mingw/html/pod/perldebug.html

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  13 <big><strong><span class="block">&nbsp;perldebug - Perl debugging</span></strong></big>
  14 </td></tr>
  15 </table>
  16
  17 <p><a name="__index__"></a></p>
  18 <!-- INDEX BEGIN -->
  19
  20 <ul>
  21
  22         <li><a href="#name">NAME</a></li>
  23         <li><a href="#description">DESCRIPTION</a></li>
  24         <li><a href="#the_perl_debugger">The Perl Debugger</a></li>
  25         <ul>
  26
  27                 <li><a href="#debugger_commands">Debugger Commands</a></li>
  28                 <li><a href="#configurable_options">Configurable Options</a></li>
  29                 <li><a href="#debugger_input_output">Debugger input/output</a></li>
  30                 <li><a href="#debugging_compiletime_statements">Debugging compile-time statements</a></li>
  31                 <li><a href="#debugger_customization">Debugger Customization</a></li>
  32                 <li><a href="#readline_support">Readline Support</a></li>
  33                 <li><a href="#editor_support_for_debugging">Editor Support for Debugging</a></li>
  34                 <li><a href="#the_perl_profiler">The Perl Profiler</a></li>
  35         </ul>
  36
  37         <li><a href="#debugging_regular_expressions">Debugging regular expressions</a></li>
  38         <li><a href="#debugging_memory_usage">Debugging memory usage</a></li>
  39         <li><a href="#see_also">SEE ALSO</a></li>
  40         <li><a href="#bugs">BUGS</a></li>
  41 </ul>
  42 <!-- INDEX END -->
  43
  44 <hr />
  45 <p>
  46 </p>
  47 <h1><a name="name_x_debug__x_debugger_">NAME
  48  </a></h1>
  49 <p>perldebug - Perl debugging</p>
  50 <p>
  51 </p>
  52 <hr />
  53 <h1><a name="description">DESCRIPTION</a></h1>
  54 <p>First of all, have you tried using the <strong>-w</strong> switch?</p>
  55 <p>If you're new to the Perl debugger, you may prefer to read
  56 <a href="file://C|\msysgit\mingw\html/pod/perldebtut.html">the perldebtut manpage</a>, which is a tutorial introduction to the debugger .</p>
  57 <p>
  58 </p>
  59 <hr />
  60 <h1><a name="the_perl_debugger">The Perl Debugger</a></h1>
  61 <p>If you invoke Perl with the <strong>-d</strong> switch, your script runs under the
  62 Perl source debugger.  This works like an interactive Perl
  63 environment, prompting for debugger commands that let you examine
  64 source code, set breakpoints, get stack backtraces, change the values of
  65 variables, etc.  This is so convenient that you often fire up
  66 the debugger all by itself just to test out Perl constructs
  67 interactively to see what they do.  For example:
  68 </p>
  69 <pre>
  70     $ perl -d -e 42</pre>
  71 <p>In Perl, the debugger is not a separate program the way it usually is in the
  72 typical compiled environment.  Instead, the <strong>-d</strong> flag tells the compiler
  73 to insert source information into the parse trees it's about to hand off
  74 to the interpreter.  That means your code must first compile correctly
  75 for the debugger to work on it.  Then when the interpreter starts up, it
  76 preloads a special Perl library file containing the debugger.</p>
  77 <p>The program will halt <em>right before</em> the first run-time executable
  78 statement (but see below regarding compile-time statements) and ask you
  79 to enter a debugger command.  Contrary to popular expectations, whenever
  80 the debugger halts and shows you a line of code, it always displays the
  81 line it's <em>about</em> to execute, rather than the one it has just executed.</p>
  82 <p>Any command not recognized by the debugger is directly executed
  83 (<a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>'d) as Perl code in the current package.  (The debugger
  84 uses the DB package for keeping its own state information.)</p>
  85 <p>Note that the said <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a> is bound by an implicit scope. As a
  86 result any newly introduced lexical variable or any modified
  87 capture buffer content is lost after the eval. The debugger is a
  88 nice environment to learn Perl, but if you interactively experiment using
  89 material which should be in the same scope, stuff it in one line.</p>
  90 <p>For any text entered at the debugger prompt, leading and trailing whitespace
  91 is first stripped before further processing.  If a debugger command
  92 coincides with some function in your own program, merely precede the
  93 function with something that doesn't look like a debugger command, such
  94 as a leading <code>;</code> or perhaps a <code>+</code>, or by wrapping it with parentheses
  95 or braces.</p>
  96 <p>
  97 </p>
  98 <h2><a name="debugger_commands">Debugger Commands</a></h2>
  99 <p>The debugger understands the following commands:</p>
 100 <dl>
 101 <dt><strong><a name="item_h_x_3cdebugger_command_2c_h_3e">h
 102 </a></strong>
 103
 104 <dd>
 105 <p>Prints out a summary help message</p>
 106 </dd>
 107 </li>
 108 <dt><strong><a name="item_h__5bcommand_5d">h [command]</a></strong>
 109
 110 <dd>
 111 <p>Prints out a help message for the given debugger command.</p>
 112 </dd>
 113 </li>
 114 <dt><strong><a name="item_h_h">h h</a></strong>
 115
 116 <dd>
 117 <p>The special argument of <a href="#item_h_h"><code>h h</code></a> produces the entire help page, which is quite long.</p>
 118 </dd>
 119 <dd>
 120 <p>If the output of the <a href="#item_h_h"><code>h h</code></a> command (or any command, for that matter) scrolls
 121 past your screen, precede the command with a leading pipe symbol so
 122 that it's run through your pager, as in</p>
 123 </dd>
 124 <dd>
 125 <pre>
 126     DB&gt; |h h</pre>
 127 </dd>
 128 <dd>
 129 <p>You may change the pager which is used via <code>o pager=...</code> command.</p>
 130 </dd>
 131 </li>
 132 <dt><strong><a name="item_p_expr_x_3cdebugger_command_2c_p_3e">p expr
 133 </a></strong>
 134
 135 <dd>
 136 <p>Same as <code>print {$DB::OUT} expr</code> in the current package.  In particular,
 137 because this is just Perl's own <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_print"><code>print</code></a> function, this means that nested
 138 data structures and objects are not dumped, unlike with the <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_x"><code>x</code></a> command.</p>
 139 </dd>
 140 <dd>
 141 <p>The <code>DB::OUT</code> filehandle is opened to <em>/dev/tty</em>, regardless of
 142 where STDOUT may be redirected to.</p>
 143 </dd>
 144 </li>
 145 <dt><strong><a name="item_x__5bmaxdepth_5d_expr_x_3cdebugger_command_2c_x_3e">x [maxdepth] expr
 146 </a></strong>
 147
 148 <dd>
 149 <p>Evaluates its expression in list context and dumps out the result in a
 150 pretty-printed fashion.  Nested data structures are printed out
 151 recursively, unlike the real <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_print"><code>print</code></a> function in Perl.  When dumping
 152 hashes, you'll probably prefer 'x \%h' rather than 'x %h'.
 153 See <a href="file://C|\msysgit\mingw\html/lib/Dumpvalue.html">the Dumpvalue manpage</a> if you'd like to do this yourself.</p>
 154 </dd>
 155 <dd>
 156 <p>The output format is governed by multiple options described under
 157 <a href="#configurable_options">Configurable Options</a>.</p>
 158 </dd>
 159 <dd>
 160 <p>If the <code>maxdepth</code> is included, it must be a numeral <em>N</em>; the value is
 161 dumped only <em>N</em> levels deep, as if the <code>dumpDepth</code> option had been
 162 temporarily set to <em>N</em>.</p>
 163 </dd>
 164 </li>
 165 <dt><strong><a name="item_v__5bpkg__5bvars_5d_5d_x_3cdebugger_command_2c_v_3">V [pkg [vars]]
 166 </a></strong>
 167
 168 <dd>
 169 <p>Display all (or some) variables in package (defaulting to <code>main</code>)
 170 using a data pretty-printer (hashes show their keys and values so
 171 you see what's what, control characters are made printable, etc.).
