mingw/html/ext/Data/Dumper/Dumper.html

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  13 <big><strong><span class="block">&nbsp;Data::Dumper - stringified perl data structures, suitable for both printing and C&lt;eval&gt;</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="#synopsis">SYNOPSIS</a></li>
  24         <li><a href="#description">DESCRIPTION</a></li>
  25         <ul>
  26
  27                 <li><a href="#methods">Methods</a></li>
  28                 <li><a href="#functions">Functions</a></li>
  29                 <li><a href="#configuration_variables_or_methods">Configuration Variables or Methods</a></li>
  30                 <li><a href="#exports">Exports</a></li>
  31         </ul>
  32
  33         <li><a href="#examples">EXAMPLES</a></li>
  34         <li><a href="#bugs">BUGS</a></li>
  35         <ul>
  36
  37                 <li><a href="#note">NOTE</a></li>
  38         </ul>
  39
  40         <li><a href="#author">AUTHOR</a></li>
  41         <li><a href="#version">VERSION</a></li>
  42         <li><a href="#see_also">SEE ALSO</a></li>
  43 </ul>
  44 <!-- INDEX END -->
  45
  46 <hr />
  47 <p>
  48 </p>
  49 <h1><a name="name">NAME</a></h1>
  50 <p>Data::Dumper - stringified perl data structures, suitable for both printing and <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a></p>
  51 <p>
  52 </p>
  53 <hr />
  54 <h1><a name="synopsis">SYNOPSIS</a></h1>
  55 <pre>
  56     use Data::Dumper;</pre>
  57 <pre>
  58     # simple procedural interface
  59     print Dumper($foo, $bar);</pre>
  60 <pre>
  61     # extended usage with names
  62     print Data::Dumper-&gt;Dump([$foo, $bar], [qw(foo *ary)]);</pre>
  63 <pre>
  64     # configuration variables
  65     {
  66       local $Data::Dumper::Purity = 1;
  67       eval Data::Dumper-&gt;Dump([$foo, $bar], [qw(foo *ary)]);
  68     }</pre>
  69 <pre>
  70     # OO usage
  71     $d = Data::Dumper-&gt;new([$foo, $bar], [qw(foo *ary)]);
  72        ...
  73     print $d-&gt;Dump;
  74        ...
  75     $d-&gt;Purity(1)-&gt;Terse(1)-&gt;Deepcopy(1);
  76     eval $d-&gt;Dump;</pre>
  77 <p>
  78 </p>
  79 <hr />
  80 <h1><a name="description">DESCRIPTION</a></h1>
  81 <p>Given a list of scalars or reference variables, writes out their contents in
  82 perl syntax. The references can also be objects.  The contents of each
  83 variable is output in a single Perl statement.  Handles self-referential
  84 structures correctly.</p>
  85 <p>The return value can be <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed to get back an identical copy of the
  86 original reference structure.</p>
  87 <p>Any references that are the same as one of those passed in will be named
  88 <code>$VAR</code><em>n</em> (where <em>n</em> is a numeric suffix), and other duplicate references
  89 to substructures within <code>$VAR</code><em>n</em> will be appropriately labeled using arrow
  90 notation.  You can specify names for individual values to be dumped if you
  91 use the <a href="#item_dump"><code>Dump()</code></a> method, or you can change the default <code>$VAR</code> prefix to
  92 something else.  See <code>$Data::Dumper::Varname</code> and <code>$Data::Dumper::Terse</code>
  93 below.</p>
  94 <p>The default output of self-referential structures can be <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed, but the
  95 nested references to <code>$VAR</code><em>n</em> will be undefined, since a recursive
  96 structure cannot be constructed using one Perl statement.  You should set the
  97 <code>Purity</code> flag to 1 to get additional statements that will correctly fill in
  98 these references.  Moreover, if <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed when strictures are in effect,
  99 you need to ensure that any variables it accesses are previously declared.</p>
