File: perldbmfilter.html

package info (click to toggle)
perl-doc-html 5.26.0-4
  • links: PTS, VCS
  • area: main
  • in suites: sid
  • size: 39,400 kB
  • sloc: xml: 36; makefile: 7
file content (555 lines) | stat: -rw-r--r-- 27,890 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <title>perldbmfilter - perldoc.perl.org</title>
  <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
  <meta http-equiv="Content-Language" content="en-gb">
  <link rel="search" type="application/opensearchdescription+xml" title="Search perldoc.perl.org" href="/static/search.xml"/>
  <link href="static/css-20100830.css" rel="stylesheet" rev="stylesheet" type="text/css" media="screen">
  <link href="static/exploreperl.css" rel="stylesheet" rev="stylesheet" type="text/css">
</head>

<body onLoad="perldoc.startup();" onPageShow="if (event.persisted) perldoc.startup();">
    <div id="page">
      
      <div id="header">
	<div id="homepage_link">
	  <a href="index.html"></a>
	</div>
	<div id="strapline">
	  Perl Programming Documentation
	</div>
	<div id="download_link" class="download">
	  <a href="http://www.perl.org/get.html">Download Perl</a>
	</div>
	<div id="explore_link" class="download">
	  <a id="explore_anchor" href="#">Explore</a>
	</div>
      </div>
      
      <div id="body">
        <div id="left_column">
          <div class="side_group">
            
	    <div class="side_panel doc_panel">
              <p>Manual</p>
              <ul>
                <li><a href="index-overview.html">Overview</a>
                <li><a href="index-tutorials.html">Tutorials</a>
                <li><a href="index-faq.html">FAQs</a>
                <li><a href="index-history.html">History / Changes</a>
                <li><a href="index-licence.html">License</a>
              </ul>
            </div>
            <div class="side_panel doc_panel">
              <p>Reference</p>
              <ul>
                <li><a href="index-language.html">Language</a>
                <li><a href="index-functions.html">Functions</a>
                <li><a href="perlop.html">Operators</a>
                <li><a href="perlvar.html">Special Variables</a>
                <li><a href="index-pragmas.html">Pragmas</a>
                <li><a href="index-utilities.html">Utilities</a>
                <li><a href="index-internals.html">Internals</a>
                <li><a href="index-platforms.html">Platform Specific</a>
              </ul>
            </div>
            <div class="side_panel doc_panel">
              <p>Modules</p>
              <ul>
		<li>
		
                
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		
                  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		
                  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		    
		  
		
                  
		
                  
		
                  
		    
		  
		
                  
		
                  
		
		
                    <a href="index-modules-A.html">A</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-B.html">B</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-C.html">C</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-D.html">D</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-E.html">E</a>
                    
                      
                        <li>
                      
                    
                
                    <a href="index-modules-F.html">F</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-G.html">G</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-H.html">H</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-I.html">I</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-L.html">L</a>
                    
                      
                        <li>
                      
                    
                
                    <a href="index-modules-M.html">M</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-N.html">N</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-O.html">O</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-P.html">P</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-S.html">S</a>
                    
                      
                        <li>
                      
                    
                
                    <a href="index-modules-T.html">T</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-U.html">U</a>
                    
                      
                        &bull;
                      
                    
                
                    <a href="index-modules-X.html">X</a>
                    
                
              </ul>
            </div>
            
	      <div class="side_panel doc_panel">
		<p>Tools</p>
		<ul>
		  <li><a href="preferences.html">Preferences</a>
		</ul>
	      </div>
            
          </div>
        </div>
        <div id="centre_column">
          <div id="content_header">
            <div id="title_bar">
              <div id="page_name">
                <h1>perldbmfilter</h1>
              </div>
              <div id="perl_version">
                Perl 5 version 26.0 documentation
              </div>
              <div class="page_links" id="page_links_top">
                <a href="#" onClick="toolbar.goToTop();return false;">Go to top</a>
		
              </div>
	      <div class="page_links" id="page_links_bottom">
		
                  <a href="#" id="page_index_toggle">Show page index</a> &bull;
		
                <a href="#" id="recent_pages_toggle">Show recent pages</a>		
	      </div>
	      <div id="search_form">
		<form action="search.html" method="GET" id="search">
		  <input type="text" name="q" id="search_box" alt="Search">
		</form>
	      </div>
            </div>
            <div id="breadcrumbs">
                