 172 Make sure you don't put the type specifier (like <code>$</code>) there, just
 173 the symbol names, like this:</p>
 174 </dd>
 175 <dd>
 176 <pre>
 177     V DB filename line</pre>
 178 </dd>
 179 <dd>
 180 <p>Use <code>~pattern</code> and <code>!pattern</code> for positive and negative regexes.</p>
 181 </dd>
 182 <dd>
 183 <p>This is similar to calling the <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_x"><code>x</code></a> command on each applicable var.</p>
 184 </dd>
 185 </li>
 186 <dt><strong><a name="item_x__5bvars_5d_x_3cdebugger_command_2c_x_3e">X [vars]
 187 </a></strong>
 188
 189 <dd>
 190 <p>Same as <code>V currentpackage [vars]</code>.</p>
 191 </dd>
 192 </li>
 193 <dt><strong><a name="item_y__5blevel__5bvars_5d_5d_x_3cdebugger_command_2c_y">y [level [vars]]
 194 </a></strong>
 195
 196 <dd>
 197 <p>Display all (or some) lexical variables (mnemonic: <code>mY</code> variables)
 198 in the current scope or <em>level</em> scopes higher.  You can limit the
 199 variables that you see with <em>vars</em> which works exactly as it does
 200 for the <code>V</code> and <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_x"><code>X</code></a> commands.  Requires the <code>PadWalker</code> module
 201 version 0.08 or higher; will warn if this isn't installed.  Output
 202 is pretty-printed in the same style as for <code>V</code> and the format is
 203 controlled by the same options.</p>
 204 </dd>
 205 </li>
 206 <dt><strong><a name="item_t_x_3cdebugger_command_2c_t_3e_x_3cbacktrace_3e_x_">T
 207   </a></strong>
 208
 209 <dd>
 210 <p>Produce a stack backtrace.  See below for details on its output.</p>
 211 </dd>
 212 </li>
 213 <dt><strong><a name="item_s__5bexpr_5d_x_3cdebugger_command_2c_s_3e_x_3cstep">s [expr]
 214  </a></strong>
 215
 216 <dd>
 217 <p>Single step.  Executes until the beginning of another
 218 statement, descending into subroutine calls.  If an expression is
 219 supplied that includes function calls, it too will be single-stepped.</p>
 220 </dd>
 221 </li>
 222 <dt><strong><a name="item_n__5bexpr_5d_x_3cdebugger_command_2c_n_3e">n [expr]
 223 </a></strong>
 224
 225 <dd>
 226 <p>Next.  Executes over subroutine calls, until the beginning
 227 of the next statement.  If an expression is supplied that includes
 228 function calls, those functions will be executed with stops before
 229 each statement.</p>
 230 </dd>
 231 </li>
 232 <dt><strong><a name="item_r_x_3cdebugger_command_2c_r_3e">r
 233 </a></strong>
 234
 235 <dd>
 236 <p>Continue until the return from the current subroutine.
 237 Dump the return value if the <code>PrintRet</code> option is set (default).</p>
 238 </dd>
 239 </li>
 240 <dt><strong><a name="item__3ccr_3e">&lt;CR&gt;</a></strong>
 241
 242 <dd>
 243 <p>Repeat last <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_n"><code>n</code></a> or <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_s"><code>s</code></a> command.</p>
 244 </dd>
 245 </li>
 246 <dt><strong><a name="item_c__5bline_7csub_5d_x_3cdebugger_command_2c_c_3e">c [line|sub]
 247 </a></strong>
 248
 249 <dd>
 250 <p>Continue, optionally inserting a one-time-only breakpoint
 251 at the specified line or subroutine.</p>
 252 </dd>
 253 </li>
 254 <dt><strong><a name="item_l_x_3cdebugger_command_2c_l_3e">l
 255 </a></strong>
 256
 257 <dd>
 258 <p>List next window of lines.</p>
 259 </dd>
 260 </li>
 261 <dt><strong><a name="item_l_min_2bincr">l min+incr</a></strong>
 262
 263 <dd>
 264 <p>List <code>incr+1</code> lines starting at <code>min</code>.</p>
 265 </dd>
 266 </li>
 267 <dt><strong><a name="item_l_min_2dmax">l min-max</a></strong>
 268
 269 <dd>
 270 <p>List lines <code>min</code> through <code>max</code>.  <code>l -</code> is synonymous to <code>-</code>.</p>
 271 </dd>
 272 </li>
 273 <dt><strong><a name="item_l_line">l line</a></strong>
 274
 275 <dd>
 276 <p>List a single line.</p>
 277 </dd>
 278 </li>
 279 <dt><strong><a name="item_l_subname">l subname</a></strong>
 280
 281 <dd>
 282 <p>List first window of lines from subroutine.  <em>subname</em> may
 283 be a variable that contains a code reference.</p>
 284 </dd>
 285 </li>
 286 <dt><strong><a name="item__2d_x_3cdebugger_command_2c__2d_3e">-
 287 </a></strong>
 288
 289 <dd>
 290 <p>List previous window of lines.</p>
 291 </dd>
 292 </li>
 293 <dt><strong><a name="item_v__5bline_5d_x_3cdebugger_command_2c_v_3e">v [line]
 294 </a></strong>
 295
 296 <dd>
 297 <p>View a few lines of code around the current line.</p>
 298 </dd>
 299 </li>
 300 <dt><strong><a name="item__2e_x_3cdebugger_command_2c__2e_3e">.
 301 </a></strong>
 302
 303 <dd>
 304 <p>Return the internal debugger pointer to the line last
 305 executed, and print out that line.</p>
 306 </dd>
 307 </li>
 308 <dt><strong><a name="item_f_filename_x_3cdebugger_command_2c_f_3e">f filename
 309 </a></strong>
 310
 311 <dd>
 312 <p>Switch to viewing a different file or <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a> statement.  If <em>filename</em>
 313 is not a full pathname found in the values of %INC, it is considered
 314 a regex.</p>
 315 </dd>
 316 <dd>
 317 <p><a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed strings (when accessible) are considered to be filenames:
 318 <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_f"><code>f (eval 7)</code></a> and <code>f eval 7\b</code> access the body of the 7th <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed string
 319 (in the order of execution).  The bodies of the currently executed <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>
 320 and of <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed strings that define subroutines are saved and thus
 321 accessible.</p>
 322 </dd>
 323 </li>
 324 <dt><strong><a name="item__2fpattern_2f">/pattern/</a></strong>
 325
 326 <dd>
 327 <p>Search forwards for pattern (a Perl regex); final / is optional.
 328 The search is case-insensitive by default.</p>
 329 </dd>
 330 </li>
 331 <dt><strong><a name="item__3fpattern_3f">?pattern?</a></strong>
 332
 333 <dd>
 334 <p>Search backwards for pattern; final ? is optional.
 335 The search is case-insensitive by default.</p>
 336 </dd>
 337 </li>
 338 <dt><strong><a name="item_l__5babw_5d_x_3cdebugger_command_2c_l_3e">L [abw]
 339 </a></strong>
 340
 341 <dd>
 342 <p>List (default all) actions, breakpoints and watch expressions</p>
 343 </dd>
 344 </li>
 345 <dt><strong><a name="item_s__5b_5b_21_5dregex_5d_x_3cdebugger_command_2c_s_3">S [[!]regex]
 346 </a></strong>
 347
 348 <dd>
 349 <p>List subroutine names [not] matching the regex.</p>
 350 </dd>
 351 </li>
 352 <dt><strong><a name="item_t_x_3cdebugger_command_2c_t_3e">t
 353 </a></strong>
 354
 355 <dd>
 356 <p>Toggle trace mode (see also the <code>AutoTrace</code> option).</p>
 357 </dd>
 358 </li>
 359 <dt><strong><a name="item_t_expr_x_3cdebugger_command_2c_t_3e">t expr
 360 </a></strong>
 361
 362 <dd>
 363 <p>Trace through execution of <code>expr</code>.