 100 <p>In the extended usage form, the references to be dumped can be given
 101 user-specified names.  If a name begins with a <code>*</code>, the output will
 102 describe the dereferenced type of the supplied reference for hashes and
 103 arrays, and coderefs.  Output of names will be avoided where possible if
 104 the <code>Terse</code> flag is set.</p>
 105 <p>In many cases, methods that are used to set the internal state of the
 106 object will return the object itself, so method calls can be conveniently
 107 chained together.</p>
 108 <p>Several styles of output are possible, all controlled by setting
 109 the <code>Indent</code> flag.  See <a href="#configuration_variables_or_methods">Configuration Variables or Methods</a> below
 110 for details.</p>
 111 <p>
 112 </p>
 113 <h2><a name="methods">Methods</a></h2>
 114 <dl>
 115 <dt><strong><a name="item_new"><em>PACKAGE</em>-&gt;new(<em>ARRAYREF [</em>, <em>ARRAYREF]</em>)</a></strong>
 116
 117 <dd>
 118 <p>Returns a newly created <code>Data::Dumper</code> object.  The first argument is an
 119 anonymous array of values to be dumped.  The optional second argument is an
 120 anonymous array of names for the values.  The names need not have a leading
 121 <code>$</code> sign, and must be comprised of alphanumeric characters.  You can begin
 122 a name with a <code>*</code> to specify that the dereferenced type must be dumped
 123 instead of the reference itself, for ARRAY and HASH references.</p>
 124 </dd>
 125 <dd>
 126 <p>The prefix specified by <code>$Data::Dumper::Varname</code> will be used with a
 127 numeric suffix if the name for a value is undefined.</p>
 128 </dd>
 129 <dd>
 130 <p>Data::Dumper will catalog all references encountered while dumping the
 131 values. Cross-references (in the form of names of substructures in perl
 132 syntax) will be inserted at all possible points, preserving any structural
 133 interdependencies in the original set of values.  Structure traversal is
 134 depth-first,  and proceeds in order from the first supplied value to
 135 the last.</p>
 136 </dd>
 137 </li>
 138 <dt><strong><a name="item_dump"><em>$OBJ</em>-&gt;Dump  <em>or</em>  <em>PACKAGE</em>-&gt;Dump(<em>ARRAYREF [</em>, <em>ARRAYREF]</em>)</a></strong>
 139
 140 <dd>
 141 <p>Returns the stringified form of the values stored in the object (preserving
 142 the order in which they were supplied to <a href="#item_new"><code>new</code></a>), subject to the
 143 configuration options below.  In a list context, it returns a list
 144 of strings corresponding to the supplied values.</p>
 145 </dd>
 146 <dd>
 147 <p>The second form, for convenience, simply calls the <a href="#item_new"><code>new</code></a> method on its
 148 arguments before dumping the object immediately.</p>
 149 </dd>
 150 </li>
 151 <dt><strong><a name="item_seen"><em>$OBJ</em>-&gt;Seen(<em>[HASHREF]</em>)</a></strong>
 152
 153 <dd>
 154 <p>Queries or adds to the internal table of already encountered references.
 155 You must use <a href="#item_reset"><code>Reset</code></a> to explicitly clear the table if needed.  Such
 156 references are not dumped; instead, their names are inserted wherever they
 157 are encountered subsequently.  This is useful especially for properly
 158 dumping subroutine references.</p>
 159 </dd>
 160 <dd>
 161 <p>Expects an anonymous hash of name =&gt; value pairs.  Same rules apply for names
 162 as in <a href="#item_new"><code>new</code></a>.  If no argument is supplied, will return the ``seen'' list of
 163 name =&gt; value pairs, in a list context.  Otherwise, returns the object
 164 itself.</p>
 165 </dd>
 166 </li>
 167 <dt><strong><a name="item_values"><em>$OBJ</em>-&gt;Values(<em>[ARRAYREF]</em>)</a></strong>
 168
 169 <dd>
 170 <p>Queries or replaces the internal array of values that will be dumped.
