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