 364 See <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html#frame_listing_output_examples">Frame Listing Output Examples in the perldebguts manpage</a> for examples.</p>
 365 </dd>
 366 </li>
 367 <dt><strong><a name="item_b_x_3cbreakpoint_3e_x_3cdebugger_command_2c_b_3e">b
 368
 369 </a></strong>
 370
 371 <dd>
 372 <p>Sets breakpoint on current line</p>
 373 </dd>
 374 </li>
 375 <dt><strong><a name="item_b__5bline_5d__5bcondition_5d_x_3cbreakpoint_3e_x_3">b [line] [condition]
 376
 377 </a></strong>
 378
 379 <dd>
 380 <p>Set a breakpoint before the given line.  If a condition
 381 is specified, it's evaluated each time the statement is reached: a
 382 breakpoint is taken only if the condition is true.  Breakpoints may
 383 only be set on lines that begin an executable statement.  Conditions
 384 don't use <code>if</code>:</p>
 385 </dd>
 386 <dd>
 387 <pre>
 388     b 237 $x &gt; 30
 389     b 237 ++$count237 &lt; 11
 390     b 33 /pattern/i</pre>
 391 </dd>
 392 </li>
 393 <dt><strong><a name="item_b_subname__5bcondition_5d_x_3cbreakpoint_3e_x_3cde">b subname [condition]
 394
 395 </a></strong>
 396
 397 <dd>
 398 <p>Set a breakpoint before the first line of the named subroutine.  <em>subname</em> may
 399 be a variable containing a code reference (in this case <em>condition</em>
 400 is not supported).</p>
 401 </dd>
 402 </li>
 403 <dt><strong><a name="item_b_postpone_subname__5bcondition_5d_x_3cbreakpoint_">b postpone subname [condition]
 404
 405 </a></strong>
 406
 407 <dd>
 408 <p>Set a breakpoint at first line of subroutine after it is compiled.</p>
 409 </dd>
 410 </li>
 411 <dt><strong><a name="item_b_load_filename_x_3cbreakpoint_3e_x_3cdebugger_com">b load filename
 412
 413 </a></strong>
 414
 415 <dd>
 416 <p>Set a breakpoint before the first executed line of the <em>filename</em>,
 417 which should be a full pathname found amongst the %INC values.</p>
 418 </dd>
 419 </li>
 420 <dt><strong><a name="item_b_compile_subname_x_3cbreakpoint_3e_x_3cdebugger_c">b compile subname
 421
 422 </a></strong>
 423
 424 <dd>
 425 <p>Sets a breakpoint before the first statement executed after the specified
 426 subroutine is compiled.</p>
 427 </dd>
 428 </li>
 429 <dt><strong><a name="item_b_line_x_3cbreakpoint_3e_x_3cdebugger_command_2c_b">B line
 430
 431 </a></strong>
 432
 433 <dd>
 434 <p>Delete a breakpoint from the specified <em>line</em>.</p>
 435 </dd>
 436 </li>
 437 <dt><strong><a name="item_b__2a_x_3cbreakpoint_3e_x_3cdebugger_command_2c_b_">B *
 438
 439 </a></strong>
 440
 441 <dd>
 442 <p>Delete all installed breakpoints.</p>
 443 </dd>
 444 </li>
 445 <dt><strong><a name="item_a__5bline_5d_command_x_3cdebugger_command_2c_a_3e">a [line] command
 446 </a></strong>
 447
 448 <dd>
 449 <p>Set an action to be done before the line is executed.  If <em>line</em> is
 450 omitted, set an action on the line about to be executed.
 451 The sequence of steps taken by the debugger is</p>
 452 </dd>
 453 <dd>
 454 <pre>
 455   1. check for a breakpoint at this line
 456   2. print the line if necessary (tracing)
 457   3. do any actions associated with that line
 458   4. prompt user if at a breakpoint or in single-step
 459   5. evaluate line</pre>
 460 </dd>
 461 <dd>
 462 <p>For example, this will print out $foo every time line
 463 53 is passed:</p>
 464 </dd>
 465 <dd>
 466 <pre>
 467     a 53 print &quot;DB FOUND $foo\n&quot;</pre>
 468 </dd>
 469 </li>
 470 <dt><strong><a name="item_a_line_x_3cdebugger_command_2c_a_3e">A line
 471 </a></strong>
 472
 473 <dd>
 474 <p>Delete an action from the specified line.</p>
 475 </dd>
 476 </li>
 477 <dt><strong><a name="item_a__2a_x_3cdebugger_command_2c_a_3e">A *
 478 </a></strong>
 479
 480 <dd>
 481 <p>Delete all installed actions.</p>
 482 </dd>
 483 </li>
 484 <dt><strong><a name="item_w_expr_x_3cdebugger_command_2c_w_3e">w expr
 485 </a></strong>
 486
 487 <dd>
 488 <p>Add a global watch-expression.  We hope you know what one of these
 489 is, because they're supposed to be obvious.</p>
 490 </dd>
 491 </li>
 492 <dt><strong><a name="item_w_expr_x_3cdebugger_command_2c_w_3e">W expr
 493 </a></strong>
 494
 495 <dd>
 496 <p>Delete watch-expression</p>
 497 </dd>
 498 </li>
 499 <dt><strong><a name="item_w__2a_x_3cdebugger_command_2c_w_3e">W *
 500 </a></strong>
 501
 502 <dd>
 503 <p>Delete all watch-expressions.</p>
 504 </dd>
 505 </li>
 506 <dt><strong><a name="item_o_x_3cdebugger_command_2c_o_3e">o
 507 </a></strong>
 508
 509 <dd>
 510 <p>Display all options</p>
 511 </dd>
 512 </li>
 513 <dt><strong><a name="item_o_booloption__2e_2e_2e_x_3cdebugger_command_2c_o_3">o booloption ...
 514 </a></strong>
 515
 516 <dd>
 517 <p>Set each listed Boolean option to the value <code>1</code>.</p>
 518 </dd>
 519 </li>
 520 <dt><strong><a name="item_o_anyoption_3f__2e_2e_2e_x_3cdebugger_command_2c_o">o anyoption? ...
 521 </a></strong>
 522
 523 <dd>
 524 <p>Print out the value of one or more options.</p>
 525 </dd>
 526 </li>
 527 <dt><strong><a name="item_o_option_3dvalue__2e_2e_2e_x_3cdebugger_command_2c">o option=value ...
 528 </a></strong>
 529
 530 <dd>
 531 <p>Set the value of one or more options.  If the value has internal
 532 whitespace, it should be quoted.  For example, you could set <code>o
 533 pager=&quot;less -MQeicsNfr&quot;</code> to call <strong>less</strong> with those specific options.
 534 You may use either single or double quotes, but if you do, you must
 535 escape any embedded instances of same sort of quote you began with,
 536 as well as any escaping any escapes that immediately precede that
 537 quote but which are not meant to escape the quote itself.  In other
 538 words, you follow single-quoting rules irrespective of the quote;
 539 eg: <code>o option='this isn\'t bad'</code> or <code>o option=&quot;She said, \&quot;Isn't
 540 it?\&quot;&quot;</code>.</p>
 541 </dd>
 542 <dd>
 543 <p>For historical reasons, the <code>=value</code> is optional, but defaults to
 544 1 only where it is safe to do so--that is, mostly for Boolean
 545 options.  It is always better to assign a specific value using <code>=</code>.
 546 The <code>option</code> can be abbreviated, but for clarity probably should
 547 not be.  Several options can be set together.  See <a href="#configurable_options">Configurable Options</a>
 548 for a list of these.</p>
 549 </dd>
 550 </li>
 551 <dt><strong><a name="item__3c__3f_x_3c_3c_debugger_command_2c__3c__3e_3e">&lt; ?
 552 &gt;</a></strong>
 553
 554 <dd>
 555 <p>List out all pre-prompt Perl command actions.</p>
 556 </dd>
 557 </li>
 558 <dt><strong><a name="item__3c__5b_command__5d_x_3c_3c_debugger_command_2c__3">&lt; [ command ]
 559 &gt;</a></strong>
 560
 561 <dd>
 562 <p>Set an action (Perl command) to happen before every debugger prompt.
 563 A multi-line command may be entered by backslashing the newlines.</p>
 564 </dd>
 565 </li>
 566 <dt><strong><a name="item__3c__2a_x_3c_3c_debugger_command_2c__3c__3e_3e">&lt; *
 567 &gt;</a></strong>
 568
 569 <dd>
 570 <p>Delete all pre-prompt Perl command actions.</p>
 571 </dd>
 572 </li>
 573 <dt><strong><a name="item__3c_3c_command_x_3c_3c_debugger_command_2c__3c_3c_">&lt;&lt; command
 574 &gt;</a></strong>
 575
 576 <dd>
 577 <p>Add an action (Perl command) to happen before every debugger prompt.
