |
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161 | List previous window of lines. |
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162 | |
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163 | =item w [line] |
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164 | |
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165 | List window (a few lines) around the current line. |
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166 | |
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167 | =item . |
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168 | |
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169 | Return debugger pointer to the last-executed line and |
170 | print it out. |
171 | |
172 | =item f filename |
173 | |
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174 | Switch to viewing a different file or eval statement. If C<filename> |
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175 | is not a full filename as found in values of %INC, it is considered as |
176 | a regexp. |
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177 | |
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178 | C<eval>ed strings (when accessible) are considered to be filenames: |
179 | C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string |
180 | (in the order of execution). The bodies of currently executed C<eval> |
181 | and of C<eval>ed strings which define subroutines are saved, thus are |
182 | accessible by this mechanism. |
183 | |
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184 | =item /pattern/ |
185 | |
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186 | Search forwards for pattern; final / is optional. |
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187 | |
188 | =item ?pattern? |
189 | |
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190 | Search backwards for pattern; final ? is optional. |
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191 | |
192 | =item L |
193 | |
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194 | List all breakpoints and actions. |
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195 | |
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196 | =item S [[!]pattern] |
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197 | |
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198 | List subroutine names [not] matching pattern. |
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199 | |
200 | =item t |
201 | |
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202 | Toggle trace mode (see also C<AutoTrace> C<O>ption). |
4e1d3b43 |
203 | |
204 | =item t expr |
205 | |
206 | Trace through execution of expr. For example: |
207 | |
208 | $ perl -de 42 |
209 | Stack dump during die enabled outside of evals. |
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210 | |
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211 | Loading DB routines from perl5db.pl patch level 0.94 |
212 | Emacs support available. |
213 | |
214 | Enter h or `h h' for help. |
215 | |
216 | main::(-e:1): 0 |
217 | DB<1> sub foo { 14 } |
218 | |
219 | DB<2> sub bar { 3 } |
220 | |
221 | DB<3> t print foo() * bar() |
222 | main::((eval 172):3): print foo() + bar(); |
223 | main::foo((eval 168):2): |
224 | main::bar((eval 170):2): |
225 | 42 |
36477c24 |
226 | |
227 | or, with the C<O>ption C<frame=2> set, |
228 | |
229 | DB<4> O f=2 |
230 | frame = '2' |
231 | DB<5> t print foo() * bar() |
232 | 3: foo() * bar() |
233 | entering main::foo |
234 | 2: sub foo { 14 }; |
235 | exited main::foo |
236 | entering main::bar |
237 | 2: sub bar { 3 }; |
238 | exited main::bar |
239 | 42 |
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240 | |
241 | =item b [line] [condition] |
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242 | |
243 | Set a breakpoint. If line is omitted, sets a breakpoint on the line |
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244 | that is about to be executed. If a condition is specified, it's |
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245 | evaluated each time the statement is reached and a breakpoint is taken |
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246 | only if the condition is true. Breakpoints may be set on only lines |
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247 | that begin an executable statement. Conditions don't use B<if>: |
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248 | |
249 | b 237 $x > 30 |
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250 | b 237 ++$count237 < 11 |
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251 | b 33 /pattern/i |
252 | |
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253 | =item b subname [condition] |
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254 | |
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255 | Set a breakpoint at the first line of the named subroutine. I<subname> may |
256 | be a variable which contains a code reference (in this case I<condition> |
257 | is not supported). |
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258 | |
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259 | =item b postpone subname [condition] |
260 | |
261 | Set breakpoint at first line of subroutine after it is compiled. |
262 | |
263 | =item b load filename |
264 | |
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265 | Set breakpoint at the first executed line of the file. Filename should |
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266 | be a full name as found in values of %INC. |
267 | |
268 | =item b compile subname |
269 | |
270 | Sets breakpoint at the first statement executed after the subroutine |
271 | is compiled. |
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272 | |
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273 | =item d [line] |
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274 | |
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275 | Delete a breakpoint at the specified line. If line is omitted, deletes |
276 | the breakpoint on the line that is about to be executed. |
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277 | |
278 | =item D |
279 | |
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280 | Delete all installed breakpoints. |
281 | |
282 | =item a [line] command |
283 | |
284 | Set an action to be done before the line is executed. |
285 | The sequence of steps taken by the debugger is |
286 | |
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287 | 1. check for a breakpoint at this line |
288 | 2. print the line if necessary (tracing) |
289 | 3. do any actions associated with that line |
290 | 4. prompt user if at a breakpoint or in single-step |
291 | 5. evaluate line |
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292 | |
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293 | For example, this will print out $foo every time line |
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294 | 53 is passed: |
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295 | |
4e1d3b43 |
296 | a 53 print "DB FOUND $foo\n" |
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297 | |
298 | =item A |
299 | |
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300 | Delete all installed actions. |
301 | |
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302 | =item W [expr] |
303 | |
304 | Add a global watch-expression. |
305 | |
306 | =item W |
307 | |
308 | Delete all watch-expressions. |
309 | |
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310 | =item r |
311 | |
312 | Continue until return from the current subroutine, and dump the return value. |
313 | |
4e1d3b43 |
314 | =item O [opt[=val]] [opt"val"] [opt?]... |
315 | |
316 | Set or query values of options. val defaults to 1. opt can |
317 | be abbreviated. Several options can be listed. |
318 | |
319 | =over 12 |
320 | |
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321 | =item C<recallCommand>, C<ShellBang> |
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322 | |
323 | The characters used to recall command or spawn shell. By |
324 | default, these are both set to C<!>. |
325 | |
e7ea3e70 |
326 | =item C<pager> |
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327 | |
328 | Program to use for output of pager-piped commands (those |
329 | beginning with a C<|> character.) By default, |
330 | C<$ENV{PAGER}> will be used. |
331 | |
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332 | =item C<tkRunning> |
36477c24 |
333 | |
334 | Run Tk while prompting (with ReadLine). |