 171 When called without arguments, returns the values.  Otherwise, returns the
 172 object itself.</p>
 173 </dd>
 174 </li>
 175 <dt><strong><a name="item_names"><em>$OBJ</em>-&gt;Names(<em>[ARRAYREF]</em>)</a></strong>
 176
 177 <dd>
 178 <p>Queries or replaces the internal array of user supplied names for the values
 179 that will be dumped.  When called without arguments, returns the names.
 180 Otherwise, returns the object itself.</p>
 181 </dd>
 182 </li>
 183 <dt><strong><a name="item_reset"><em>$OBJ</em>-&gt;Reset</a></strong>
 184
 185 <dd>
 186 <p>Clears the internal table of ``seen'' references and returns the object
 187 itself.</p>
 188 </dd>
 189 </li>
 190 </dl>
 191 <p>
 192 </p>
 193 <h2><a name="functions">Functions</a></h2>
 194 <dl>
 195 <dt><strong><a name="item_dumper">Dumper(<em>LIST</em>)</a></strong>
 196
 197 <dd>
 198 <p>Returns the stringified form of the values in the list, subject to the
 199 configuration options below.  The values will be named <code>$VAR</code><em>n</em> in the
 200 output, where <em>n</em> is a numeric suffix.  Will return a list of strings
 201 in a list context.</p>
 202 </dd>
 203 </li>
 204 </dl>
 205 <p>
 206 </p>
 207 <h2><a name="configuration_variables_or_methods">Configuration Variables or Methods</a></h2>
 208 <p>Several configuration variables can be used to control the kind of output
 209 generated when using the procedural interface.  These variables are usually
 210 <code>local</code>ized in a block so that other parts of the code are not affected by
 211 the change.</p>
 212 <p>These variables determine the default state of the object created by calling
 213 the <a href="#item_new"><code>new</code></a> method, but cannot be used to alter the state of the object
 214 thereafter.  The equivalent method names should be used instead to query
 215 or set the internal state of the object.</p>
 216 <p>The method forms return the object itself when called with arguments,
 217 so that they can be chained together nicely.</p>
 218 <ul>
 219 <li>
 220 <p>$Data::Dumper::Indent  <em>or</em>  <em>$OBJ</em>-&gt;Indent(<em>[NEWVAL]</em>)</p>
 221 <p>Controls the style of indentation.  It can be set to 0, 1, 2 or 3.  Style 0
 222 spews output without any newlines, indentation, or spaces between list
 223 items.  It is the most compact format possible that can still be called
 224 valid perl.  Style 1 outputs a readable form with newlines but no fancy
 225 indentation (each level in the structure is simply indented by a fixed
 226 amount of whitespace).  Style 2 (the default) outputs a very readable form
 227 which takes into account the length of hash keys (so the hash value lines
 228 up).  Style 3 is like style 2, but also annotates the elements of arrays
 229 with their index (but the comment is on its own line, so array output
 230 consumes twice the number of lines).  Style 2 is the default.</p>
 231 </li>
 232 <li>
 233 <p>$Data::Dumper::Purity  <em>or</em>  <em>$OBJ</em>-&gt;Purity(<em>[NEWVAL]</em>)</p>
 234 <p>Controls the degree to which the output can be <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>ed to recreate the
 235 supplied reference structures.  Setting it to 1 will output additional perl
 236 statements that will correctly recreate nested references.  The default is
 237 0.</p>
 238 </li>
 239 <li>
 240 <p>$Data::Dumper::Pad  <em>or</em>  <em>$OBJ</em>-&gt;Pad(<em>[NEWVAL]</em>)</p>
 241 <p>Specifies the string that will be prefixed to every line of the output.