 578 A multi-line command may be entered by backwhacking the newlines.</p>
 579 </dd>
 580 </li>
 581 <dt><strong><a name="item__3e__3f_x_3c_3c_debugger_command_2c__3e__3e_3e">&gt; ?
 582  &gt;&gt;</a></strong>
 583
 584 <dd>
 585 <p>List out post-prompt Perl command actions.</p>
 586 </dd>
 587 </li>
 588 <dt><strong><a name="item__3e_command_x_3c_3c_debugger_command_2c__3e__3e_3e">&gt; command
 589  &gt;&gt;</a></strong>
 590
 591 <dd>
 592 <p>Set an action (Perl command) to happen after the prompt when you've
 593 just given a command to return to executing the script.  A multi-line
 594 command may be entered by backslashing the newlines (we bet you
 595 couldn't've guessed this by now).</p>
 596 </dd>
 597 </li>
 598 <dt><strong><a name="item__3e__2a_x_3c_3c_debugger_command_2c__3e__3e_3e">&gt; *
 599  &gt;&gt;</a></strong>
 600
 601 <dd>
 602 <p>Delete all post-prompt Perl command actions.</p>
 603 </dd>
 604 </li>
 605 <dt><strong><a name="item__3e_3e_command_x_3c_3c_3c_debugger_command_2c__3e_">&gt;&gt; command
 606 &gt; &gt;&gt;&gt;</a></strong>
 607
 608 <dd>
 609 <p>Adds an action (Perl command) to happen after the prompt when you've
 610 just given a command to return to executing the script.  A multi-line
 611 command may be entered by backslashing the newlines.</p>
 612 </dd>
 613 </li>
 614 <dt><strong><a name="item__7b__3f_x_3cdebugger_command_2c__7b_3e">{ ?
 615 </a></strong>
 616
 617 <dd>
 618 <p>List out pre-prompt debugger commands.</p>
 619 </dd>
 620 </li>
 621 <dt><strong><a name="item__7b__5b_command__5d">{ [ command ]</a></strong>
 622
 623 <dd>
 624 <p>Set an action (debugger command) to happen before every debugger prompt.
 625 A multi-line command may be entered in the customary fashion.</p>
 626 </dd>
 627 <dd>
 628 <p>Because this command is in some senses new, a warning is issued if
 629 you appear to have accidentally entered a block instead.  If that's
 630 what you mean to do, write it as with <code>;{ ... }</code> or even
 631 <code>do { ... }</code>.</p>
 632 </dd>
 633 </li>
 634 <dt><strong><a name="item__7b__2a_x_3cdebugger_command_2c__7b_3e">{ *
 635 </a></strong>
 636
 637 <dd>
 638 <p>Delete all pre-prompt debugger commands.</p>
 639 </dd>
 640 </li>
 641 <dt><strong><a name="item__7b_7b_command_x_3cdebugger_command_2c__7b_7b_3e">{{ command
 642 </a></strong>
 643
 644 <dd>
 645 <p>Add an action (debugger command) to happen before every debugger prompt.
 646 A multi-line command may be entered, if you can guess how: see above.</p>
 647 </dd>
 648 </li>
 649 <dt><strong><a name="item__21_number_x_3cdebugger_command_2c__21_3e">! number
 650 </a></strong>
 651
 652 <dd>
 653 <p>Redo a previous command (defaults to the previous command).</p>
 654 </dd>
 655 </li>
 656 <dt><strong><a name="item__21__2dnumber_x_3cdebugger_command_2c__21_3e">! -number
 657 </a></strong>
 658
 659 <dd>
 660 <p>Redo number'th previous command.</p>
 661 </dd>
 662 </li>
 663 <dt><strong><a name="item__21_pattern_x_3cdebugger_command_2c__21_3e">! pattern
 664 </a></strong>
 665
 666 <dd>
 667 <p>Redo last command that started with pattern.
 668 See <code>o recallCommand</code>, too.</p>
 669 </dd>
 670 </li>
 671 <dt><strong><a name="item__21_21_cmd_x_3cdebugger_command_2c__21_21_3e">!! cmd
 672 </a></strong>
 673
 674 <dd>
 675 <p>Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See
 676 <code>o shellBang</code>, also.  Note that the user's current shell (well,
 677 their <code>$ENV{SHELL}</code> variable) will be used, which can interfere
 678 with proper interpretation of exit status or signal and coredump
 679 information.</p>
 680 </dd>
 681 </li>
 682 <dt><strong><a name="item_source_file_x_3cdebugger_command_2c_source_3e">source file
 683 </a></strong>
 684
 685 <dd>
 686 <p>Read and execute debugger commands from <em>file</em>.
 687 <em>file</em> may itself contain <code>source</code> commands.</p>
 688 </dd>
 689 </li>
 690 <dt><strong><a name="item_h__2dnumber_x_3cdebugger_command_2c_h_3e">H -number
 691 </a></strong>
 692
 693 <dd>
 694 <p>Display last n commands.  Only commands longer than one character are
 695 listed.  If <em>number</em> is omitted, list them all.</p>
 696 </dd>
 697 </li>
 698 <dt><strong><a name="item_q_or__5ed_x_3cdebugger_command_2c_q_3e_x_3cdebugge">q or ^D
 699
 700 </a></strong>
 701
 702 <dd>
 703 <p>Quit.  (``quit'' doesn't work for this, unless you've made an alias)
 704 This is the only supported way to exit the debugger, though typing
 705 <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_exit"><code>exit</code></a> twice might work.</p>
 706 </dd>
 707 <dd>
 708 <p>Set the <code>inhibit_exit</code> option to 0 if you want to be able to step
 709 off the end the script.  You may also need to set $finished to 0
 710 if you want to step through global destruction.</p>
 711 </dd>
 712 </li>
 713 <dt><strong><a name="item_r_x_3cdebugger_command_2c_r_3e">R
 714 </a></strong>
 715
 716 <dd>
 717 <p>Restart the debugger by <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_exec"><code>exec()</code></a>ing a new session.  We try to maintain
 718 your history across this, but internal settings and command-line options
 719 may be lost.</p>
 720 </dd>
 721 <dd>
 722 <p>The following setting are currently preserved: history, breakpoints,
 723 actions, debugger options, and the Perl command-line
 724 options <strong>-w</strong>, <strong>-I</strong>, and <strong>-e</strong>.</p>
 725 </dd>
 726 </li>
 727 <dt><strong><a name="item__7cdbcmd_x_3cdebugger_command_2c__7c_3e">|dbcmd
 728 </a></strong>
 729
 730 <dd>
 731 <p>Run the debugger command, piping DB::OUT into your current pager.</p>
 732 </dd>
 733 </li>
 734 <dt><strong><a name="item__7c_7cdbcmd_x_3cdebugger_command_2c__7c_7c_3e">||dbcmd
 735 </a></strong>
 736
 737 <dd>
 738 <p>Same as <code>|dbcmd</code> but DB::OUT is temporarily <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_select"><code>select</code></a>ed as well.</p>
 739 </dd>
 740 </li>
 741 <dt><strong><a name="item__3d__5balias_value_5d_x_3cdebugger_command_2c__3d_">= [alias value]
 742 </a></strong>
 743
 744 <dd>
 745 <p>Define a command alias, like</p>
 746 </dd>
 747 <dd>
 748 <pre>
 749     = quit q</pre>
 750 </dd>
 751 <dd>
 752 <p>or list current aliases.</p>
 753 </dd>
 754 </li>
 755 <dt><strong><a name="item_command">command</a></strong>
 756
 757 <dd>
 758 <p>Execute command as a Perl statement.  A trailing semicolon will be
 759 supplied.  If the Perl statement would otherwise be confused for a
 760 Perl debugger, use a leading semicolon, too.</p>
 761 </dd>
 762 </li>
 763 <dt><strong><a name="item_m_expr_x_3cdebugger_command_2c_m_3e">m expr
 764 </a></strong>
 765
 766 <dd>
 767 <p>List which methods may be called on the result of the evaluated
 768 expression.  The expression may evaluated to a reference to a
 769 blessed object, or to a package name.</p>
 770 </dd>
 771 </li>
 772 <dt><strong><a name="item_m_x_3cdebugger_command_2c_m_3e">M
 773 </a></strong>
 774
 775 <dd>
 776 <p>Displays all loaded modules and their versions</p>
 777 </dd>
 778 </li>
 779 <dt><strong><a name="item_man__5bmanpage_5d_x_3cdebugger_command_2c_man_3e">man [manpage]
 780 </a></strong>
 781
 782 <dd>
 783 <p>Despite its name, this calls your system's default documentation
 784 viewer on the given page, or on the viewer itself if <em>manpage</em> is
 785 omitted.  If that viewer is <strong>man</strong>, the current <code>Config</code> information
 786 is used to invoke <strong>man</strong> using the proper MANPATH or <strong>-M</strong>
 787 <em>manpath</em> option.  Failed lookups of the form <code>XXX</code> that match
 788 known manpages of the form <em>perlXXX</em> will be retried.  This lets
 789 you type <code>man debug</code> or <code>man op</code> from the debugger.</p>
 790 </dd>
 791 <dd>
 792 <p>On systems traditionally bereft of a usable <strong>man</strong> command, the
 793 debugger invokes <strong>perldoc</strong>.  Occasionally this determination is
 794 incorrect due to recalcitrant vendors or rather more felicitously,
 795 to enterprising users.  If you fall into either category, just
 796 manually set the $DB::doccmd variable to whatever viewer to view
 797 the Perl documentation on your system.  This may be set in an rc
 798 file, or through direct assignment.  We're still waiting for a
 799 working example of something along the lines of:</p>
 800 </dd>
 801 <dd>
 802 <pre>
 803     $DB::doccmd = 'netscape -remote <a href="http://something.here/">http://something.here/</a>';</pre>
 804 </dd>
 805 </li>
 806 </dl>
 807 <p>
 808 </p>
 809 <h2><a name="configurable_options">Configurable Options</a></h2>
 810 <p>The debugger has numerous options settable using the <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_o"><code>o</code></a> command,
 811 either interactively or from the environment or an rc file.