335 | |
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336 | =item C<signalLevel>, C<warnLevel>, C<dieLevel> |
337 | |
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338 | Level of verbosity. By default the debugger is in a sane verbose mode, |
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339 | thus it will print backtraces on all the warnings and die-messages |
340 | which are going to be printed out, and will print a message when |
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341 | interesting uncaught signals arrive. |
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342 | |
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343 | To disable this behaviour, set these values to 0. If C<dieLevel> is 2, |
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344 | then the messages which will be caught by surrounding C<eval> are also |
345 | printed. |
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346 | |
e7ea3e70 |
347 | =item C<AutoTrace> |
36477c24 |
348 | |
e7ea3e70 |
349 | Trace mode (similar to C<t> command, but can be put into |
350 | C<PERLDB_OPTS>). |
36477c24 |
351 | |
e7ea3e70 |
352 | =item C<LineInfo> |
36477c24 |
353 | |
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354 | File or pipe to print line number info to. If it is a pipe (say, |
355 | C<|visual_perl_db>), then a short, "emacs like" message is used. |
36477c24 |
356 | |
357 | =item C<inhibit_exit> |
358 | |
359 | If 0, allows I<stepping off> the end of the script. |
360 | |
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361 | =item C<PrintRet> |
36477c24 |
362 | |
363 | affects printing of return value after C<r> command. |
364 | |
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365 | =item C<ornaments> |
366 | |
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367 | affects screen appearance of the command line (see L<Term::ReadLine>). |
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368 | |
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369 | =item C<frame> |
36477c24 |
370 | |
371 | affects printing messages on entry and exit from subroutines. If |
372 | C<frame & 2> is false, messages are printed on entry only. (Printing |
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373 | on exit may be useful if inter(di)spersed with other messages.) |
36477c24 |
374 | |
375 | If C<frame & 4>, arguments to functions are printed as well as the |
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376 | context and caller info. If C<frame & 8>, overloaded C<stringify> and |
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377 | C<tie>d C<FETCH> are enabled on the printed arguments. If C<frame & |
378 | 16>, the return value from the subroutine is printed as well. |
379 | |
380 | The length at which the argument list is truncated is governed by the |
381 | next option: |
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382 | |
383 | =item C<maxTraceLen> |
384 | |
385 | length at which the argument list is truncated when C<frame> option's |
386 | bit 4 is set. |
36477c24 |
387 | |
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388 | =back |
389 | |
390 | The following options affect what happens with C<V>, C<X>, and C<x> |
391 | commands: |
392 | |
393 | =over 12 |
394 | |
e7ea3e70 |
395 | =item C<arrayDepth>, C<hashDepth> |
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396 | |
397 | Print only first N elements ('' for all). |
398 | |
e7ea3e70 |
399 | =item C<compactDump>, C<veryCompact> |
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400 | |
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401 | Change style of array and hash dump. If C<compactDump>, short array |
e7ea3e70 |
402 | may be printed on one line. |
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403 | |
e7ea3e70 |
404 | =item C<globPrint> |
4e1d3b43 |
405 | |
406 | Whether to print contents of globs. |
407 | |
e7ea3e70 |
408 | =item C<DumpDBFiles> |
4e1d3b43 |
409 | |
410 | Dump arrays holding debugged files. |
411 | |
e7ea3e70 |
412 | =item C<DumpPackages> |
4e1d3b43 |
413 | |
414 | Dump symbol tables of packages. |
415 | |
6ee623d5 |
416 | =item C<DumpReused> |
417 | |
418 | Dump contents of "reused" addresses. |
419 | |
e7ea3e70 |
420 | =item C<quote>, C<HighBit>, C<undefPrint> |
421 | |
774d564b |
422 | Change style of string dump. Default value of C<quote> is C<auto>, one |
e7ea3e70 |
423 | can enable either double-quotish dump, or single-quotish by setting it |
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424 | to C<"> or C<'>. By default, characters with high bit set are printed |
e7ea3e70 |
425 | I<as is>. |
426 | |
54310121 |
427 | =item C<UsageOnly> |
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428 | |
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429 | I<very> rudimentally per-package memory usage dump. Calculates total |
e7ea3e70 |
430 | size of strings in variables in the package. |
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431 | |
36477c24 |
432 | =back |
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433 | |
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434 | During startup options are initialized from C<$ENV{PERLDB_OPTS}>. |
435 | You can put additional initialization options C<TTY>, C<noTTY>, |
436 | C<ReadLine>, and C<NonStop> there. |
437 | |
438 | Example rc file: |
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439 | |
e7ea3e70 |
440 | &parse_options("NonStop=1 LineInfo=db.out AutoTrace"); |
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441 | |
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442 | The script will run without human intervention, putting trace information |
443 | into the file I<db.out>. (If you interrupt it, you would better reset |
444 | C<LineInfo> to something "interactive"!) |
4e1d3b43 |
445 | |
36477c24 |
446 | =over 12 |
4e1d3b43 |
447 | |
36477c24 |
448 | =item C<TTY> |
4e1d3b43 |
449 | |
36477c24 |
450 | The TTY to use for debugging I/O. |
451 | |
36477c24 |
452 | =item C<noTTY> |
453 | |
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454 | If set, goes in C<NonStop> mode, and would not connect to a TTY. If |
36477c24 |
455 | interrupt (or if control goes to debugger via explicit setting of |
456 | $DB::signal or $DB::single from the Perl script), connects to a TTY |
457 | specified by the C<TTY> option at startup, or to a TTY found at |
458 | runtime using C<Term::Rendezvous> module of your choice. |
459 | |
460 | This module should implement a method C<new> which returns an object |
461 | with two methods: C<IN> and C<OUT>, returning two filehandles to use |
774d564b |
462 | for debugging input and output correspondingly. Method C<new> may |
36477c24 |
463 | inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at |
464 | startup, or is C<"/tmp/perldbtty$$"> otherwise. |
465 | |
466 | =item C<ReadLine> |
467 | |
468 | If false, readline support in debugger is disabled, so you can debug |
469 | ReadLine applications. |
470 | |
471 | =item C<NonStop> |
472 | |
54310121 |
473 | If set, debugger goes into noninteractive mode until interrupted, or |
36477c24 |
474 | programmatically by setting $DB::signal or $DB::single. |
475 | |
476 | =back |
477 | |
478 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: |
4e1d3b43 |
479 | |
e7ea3e70 |
480 | $ PERLDB_OPTS="N f=2" perl -d myprogram |
4e1d3b43 |
481 | |
482 | will run the script C<myprogram> without human intervention, printing |
483 | out the call tree with entry and exit points. Note that C<N f=2> is |
774d564b |
484 | equivalent to C<NonStop=1 frame=2>. Note also that at the moment when |
4e1d3b43 |
485 | this documentation was written all the options to the debugger could |
36477c24 |
486 | be uniquely abbreviated by the first letter (with exception of |
487 | C<Dump*> options). |
4e1d3b43 |
488 | |
36477c24 |
489 | Other examples may include |
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490 | |
e7ea3e70 |
491 | $ PERLDB_OPTS="N f A L=listing" perl -d myprogram |
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492 | |
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493 | - runs script noninteractively, printing info on each entry into a |
36477c24 |
494 | subroutine and each executed line into the file F<listing>. (If you |
495 | interrupt it, you would better reset C<LineInfo> to something |
496 | "interactive"!) |
497 | |
498 | |
e7ea3e70 |
499 | $ env "PERLDB_OPTS=R=0 TTY=/dev/ttyc" perl -d myprogram |
36477c24 |
500 | |