 242 Empty string by default.</p>
 243 </li>
 244 <li>
 245 <p>$Data::Dumper::Varname  <em>or</em>  <em>$OBJ</em>-&gt;Varname(<em>[NEWVAL]</em>)</p>
 246 <p>Contains the prefix to use for tagging variable names in the output. The
 247 default is ``VAR''.</p>
 248 </li>
 249 <li>
 250 <p>$Data::Dumper::Useqq  <em>or</em>  <em>$OBJ</em>-&gt;Useqq(<em>[NEWVAL]</em>)</p>
 251 <p>When set, enables the use of double quotes for representing string values.
 252 Whitespace other than space will be represented as <code>[\n\t\r]</code>, ``unsafe''
 253 characters will be backslashed, and unprintable characters will be output as
 254 quoted octal integers.  Since setting this variable imposes a performance
 255 penalty, the default is 0.  <a href="#item_dump"><code>Dump()</code></a> will run slower if this flag is set,
 256 since the fast XSUB implementation doesn't support it yet.</p>
 257 </li>
 258 <li>
 259 <p>$Data::Dumper::Terse  <em>or</em>  <em>$OBJ</em>-&gt;Terse(<em>[NEWVAL]</em>)</p>
 260 <p>When set, Data::Dumper will emit single, non-self-referential values as
 261 atoms/terms rather than statements.  This means that the <code>$VAR</code><em>n</em> names
 262 will be avoided where possible, but be advised that such output may not
 263 always be parseable by <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a>.</p>
 264 </li>
 265 <li>
 266 <p>$Data::Dumper::Freezer  <em>or</em>  $<em>OBJ</em>-&gt;Freezer(<em>[NEWVAL]</em>)</p>
 267 <p>Can be set to a method name, or to an empty string to disable the feature.
 268 Data::Dumper will invoke that method via the object before attempting to
 269 stringify it.  This method can alter the contents of the object (if, for
 270 instance, it contains data allocated from C), and even rebless it in a
 271 different package.  The client is responsible for making sure the specified
 272 method can be called via the object, and that the object ends up containing
 273 only perl data types after the method has been called.  Defaults to an empty
 274 string.</p>
 275 <p>If an object does not support the method specified (determined using
 276 UNIVERSAL::can()) then the call will be skipped.  If the method dies a
 277 warning will be generated.</p>
 278 </li>
 279 <li>
 280 <p>$Data::Dumper::Toaster  <em>or</em>  $<em>OBJ</em>-&gt;Toaster(<em>[NEWVAL]</em>)</p>
 281 <p>Can be set to a method name, or to an empty string to disable the feature.
 282 Data::Dumper will emit a method call for any objects that are to be dumped
 283 using the syntax <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_bless"><code>bless(DATA, CLASS)-&gt;METHOD()</code></a>.  Note that this means that
 284 the method specified will have to perform any modifications required on the
 285 object (like creating new state within it, and/or reblessing it in a
 286 different package) and then return it.  The client is responsible for making
 287 sure the method can be called via the object, and that it returns a valid
 288 object.  Defaults to an empty string.</p>
 289 </li>
 290 <li>
 291 <p>$Data::Dumper::Deepcopy  <em>or</em>  $<em>OBJ</em>-&gt;Deepcopy(<em>[NEWVAL]</em>)</p>
 292 <p>Can be set to a boolean value to enable deep copies of structures.
 293 Cross-referencing will then only be done when absolutely essential
 294 (i.e., to break reference cycles).  Default is 0.</p>
 295 </li>
 296 <li>
 297 <p>$Data::Dumper::Quotekeys  <em>or</em>  $<em>OBJ</em>-&gt;Quotekeys(<em>[NEWVAL]</em>)</p>
 298 <p>Can be set to a boolean value to control whether hash keys are quoted.
 299 A false value will avoid quoting hash keys when it looks like a simple
 300 string.  Default is 1, which will always enclose hash keys in quotes.</p>
 301 </li>
 302 <li>
 303 <p>$Data::Dumper::Bless  <em>or</em>  $<em>OBJ</em>-&gt;Bless(<em>[NEWVAL]</em>)</p>
 304 <p>Can be set to a string that specifies an alternative to the <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_bless"><code>bless</code></a>
 305 builtin operator used to create objects.  A function with the specified
 306 name should exist, and should accept the same arguments as the builtin.
