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            <h1>SDBM_File</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><ul><li><a href="#Tie">Tie</a></ul><li><a href="#EXPORTS">EXPORTS</a><li><a href="#DIAGNOSTICS">DIAGNOSTICS</a><ul><li><a href="#sdbm-store-returned--1%2c-errno-22%2c-key-%22...%22-at-...">sdbm store returned -1, errno 22, key "..." at ...</a></ul><li><a href="#BUGS-AND-WARNINGS">BUGS AND WARNINGS</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>SDBM_File - Tied access to sdbm files</p>
<a name="SYNOPSIS"></a><h1>SYNOPSIS</h1>
<pre class="verbatim"><ol><li> <a class="l_k" href="functions/use.html">use</a> <span class="w">Fcntl</span><span class="sc">;</span>   <span class="c"># For O_RDWR, O_CREAT, etc.</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></li><li> <a class="l_k" href="functions/tie.html">tie</a><span class="s">(</span><span class="i">%h</span><span class="cm">,</span> <span class="q">&#39;SDBM_File&#39;</span><span class="cm">,</span> <span class="q">&#39;filename&#39;</span><span class="cm">,</span> <span class="w">O_RDWR</span>|<span class="w">O_CREAT</span><span class="cm">,</span> <span class="n">0666</span><span class="s">)</span></li><li>   or <a class="l_k" href="functions/die.html">die</a> <span class="q">&quot;Couldn&#39;t tie SDBM file &#39;filename&#39;: $!; aborting&quot;</span><span class="sc">;</span></li><li></li><li> <span class="c"># Now read and change the hash</span></li><li> <span class="i">$h</span>{<span class="w">newkey</span>} = <span class="w">newvalue</span><span class="sc">;</span></li><li> <a class="l_k" href="functions/print.html">print</a> <span class="i">$h</span>{<span class="w">oldkey</span>}<span class="sc">;</span> </li><li> ...</li><li></li><li> <a class="l_k" href="functions/untie.html">untie</a> <span class="i">%h</span><span class="sc">;</span></li></ol></pre><a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p><code class="inline"><span class="w">SDBM_File</span></code>
 establishes a connection between a Perl hash variable and
a file in SDBM_File format.  You can manipulate the data in the file
just as if it were in a Perl hash, but when your program exits, the
data will remain in the file, to be used the next time your program
runs.</p>
<a name="Tie"></a><h2>Tie</h2>
<p>Use <code class="inline"><span class="w">SDBM_File</span></code>
 with the Perl built-in <code class="inline"><a class="l_k" href="functions/tie.html">tie</a></code> function to establish
the connection between the variable and the file.</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/tie.html">tie</a> <span class="i">%hash</span><span class="cm">,</span> <span class="q">&#39;SDBM_File&#39;</span><span class="cm">,</span> <span class="i">$basename</span><span class="cm">,</span> <span class="i">$modeflags</span><span class="cm">,</span> <span class="i">$perms</span><span class="sc">;</span></li><li></li><li>    <a class="l_k" href="functions/tie.html">tie</a> <span class="i">%hash</span><span class="cm">,</span> <span class="q">&#39;SDBM_File&#39;</span><span class="cm">,</span> <span class="i">$dirfile</span><span class="cm">,</span>  <span class="i">$modeflags</span><span class="cm">,</span> <span class="i">$perms</span><span class="cm">,</span> <span class="i">$pagfilename</span><span class="sc">;</span></li></ol></pre><p><code class="inline"><span class="i">$basename</span></code>
 is the base filename for the database.  The database is two
files with ".dir" and ".pag" extensions appended to <code class="inline"><span class="i">$basename</span></code>
,</p>
<pre class="verbatim"><ol><li>    <span class="i">$basename</span>.<span class="w">dir</span>     <span class="s">(</span><a class="l_k" href="functions/or.html">or</a> .<span class="w">sdbm_dir</span> <span class="w">on</span> <span class="w">VMS</span><span class="cm">,</span> <span class="w">per</span> <span class="w">DIRFEXT</span> <span class="w">constant</span><span class="s">)</span></li><li>    <span class="i">$basename</span>.<span class="w">pag</span></li></ol></pre><p>The two filenames can also be given separately in full as <code class="inline"><span class="i">$dirfile</span></code>