501 | may be useful for debugging a program which uses C<Term::ReadLine> |
774d564b |
502 | itself. Do not forget detach shell from the TTY in the window which |
36477c24 |
503 | corresponds to F</dev/ttyc>, say, by issuing a command like |
504 | |
e7ea3e70 |
505 | $ sleep 1000000 |
36477c24 |
506 | |
507 | See L<"Debugger Internals"> below for more details. |
508 | |
509 | =item E<lt> [ command ] |
510 | |
511 | Set an action (Perl command) to happen before every debugger prompt. |
4a6725af |
512 | A multi-line command may be entered by backslashing the newlines. If |
36477c24 |
513 | C<command> is missing, resets the list of actions. |
514 | |
515 | =item E<lt>E<lt> command |
516 | |
517 | Add an action (Perl command) to happen before every debugger prompt. |
4a6725af |
518 | A multi-line command may be entered by backslashing the newlines. |
a0d0e21e |
519 | |
184e9718 |
520 | =item E<gt> command |
a0d0e21e |
521 | |
36477c24 |
522 | Set an action (Perl command) to happen after the prompt when you've |
4a6725af |
523 | just given a command to return to executing the script. A multi-line |
36477c24 |
524 | command may be entered by backslashing the newlines. If C<command> is |
525 | missing, resets the list of actions. |
526 | |
527 | =item E<gt>E<gt> command |
528 | |
529 | Adds an action (Perl command) to happen after the prompt when you've |
4a6725af |
530 | just given a command to return to executing the script. A multi-line |
36477c24 |
531 | command may be entered by backslashing the newlines. |
532 | |
533 | =item { [ command ] |
534 | |
535 | Set an action (debugger command) to happen before every debugger prompt. |
4a6725af |
536 | A multi-line command may be entered by backslashing the newlines. If |
36477c24 |
537 | C<command> is missing, resets the list of actions. |
538 | |
539 | =item {{ command |
540 | |
541 | Add an action (debugger command) to happen before every debugger prompt. |
4a6725af |
542 | A multi-line command may be entered by backslashing the newlines. |
a0d0e21e |
543 | |
4e1d3b43 |
544 | =item ! number |
a0d0e21e |
545 | |
4e1d3b43 |
546 | Redo a previous command (default previous command). |
a0d0e21e |
547 | |
4e1d3b43 |
548 | =item ! -number |
a0d0e21e |
549 | |
4e1d3b43 |
550 | Redo number'th-to-last command. |
a0d0e21e |
551 | |
4e1d3b43 |
552 | =item ! pattern |
a0d0e21e |
553 | |
4e1d3b43 |
554 | Redo last command that started with pattern. |
555 | See C<O recallCommand>, too. |
a0d0e21e |
556 | |
4e1d3b43 |
557 | =item !! cmd |
a0d0e21e |
558 | |
4e1d3b43 |
559 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) |
560 | See C<O shellBang> too. |
a0d0e21e |
561 | |
562 | =item H -number |
563 | |
564 | Display last n commands. Only commands longer than one character are |
565 | listed. If number is omitted, lists them all. |
566 | |
567 | =item q or ^D |
568 | |
36477c24 |
569 | Quit. ("quit" doesn't work for this.) This is the only supported way |
570 | to exit the debugger, though typing C<exit> twice may do it too. |
571 | |
572 | Set an C<O>ption C<inhibit_exit> to 0 if you want to be able to I<step |
19799a22 |
573 | off> the end the script. You may also need to set $finished to 0 at |
36477c24 |
574 | some moment if you want to step through global destruction. |
a0d0e21e |
575 | |
4e1d3b43 |
576 | =item R |
577 | |
578 | Restart the debugger by B<exec>ing a new session. It tries to maintain |
579 | your history across this, but internal settings and command line options |
580 | may be lost. |
581 | |
5f05dabc |
582 | Currently the following setting are preserved: history, breakpoints, |
54310121 |
583 | actions, debugger C<O>ptions, and the following command line |
5f05dabc |
584 | options: B<-w>, B<-I>, and B<-e>. |
36477c24 |
585 | |
4e1d3b43 |
586 | =item |dbcmd |
587 | |
588 | Run debugger command, piping DB::OUT to current pager. |
589 | |
590 | =item ||dbcmd |
591 | |
592 | Same as C<|dbcmd> but DB::OUT is temporarily B<select>ed as well. |
593 | Often used with commands that would otherwise produce long |
594 | output, such as |
595 | |
596 | |V main |
597 | |
598 | =item = [alias value] |
599 | |
e7ea3e70 |
600 | Define a command alias, like |
601 | |
602 | = quit q |
603 | |
604 | or list current aliases. |
4e1d3b43 |
605 | |
a0d0e21e |
606 | =item command |
607 | |
608 | Execute command as a Perl statement. A missing semicolon will be |
609 | supplied. |
610 | |
e7ea3e70 |
611 | =item m expr |
a0d0e21e |
612 | |
e7ea3e70 |
613 | The expression is evaluated, and the methods which may be applied to |
614 | the result are listed. |
615 | |
616 | =item m package |
617 | |
618 | The methods which may be applied to objects in the C<package> are listed. |
a0d0e21e |
619 | |
620 | =back |
621 | |
e7ea3e70 |
622 | =head2 Debugger input/output |
623 | |
624 | =over 8 |
625 | |
626 | =item Prompt |
627 | |
4e1d3b43 |
628 | The debugger prompt is something like |
629 | |
630 | DB<8> |
631 | |
632 | or even |
633 | |
634 | DB<<17>> |
635 | |
636 | where that number is the command number, which you'd use to access with |
54310121 |
637 | the builtin B<csh>-like history mechanism, e.g., C<!17> would repeat |
4e1d3b43 |
638 | command number 17. The number of angle brackets indicates the depth of |
639 | the debugger. You could get more than one set of brackets, for example, if |
640 | you'd already at a breakpoint and then printed out the result of a |
36477c24 |
641 | function call that itself also has a breakpoint, or you step into an |
642 | expression via C<s/n/t expression> command. |
4e1d3b43 |
643 | |
54310121 |
644 | =item Multiline commands |
e7ea3e70 |
645 | |
4a6725af |
646 | If you want to enter a multi-line command, such as a subroutine |
e7ea3e70 |
647 | definition with several statements, or a format, you may escape the |
648 | newline that would normally end the debugger command with a backslash. |
649 | Here's an example: |
a0d0e21e |
650 | |
4e1d3b43 |
651 | DB<1> for (1..4) { \ |
652 | cont: print "ok\n"; \ |
653 | cont: } |
654 | ok |
655 | ok |
656 | ok |
657 | ok |
658 | |
659 | Note that this business of escaping a newline is specific to interactive |
660 | commands typed into the debugger. |
661 | |
e7ea3e70 |
662 | =item Stack backtrace |
663 | |
68dc0745 |
664 | Here's an example of what a stack backtrace via C<T> command might |
e7ea3e70 |
665 | look like: |
4e1d3b43 |
666 | |
667 | $ = main::infested called from file `Ambulation.pm' line 10 |
668 | @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7 |
669 | $ = main::pests('bactrian', 4) called from file `camel_flea' line 4 |
670 | |
671 | The left-hand character up there tells whether the function was called |
672 | in a scalar or list context (we bet you can tell which is which). What |
673 | that says is that you were in the function C<main::infested> when you ran |
674 | the stack dump, and that it was called in a scalar context from line 10 |
675 | of the file I<Ambulation.pm>, but without any arguments at all, meaning |
676 | it was called as C<&infested>. The next stack frame shows that the |
677 | function C<Ambulation::legs> was called in a list context from the |
678 | I<camel_flea> file with four arguments. The last stack frame shows that |
679 | C<main::pests> was called in a scalar context, also from I<camel_flea>, |
680 | but from line 4. |
681 | |
e7ea3e70 |
682 | Note that if you execute C<T> command from inside an active C<use> |
7b8d334a |
683 | statement, the backtrace will contain both C<require> |
684 | frame and an C<eval>) frame. |
e7ea3e70 |
685 | |
686 | =item Listing |
687 | |
688 | Listing given via different flavors of C<l> command looks like this: |
689 | |
690 | DB<<13>> l |
691 | 101: @i{@i} = (); |
692 | 102:b @isa{@i,$pack} = () |
693 | 103 if(exists $i{$prevpack} || exists $isa{$pack}); |
694 | 104 } |
695 | 105 |
696 | 106 next |
697 | 107==> if(exists $isa{$pack}); |
698 | 108 |
699 | 109:a if ($extra-- > 0) { |
700 | 110: %isa = ($pack,1); |
701 | |
702 | Note that the breakable lines are marked with C<:>, lines with |
703 | breakpoints are marked by C<b>, with actions by C<a>, and the |
704 | next executed line is marked by C<==E<gt>>. |
705 | |
706 | =item Frame listing |
707 | |
708 | When C<frame> option is set, debugger would print entered (and |
709 | optionally exited) subroutines in different styles. |
710 | |
54310121 |
711 | What follows is the start of the listing of |
e7ea3e70 |
712 | |
28d1fb14 |
713 | env "PERLDB_OPTS=f=n N" perl -d -V |
714 | |
715 | for different values of C<n>: |
e7ea3e70 |
716 | |
717 | =over 4 |
718 | |