 307 Default is <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_bless"><code>bless</code></a>.</p>
 308 </li>
 309 <li>
 310 <p>$Data::Dumper::Pair  <em>or</em>  $<em>OBJ</em>-&gt;Pair(<em>[NEWVAL]</em>)</p>
 311 <p>Can be set to a string that specifies the separator between hash keys
 312 and values. To dump nested hash, array and scalar values to JavaScript,
 313 use: <code>$Data::Dumper::Pair = ' : ';</code>. Implementing <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_bless"><code>bless</code></a> in JavaScript
 314 is left as an exercise for the reader.
 315 A function with the specified name exists, and accepts the same arguments
 316 as the builtin.</p>
 317 <p>Default is: <code> =&gt; </code>.</p>
 318 </li>
 319 <li>
 320 <p>$Data::Dumper::Maxdepth  <em>or</em>  $<em>OBJ</em>-&gt;Maxdepth(<em>[NEWVAL]</em>)</p>
 321 <p>Can be set to a positive integer that specifies the depth beyond which
 322 which we don't venture into a structure.  Has no effect when
 323 <code>Data::Dumper::Purity</code> is set.  (Useful in debugger when we often don't
 324 want to see more than enough).  Default is 0, which means there is
 325 no maximum depth.</p>
 326 </li>
 327 <li>
 328 <p>$Data::Dumper::Useperl  <em>or</em>  $<em>OBJ</em>-&gt;Useperl(<em>[NEWVAL]</em>)</p>
 329 <p>Can be set to a boolean value which controls whether the pure Perl
 330 implementation of <code>Data::Dumper</code> is used. The <code>Data::Dumper</code> module is
 331 a dual implementation, with almost all functionality written in both
 332 pure Perl and also in XS ('C'). Since the XS version is much faster, it
 333 will always be used if possible. This option lets you override the
 334 default behavior, usually for testing purposes only. Default is 0, which
 335 means the XS implementation will be used if possible.</p>
 336 </li>
 337 <li>
 338 <p>$Data::Dumper::Sortkeys  <em>or</em>  $<em>OBJ</em>-&gt;Sortkeys(<em>[NEWVAL]</em>)</p>
 339 <p>Can be set to a boolean value to control whether hash keys are dumped in
 340 sorted order. A true value will cause the keys of all hashes to be
 341 dumped in Perl's default sort order. Can also be set to a subroutine
 342 reference which will be called for each hash that is dumped. In this
 343 case <code>Data::Dumper</code> will call the subroutine once for each hash,
 344 passing it the reference of the hash. The purpose of the subroutine is
 345 to return a reference to an array of the keys that will be dumped, in
 346 the order that they should be dumped. Using this feature, you can
 347 control both the order of the keys, and which keys are actually used. In
 348 other words, this subroutine acts as a filter by which you can exclude
 349 certain keys from being dumped. Default is 0, which means that hash keys
 350 are not sorted.</p>
 351 </li>
 352 <li>
 353 <p>$Data::Dumper::Deparse  <em>or</em>  $<em>OBJ</em>-&gt;Deparse(<em>[NEWVAL]</em>)</p>
 354 <p>Can be set to a boolean value to control whether code references are
 355 turned into perl source code. If set to a true value, <code>B::Deparse</code>
 356 will be used to get the source of the code reference. Using this option
 357 will force using the Perl implementation of the dumper, since the fast
 358 XSUB implementation doesn't support it.</p>