    <a href="index.html">Home</a> &gt;
    
      
        <a href="index-language.html">Language reference</a> &gt;
      
    
    perldbmfilter
  

            </div>
          </div>
          <div id="content_body">
	    <!--[if lt IE 7]>
 <div class="noscript">
   <p>
     <strong>It looks like you're using Internet Explorer 6. This is a very old
     browser which does not offer full support for modern websites.</strong>
   </p>
   <p>
     Unfortunately this means that this website will not work on
     your computer.
   </p>
   <p>
     Don't miss out though! To view the site (and get a better experience from
     many other websites), simply upgrade to
     <a href="http://www.microsoft.com/windows/Internet-explorer/default.aspx">Internet
Explorer 8</a>
     or download an alternative browser such as
     <a href="http://www.mozilla.com/en-US/firefox/firefox.html">Firefox</a>,
     <a href="http://www.apple.com/safari/download/">Safari</a>, or
     <a href="http://www.google.co.uk/chrome">Google Chrome</a>.
   </p>
   <p>
     All of these browsers are free. If you're using a PC at work, you may
     need to contact your IT administrator.
   </p>
 </div>
<![endif]-->
	    <noscript>
	      <div class="noscript">
	      <p>
                <strong>Please note: Many features of this site require JavaScript. You appear to have JavaScript disabled,
	        or are running a non-JavaScript capable web browser.</strong>
	      </p>
	      <p>
		To get the best experience, please enable JavaScript or download a modern web browser such as <a href="http://www.microsoft.com/windows/Internet-explorer/default.aspx">Internet Explorer 8</a>, <a href="http://www.mozilla.com/en-US/firefox/firefox.html">Firefox</a>, <a href="http://www.apple.com/safari/download/">Safari</a>, or <a href="http://www.google.co.uk/chrome">Google Chrome</a>.
              </p>
	      </div>
	    </noscript>

	    <div id="recent_pages" class="hud_container">
	      <div id="recent_pages_header" class="hud_header">
		<div id="recent_pages_close" class="hud_close"><a href="#" onClick="recentPages.hide();return false;"></a></div>
		<div id="recent_pages_title" class="hud_title"><span class="hud_span_top">Recently read</span></div>
		<div id="recent_pages_topright" class="hud_topright"></div>
	      </div>
	      <div id="recent_pages_content" class="hud_content">
	      </div>
	      <div id="recent_pages_footer" class="hud_footer">
		<div id="recent_pages_bottomleft" class="hud_bottomleft"></div>
		<div id="recent_pages_bottom" class="hud_bottom"><span class="hud_span_bottom"></span></div>
		<div id="recent_pages_resize" class="hud_resize"></div>
	      </div>
	    </div>
  