719 | =item 1 |
720 | |
721 | entering main::BEGIN |
722 | entering Config::BEGIN |
723 | Package lib/Exporter.pm. |
724 | Package lib/Carp.pm. |
725 | Package lib/Config.pm. |
726 | entering Config::TIEHASH |
727 | entering Exporter::import |
728 | entering Exporter::export |
729 | entering Config::myconfig |
730 | entering Config::FETCH |
731 | entering Config::FETCH |
732 | entering Config::FETCH |
733 | entering Config::FETCH |
734 | |
735 | =item 2 |
736 | |
737 | entering main::BEGIN |
738 | entering Config::BEGIN |
739 | Package lib/Exporter.pm. |
740 | Package lib/Carp.pm. |
741 | exited Config::BEGIN |
742 | Package lib/Config.pm. |
743 | entering Config::TIEHASH |
744 | exited Config::TIEHASH |
745 | entering Exporter::import |
746 | entering Exporter::export |
747 | exited Exporter::export |
748 | exited Exporter::import |
749 | exited main::BEGIN |
750 | entering Config::myconfig |
751 | entering Config::FETCH |
752 | exited Config::FETCH |
753 | entering Config::FETCH |
754 | exited Config::FETCH |
755 | entering Config::FETCH |
756 | |
757 | =item 4 |
758 | |
759 | in $=main::BEGIN() from /dev/nul:0 |
760 | in $=Config::BEGIN() from lib/Config.pm:2 |
761 | Package lib/Exporter.pm. |
762 | Package lib/Carp.pm. |
763 | Package lib/Config.pm. |
764 | in $=Config::TIEHASH('Config') from lib/Config.pm:644 |
765 | in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 |
766 | in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li |
767 | in @=Config::myconfig() from /dev/nul:0 |
768 | in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 |
769 | in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 |
cceca5ed |
770 | in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 |
771 | in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574 |
e7ea3e70 |
772 | in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574 |
773 | in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574 |
774 | |
775 | =item 6 |
776 | |
777 | in $=main::BEGIN() from /dev/nul:0 |
778 | in $=Config::BEGIN() from lib/Config.pm:2 |
779 | Package lib/Exporter.pm. |
780 | Package lib/Carp.pm. |
781 | out $=Config::BEGIN() from lib/Config.pm:0 |
782 | Package lib/Config.pm. |
783 | in $=Config::TIEHASH('Config') from lib/Config.pm:644 |
784 | out $=Config::TIEHASH('Config') from lib/Config.pm:644 |
785 | in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 |
786 | in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ |
787 | out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ |
788 | out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 |
789 | out $=main::BEGIN() from /dev/nul:0 |
790 | in @=Config::myconfig() from /dev/nul:0 |
791 | in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 |
792 | out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 |
793 | in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 |
794 | out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 |
cceca5ed |
795 | in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 |
796 | out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 |
797 | in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574 |
e7ea3e70 |
798 | |
799 | =item 14 |
800 | |
801 | in $=main::BEGIN() from /dev/nul:0 |
802 | in $=Config::BEGIN() from lib/Config.pm:2 |
803 | Package lib/Exporter.pm. |
804 | Package lib/Carp.pm. |
805 | out $=Config::BEGIN() from lib/Config.pm:0 |
806 | Package lib/Config.pm. |
807 | in $=Config::TIEHASH('Config') from lib/Config.pm:644 |
808 | out $=Config::TIEHASH('Config') from lib/Config.pm:644 |
809 | in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 |
810 | in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E |
811 | out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E |
812 | out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/nul:0 |
813 | out $=main::BEGIN() from /dev/nul:0 |
814 | in @=Config::myconfig() from /dev/nul:0 |
815 | in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 |
816 | out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 |
817 | in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 |
818 | out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 |
819 | |
28d1fb14 |
820 | =item 30 |
821 | |
822 | in $=CODE(0x15eca4)() from /dev/null:0 |
823 | in $=CODE(0x182528)() from lib/Config.pm:2 |
824 | Package lib/Exporter.pm. |
825 | out $=CODE(0x182528)() from lib/Config.pm:0 |
826 | scalar context return from CODE(0x182528): undef |
827 | Package lib/Config.pm. |
828 | in $=Config::TIEHASH('Config') from lib/Config.pm:628 |
829 | out $=Config::TIEHASH('Config') from lib/Config.pm:628 |
830 | scalar context return from Config::TIEHASH: empty hash |
831 | in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
832 | in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 |
833 | out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 |
834 | scalar context return from Exporter::export: '' |
835 | out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
836 | scalar context return from Exporter::import: '' |
837 | |
838 | |
e7ea3e70 |
839 | =back |
840 | |
841 | In all the cases indentation of lines shows the call tree, if bit 2 of |
842 | C<frame> is set, then a line is printed on exit from a subroutine as |
843 | well, if bit 4 is set, then the arguments are printed as well as the |
844 | caller info, if bit 8 is set, the arguments are printed even if they |
28d1fb14 |
845 | are tied or references, if bit 16 is set, the return value is printed |
846 | as well. |
e7ea3e70 |
847 | |
848 | When a package is compiled, a line like this |
849 | |
850 | Package lib/Carp.pm. |
851 | |
852 | is printed with proper indentation. |
853 | |
854 | =back |
855 | |
856 | =head2 Debugging compile-time statements |
857 | |
4e1d3b43 |
858 | If you have any compile-time executable statements (code within a BEGIN |
859 | block or a C<use> statement), these will C<NOT> be stopped by debugger, |
36477c24 |
860 | although C<require>s will (and compile-time statements can be traced |
54310121 |
861 | with C<AutoTrace> option set in C<PERLDB_OPTS>). From your own Perl |
36477c24 |
862 | code, however, you can |
4e1d3b43 |
863 | transfer control back to the debugger using the following statement, |
864 | which is harmless if the debugger is not running: |
a0d0e21e |
865 | |
866 | $DB::single = 1; |
867 | |
4e1d3b43 |
868 | If you set C<$DB::single> to the value 2, it's equivalent to having |
869 | just typed the C<n> command, whereas a value of 1 means the C<s> |
870 | command. The C<$DB::trace> variable should be set to 1 to simulate |
871 | having typed the C<t> command. |
872 | |
e7ea3e70 |
873 | Another way to debug compile-time code is to start debugger, set a |
874 | breakpoint on I<load> of some module thusly |
875 | |
876 | DB<7> b load f:/perllib/lib/Carp.pm |
877 | Will stop on load of `f:/perllib/lib/Carp.pm'. |
878 | |
774d564b |
879 | and restart debugger by C<R> command (if possible). One can use C<b |
e7ea3e70 |
880 | compile subname> for the same purpose. |
881 | |
4e1d3b43 |
882 | =head2 Debugger Customization |
a0d0e21e |
883 | |
7b8d334a |
884 | Most probably you do not want to modify the debugger, it contains enough |
774d564b |
885 | hooks to satisfy most needs. You may change the behaviour of debugger |
36477c24 |
886 | from the debugger itself, using C<O>ptions, from the command line via |
887 | C<PERLDB_OPTS> environment variable, and from I<customization files>. |
a0d0e21e |
888 | |
889 | You can do some customization by setting up a F<.perldb> file which |
890 | contains initialization code. For instance, you could make aliases |
4e1d3b43 |
891 | like these (the last one is one people expect to be there): |
a0d0e21e |
892 | |
4e1d3b43 |
893 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; |
a0d0e21e |
894 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; |
4e1d3b43 |
895 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; |
896 | $DB::alias{'quit'} = 's/^quit(\s*)/exit\$/'; |
897 | |
36477c24 |
898 | One changes options from F<.perldb> file via calls like this one; |
899 | |
900 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); |
901 | |
774d564b |
902 | (the code is executed in the package C<DB>). Note that F<.perldb> is |
903 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the |
36477c24 |
904 | subroutine C<afterinit>, it is called after all the debugger |
774d564b |
905 | initialization ends. F<.perldb> may be contained in the current |
36477c24 |
906 | directory, or in the C<LOGDIR>/C<HOME> directory. |
907 | |