 359 <p>Caution : use this option only if you know that your coderefs will be
 360 properly reconstructed by <code>B::Deparse</code>.</p>
 361 </li>
 362 </ul>
 363 <p>
 364 </p>
 365 <h2><a name="exports">Exports</a></h2>
 366 <dl>
 367 <dt><strong>Dumper</strong>
 368
 369 </dl>
 370 <p>
 371 </p>
 372 <hr />
 373 <h1><a name="examples">EXAMPLES</a></h1>
 374 <p>Run these code snippets to get a quick feel for the behavior of this
 375 module.  When you are through with these examples, you may want to
 376 add or change the various configuration variables described above,
 377 to see their behavior.  (See the testsuite in the Data::Dumper
 378 distribution for more examples.)</p>
 379 <pre>
 380     use Data::Dumper;</pre>
 381 <pre>
 382     package Foo;
 383     sub new {bless {'a' =&gt; 1, 'b' =&gt; sub { return &quot;foo&quot; }}, $_[0]};</pre>
 384 <pre>
 385     package Fuz;                       # a weird REF-REF-SCALAR object
 386     sub new {bless \($_ = \ 'fu\'z'), $_[0]};</pre>
 387 <pre>
 388     package main;
 389     $foo = Foo-&gt;new;
 390     $fuz = Fuz-&gt;new;
 391     $boo = [ 1, [], &quot;abcd&quot;, \*foo,
 392              {1 =&gt; 'a', 023 =&gt; 'b', 0x45 =&gt; 'c'},
 393              \\&quot;p\q\'r&quot;, $foo, $fuz];</pre>
 394 <pre>
 395     ########
 396     # simple usage
 397     ########</pre>
 398 <pre>
 399     $bar = eval(Dumper($boo));
 400     print($@) if $@;
 401     print Dumper($boo), Dumper($bar);  # pretty print (no array indices)</pre>
 402 <pre>
 403     $Data::Dumper::Terse = 1;          # don't output names where feasible
 404     $Data::Dumper::Indent = 0;         # turn off all pretty print
 405     print Dumper($boo), &quot;\n&quot;;</pre>
 406 <pre>
 407     $Data::Dumper::Indent = 1;         # mild pretty print
 408     print Dumper($boo);</pre>
 409 <pre>
 410     $Data::Dumper::Indent = 3;         # pretty print with array indices
 411     print Dumper($boo);</pre>
 412 <pre>
 413     $Data::Dumper::Useqq = 1;          # print strings in double quotes
 414     print Dumper($boo);</pre>
 415 <pre>
 416     $Data::Dumper::Pair = &quot; : &quot;;       # specify hash key/value separator
 417     print Dumper($boo);</pre>
 418 <pre>
 419     ########
 420     # recursive structures
 421     ########</pre>
 422 <pre>
 423     @c = ('c');
 424     $c = \@c;
 425     $b = {};
 426     $a = [1, $b, $c];
 427     $b-&gt;{a} = $a;
 428     $b-&gt;{b} = $a-&gt;[1];
 429     $b-&gt;{c} = $a-&gt;[2];
 430     print Data::Dumper-&gt;Dump([$a,$b,$c], [qw(a b c)]);</pre>
 431 <pre>
 432     $Data::Dumper::Purity = 1;         # fill in the holes for eval
 433     print Data::Dumper-&gt;Dump([$a, $b], [qw(*a b)]); # print as @a
 434     print Data::Dumper-&gt;Dump([$b, $a], [qw(*b a)]); # print as %b</pre>
 435 <pre>
 436     $Data::Dumper::Deepcopy = 1;       # avoid cross-refs
 437     print Data::Dumper-&gt;Dump([$b, $a], [qw(*b a)]);</pre>
 438 <pre>
 439     $Data::Dumper::Purity = 0;         # avoid cross-refs
 440     print Data::Dumper-&gt;Dump([$b, $a], [qw(*b a)]);</pre>
 441 <pre>
 442     ########
 443     # deep structures
 444     ########</pre>
 445 <pre>
 446     $a = &quot;pearl&quot;;
 447     $b = [ $a ];
 448     $c = { 'b' =&gt; $b };
 449     $d = [ $c ];