 812 (./.perldb or ~/.perldb under Unix.)</p>
 813 <dl>
 814 <dt><strong><a name="item_recallcommand_2c_shellbang_x_3cdebugger_option_2c_"><code>recallCommand</code>, <code>ShellBang</code>
 815
 816 </a></strong>
 817
 818 <dd>
 819 <p>The characters used to recall command or spawn shell.  By
 820 default, both are set to <code>!</code>, which is unfortunate.</p>
 821 </dd>
 822 </li>
 823 <dt><strong><a name="item_pager_x_3cdebugger_option_2c_pager_3e"><code>pager</code>
 824 </a></strong>
 825
 826 <dd>
 827 <p>Program to use for output of pager-piped commands (those beginning
 828 with a <code>|</code> character.)  By default, <code>$ENV{PAGER}</code> will be used.
 829 Because the debugger uses your current terminal characteristics
 830 for bold and underlining, if the chosen pager does not pass escape
 831 sequences through unchanged, the output of some debugger commands
 832 will not be readable when sent through the pager.</p>
 833 </dd>
 834 </li>
 835 <dt><strong><a name="item_tkrunning_x_3cdebugger_option_2c_tkrunning_3e"><code>tkRunning</code>
 836 </a></strong>
 837
 838 <dd>
 839 <p>Run Tk while prompting (with ReadLine).</p>
 840 </dd>
 841 </li>
 842 <dt><strong><a name="item_signallevel_2c_warnlevel_2c_dielevel_x_3cdebugger_"><code>signalLevel</code>, <code>warnLevel</code>, <code>dieLevel</code>
 843
 844 </a></strong>
 845
 846 <dd>
 847 <p>Level of verbosity.  By default, the debugger leaves your exceptions
 848 and warnings alone, because altering them can break correctly running
 849 programs.  It will attempt to print a message when uncaught INT, BUS, or
 850 SEGV signals arrive.  (But see the mention of signals in <em>BUGS</em> below.)</p>
 851 </dd>
 852 <dd>
 853 <p>To disable this default safe mode, set these values to something higher
 854 than 0.  At a level of 1, you get backtraces upon receiving any kind
 855 of warning (this is often annoying) or exception (this is
 856 often valuable).  Unfortunately, the debugger cannot discern fatal
 857 exceptions from non-fatal ones.  If <code>dieLevel</code> is even 1, then your
 858 non-fatal exceptions are also traced and unceremoniously altered if they
 859 came from <code>eval'd</code> strings or from any kind of <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a> within modules
 860 you're attempting to load.  If <code>dieLevel</code> is 2, the debugger doesn't
 861 care where they came from:  It usurps your exception handler and prints
 862 out a trace, then modifies all exceptions with its own embellishments.
 863 This may perhaps be useful for some tracing purposes, but tends to hopelessly
 864 destroy any program that takes its exception handling seriously.</p>
 865 </dd>
 866 </li>
 867 <dt><strong><a name="item_autotrace_x_3cdebugger_option_2c_autotrace_3e"><code>AutoTrace</code>
 868 </a></strong>
 869
 870 <dd>
 871 <p>Trace mode (similar to <code>t</code> command, but can be put into
 872 <code>PERLDB_OPTS</code>).</p>
 873 </dd>
 874 </li>
 875 <dt><strong><a name="item_lineinfo_x_3cdebugger_option_2c_lineinfo_3e"><code>LineInfo</code>
 876 </a></strong>
 877
 878 <dd>
 879 <p>File or pipe to print line number info to.  If it is a pipe (say,
 880 <code>|visual_perl_db</code>), then a short message is used.  This is the
 881 mechanism used to interact with a slave editor or visual debugger,
 882 such as the special <code>vi</code> or <code>emacs</code> hooks, or the <code>ddd</code> graphical
 883 debugger.</p>
 884 </dd>
 885 </li>
 886 <dt><strong><a name="item_inhibit_exit_x_3cdebugger_option_2c_inhibit_exit_3"><code>inhibit_exit</code>
 887 </a></strong>
 888
 889 <dd>
 890 <p>If 0, allows <em>stepping off</em> the end of the script.</p>
 891 </dd>
 892 </li>
 893 <dt><strong><a name="item_printret_x_3cdebugger_option_2c_printret_3e"><code>PrintRet</code>
 894 </a></strong>
 895
 896 <dd>
 897 <p>Print return value after <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_r"><code>r</code></a> command if set (default).</p>
 898 </dd>
 899 </li>
 900 <dt><strong><a name="item_ornaments_x_3cdebugger_option_2c_ornaments_3e"><code>ornaments</code>
 901 </a></strong>
 902
 903 <dd>
 904 <p>Affects screen appearance of the command line (see <a href="file://C|\msysgit\mingw\html/lib/Term/ReadLine.html">the Term::ReadLine manpage</a>).
 905 There is currently no way to disable these, which can render
 906 some output illegible on some displays, or with some pagers.
 907 This is considered a bug.</p>
 908 </dd>
 909 </li>
 910 <dt><strong><a name="item_frame_x_3cdebugger_option_2c_frame_3e"><code>frame</code>
 911 </a></strong>
 912
 913 <dd>
 914 <p>Affects the printing of messages upon entry and exit from subroutines.  If
 915 <code>frame &amp; 2</code> is false, messages are printed on entry only. (Printing
 916 on exit might be useful if interspersed with other messages.)</p>
 917 </dd>
 918 <dd>
 919 <p>If <code>frame &amp; 4</code>, arguments to functions are printed, plus context
 920 and caller info.  If <code>frame &amp; 8</code>, overloaded <code>stringify</code> and
 921 <code>tie</code>d <code>FETCH</code> is enabled on the printed arguments.  If <code>frame
 922 &amp; 16</code>, the return value from the subroutine is printed.</p>
 923 </dd>
 924 <dd>
 925 <p>The length at which the argument list is truncated is governed by the
 926 next option:</p>
 927 </dd>
 928 </li>
 929 <dt><strong><a name="item_maxtracelen_x_3cdebugger_option_2c_maxtracelen_3e"><code>maxTraceLen</code>
 930 </a></strong>
 931
 932 <dd>
 933 <p>Length to truncate the argument list when the <code>frame</code> option's
 934 bit 4 is set.</p>
 935 </dd>
 936 </li>
 937 <dt><strong><a name="item_windowsize_x_3cdebugger_option_2c_windowsize_3e"><code>windowSize</code>
 938 </a></strong>
 939
 940 <dd>
 941 <p>Change the size of code list window (default is 10 lines).</p>
 942 </dd>
 943 </li>
 944 </dl>
 945 <p>The following options affect what happens with <code>V</code>, <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_x"><code>X</code></a>, and <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_x"><code>x</code></a>
 946 commands:</p>
 947 <dl>
 948 <dt><strong><a name="item_arraydepth_2c_hashdepth_x_3cdebugger_option_2c_arr"><code>arrayDepth</code>, <code>hashDepth</code>
 949  </a></strong>
 950
 951 <dd>
 952 <p>Print only first N elements ('' for all).</p>
 953 </dd>
 954 </li>
 955 <dt><strong><a name="item_dumpdepth_x_3cdebugger_option_2c_dumpdepth_3e"><code>dumpDepth</code>
 956 </a></strong>
 957
 958 <dd>
 959 <p>Limit recursion depth to N levels when dumping structures.