908 | If you want to modify the debugger, copy F<perl5db.pl> from the Perl |
909 | library to another name and modify it as necessary. You'll also want |
910 | to set your C<PERL5DB> environment variable to say something like this: |
911 | |
912 | BEGIN { require "myperl5db.pl" } |
913 | |
914 | As the last resort, one can use C<PERL5DB> to customize debugger by |
915 | directly setting internal variables or calling debugger functions. |
916 | |
4e1d3b43 |
917 | =head2 Readline Support |
918 | |
919 | As shipped, the only command line history supplied is a simplistic one |
920 | that checks for leading exclamation points. However, if you install |
921 | the Term::ReadKey and Term::ReadLine modules from CPAN, you will |
922 | have full editing capabilities much like GNU I<readline>(3) provides. |
923 | Look for these in the F<modules/by-module/Term> directory on CPAN. |
924 | |
54310121 |
925 | A rudimentary command line completion is also available. |
e7ea3e70 |
926 | Unfortunately, the names of lexical variables are not available for |
927 | completion. |
928 | |
4e1d3b43 |
929 | =head2 Editor Support for Debugging |
930 | |
931 | If you have GNU B<emacs> installed on your system, it can interact with |
932 | the Perl debugger to provide an integrated software development |
933 | environment reminiscent of its interactions with C debuggers. |
934 | |
935 | Perl is also delivered with a start file for making B<emacs> act like a |
936 | syntax-directed editor that understands (some of) Perl's syntax. Look in |
937 | the I<emacs> directory of the Perl source distribution. |
938 | |
939 | (Historically, a similar setup for interacting with B<vi> and the |
940 | X11 window system had also been available, but at the time of this |
941 | writing, no debugger support for B<vi> currently exists.) |
942 | |
943 | =head2 The Perl Profiler |
944 | |
945 | If you wish to supply an alternative debugger for Perl to run, just |
946 | invoke your script with a colon and a package argument given to the B<-d> |
947 | flag. One of the most popular alternative debuggers for Perl is |
948 | B<DProf>, the Perl profiler. As of this writing, B<DProf> is not |
949 | included with the standard Perl distribution, but it is expected to |
950 | be included soon, for certain values of "soon". |
951 | |
952 | Meanwhile, you can fetch the Devel::Dprof module from CPAN. Assuming |
953 | it's properly installed on your system, to profile your Perl program in |
954 | the file F<mycode.pl>, just type: |
955 | |
956 | perl -d:DProf mycode.pl |
957 | |
958 | When the script terminates the profiler will dump the profile information |
959 | to a file called F<tmon.out>. A tool like B<dprofpp> (also supplied with |
960 | the Devel::DProf package) can be used to interpret the information which is |
961 | in that profile. |
962 | |
36477c24 |
963 | =head2 Debugger support in perl |
4e1d3b43 |
964 | |
e7ea3e70 |
965 | When you call the B<caller> function (see L<perlfunc/caller>) from the |
966 | package DB, Perl sets the array @DB::args to contain the arguments the |
54310121 |
967 | corresponding stack frame was called with. |
4e1d3b43 |
968 | |
36477c24 |
969 | If perl is run with B<-d> option, the following additional features |
84902520 |
970 | are enabled (cf. L<perlvar/$^P>): |
a0d0e21e |
971 | |
36477c24 |
972 | =over |
4e1d3b43 |
973 | |
36477c24 |
974 | =item * |
4e1d3b43 |
975 | |
36477c24 |
976 | Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require |
977 | 'perl5db.pl'}> if not present) before the first line of the |
978 | application. |
4e1d3b43 |
979 | |
36477c24 |
980 | =item * |
4e1d3b43 |
981 | |
7b8d334a |
982 | The array C<@{"_E<lt>$filename"}> is the line-by-line contents of |
774d564b |
983 | $filename for all the compiled files. Same for C<eval>ed strings which |
19799a22 |
984 | contain subroutines, or which are currently executed. The $filename |
36477c24 |
985 | for C<eval>ed strings looks like C<(eval 34)>. |
4e1d3b43 |
986 | |
36477c24 |
987 | =item * |
4e1d3b43 |
988 | |
7b8d334a |
989 | The hash C<%{"_E<lt>$filename"}> contains breakpoints and action (it is |
36477c24 |
990 | keyed by line number), and individual entries are settable (as opposed |
774d564b |
991 | to the whole hash). Only true/false is important to Perl, though the |
36477c24 |
992 | values used by F<perl5db.pl> have the form |
774d564b |
993 | C<"$break_condition\0$action">. Values are magical in numeric context: |
36477c24 |
994 | they are zeros if the line is not breakable. |
4e1d3b43 |
995 | |
36477c24 |
996 | Same for evaluated strings which contain subroutines, or which are |
7b8d334a |
997 | currently executed. The $filename for C<eval>ed strings looks like |
36477c24 |
998 | C<(eval 34)>. |
4e1d3b43 |
999 | |
36477c24 |
1000 | =item * |
4e1d3b43 |
1001 | |
7b8d334a |
1002 | The scalar C<${"_E<lt>$filename"}> contains C<"_E<lt>$filename">. Same for |
36477c24 |
1003 | evaluated strings which contain subroutines, or which are currently |
7b8d334a |
1004 | executed. The $filename for C<eval>ed strings looks like C<(eval |
36477c24 |
1005 | 34)>. |
4e1d3b43 |
1006 | |
36477c24 |
1007 | =item * |
4e1d3b43 |
1008 | |
36477c24 |
1009 | After each C<require>d file is compiled, but before it is executed, |
7b8d334a |
1010 | C<DB::postponed(*{"_E<lt>$filename"})> is called (if subroutine |
774d564b |
1011 | C<DB::postponed> exists). Here the $filename is the expanded name of |
7b8d334a |
1012 | the C<require>d file (as found in values of %INC). |
4e1d3b43 |
1013 | |
36477c24 |
1014 | =item * |
4e1d3b43 |
1015 | |
36477c24 |
1016 | After each subroutine C<subname> is compiled existence of |
774d564b |
1017 | C<$DB::postponed{subname}> is checked. If this key exists, |
36477c24 |
1018 | C<DB::postponed(subname)> is called (if subroutine C<DB::postponed> |
1019 | exists). |
4e1d3b43 |
1020 | |
36477c24 |
1021 | =item * |
4e1d3b43 |
1022 | |
36477c24 |
1023 | A hash C<%DB::sub> is maintained, with keys being subroutine names, |
774d564b |
1024 | values having the form C<filename:startline-endline>. C<filename> has |
36477c24 |
1025 | the form C<(eval 31)> for subroutines defined inside C<eval>s. |
4e1d3b43 |
1026 | |
36477c24 |
1027 | =item * |
1028 | |
5f05dabc |
1029 | When execution of the application reaches a place that can have |
1030 | a breakpoint, a call to C<DB::DB()> is performed if any one of |
1031 | variables $DB::trace, $DB::single, or $DB::signal is true. (Note that |
36477c24 |
1032 | these variables are not C<local>izable.) This feature is disabled when |
1033 | the control is inside C<DB::DB()> or functions called from it (unless |
e7ea3e70 |
1034 | C<$^D & (1E<lt>E<lt>30)>). |
36477c24 |
1035 | |
1036 | =item * |
1037 | |
5f05dabc |
1038 | When execution of the application reaches a subroutine call, a call |
36477c24 |
1039 | to C<&DB::sub>(I<args>) is performed instead, with C<$DB::sub> being |
1040 | the name of the called subroutine. (Unless the subroutine is compiled |
1041 | in the package C<DB>.) |
4e1d3b43 |
1042 | |
1043 | =back |
a0d0e21e |
1044 | |
84902520 |
1045 | Note that if C<&DB::sub> needs some external data to be setup for it |
1046 | to work, no subroutine call is possible until this is done. For the |
1047 | standard debugger C<$DB::deep> (how many levels of recursion deep into |
1048 | the debugger you can go before a mandatory break) gives an example of |
1049 | such a dependency. |
e7ea3e70 |
1050 | |
84902520 |
1051 | The minimal working debugger consists of one line |
e7ea3e70 |
1052 | |
1053 | sub DB::DB {} |
1054 | |
1055 | which is quite handy as contents of C<PERL5DB> environment |
1056 | variable: |
1057 | |
1058 | env "PERL5DB=sub DB::DB {}" perl -d your-script |
1059 | |
1060 | Another (a little bit more useful) minimal debugger can be created |
1061 | with the only line being |
1062 | |
1063 | sub DB::DB {print ++$i; scalar <STDIN>} |
1064 | |
1065 | This debugger would print the sequential number of encountered |
1066 | statement, and would wait for your C<CR> to continue. |
1067 | |
1068 | The following debugger is quite functional: |
1069 | |
54310121 |
1070 | { |
1071 | package DB; |
1072 | sub DB {} |
e7ea3e70 |
1073 | sub sub {print ++$i, " $sub\n"; &$sub} |
1074 | } |
1075 | |
1076 | It prints the sequential number of subroutine call and the name of the |
774d564b |
1077 | called subroutine. Note that C<&DB::sub> should be compiled into the |
e7ea3e70 |
1078 | package C<DB>. |
36477c24 |
1079 | |
1080 | =head2 Debugger Internals |
1081 | |
1082 | At the start, the debugger reads your rc file (F<./.perldb> or |