 450     $e = { 'd' =&gt; $d };
 451     $f = { 'e' =&gt; $e };
 452     print Data::Dumper-&gt;Dump([$f], [qw(f)]);</pre>
 453 <pre>
 454     $Data::Dumper::Maxdepth = 3;       # no deeper than 3 refs down
 455     print Data::Dumper-&gt;Dump([$f], [qw(f)]);</pre>
 456 <pre>
 457     ########
 458     # object-oriented usage
 459     ########</pre>
 460 <pre>
 461     $d = Data::Dumper-&gt;new([$a,$b], [qw(a b)]);
 462     $d-&gt;Seen({'*c' =&gt; $c});            # stash a ref without printing it
 463     $d-&gt;Indent(3);
 464     print $d-&gt;Dump;
 465     $d-&gt;Reset-&gt;Purity(0);              # empty the seen cache
 466     print join &quot;----\n&quot;, $d-&gt;Dump;</pre>
 467 <pre>
 468     ########
 469     # persistence
 470     ########</pre>
 471 <pre>
 472     package Foo;
 473     sub new { bless { state =&gt; 'awake' }, shift }
 474     sub Freeze {
 475         my $s = shift;
 476         print STDERR &quot;preparing to sleep\n&quot;;
 477         $s-&gt;{state} = 'asleep';
 478         return bless $s, 'Foo::ZZZ';
 479     }</pre>
 480 <pre>
 481     package Foo::ZZZ;
 482     sub Thaw {
 483         my $s = shift;
 484         print STDERR &quot;waking up\n&quot;;
 485         $s-&gt;{state} = 'awake';
 486         return bless $s, 'Foo';
 487     }</pre>
 488 <pre>
 489     package Foo;
 490     use Data::Dumper;
 491     $a = Foo-&gt;new;
 492     $b = Data::Dumper-&gt;new([$a], ['c']);
 493     $b-&gt;Freezer('Freeze');
 494     $b-&gt;Toaster('Thaw');
 495     $c = $b-&gt;Dump;
 496     print $c;
 497     $d = eval $c;
 498     print Data::Dumper-&gt;Dump([$d], ['d']);</pre>
 499 <pre>
 500     ########
 501     # symbol substitution (useful for recreating CODE refs)
 502     ########</pre>
 503 <pre>
 504     sub foo { print &quot;foo speaking\n&quot; }
 505     *other = \&amp;foo;
 506     $bar = [ \&amp;other ];
 507     $d = Data::Dumper-&gt;new([\&amp;other,$bar],['*other','bar']);
 508     $d-&gt;Seen({ '*foo' =&gt; \&amp;foo });
 509     print $d-&gt;Dump;</pre>
 510 <pre>
 511     ########
 512     # sorting and filtering hash keys
 513     ########</pre>
 514 <pre>
 515     $Data::Dumper::Sortkeys = \&amp;my_filter;
 516     my $foo = { map { (ord, &quot;$_$_$_&quot;) } 'I'..'Q' };
 517     my $bar = { %$foo };
 518     my $baz = { reverse %$foo };
 519     print Dumper [ $foo, $bar, $baz ];</pre>
 520 <pre>
 521     sub my_filter {
 522         my ($hash) = @_;
 523         # return an array ref containing the hash keys to dump
 524         # in the order that you want them to be dumped
 525         return [
 526           # Sort the keys of %$foo in reverse numeric order
 527             $hash eq $foo ? (sort {$b &lt;=&gt; $a} keys %$hash) :
 528           # Only dump the odd number keys of %$bar
 529             $hash eq $bar ? (grep {$_ % 2} keys %$hash) :
 530           # Sort keys in default order for all other hashes
 531             (sort keys %$hash)
 532         ];
 533     }</pre>
 534 <p>
 535 </p>
 536 <hr />
 537 <h1><a name="bugs">BUGS</a></h1>
 538 <p>Due to limitations of Perl subroutine call semantics, you cannot pass an
 539 array or hash.  Prepend it with a <code>\</code> to pass its reference instead.  This
 540 will be remedied in time, now that Perl has subroutine prototypes.