 960 Negative values are interpreted as infinity.  Default: infinity.</p>
 961 </dd>
 962 </li>
 963 <dt><strong><a name="item_compactdump_2c_verycompact_x_3cdebugger_option_2c_"><code>compactDump</code>, <code>veryCompact</code>
 964  </a></strong>
 965
 966 <dd>
 967 <p>Change the style of array and hash output.  If <code>compactDump</code>, short array
 968 may be printed on one line.</p>
 969 </dd>
 970 </li>
 971 <dt><strong><a name="item_globprint_x_3cdebugger_option_2c_globprint_3e"><code>globPrint</code>
 972 </a></strong>
 973
 974 <dd>
 975 <p>Whether to print contents of globs.</p>
 976 </dd>
 977 </li>
 978 <dt><strong><a name="item_dumpdbfiles_x_3cdebugger_option_2c_dumpdbfiles_3e"><code>DumpDBFiles</code>
 979 </a></strong>
 980
 981 <dd>
 982 <p>Dump arrays holding debugged files.</p>
 983 </dd>
 984 </li>
 985 <dt><strong><a name="item_dumppackages_x_3cdebugger_option_2c_dumppackages_3"><code>DumpPackages</code>
 986 </a></strong>
 987
 988 <dd>
 989 <p>Dump symbol tables of packages.</p>
 990 </dd>
 991 </li>
 992 <dt><strong><a name="item_dumpreused_x_3cdebugger_option_2c_dumpreused_3e"><code>DumpReused</code>
 993 </a></strong>
 994
 995 <dd>
 996 <p>Dump contents of ``reused'' addresses.</p>
 997 </dd>
 998 </li>
 999 <dt><strong><a name="item_quote_2c_highbit_2c_undefprint_x_3cdebugger_option"><code>quote</code>, <code>HighBit</code>, <code>undefPrint</code>
1000
1001 </a></strong>
1002
1003 <dd>
1004 <p>Change the style of string dump.  The default value for <code>quote</code>
1005 is <code>auto</code>; one can enable double-quotish or single-quotish format
1006 by setting it to <code>&quot;</code> or <code>'</code>, respectively.  By default, characters
1007 with their high bit set are printed verbatim.</p>
1008 </dd>
1009 </li>
1010 <dt><strong><a name="item_usageonly_x_3cdebugger_option_2c_usageonly_3e"><code>UsageOnly</code>
1011 </a></strong>
1012
1013 <dd>
1014 <p>Rudimentary per-package memory usage dump.  Calculates total
1015 size of strings found in variables in the package.  This does not
1016 include lexicals in a module's file scope, or lost in closures.</p>
1017 </dd>
1018 </li>
1019 </dl>
1020 <p>After the rc file is read, the debugger reads the <code>$ENV{PERLDB_OPTS}</code>
1021 environment variable and parses this as the remainder of a ``O ...''
1022 line as one might enter at the debugger prompt.  You may place the
1023 initialization options <code>TTY</code>, <code>noTTY</code>, <code>ReadLine</code>, and <code>NonStop</code>
1024 there.</p>
1025 <p>If your rc file contains:</p>
1026 <pre>
1027   parse_options(&quot;NonStop=1 LineInfo=db.out AutoTrace&quot;);</pre>
1028 <p>then your script will run without human intervention, putting trace
1029 information into the file <em>db.out</em>.  (If you interrupt it, you'd
1030 better reset <code>LineInfo</code> to <em>/dev/tty</em> if you expect to see anything.)</p>
1031 <dl>
1032 <dt><strong><a name="item_tty_x_3cdebugger_option_2c_tty_3e"><code>TTY</code>
1033 </a></strong>
1034
1035 <dd>
1036 <p>The TTY to use for debugging I/O.</p>
1037 </dd>
1038 </li>
1039 <dt><strong><a name="item_notty_x_3cdebugger_option_2c_notty_3e"><code>noTTY</code>
1040 </a></strong>
1041
1042 <dd>
1043 <p>If set, the debugger goes into <code>NonStop</code> mode and will not connect to a TTY.  If
1044 interrupted (or if control goes to the debugger via explicit setting of
1045 $DB::signal or $DB::single from the Perl script), it connects to a TTY
1046 specified in the <code>TTY</code> option at startup, or to a tty found at
1047 runtime using the <code>Term::Rendezvous</code> module of your choice.</p>
1048 </dd>
1049 <dd>
1050 <p>This module should implement a method named <code>new</code> that returns an object
1051 with two methods: <code>IN</code> and <code>OUT</code>.  These should return filehandles to use
1052 for debugging input and output correspondingly.  The <code>new</code> method should
1053 inspect an argument containing the value of <code>$ENV{PERLDB_NOTTY}</code> at
1054 startup, or <code>&quot;$ENV{HOME}/.perldbtty$$&quot;</code> otherwise.  This file is not
1055 inspected for proper ownership, so security hazards are theoretically
1056 possible.</p>
1057 </dd>
1058 </li>
1059 <dt><strong><a name="item_readline_x_3cdebugger_option_2c_readline_3e"><code>ReadLine</code>
1060 </a></strong>
1061
1062 <dd>
1063 <p>If false, readline support in the debugger is disabled in order
1064 to debug applications that themselves use ReadLine.</p>
1065 </dd>
1066 </li>
1067 <dt><strong><a name="item_nonstop_x_3cdebugger_option_2c_nonstop_3e"><code>NonStop</code>
1068 </a></strong>
1069
1070 <dd>
1071 <p>If set, the debugger goes into non-interactive mode until interrupted, or
1072 programmatically by setting $DB::signal or $DB::single.</p>
1073 </dd>
1074 </li>
1075 </dl>
1076 <p>Here's an example of using the <code>$ENV{PERLDB_OPTS}</code> variable:</p>
1077 <pre>
1078     $ PERLDB_OPTS=&quot;NonStop frame=2&quot; perl -d myprogram</pre>
1079 <p>That will run the script <strong>myprogram</strong> without human intervention,
1080 printing out the call tree with entry and exit points.  Note that
1081 <code>NonStop=1 frame=2</code> is equivalent to <code>N f=2</code>, and that originally,
1082 options could be uniquely abbreviated by the first letter (modulo
1083 the <code>Dump*</code> options).  It is nevertheless recommended that you
1084 always spell them out in full for legibility and future compatibility.</p>
1085 <p>Other examples include</p>
1086 <pre>
1087     $ PERLDB_OPTS=&quot;NonStop LineInfo=listing frame=2&quot; perl -d myprogram</pre>
1088 <p>which runs script non-interactively, printing info on each entry
1089 into a subroutine and each executed line into the file named <em>listing</em>.