54310121 |
1083 | F<~/.perldb> under Unix), which can set important options. This file may |
36477c24 |
1084 | define a subroutine C<&afterinit> to be executed after the debugger is |
1085 | initialized. |
1086 | |
5f05dabc |
1087 | After the rc file is read, the debugger reads environment variable |
36477c24 |
1088 | PERLDB_OPTS and parses it as a rest of C<O ...> line in debugger prompt. |
1089 | |
1090 | It also maintains magical internal variables, such as C<@DB::dbline>, |
1091 | C<%DB::dbline>, which are aliases for C<@{"::_<current_file"}> |
774d564b |
1092 | C<%{"::_<current_file"}>. Here C<current_file> is the currently |
36477c24 |
1093 | selected (with the debugger's C<f> command, or by flow of execution) |
1094 | file. |
1095 | |
774d564b |
1096 | Some functions are provided to simplify customization. See L<"Debugger |
1097 | Customization"> for description of C<DB::parse_options(string)>. The |
36477c24 |
1098 | function C<DB::dump_trace(skip[, count])> skips the specified number |
1d2dff63 |
1099 | of frames, and returns a list containing info about the caller |
774d564b |
1100 | frames (all if C<count> is missing). Each entry is a hash with keys |
36477c24 |
1101 | C<context> (C<$> or C<@>), C<sub> (subroutine name, or info about |
5f05dabc |
1102 | eval), C<args> (C<undef> or a reference to an array), C<file>, and |
36477c24 |
1103 | C<line>. |
1104 | |
54310121 |
1105 | The function C<DB::print_trace(FH, skip[, count[, short]])> prints |
774d564b |
1106 | formatted info about caller frames. The last two functions may be |
36477c24 |
1107 | convenient as arguments to C<E<lt>>, C<E<lt>E<lt>> commands. |
1108 | |
a0d0e21e |
1109 | =head2 Other resources |
1110 | |
1111 | You did try the B<-w> switch, didn't you? |
1112 | |
a77df738 |
1113 | =head2 BUGS |
a0d0e21e |
1114 | |
4e1d3b43 |
1115 | You cannot get the stack frame information or otherwise debug functions |
1116 | that were not compiled by Perl, such as C or C++ extensions. |
a0d0e21e |
1117 | |
4e1d3b43 |
1118 | If you alter your @_ arguments in a subroutine (such as with B<shift> |
68dc0745 |
1119 | or B<pop>, the stack backtrace will not show the original values. |
a77df738 |
1120 | |
1121 | =head1 Debugging Perl memory usage |
1122 | |
1123 | Perl is I<very> frivolous with memory. There is a saying that to |
1124 | estimate memory usage of Perl, assume a reasonable algorithm of |
c2611fb3 |
1125 | allocation, and multiply your estimates by 10. This is not absolutely |
a77df738 |
1126 | true, but may give you a good grasp of what happens. |
1127 | |
1128 | Say, an integer cannot take less than 20 bytes of memory, a float |
1129 | cannot take less than 24 bytes, a string cannot take less than 32 |
1130 | bytes (all these examples assume 32-bit architectures, the result are |
1131 | much worse on 64-bit architectures). If a variable is accessed in two |
1132 | of three different ways (which require an integer, a float, or a |
1133 | string), the memory footprint may increase by another 20 bytes. A |
1134 | sloppy malloc() implementation will make these numbers yet more. |
1135 | |
1136 | On the opposite end of the scale, a declaration like |
1137 | |
1138 | sub foo; |
1139 | |
1140 | may take (on some versions of perl) up to 500 bytes of memory. |
1141 | |
1142 | Off-the-cuff anecdotal estimates of a code bloat give a factor around |
1143 | 8. This means that the compiled form of reasonable (commented |
1144 | indented etc.) code will take approximately 8 times more than the |
1145 | disk space the code takes. |
1146 | |
1147 | There are two Perl-specific ways to analyze the memory usage: |
1148 | $ENV{PERL_DEBUG_MSTATS} and B<-DL> switch. First one is available |
1149 | only if perl is compiled with Perl's malloc(), the second one only if |
1150 | Perl compiled with C<-DDEBUGGING> (as with giving C<-D optimise=-g> |
1151 | option to F<Configure>). |
1152 | |
1153 | =head2 Using C<$ENV{PERL_DEBUG_MSTATS}> |
1154 | |
1155 | If your perl is using Perl's malloc(), and compiled with correct |
1156 | switches (this is the default), then it will print memory usage |
1157 | statistics after compiling your code (if C<$ENV{PERL_DEBUG_MSTATS}> > |
1158 | 1), and before termination of the script (if |
1159 | C<$ENV{PERL_DEBUG_MSTATS}> >= 1). The report format is similar to one |
1160 | in the following example: |
1161 | |
1162 | env PERL_DEBUG_MSTATS=2 perl -e "require Carp" |
1163 | Memory allocation statistics after compilation: (buckets 4(4)..8188(8192) |
1164 | 14216 free: 130 117 28 7 9 0 2 2 1 0 0 |
1165 | 437 61 36 0 5 |
1166 | 60924 used: 125 137 161 55 7 8 6 16 2 0 1 |
1167 | 74 109 304 84 20 |
1168 | Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048. |
1169 | Memory allocation statistics after execution: (buckets 4(4)..8188(8192) |
1170 | 30888 free: 245 78 85 13 6 2 1 3 2 0 1 |
1171 | 315 162 39 42 11 |
1172 | 175816 used: 265 176 1112 111 26 22 11 27 2 1 1 |
1173 | 196 178 1066 798 39 |
1174 | Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144. |
1175 | |
1176 | It is possible to ask for such a statistic at arbitrary moment by |
c2611fb3 |
1177 | using Devel::Peek::mstats() (module Devel::Peek is available on CPAN). |
a77df738 |
1178 | |
1179 | Here is the explanation of different parts of the format: |
1180 | |
1181 | =over |
1182 | |
1183 | =item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)> |
1184 | |
1185 | Perl's malloc() uses bucketed allocations. Every request is rounded |
1186 | up to the closest bucket size available, and a bucket of these size is |
1187 | taken from the pool of the buckets of this size. |
1188 | |
1189 | The above line describes limits of buckets currently in use. Each |
1190 | bucket has two sizes: memory footprint, and the maximal size of user |
1191 | data which may be put into this bucket. Say, in the above example the |
1192 | smallest bucket is both sizes 4. The biggest bucket has usable size |
1193 | 8188, and the memory footprint 8192. |
1194 | |
1195 | With debugging Perl some buckets may have negative usable size. This |
1196 | means that these buckets cannot (and will not) be used. For greater |
1197 | buckets the memory footprint may be one page greater than a power of |
1198 | 2. In such a case the corresponding power of two is printed instead |
1199 | in the C<APPROX> field above. |
1200 | |
1201 | =item Free/Used |
1202 | |
1203 | The following 1 or 2 rows of numbers correspond to the number of |
1204 | buckets of each size between C<SMALLEST> and C<GREATEST>. In the |
1205 | first row the sizes (memory footprints) of buckets are powers of two |
1206 | (or possibly one page greater). In the second row (if present) the |
1207 | memory footprints of the buckets are between memory footprints of two |
1208 | buckets "above". |
1209 | |
1210 | Say, with the above example the memory footprints are (with current |
c2611fb3 |
1211 | algorithm) |
a77df738 |
1212 | |
1213 | free: 8 16 32 64 128 256 512 1024 2048 4096 8192 |
1214 | 4 12 24 48 80 |
1215 | |
1216 | With non-C<DEBUGGING> perl the buckets starting from C<128>-long ones |
1217 | have 4-byte overhead, thus 8192-long bucket may take up to |
1218 | 8188-byte-long allocations. |
1219 | |
1220 | =item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS> |
1221 | |
1222 | The first two fields give the total amount of memory perl sbrk()ed, |
1223 | and number of sbrk()s used. The third number is what perl thinks |
1224 | about continuity of returned chunks. As far as this number is |
1225 | positive, malloc() will assume that it is probable that sbrk() will |
1226 | provide continuous memory. |
1227 | |
1228 | The amounts sbrk()ed by external libraries is not counted. |
1229 | |
1230 | =item C<pad: 0> |
1231 | |
1232 | The amount of sbrk()ed memory needed to keep buckets aligned. |
1233 | |
1234 | =item C<heads: 2192> |
1235 | |
1236 | While memory overhead of bigger buckets is kept inside the bucket, for |
1237 | smaller buckets it is kept in separate areas. This field gives the |
1238 | total size of these areas. |
1239 | |
1240 | =item C<chain: 0> |
1241 | |
1242 | malloc() may want to subdivide a bigger bucket into smaller buckets. |
1243 | If only a part of the deceased-bucket is left non-subdivided, the rest |
1244 | is kept as an element of a linked list. This field gives the total |
1245 | size of these chunks. |
1246 | |
1247 | =item C<tail: 6144> |
1248 | |
1249 | To minimize amount of sbrk()s malloc() asks for more memory. This |
1250 | field gives the size of the yet-unused part, which is sbrk()ed, but |