 541 For now, you need to use the extended usage form, and prepend the
 542 name with a <code>*</code> to output it as a hash or array.</p>
 543 <p><code>Data::Dumper</code> cheats with CODE references.  If a code reference is
 544 encountered in the structure being processed (and if you haven't set
 545 the <code>Deparse</code> flag), an anonymous subroutine that
 546 contains the string '``DUMMY''' will be inserted in its place, and a warning
 547 will be printed if <code>Purity</code> is set.  You can <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_eval"><code>eval</code></a> the result, but bear
 548 in mind that the anonymous sub that gets created is just a placeholder.
 549 Someday, perl will have a switch to cache-on-demand the string
 550 representation of a compiled piece of code, I hope.  If you have prior
 551 knowledge of all the code refs that your data structures are likely
 552 to have, you can use the <a href="#item_seen"><code>Seen</code></a> method to pre-seed the internal reference
 553 table and make the dumped output point to them, instead.  See <a href="#examples">EXAMPLES</a>
 554 above.</p>
 555 <p>The <code>Useqq</code> and <code>Deparse</code> flags makes <a href="#item_dump"><code>Dump()</code></a> run slower, since the
 556 XSUB implementation does not support them.</p>
 557 <p>SCALAR objects have the weirdest looking <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_bless"><code>bless</code></a> workaround.</p>
 558 <p>Pure Perl version of <code>Data::Dumper</code> escapes UTF-8 strings correctly
 559 only in Perl 5.8.0 and later.</p>
 560 <p>
 561 </p>
 562 <h2><a name="note">NOTE</a></h2>
 563 <p>Starting from Perl 5.8.1 different runs of Perl will have different
 564 ordering of hash keys.  The change was done for greater security,
 565 see <a href="file://C|\msysgit\mingw\html/pod/perlsec.html#algorithmic_complexity_attacks">Algorithmic Complexity Attacks in the perlsec manpage</a>.  This means that
 566 different runs of Perl will have different Data::Dumper outputs if
 567 the data contains hashes.  If you need to have identical Data::Dumper
 568 outputs from different runs of Perl, use the environment variable
 569 PERL_HASH_SEED, see <a href="file://C|\msysgit\mingw\html/pod/perlrun.html#perl_hash_seed">PERL_HASH_SEED in the perlrun manpage</a>.  Using this restores
 570 the old (platform-specific) ordering: an even prettier solution might
 571 be to use the <code>Sortkeys</code> filter of Data::Dumper.</p>
 572 <p>
 573 </p>
 574 <hr />
 575 <h1><a name="author">AUTHOR</a></h1>
 576 <p>Gurusamy Sarathy        <a href="mailto:gsar@activestate.com">gsar@activestate.com</a></p>
 577 <p>Copyright (c) 1996-98 Gurusamy Sarathy. All rights reserved.
 578 This program is free software; you can redistribute it and/or
 579 modify it under the same terms as Perl itself.</p>
 580 <p>
 581 </p>
 582 <hr />
 583 <h1><a name="version">VERSION</a></h1>
 584 <p>Version 2.121  (Aug 24 2003)</p>
 585 <p>
 586 </p>
 587 <hr />
 588 <h1><a name="see_also">SEE ALSO</a></h1>
 589 <p><code>perl(1)</code></p>
 590 <table border="0" width="100%" cellspacing="0" cellpadding="3">
 591 <tr><td class="block" style="background-color: #cccccc" valign="middle">
 592 <big><strong><span class="block">&nbsp;Data::Dumper - stringified perl data structures, suitable for both printing and C&lt;eval&gt;</span></strong></big>
 593 </td></tr>
 594 </table>
 595
 596 </body>
 597
 598 </html>