1090 (If you interrupt it, you would better reset <code>LineInfo</code> to something
1091 ``interactive''!)</p>
1092 <p>Other examples include (using standard shell syntax to show environment
1093 variable settings):</p>
1094 <pre>
1095   $ ( PERLDB_OPTS=&quot;NonStop frame=1 AutoTrace LineInfo=tperl.out&quot;
1096       perl -d myprogram )</pre>
1097 <p>which may be useful for debugging a program that uses <code>Term::ReadLine</code>
1098 itself.  Do not forget to detach your shell from the TTY in the window that
1099 corresponds to <em>/dev/ttyXX</em>, say, by issuing a command like</p>
1100 <pre>
1101   $ sleep 1000000</pre>
1102 <p>See <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html#debugger_internals">Debugger Internals in the perldebguts manpage</a> for details.</p>
1103 <p>
1104 </p>
1105 <h2><a name="debugger_input_output">Debugger input/output</a></h2>
1106 <dl>
1107 <dt><strong><a name="item_prompt">Prompt</a></strong>
1108
1109 <dd>
1110 <p>The debugger prompt is something like</p>
1111 </dd>
1112 <dd>
1113 <pre>
1114     DB&lt;8&gt;</pre>
1115 </dd>
1116 <dd>
1117 <p>or even</p>
1118 </dd>
1119 <dd>
1120 <pre>
1121     DB&lt;&lt;17&gt;&gt;</pre>
1122 </dd>
1123 <dd>
1124 <p>where that number is the command number, and which you'd use to
1125 access with the built-in <strong>csh</strong>-like history mechanism.  For example,
1126 <code>!17</code> would repeat command number 17.  The depth of the angle
1127 brackets indicates the nesting depth of the debugger.  You could
1128 get more than one set of brackets, for example, if you'd already
1129 at a breakpoint and then printed the result of a function call that
1130 itself has a breakpoint, or you step into an expression via <code>s/n/t
1131 expression</code> command.</p>
1132 </dd>
1133 </li>
1134 <dt><strong><a name="item_multiline_commands">Multiline commands</a></strong>
1135
1136 <dd>
1137 <p>If you want to enter a multi-line command, such as a subroutine
1138 definition with several statements or a format, escape the newline
1139 that would normally end the debugger command with a backslash.
1140 Here's an example:</p>
1141 </dd>
1142 <dd>
1143 <pre>
1144       DB&lt;1&gt; for (1..4) {         \
1145       cont:     print &quot;ok\n&quot;;   \
1146       cont: }
1147       ok
1148       ok
1149       ok
1150       ok</pre>
1151 </dd>
1152 <dd>
1153 <p>Note that this business of escaping a newline is specific to interactive
1154 commands typed into the debugger.</p>
1155 </dd>
1156 </li>
1157 <dt><strong><a name="item_stack_backtrace_x_3cbacktrace_3e_x_3cstack_2c_back">Stack backtrace
1158  </a></strong>
1159
1160 <dd>
1161 <p>Here's an example of what a stack backtrace via <code>T</code> command might
1162 look like:</p>
1163 </dd>
1164 <dd>
1165 <pre>
1166     $ = main::infested called from file `Ambulation.pm' line 10
1167     @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7
1168     $ = main::pests('bactrian', 4) called from file `camel_flea' line 4</pre>
1169 </dd>
1170 <dd>
1171 <p>The left-hand character up there indicates the context in which the
1172 function was called, with <code>$</code> and <code>@</code> meaning scalar or list
1173 contexts respectively, and <code>.</code> meaning void context (which is
1174 actually a sort of scalar context).  The display above says
1175 that you were in the function <code>main::infested</code> when you ran the
1176 stack dump, and that it was called in scalar context from line
1177 10 of the file <em>Ambulation.pm</em>, but without any arguments at all,
1178 meaning it was called as <code>&amp;infested</code>.  The next stack frame shows
1179 that the function <code>Ambulation::legs</code> was called in list context
1180 from the <em>camel_flea</em> file with four arguments.  The last stack
1181 frame shows that <code>main::pests</code> was called in scalar context,
1182 also from <em>camel_flea</em>, but from line 4.</p>
1183 </dd>
1184 <dd>
1185 <p>If you execute the <code>T</code> command from inside an active <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_use"><code>use</code></a>
1186 statement, the backtrace will contain both a <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_require"><code>require</code></a> frame and
1187 an <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>) frame.</p>
1188 </dd>
1189 </li>
1190 <dt><strong><a name="item_line_listing_format">Line Listing Format</a></strong>
1191
1192 <dd>
1193 <p>This shows the sorts of output the <code>l</code> command can produce:</p>
1194 </dd>
1195 <dd>
1196 <pre>
1197     DB&lt;&lt;13&gt;&gt; l
1198   101:                @i{@i} = ();
1199   102:b               @isa{@i,$pack} = ()
1200   103                     if(exists $i{$prevpack} || exists $isa{$pack});
1201   104             }
1202   105
1203   106             next
1204   107==&gt;              if(exists $isa{$pack});
1205   108
1206   109:a           if ($extra-- &gt; 0) {
1207   110:                %isa = ($pack,1);</pre>
1208 </dd>
1209 <dd>
1210 <p>Breakable lines are marked with <code>:</code>.  Lines with breakpoints are
1211 marked by <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_b"><code>b</code></a> and those with actions by <code>a</code>.  The line that's
1212 about to be executed is marked by <code>==&gt;</code>.</p>
1213 </dd>
1214 <dd>
1215 <p>Please be aware that code in debugger listings may not look the same
1216 as your original source code.  Line directives and external source
1217 filters can alter the code before Perl sees it, causing code to move
1218 from its original positions or take on entirely different forms.</p>
1219 </dd>
1220 </li>
1221 <dt><strong><a name="item_frame_listing">Frame listing</a></strong>
1222
1223 <dd>
1224 <p>When the <code>frame</code> option is set, the debugger would print entered (and
1225 optionally exited) subroutines in different styles.  See <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html">the perldebguts manpage</a>
1226 for incredibly long examples of these.</p>
1227 </dd>
1228 </li>
1229 </dl>
1230 <p>
1231 </p>
1232 <h2><a name="debugging_compiletime_statements">Debugging compile-time statements</a></h2>
1233 <p>If you have compile-time executable statements (such as code within
1234 BEGIN and CHECK blocks or <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_use"><code>use</code></a> statements), these will <em>not</em> be
1235 stopped by debugger, although <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_require"><code>require</code></a>s and INIT blocks will, and
1236 compile-time statements can be traced with <code>AutoTrace</code> option set
1237 in <code>PERLDB_OPTS</code>).  From your own Perl code, however, you can
1238 transfer control back to the debugger using the following statement,
1239 which is harmless if the debugger is not running:</p>
1240 <pre>
1241     $DB::single = 1;</pre>
1242 <p>If you set <code>$DB::single</code> to 2, it's equivalent to having
1243 just typed the <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_n"><code>n</code></a> command, whereas a value of 1 means the <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_s"><code>s</code></a>
1244 command.  The <code>$DB::trace</code>  variable should be set to 1 to simulate
1245 having typed the <code>t</code> command.</p>
1246 <p>Another way to debug compile-time code is to start the debugger, set a
1247 breakpoint on the <em>load</em> of some module:</p>
1248 <pre>
1249     DB&lt;7&gt; b load f:/perllib/lib/Carp.pm
1250   Will stop on load of `f:/perllib/lib/Carp.pm'.</pre>
1251 <p>and then restart the debugger using the <code>R</code> command (if possible).  One can use <code>b
1252 compile subname</code> for the same purpose.</p>
1253 <p>
1254 </p>
1255 <h2><a name="debugger_customization">Debugger Customization</a></h2>
1256 <p>The debugger probably contains enough configuration hooks that you
1257 won't ever have to modify it yourself.  You may change the behaviour
1258 of debugger from within the debugger using its <a href="file://C|\msysgit\mingw\html/pod/perlguts.html#item_o"><code>o</code></a> command, from
1259 the command line via the <code>PERLDB_OPTS</code> environment variable, and
1260 from customization files.</p>
1261 <p>You can do some customization by setting up a <em>.perldb</em> file, which
1262 contains initialization code.  For instance, you could make aliases
1263 like these (the last one is one people expect to be there):</p>
1264 <pre>
1265     $DB::alias{'len'}  = 's/^len(.*)/p length($1)/';
1266     $DB::alias{'stop'} = 's/^stop (at|in)/b/';
1267     $DB::alias{'ps'}   = 's/^ps\b/p scalar /';
1268     $DB::alias{'quit'} = 's/^quit(\s*)/exit/';</pre>
1269 <p>You can change options from <em>.perldb</em> by using calls like this one;</p>
1270 <pre>
1271     parse_options(&quot;NonStop=1 LineInfo=db.out AutoTrace=1 frame=2&quot;);</pre>
1272 <p>The code is executed in the package <code>DB</code>.  Note that <em>.perldb</em> is
1273 processed before processing <code>PERLDB_OPTS</code>.  If <em>.perldb</em> defines the
1274 subroutine <code>afterinit</code>, that function is called after debugger
1275 initialization ends.  <em>.perldb</em> may be contained in the current
1276 directory, or in the home directory.  Because this file is sourced
1277 in by Perl and may contain arbitrary commands, for security reasons,
1278 it must be owned by the superuser or the current user, and writable
1279 by no one but its owner.</p>
1280 <p>You can mock TTY input to debugger by adding arbitrary commands to
1281 @DB::typeahead. For example, your <em>.perldb</em> file might contain:</p>
1282 <pre>
1283     sub afterinit { push @DB::typeahead, &quot;b 4&quot;, &quot;b 6&quot;; }</pre>