1251 | never touched. |
1252 | |
1253 | =back |
1254 | |
1255 | =head2 Example of using B<-DL> switch |
1256 | |
1257 | Below we show how to analyse memory usage by |
1258 | |
1259 | do 'lib/auto/POSIX/autosplit.ix'; |
1260 | |
1261 | The file in question contains a header and 146 lines similar to |
1262 | |
1263 | sub getcwd ; |
1264 | |
1265 | B<Note:> I<the discussion below supposes 32-bit architecture. In the |
1266 | newer versions of perl the memory usage of the constructs discussed |
1267 | here is much improved, but the story discussed below is a real-life |
1268 | story. This story is very terse, and assumes more than cursory |
1269 | knowledge of Perl internals.> |
1270 | |
1271 | Here is the itemized list of Perl allocations performed during parsing |
1272 | of this file: |
1273 | |
1274 | !!! "after" at test.pl line 3. |
1275 | Id subtot 4 8 12 16 20 24 28 32 36 40 48 56 64 72 80 80+ |
1276 | 0 02 13752 . . . . 294 . . . . . . . . . . 4 |
1277 | 0 54 5545 . . 8 124 16 . . . 1 1 . . . . . 3 |
1278 | 5 05 32 . . . . . . . 1 . . . . . . . . |
1279 | 6 02 7152 . . . . . . . . . . 149 . . . . . |
1280 | 7 02 3600 . . . . . 150 . . . . . . . . . . |
1281 | 7 03 64 . -1 . 1 . . 2 . . . . . . . . . |
1282 | 7 04 7056 . . . . . . . . . . . . . . . 7 |
1283 | 7 17 38404 . . . . . . . 1 . . 442 149 . . 147 . |
1284 | 9 03 2078 17 249 32 . . . . 2 . . . . . . . . |
1285 | |
1286 | |
1287 | To see this list insert two C<warn('!...')> statements around the call: |
1288 | |
1289 | warn('!'); |
1290 | do 'lib/auto/POSIX/autosplit.ix'; |
1291 | warn('!!! "after"'); |
1292 | |
1293 | and run it with B<-DL> option. The first warn() will print memory |
1294 | allocation info before the parsing of the file, and will memorize the |
1295 | statistics at this point (we ignore what it prints). The second warn() |
1296 | will print increments w.r.t. this memorized statistics. This is the |
1297 | above printout. |
1298 | |
1299 | Different I<Id>s on the left correspond to different subsystems of |
1300 | perl interpreter, they are just first argument given to perl memory |
1301 | allocation API New(). To find what C<9 03> means C<grep> the perl |
1302 | source for C<903>. You will see that it is F<util.c>, function |
1303 | savepvn(). This function is used to store a copy of existing chunk of |
1304 | memory. Using C debugger, one can see that it is called either |
1305 | directly from gv_init(), or via sv_magic(), and gv_init() is called |
1306 | from gv_fetchpv() - which is called from newSUB(). |
1307 | |
1308 | B<Note:> to reach this place in debugger and skip all the calls to |
1309 | savepvn during the compilation of the main script, set a C breakpoint |
1310 | in Perl_warn(), C<continue> this point is reached, I<then> set |
1311 | breakpoint in Perl_savepvn(). Note that you may need to skip a |
1312 | handful of Perl_savepvn() which do not correspond to mass production |
1313 | of CVs (there are more C<903> allocations than 146 similar lines of |
1314 | F<lib/auto/POSIX/autosplit.ix>). Note also that C<Perl_> prefixes are |
1315 | added by macroization code in perl header files to avoid conflicts |
1316 | with external libraries. |
1317 | |
1318 | Anyway, we see that C<903> ids correspond to creation of globs, twice |
1319 | per glob - for glob name, and glob stringification magic. |
1320 | |
1321 | Here are explanations for other I<Id>s above: |
1322 | |
1323 | =over |
1324 | |
1325 | =item C<717> |
1326 | |
1327 | is for creation of bigger C<XPV*> structures. In the above case it |
1328 | creates 3 C<AV> per subroutine, one for a list of lexical variable |
1329 | names, one for a scratchpad (which contains lexical variables and |
1330 | C<targets>), and one for the array of scratchpads needed for |
1331 | recursion. |
1332 | |
1333 | It also creates a C<GV> and a C<CV> per subroutine (all called from |
1334 | start_subparse()). |
1335 | |
1336 | =item C<002> |
1337 | |
1338 | Creates C array corresponding to the C<AV> of scratchpads, and the |
1339 | scratchpad itself (the first fake entry of this scratchpad is created |
1340 | though the subroutine itself is not defined yet). |
1341 | |
1342 | It also creates C arrays to keep data for the stash (this is one HV, |
1343 | but it grows, thus there are 4 big allocations: the big chunks are not |
c2611fb3 |
1344 | freed, but are kept as additional arenas for C<SV> allocations). |
a77df738 |
1345 | |
1346 | =item C<054> |
1347 | |
1348 | creates a C<HEK> for the name of the glob for the subroutine (this |
1349 | name is a key in a I<stash>). |
1350 | |
1351 | Big allocations with this I<Id> correspond to allocations of new |
1352 | arenas to keep C<HE>. |
1353 | |
1354 | =item C<602> |
1355 | |
1356 | creates a C<GP> for the glob for the subroutine. |
1357 | |
1358 | =item C<702> |
1359 | |
1360 | creates the C<MAGIC> for the glob for the subroutine. |
1361 | |
1362 | =item C<704> |
1363 | |
1364 | creates I<arenas> which keep SVs. |
1365 | |
1366 | =back |
1367 | |
1368 | =head2 B<-DL> details |
1369 | |
1370 | If Perl is run with B<-DL> option, then warn()s which start with `!' |
1371 | behave specially. They print a list of I<categories> of memory |
1372 | allocations, and statistics of allocations of different sizes for |
1373 | these categories. |
1374 | |
1375 | If warn() string starts with |
1376 | |
1377 | =over |
1378 | |
1379 | =item C<!!!> |
1380 | |
1381 | print changed categories only, print the differences in counts of allocations; |
1382 | |
1383 | =item C<!!> |
1384 | |
1385 | print grown categories only; print the absolute values of counts, and totals; |
1386 | |
1387 | =item C<!> |
1388 | |
1389 | print nonempty categories, print the absolute values of counts and totals. |
1390 | |
1391 | =back |
1392 | |
1393 | =head2 Limitations of B<-DL> statistic |
1394 | |
1395 | If an extension or an external library does not use Perl API to |
1396 | allocate memory, these allocations are not counted. |
1397 | |
54dc92de |
1398 | =head1 Debugging regular expressions |
1399 | |
1400 | There are two ways to enable debugging output for regular expressions. |
1401 | |
1402 | If your perl is compiled with C<-DDEBUGGING>, you may use the |
1403 | B<-Dr> flag on the command line. |
1404 | |
1405 | Otherwise, one can C<use re 'debug'>, which has effects both at |
1406 | compile time, and at run time (and is I<not> lexically scoped). |
1407 | |
1408 | =head2 Compile-time output |
1409 | |
1410 | The debugging output for the compile time looks like this: |
1411 | |
1412 | compiling RE `[bc]d(ef*g)+h[ij]k$' |
1413 | size 43 first at 1 |
1414 | 1: ANYOF(11) |
1415 | 11: EXACT <d>(13) |
1416 | 13: CURLYX {1,32767}(27) |
1417 | 15: OPEN1(17) |
1418 | 17: EXACT <e>(19) |
1419 | 19: STAR(22) |
1420 | 20: EXACT <f>(0) |
1421 | 22: EXACT <g>(24) |
1422 | 24: CLOSE1(26) |
1423 | 26: WHILEM(0) |
1424 | 27: NOTHING(28) |
1425 | 28: EXACT <h>(30) |
1426 | 30: ANYOF(40) |
1427 | 40: EXACT <k>(42) |
1428 | 42: EOL(43) |
1429 | 43: END(0) |
1430 | anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating) |
1431 | stclass `ANYOF' minlen 7 |
1432 | |
1433 | The first line shows the pre-compiled form of the regexp, and the |
1434 | second shows the size of the compiled form (in arbitrary units, |
1435 | usually 4-byte words) and the label I<id> of the first node which |
1436 | does a match. |
1437 | |
1438 | The last line (split into two lines in the above) contains the optimizer |
1439 | info. In the example shown, the optimizer found that the match |
1440 | should contain a substring C<de> at the offset 1, and substring C<gh> |
1441 | at some offset between 3 and infinity. Moreover, when checking for |
1442 | these substrings (to abandon impossible matches quickly) it will check |
1443 | for the substring C<gh> before checking for the substring C<de>. The |
1444 | optimizer may also use the knowledge that the match starts (at the |
1445 | C<first> I<id>) with a character class, and the match cannot be |
1446 | shorter than 7 chars. |
1447 | |
1448 | The fields of interest which may appear in the last line are |
1449 | |
1450 | =over |
1451 | |
1452 | =item C<anchored> I<STRING> C<at> I<POS> |
1453 | |
1454 | =item C<floating> I<STRING> C<at> I<POS1..POS2> |
1455 | |
1456 | see above; |
1457 | |
1458 | =item C<matching floating/anchored> |
1459 | |
1460 | which substring to check first; |
1461 | |
1462 | =item C<minlen> |
1463 | |
1464 | the minimal length of the match; |
1465 | |
1466 | =item C<stclass> I<TYPE> |
1467 | |