	    <div id="from_search"></div>
            <h1>perldbmfilter</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><ul><li><a href="#The-Filter">The Filter</a><li><a href="#An-Example%3a-the-NULL-termination-problem.">An Example: the NULL termination problem.</a><li><a href="#Another-Example%3a-Key-is-a-C-int.">Another Example: Key is a C int.</a></ul><li><a href="#SEE-ALSO">SEE ALSO</a><li><a href="#AUTHOR">AUTHOR</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>perldbmfilter - Perl DBM Filters</p>
<a name="SYNOPSIS"></a><h1>SYNOPSIS</h1>
<pre class="verbatim"><ol><li>    <span class="i">$db</span> = <a class="l_k" href="functions/tie.html">tie</a> <span class="i">%hash</span><span class="cm">,</span> <span class="q">&#39;DBM&#39;</span><span class="cm">,</span> ...</li><li></li><li>    <span class="i">$old_filter</span> = <span class="i">$db</span><span class="i">-&gt;filter_store_key</span>  <span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> ... <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$old_filter</span> = <span class="i">$db</span><span class="i">-&gt;filter_store_value</span><span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> ... <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$old_filter</span> = <span class="i">$db</span><span class="i">-&gt;filter_fetch_key</span>  <span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> ... <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$old_filter</span> = <span class="i">$db</span><span class="i">-&gt;filter_fetch_value</span><span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> ... <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li></ol></pre><a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>The four <code class="inline"><span class="w">filter_</span>*</code>
 methods shown above are available in all the DBM
modules that ship with Perl, namely DB_File, GDBM_File, NDBM_File,
ODBM_File and SDBM_File.</p>
<p>Each of the methods works identically, and is used to install (or
uninstall) a single DBM Filter. The only difference between them is the
place that the filter is installed.</p>
<p>To summarise:</p>
<ul>
<li><a name="*filter_store_key*"></a><b><b>filter_store_key</b></b>
<p>If a filter has been installed with this method, it will be invoked
every time you write a key to a DBM database.</p>
</li>
<li><a name="*filter_store_value*"></a><b><b>filter_store_value</b></b>
<p>If a filter has been installed with this method, it will be invoked
every time you write a value to a DBM database.</p>
</li>
<li><a name="*filter_fetch_key*"></a><b><b>filter_fetch_key</b></b>
<p>If a filter has been installed with this method, it will be invoked
every time you read a key from a DBM database.</p>
</li>
<li><a name="*filter_fetch_value*"></a><b><b>filter_fetch_value</b></b>
<p>If a filter has been installed with this method, it will be invoked
every time you read a value from a DBM database.</p>
</li>
</ul>
<p>You can use any combination of the methods from none to all four.</p>
<p>All filter methods return the existing filter, if present, or <code class="inline"><a class="l_k" href="functions/undef.html">undef</a></code>
if not.</p>
<p>To delete a filter pass <code class="inline"><a class="l_k" href="functions/undef.html">undef</a></code> to it.</p>
<a name="The-Filter"></a><h2>The Filter</h2>
<p>When each filter is called by Perl, a local copy of <code class="inline"><span class="i">$_</span></code>
 will contain
the key or value to be filtered. Filtering is achieved by modifying
the contents of <code class="inline"><span class="i">$_</span></code>
. The return code from the filter is ignored.</p>
<a name="An-Example%3a-the-NULL-termination-problem."></a><h2>An Example: the NULL termination problem.</h2>
<p>DBM Filters are useful for a class of problems where you <i>always</i>
want to make the same transformation to all keys, all values or both.</p>
<p>For example, consider the following scenario. You have a DBM database
that you need to share with a third-party C application. The C application
assumes that <i>all</i> keys and values are NULL terminated. Unfortunately
when Perl writes to DBM databases it doesn't use NULL termination, so
your Perl application will have to manage NULL termination itself. When
you write to the database you will have to use something like this:</p>
<pre class="verbatim"><ol><li>    <span class="i">$hash</span>{<span class="q">&quot;$key\0&quot;</span>} = <span class="q">&quot;$value\0&quot;</span><span class="sc">;</span></li></ol></pre><p>Similarly the NULL needs to be taken into account when you are considering
the length of existing keys/values.</p>
<p>It would be much better if you could ignore the NULL terminations issue
in the main application code and have a mechanism that automatically
added the terminating NULL to all keys and values whenever you write to
the database and have them removed when you read from the database. As I'm
sure you have already guessed, this is a problem that DBM Filters can
fix very easily.</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">warnings</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">SDBM_File</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">Fcntl</span><span class="sc">;</span></li><li></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">%hash</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$filename</span> = <span class="q">&quot;filt&quot;</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/unlink.html">unlink</a> <span class="i">$filename</span><span class="sc">;</span></li><li></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$db</span> = <a class="l_k" href="functions/tie.html">tie</a><span class="s">(</span><span class="i">%hash</span><span class="cm">,</span> <span class="q">&#39;SDBM_File&#39;</span><span class="cm">,</span> <span class="i">$filename</span><span class="cm">,</span> <span class="w">O_RDWR</span>|<span class="w">O_CREAT</span><span class="cm">,</span> <span class="n">0640</span><span class="s">)</span></li><li>      or <a class="l_k" href="functions/die.html">die</a> <span class="q">&quot;Cannot open $filename: $!