1284 <p>Which would attempt to set breakpoints on lines 4 and 6 immediately
1285 after debugger initialization. Note that @DB::typeahead is not a supported
1286 interface and is subject to change in future releases.</p>
1287 <p>If you want to modify the debugger, copy <em>perl5db.pl</em> from the
1288 Perl library to another name and hack it to your heart's content.
1289 You'll then want to set your <code>PERL5DB</code> environment variable to say
1290 something like this:</p>
1291 <pre>
1292     BEGIN { require &quot;myperl5db.pl&quot; }</pre>
1293 <p>As a last resort, you could also use <code>PERL5DB</code> to customize the debugger
1294 by directly setting internal variables or calling debugger functions.</p>
1295 <p>Note that any variables and functions that are not documented in
1296 this document (or in <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html">the perldebguts manpage</a>) are considered for internal
1297 use only, and as such are subject to change without notice.</p>
1298 <p>
1299 </p>
1300 <h2><a name="readline_support">Readline Support</a></h2>
1301 <p>As shipped, the only command-line history supplied is a simplistic one
1302 that checks for leading exclamation points.  However, if you install
1303 the Term::ReadKey and Term::ReadLine modules from CPAN, you will
1304 have full editing capabilities much like GNU <em>readline</em>(3) provides.
1305 Look for these in the <em>modules/by-module/Term</em> directory on CPAN.
1306 These do not support normal <strong>vi</strong> command-line editing, however.</p>
1307 <p>A rudimentary command-line completion is also available.
1308 Unfortunately, the names of lexical variables are not available for
1309 completion.</p>
1310 <p>
1311 </p>
1312 <h2><a name="editor_support_for_debugging">Editor Support for Debugging</a></h2>
1313 <p>If you have the FSF's version of <strong>emacs</strong> installed on your system,
1314 it can interact with the Perl debugger to provide an integrated
1315 software development environment reminiscent of its interactions
1316 with C debuggers.</p>
1317 <p>Perl comes with a start file for making <strong>emacs</strong> act like a
1318 syntax-directed editor that understands (some of) Perl's syntax.
1319 Look in the <em>emacs</em> directory of the Perl source distribution.</p>
1320 <p>A similar setup by Tom Christiansen for interacting with any
1321 vendor-shipped <strong>vi</strong> and the X11 window system is also available.
1322 This works similarly to the integrated multiwindow support that
1323 <strong>emacs</strong> provides, where the debugger drives the editor.  At the
1324 time of this writing, however, that tool's eventual location in the
1325 Perl distribution was uncertain.</p>
1326 <p>Users of <strong>vi</strong> should also look into <strong>vim</strong> and <strong>gvim</strong>, the mousey
1327 and windy version, for coloring of Perl keywords.</p>
1328 <p>Note that only perl can truly parse Perl, so all such CASE tools
1329 fall somewhat short of the mark, especially if you don't program
1330 your Perl as a C programmer might.</p>
1331 <p>
1332 </p>
1333 <h2><a name="the_perl_profiler_x_profile__x_profiling__x_profiler_">The Perl Profiler
1334   </a></h2>
1335 <p>If you wish to supply an alternative debugger for Perl to run, just
1336 invoke your script with a colon and a package argument given to the
1337 <strong>-d</strong> flag.  The most popular alternative debuggers for Perl is the
1338 Perl profiler.  Devel::DProf is now included with the standard Perl
1339 distribution.  To profile your Perl program in the file <em>mycode.pl</em>,
1340 just type:</p>
1341 <pre>
1342     $ perl -d:DProf mycode.pl</pre>
1343 <p>When the script terminates the profiler will dump the profile
1344 information to a file called <em>tmon.out</em>.  A tool like <strong>dprofpp</strong>,
1345 also supplied with the standard Perl distribution, can be used to
1346 interpret the information in that profile.</p>
1347 <p>
1348 </p>
1349 <hr />
1350 <h1><a name="debugging_regular_expressions_x_regular_expression__debugging__x_regex__debugging__x_regexp__debugging_">Debugging regular expressions
1351
1352  </a></h1>
1353 <p><code>use re 'debug'</code> enables you to see the gory details of how the Perl
1354 regular expression engine works. In order to understand this typically
1355 voluminous output, one must not only have some idea about how regular
1356 expression matching works in general, but also know how Perl's regular
1357 expressions are internally compiled into an automaton. These matters
1358 are explored in some detail in
1359 <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html#debugging_regular_expressions">Debugging regular expressions in the perldebguts manpage</a>.</p>
1360 <p>
1361 </p>
1362 <hr />
1363 <h1><a name="debugging_memory_usage_x_memory_usage_">Debugging memory usage
1364 </a></h1>
1365 <p>Perl contains internal support for reporting its own memory usage,
1366 but this is a fairly advanced concept that requires some understanding
1367 of how memory allocation works.
1368 See <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html#debugging_perl_memory_usage">Debugging Perl memory usage in the perldebguts manpage</a> for the details.</p>
1369 <p>
1370 </p>
1371 <hr />
1372 <h1><a name="see_also">SEE ALSO</a></h1>
1373 <p>You did try the <strong>-w</strong> switch, didn't you?</p>
1374 <p><a href="file://C|\msysgit\mingw\html/pod/perldebtut.html">the perldebtut manpage</a>,
1375 <a href="file://C|\msysgit\mingw\html/pod/perldebguts.html">the perldebguts manpage</a>,
1376 <a href="file://C|\msysgit\mingw\html/lib/re.html">the re manpage</a>,
1377 <a href="file://C|\msysgit\mingw\html/lib/DB.html">the DB manpage</a>,
1378 <a href="file://C|\msysgit\mingw\html/lib/Devel/DProf.html">the Devel::DProf manpage</a>,
1379 <a href="file://C|\msysgit\mingw\html/utils/dprofpp.html">the dprofpp manpage</a>,
1380 <a href="file://C|\msysgit\mingw\html/lib/Dumpvalue.html">the Dumpvalue manpage</a>,
1381 and
1382 <a href="file://C|\msysgit\mingw\html/pod/perlrun.html">the perlrun manpage</a>.</p>
1383 <p>When debugging a script that uses #! and is thus normally found in
1384 $PATH, the -S option causes perl to search $PATH for it, so you don't
1385 have to type the path or <code>which $scriptname</code>.</p>
1386 <pre>
1387   $ perl -Sd foo.pl</pre>
1388 <p>
1389 </p>
1390 <hr />
1391 <h1><a name="bugs">BUGS</a></h1>
1392 <p>You cannot get stack frame information or in any fashion debug functions
1393 that were not compiled by Perl, such as those from C or C++ extensions.</p>
1394 <p>If you alter your @_ arguments in a subroutine (such as with <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_shift"><code>shift</code></a>
1395 or <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_pop"><code>pop</code></a>), the stack backtrace will not show the original values.</p>
1396 <p>The debugger does not currently work in conjunction with the <strong>-W</strong>
1397 command-line switch, because it itself is not free of warnings.</p>
1398 <p>If you're in a slow syscall (like <code>wait</code>ing, <code>accept</code>ing, or <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_read"><code>read</code></a>ing
1399 from your keyboard or a socket) and haven't set up your own <code>$SIG{INT}</code>
1400 handler, then you won't be able to CTRL-C your way back to the debugger,
1401 because the debugger's own <code>$SIG{INT}</code> handler doesn't understand that
1402 it needs to raise an exception to <code>longjmp(3)</code> out of slow syscalls.</p>
1403 <table border="0" width="100%" cellspacing="0" cellpadding="3">
1404 <tr><td class="block" style="background-color: #cccccc" valign="middle">
1405 <big><strong><span class="block">&nbsp;perldebug - Perl debugging</span></strong></big>
1406 </td></tr>
1407 </table>
1408
1409 </body>
1410
1411 </html>