1468 | The type of the first matching node. |
1469 | |
1470 | =item C<noscan> |
1471 | |
1472 | which advises to not scan for the found substrings; |
1473 | |
1474 | =item C<isall> |
1475 | |
1476 | which says that the optimizer info is in fact all that the regular |
1477 | expression contains (thus one does not need to enter the RE engine at |
1478 | all); |
1479 | |
1480 | =item C<GPOS> |
1481 | |
1482 | if the pattern contains C<\G>; |
1483 | |
1484 | =item C<plus> |
1485 | |
1486 | if the pattern starts with a repeated char (as in C<x+y>); |
1487 | |
1488 | =item C<implicit> |
1489 | |
1490 | if the pattern starts with C<.*>; |
1491 | |
1492 | =item C<with eval> |
1493 | |
1494 | if the pattern contain eval-groups (see L<perlre/(?{ code })>); |
1495 | |
1496 | =item C<anchored(TYPE)> |
1497 | |
1498 | if the pattern may |
1499 | match only at a handful of places (with C<TYPE> being |
1500 | C<BOL>, C<MBOL>, or C<GPOS>, see the table below). |
1501 | |
1502 | =back |
1503 | |
1504 | If a substring is known to match at end-of-line only, it may be |
1505 | followed by C<$>, as in C<floating `k'$>. |
1506 | |
1507 | The optimizer-specific info is used to avoid entering (a slow) RE |
1508 | engine on strings which will definitely not match. If C<isall> flag |
1509 | is set, a call to the RE engine may be avoided even when optimizer |
1510 | found an appropriate place for the match. |
1511 | |
1512 | The rest of the output contains the list of I<nodes> of the compiled |
1513 | form of the RE. Each line has format |
1514 | |
1515 | C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>) |
1516 | |
1517 | =head2 Types of nodes |
1518 | |
1519 | Here is the list of possible types with short descriptions: |
1520 | |
1521 | # TYPE arg-description [num-args] [longjump-len] DESCRIPTION |
1522 | |
1523 | # Exit points |
1524 | END no End of program. |
1525 | SUCCEED no Return from a subroutine, basically. |
1526 | |
1527 | # Anchors: |
1528 | BOL no Match "" at beginning of line. |
1529 | MBOL no Same, assuming multiline. |
1530 | SBOL no Same, assuming singleline. |
1531 | EOS no Match "" at end of string. |
1532 | EOL no Match "" at end of line. |
1533 | MEOL no Same, assuming multiline. |
1534 | SEOL no Same, assuming singleline. |
1535 | BOUND no Match "" at any word boundary |
1536 | BOUNDL no Match "" at any word boundary |
1537 | NBOUND no Match "" at any word non-boundary |
1538 | NBOUNDL no Match "" at any word non-boundary |
1539 | GPOS no Matches where last m//g left off. |
1540 | |
1541 | # [Special] alternatives |
1542 | ANY no Match any one character (except newline). |
1543 | SANY no Match any one character. |
1544 | ANYOF sv Match character in (or not in) this class. |
1545 | ALNUM no Match any alphanumeric character |
1546 | ALNUML no Match any alphanumeric char in locale |
1547 | NALNUM no Match any non-alphanumeric character |
1548 | NALNUML no Match any non-alphanumeric char in locale |
1549 | SPACE no Match any whitespace character |
1550 | SPACEL no Match any whitespace char in locale |
1551 | NSPACE no Match any non-whitespace character |
1552 | NSPACEL no Match any non-whitespace char in locale |
1553 | DIGIT no Match any numeric character |
1554 | NDIGIT no Match any non-numeric character |
1555 | |
1556 | # BRANCH The set of branches constituting a single choice are hooked |
1557 | # together with their "next" pointers, since precedence prevents |
1558 | # anything being concatenated to any individual branch. The |
1559 | # "next" pointer of the last BRANCH in a choice points to the |
1560 | # thing following the whole choice. This is also where the |
1561 | # final "next" pointer of each individual branch points; each |
1562 | # branch starts with the operand node of a BRANCH node. |
1563 | # |
1564 | BRANCH node Match this alternative, or the next... |
1565 | |
1566 | # BACK Normal "next" pointers all implicitly point forward; BACK |
1567 | # exists to make loop structures possible. |
1568 | # not used |
1569 | BACK no Match "", "next" ptr points backward. |
1570 | |
1571 | # Literals |
1572 | EXACT sv Match this string (preceded by length). |
1573 | EXACTF sv Match this string, folded (prec. by length). |
1574 | EXACTFL sv Match this string, folded in locale (w/len). |
1575 | |
1576 | # Do nothing |
1577 | NOTHING no Match empty string. |
1578 | # A variant of above which delimits a group, thus stops optimizations |
1579 | TAIL no Match empty string. Can jump here from outside. |
1580 | |
1581 | # STAR,PLUS '?', and complex '*' and '+', are implemented as circular |
1582 | # BRANCH structures using BACK. Simple cases (one character |
1583 | # per match) are implemented with STAR and PLUS for speed |
1584 | # and to minimize recursive plunges. |
1585 | # |
1586 | STAR node Match this (simple) thing 0 or more times. |
1587 | PLUS node Match this (simple) thing 1 or more times. |
1588 | |
1589 | CURLY sv 2 Match this simple thing {n,m} times. |
1590 | CURLYN no 2 Match next-after-this simple thing |
1591 | # {n,m} times, set parenths. |
1592 | CURLYM no 2 Match this medium-complex thing {n,m} times. |
1593 | CURLYX sv 2 Match this complex thing {n,m} times. |
1594 | |
1595 | # This terminator creates a loop structure for CURLYX |
1596 | WHILEM no Do curly processing and see if rest matches. |
1597 | |
1598 | # OPEN,CLOSE,GROUPP ...are numbered at compile time. |
1599 | OPEN num 1 Mark this point in input as start of #n. |
1600 | CLOSE num 1 Analogous to OPEN. |
1601 | |
1602 | REF num 1 Match some already matched string |
1603 | REFF num 1 Match already matched string, folded |
1604 | REFFL num 1 Match already matched string, folded in loc. |
1605 | |
1606 | # grouping assertions |
1607 | IFMATCH off 1 2 Succeeds if the following matches. |
1608 | UNLESSM off 1 2 Fails if the following matches. |
1609 | SUSPEND off 1 1 "Independent" sub-RE. |
1610 | IFTHEN off 1 1 Switch, should be preceeded by switcher . |
1611 | GROUPP num 1 Whether the group matched. |
1612 | |
1613 | # Support for long RE |
1614 | LONGJMP off 1 1 Jump far away. |
1615 | BRANCHJ off 1 1 BRANCH with long offset. |
1616 | |
1617 | # The heavy worker |
1618 | EVAL evl 1 Execute some Perl code. |
1619 | |
1620 | # Modifiers |
1621 | MINMOD no Next operator is not greedy. |
1622 | LOGICAL no Next opcode should set the flag only. |
1623 | |
1624 | # This is not used yet |
1625 | RENUM off 1 1 Group with independently numbered parens. |
1626 | |
1627 | # This is not really a node, but an optimized away piece of a "long" node. |
1628 | # To simplify debugging output, we mark it as if it were a node |
1629 | OPTIMIZED off Placeholder for dump. |
1630 | |
1631 | =head2 Run-time output |
1632 | |
1633 | First of all, when doing a match, one may get no run-time output even |
1634 | if debugging is enabled. this means that the RE engine was never |
1635 | entered, all of the job was done by the optimizer. |
1636 | |
1637 | If RE engine was entered, the output may look like this: |
1638 | |
1639 | Matching `[bc]d(ef*g)+h[ij]k$' against `abcdefg__gh__' |
1640 | Setting an EVAL scope, savestack=3 |
1641 | 2 <ab> <cdefg__gh_> | 1: ANYOF |
1642 | 3 <abc> <defg__gh_> | 11: EXACT <d> |
1643 | 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767} |
1644 | 4 <abcd> <efg__gh_> | 26: WHILEM |
1645 | 0 out of 1..32767 cc=effff31c |
1646 | 4 <abcd> <efg__gh_> | 15: OPEN1 |
1647 | 4 <abcd> <efg__gh_> | 17: EXACT <e> |
1648 | 5 <abcde> <fg__gh_> | 19: STAR |
1649 | EXACT <f> can match 1 times out of 32767... |
1650 | Setting an EVAL scope, savestack=3 |
1651 | 6 <bcdef> <g__gh__> | 22: EXACT <g> |
1652 | 7 <bcdefg> <__gh__> | 24: CLOSE1 |
1653 | 7 <bcdefg> <__gh__> | 26: WHILEM |
1654 | 1 out of 1..32767 cc=effff31c |
1655 | Setting an EVAL scope, savestack=12 |
1656 | 7 <bcdefg> <__gh__> | 15: OPEN1 |
1657 | 7 <bcdefg> <__gh__> | 17: EXACT <e> |
1658 | restoring \1 to 4(4)..7 |
1659 | failed, try continuation... |
1660 | 7 <bcdefg> <__gh__> | 27: NOTHING |
1661 | 7 <bcdefg> <__gh__> | 28: EXACT <h> |
1662 | failed... |
1663 | failed... |
1664 | |
1665 | The most significant information in the output is about the particular I<node> |
1666 | of the compiled RE which is currently being tested against the target string. |
1667 | The format of these lines is |
1668 | |
1669 | C< >I<STRING-OFFSET> <I<PRE-STRING>> <I<POST-STRING>> |I<ID>: I<TYPE> |
1670 | |
1671 | The I<TYPE> info is indented with respect to the backtracking level. |
1672 | Other incidental information appears interspersed within. |
1673 | |
a77df738 |
1674 | =cut |