\n&quot;</span><span class="sc">;</span></li><li></li><li>    <span class="c"># Install DBM Filters</span></li><li>    <span class="i">$db</span><span class="i">-&gt;filter_fetch_key</span>  <span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> <span class="q">s/\0$//</span>    <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$db</span><span class="i">-&gt;filter_store_key</span>  <span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> <span class="i">$_</span> .= <span class="q">&quot;\0&quot;</span> <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$db</span><span class="i">-&gt;filter_fetch_value</span><span class="s">(</span> </li><li>        <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> <a class="l_k" href="functions/no.html">no</a> <span class="w">warnings</span> <span class="q">&#39;uninitialized&#39;</span><span class="sc">;</span> <span class="q">s/\0$//</span> <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$db</span><span class="i">-&gt;filter_store_value</span><span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> <span class="i">$_</span> .= <span class="q">&quot;\0&quot;</span> <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li></li><li>    <span class="i">$hash</span>{<span class="q">&quot;abc&quot;</span>} = <span class="q">&quot;def&quot;</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$a</span> = <span class="i">$hash</span>{<span class="q">&quot;ABC&quot;</span>}<span class="sc">;</span></li><li>    <span class="c"># ...</span></li><li>    <a class="l_k" href="functions/undef.html">undef</a> <span class="i">$db</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/untie.html">untie</a> <span class="i">%hash</span><span class="sc">;</span></li></ol></pre><p>The code above uses SDBM_File, but it will work with any of the DBM
modules.</p>
<p>Hopefully the contents of each of the filters should be
self-explanatory. Both "fetch" filters remove the terminating NULL,
and both "store" filters add a terminating NULL.</p>
<a name="Another-Example%3a-Key-is-a-C-int."></a><h2>Another Example: Key is a C int.</h2>
<p>Here is another real-life example. By default, whenever Perl writes to
a DBM database it always writes the key and value as strings. So when
you use this:</p>
<pre class="verbatim"><ol><li>    <span class="i">$hash</span>{<span class="n">12345</span>} = <span class="q">&quot;something&quot;</span><span class="sc">;</span></li></ol></pre><p>the key 12345 will get stored in the DBM database as the 5 byte string
"12345". If you actually want the key to be stored in the DBM database
as a C int, you will have to use <code class="inline"><a class="l_k" href="functions/pack.html">pack</a></code> when writing, and <code class="inline"><a class="l_k" href="functions/unpack.html">unpack</a></code>
when reading.</p>
<p>Here is a DBM Filter that does it:</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">warnings</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">DB_File</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">%hash</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$filename</span> = <span class="q">&quot;filt&quot;</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/unlink.html">unlink</a> <span class="i">$filename</span><span class="sc">;</span></li><li></li><li></li><li>    <a class="l_k" href="functions/my.html">my</a> <span class="i">$db</span> = <a class="l_k" href="functions/tie.html">tie</a> <span class="i">%hash</span><span class="cm">,</span> <span class="q">&#39;DB_File&#39;</span><span class="cm">,</span> <span class="i">$filename</span><span class="cm">,</span> <span class="w">O_CREAT</span>|<span class="w">O_RDWR</span><span class="cm">,</span> <span class="n">0666</span><span class="cm">,</span></li><li>        <span class="i">$DB_HASH</span> <a class="l_k" href="functions/or.html">or</a> <a class="l_k" href="functions/die.html">die</a> <span class="q">&quot;Cannot open $filename: $!\n&quot;</span><span class="sc">;</span></li><li></li><li>    <span class="i">$db</span><span class="i">-&gt;filter_fetch_key</span>  <span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> <span class="i">$_</span> = <a class="l_k" href="functions/unpack.html">unpack</a><span class="s">(</span><span class="q">&quot;i&quot;</span><span class="cm">,</span> <span class="i">$_</span><span class="s">)</span> <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$db</span><span class="i">-&gt;filter_store_key</span>  <span class="s">(</span> <a class="l_k" href="functions/sub.html">sub</a> <span class="s">{</span> <span class="i">$_</span> = <a class="l_k" href="functions/pack.html">pack</a> <span class="s">(</span><span class="q">&quot;i&quot;</span><span class="cm">,</span> <span class="i">$_</span><span class="s">)</span> <span class="s">}</span> <span class="s">)</span><span class="sc">;</span></li><li>    <span class="i">$hash</span>{<span class="n">123</span>} = <span class="q">&quot;def&quot;</span><span class="sc">;</span></li><li>    <span class="c"># ...</span></li><li>    <a class="l_k" href="functions/undef.html">undef</a> <span class="i">$db</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/untie.html">untie</a> <span class="i">%hash</span><span class="sc">;</span></li></ol></pre><p>The code above uses DB_File, but again it will work with any of the
DBM modules.</p>
<p>This time only two filters have been used; we only need to manipulate
the contents of the key, so it wasn't necessary to install any value
filters.</p>
<a name="SEE-ALSO"></a><h1>SEE ALSO</h1>
<p><a href="DB_File.html">DB_File</a>, <a href="http://search.cpan.org/perldoc/GDBM_File">GDBM_File</a>, <a href="NDBM_File.html">NDBM_File</a>, <a href="http://search.cpan.org/perldoc/ODBM_File">ODBM_File</a> and <a href="SDBM_File.html">SDBM_File</a>.</p>
<a name="AUTHOR"></a><h1>AUTHOR</h1>
<p>Paul Marquess</p>