and <code class="inline"><span class="i">$pagfilename</span></code>
.  This suits for two files without ".dir" and ".pag"
extensions, perhaps for example two files from <a href="File/Temp.html">File::Temp</a>.</p>
<p><code class="inline"><span class="i">$modeflags</span></code>
 can be the following constants from the <code class="inline"><span class="w">Fcntl</span></code>
 module (in
the style of the <i>open(2)</i> system call),</p>
<pre class="verbatim"><ol><li>    <span class="w">O_RDONLY</span>          <a class="l_k" href="functions/read.html">read</a>-<span class="w">only</span> <span class="w">access</span></li><li>    <span class="w">O_WRONLY</span>          <a class="l_k" href="functions/write.html">write</a>-<span class="w">only</span> <span class="w">access</span></li><li>    <span class="w">O_RDWR</span>            <a class="l_k" href="functions/read.html">read</a> <a class="l_k" href="functions/and.html">and</a> <a class="l_k" href="functions/write.html">write</a> <span class="w">access</span></li></ol></pre><p>If you want to create the file if it does not already exist then bitwise-OR
(<code class="inline">|</code>) <code class="inline"><span class="w">O_CREAT</span></code>
 too.  If you omit <code class="inline"><span class="w">O_CREAT</span></code>
 and the database does not
already exist then the <code class="inline"><a class="l_k" href="functions/tie.html">tie</a></code> call will fail.</p>
<pre class="verbatim"><ol><li>    <span class="w">O_CREAT</span>           <span class="w">create</span> <span class="w">database</span> <a class="l_k" href="functions/if.html">if</a> <span class="w">doesn&#39;t</span> <span class="w">already</span> <span class="w">exist</span></li></ol></pre><p><code class="inline"><span class="i">$perms</span></code>
 is the file permissions bits to use if new database files are
created.  This parameter is mandatory even when not creating a new database.
The permissions will be reduced by the user's umask so the usual value here
would be 0666, or if some very private data then 0600.  (See
<a href="functions/umask.html">umask</a>.)</p>
<a name="EXPORTS"></a><h1>EXPORTS</h1>
<p>SDBM_File optionally exports the following constants:</p>
<ul>
<li>
<p><code class="inline"><span class="w">PAGFEXT</span></code>
 - the extension used for the page file, usually <code class="inline">.<span class="w">pag</span></code>
.</p>
</li>
<li>
<p><code class="inline"><span class="w">DIRFEXT</span></code>
 - the extension used for the directory file, <code class="inline">.<span class="w">dir</span></code>

everywhere but VMS, where it is <code class="inline">.<span class="w">sdbm_dir</span></code>
.</p>
</li>
<li>
<p><code class="inline"><span class="w">PAIRMAX</span></code>
 - the maximum size of a stored hash entry, including the
length of both the key and value.</p>
</li>
</ul>
<p>These constants can also be used with fully qualified names,
eg. <code class="inline"><span class="w">SDBM_File::PAGFEXT</span></code>
.</p>
<a name="DIAGNOSTICS"></a><h1>DIAGNOSTICS</h1>
<p>On failure, the <code class="inline"><a class="l_k" href="functions/tie.html">tie</a></code> call returns an undefined value and probably
sets <code class="inline"><span class="i">$!</span></code>
 to contain the reason the file could not be tied.</p>
<a name="sdbm-store-returned--1%2c-errno-22%2c-key-%22...%22-at-..."></a><h2><code class="inline">sdbm store returned -1, errno 22, key "..." at ...</code></h2>
<p>This warning is emitted when you try to store a key or a value that
is too long.  It means that the change was not recorded in the
database.  See BUGS AND WARNINGS below.</p>
<a name="BUGS-AND-WARNINGS"></a><h1>BUGS AND WARNINGS</h1>
<p>There are a number of limits on the size of the data that you can
store in the SDBM file.  The most important is that the length of a
key, plus the length of its associated value, may not exceed 1008
bytes.</p>
<p>See <a href="functions/tie.html">tie</a>, <a href="perldbmfilter.html">perldbmfilter</a>, <a href="Fcntl.html">Fcntl</a></p>




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