  <div id="page_index" class="hud_container">
    <div id="page_index_header" class="hud_header">
      <div id="page_index_close" class="hud_close"><a href="#" onClick="pageIndex.hide();return false;"></a></div>
      <div id="page_index_title" class="hud_title"><span class="hud_span_top">Page index</span></div>
      <div id="page_index_topright" class="hud_topright"></div>
    </div>
    <div id="page_index_content" class="hud_content">
      <ul><li><a href="#NAME">NAME</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><ul><li><a href="#The-Filter">The Filter</a><li><a href="#An-Example%3a-the-NULL-termination-problem.">An Example: the NULL termination problem.</a><li><a href="#Another-Example%3a-Key-is-a-C-int.">Another Example: Key is a C int.</a></ul><li><a href="#SEE-ALSO">SEE ALSO</a><li><a href="#AUTHOR">AUTHOR</a></ul>
    </div>
    <div id="page_index_footer" class="hud_footer">
      <div id="page_index_bottomleft" class="hud_bottomleft"></div>
      <div id="page_index_bottom" class="hud_bottom"><span class="hud_span_bottom"></span></div>
      <div id="page_index_resize" class="hud_resize"></div>
    </div>
  </div>


	    &nbsp;
          </div>
          <div id="content_footer">
          </div>
        </div>
        <div class="clear"></div>
      </div>
      
    <div id="footer">
      <div id="footer_content">
        <div id="footer_strapline">
          perldoc.perl.org - Official documentation for the Perl programming language
        </div>
        <div id="footer_links">
          <div id="address">
            <p class="name">Contact details</p>
            <p class="address">
	      Site maintained by <a href="mailto:jj@jonallen.info">Jon Allen (JJ)</a><br>
	    </p>
            <p class="contact">
              Documentation maintained by the <a href="http://lists.cpan.org/showlist.cgi?name=perl5-porters">Perl 5 Porters</a>
            </p>
          </div>
          <ul class="f1">
            <li>Manual
              <ul class="f2">
                <li><a href="index-overview.html">Overview</a>
                <li><a href="index-tutorials.html">Tutorials</a>
                <li><a href="index-faq.html">FAQs</a>
                <li><a href="index-history.html">Changes</a>
              </ul>
            <li>Reference
              <ul class="f2">
                <li><a href="index-language.html">Language</a>
                <li><a href="index-functions.html">Functions</a>
                <li><a href="perlop.html">Operators</a>
                <li><a href="perlvar.html">Variables</a>
              </ul>
            <li>Modules
              <ul class="f2">
                <li><a href="index-modules-A.html">Modules</a>
                <li><a href="index-pragmas.html">Pragmas</a>
                <li><a href="index-utilities.html">Utilities</a>
              </ul>
            <li>Misc
              <ul class="f2">
                <li><a href="index-licence.html">License</a>
                <li><a href="index-internals.html">Internals</a>
                <li><a href="index-platforms.html">Platforms</a>
              </ul>          </ul>
          <div class="clear"></div>
        </div>
      </div>
      <div id="footer_end">
      </div>
    </div>
      
    </div>
      <script language="JavaScript" type="text/javascript" src="static/exploreperl.js"></script>
      <script language="JavaScript" src="static/combined-20100403.js" type="text/javascript"></script>
<script language="JavaScript" type="text/javascript">
  perldoc.setPath(0);
  perldoc.pageName    = 'perldbmfilter';
  perldoc.pageAddress = 'perldbmfilter.html';
  perldoc.contentPage = 1;
  explorePerl.render();
  explorePerl.addEvents('explore_anchor');
</script>
    
  </body>
</html>