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<h1>use</h1>
<div class="mod_az_list">
<a href="../index-functions.html">Perl functions A-Z</a> |
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<ul>
<li><a name="use-Module-VERSION-LIST"></a><b>use Module VERSION LIST</b>
<p> </p>
</li>
</ul>
<ul>
<li><a name="use-Module-VERSION"></a><b>use Module VERSION</b>
</li>
<li><a name="use-Module-LIST"></a><b>use Module LIST</b>
</li>
<li><a name="use-Module"></a><b>use Module</b>
</li>
<li><a name="use-VERSION"></a><b>use VERSION</b>
<p>Imports some semantics into the current package from the named module,
generally by aliasing certain subroutine or variable names into your
package. It is exactly equivalent to</p>
<pre class="verbatim"><ol><li> BEGIN <span class="s">{</span> <a class="l_k" href="../functions/require.html">require</a> <span class="w">Module</span><span class="sc">;</span> <span class="w">Module</span><span class="w">->import</span><span class="s">(</span> <span class="w">LIST</span> <span class="s">)</span><span class="sc">;</span> <span class="s">}</span></li></ol></pre><p>except that Module <i>must</i> be a bareword.</p>
<p>In the peculiar <code class="inline"><a class="l_k" href="../functions/use.html">use</a> <span class="w">VERSION</span></code>
form, VERSION may be either a numeric
argument such as 5.006, which will be compared to <code class="inline"><span class="i">$]</span></code>
, or a literal of
the form v5.6.1, which will be compared to <code class="inline"><span class="i">$^V</span></code>
(aka $PERL_VERSION). A
fatal error is produced if VERSION is greater than the version of the
current Perl interpreter; Perl will not attempt to parse the rest of the
file. Compare with <a href="../functions/require.html">"require"</a>, which can do a similar check at run time.
Symmetrically, <code class="inline"><a class="l_k" href="../functions/no.html">no</a> <span class="w">VERSION</span></code>
allows you to specify that you want a version
of perl older than the specified one.</p>
<p>Specifying VERSION as a literal of the form v5.6.1 should generally be
avoided, because it leads to misleading error messages under earlier
versions of Perl (that is, prior to 5.6.0) that do not support this
syntax. The equivalent numeric version should be used instead.</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/use.html">use</a> <span class="v">v5.6.1</span><span class="sc">;</span> <span class="c"># compile time version check</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="v">5.6.1</span><span class="sc">;</span> <span class="c"># ditto</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="n">5.006_001</span><span class="sc">;</span> <span class="c"># ditto; preferred for backwards compatibility</span></li></ol></pre><p>This is often useful if you need to check the current Perl version before
<code class="inline"><a class="l_k" href="../functions/use.html">use</a></code>ing library modules that won't work with older versions of Perl.
(We try not to do this more than we have to.)</p>
<p>Also, if the specified perl version is greater than or equal to 5.9.5,
<code class="inline"><a class="l_k" href="../functions/use.html">use</a> <span class="w">VERSION</span></code>
will also load the <code class="inline"><span class="w">feature</span></code>
pragma and enable all
features available in the requested version. See <a href="../feature.html">feature</a>.</p>
<p>The <code class="inline">BEGIN</code>
forces the <code class="inline"><a class="l_k" href="../functions/require.html">require</a></code> and <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> to happen at compile time. The
<code class="inline"><a class="l_k" href="../functions/require.html">require</a></code> makes sure the module is loaded into memory if it hasn't been
yet. The <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> is not a builtin--it's just an ordinary static method
call into the <code class="inline"><span class="w">Module</span></code>
package to tell the module to import the list of
features back into the current package. The module can implement its
<code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> method any way it likes, though most modules just choose to
derive their <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> method via inheritance from the <code class="inline"><span class="w">Exporter</span></code>
class that
is defined in the <code class="inline"><span class="w">Exporter</span></code>
module. See <a href="../Exporter.html">Exporter</a>. If no <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code>
method can be found then the call is skipped, even if there is an AUTOLOAD
method.</p>
<p>If you do not want to call the package's <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> method (for instance,
to stop your namespace from being altered), explicitly supply the empty list:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">Module</span> <span class="s">(</span><span class="s">)</span><span class="sc">;</span></li></ol></pre><p>That is exactly equivalent to</p>
<pre class="verbatim"><ol><li> BEGIN <span class="s">{</span> <a class="l_k" href="../functions/require.html">require</a> <span class="w">Module</span> <span class="s">}</span></li></ol></pre><p>If the VERSION argument is present between Module and LIST, then the
<code class="inline"><a class="l_k" href="../functions/use.html">use</a></code> will call the VERSION method in class Module with the given
version as an argument. The default VERSION method, inherited from
the UNIVERSAL class, croaks if the given version is larger than the
value of the variable <code class="inline"><span class="i">$Module::VERSION</span></code>
.</p>
<p>Again, there is a distinction between omitting LIST (<code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> called
with no arguments) and an explicit empty LIST <code class="inline"><span class="s">(</span><span class="s">)</span></code>
(<code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> not
called). Note that there is no comma after VERSION!</p>
<p>Because this is a wide-open interface, pragmas (compiler directives)
are also implemented this way. Currently implemented pragmas are:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">constant</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">diagnostics</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">integer</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">sigtrap</span> <span class="q">qw(SEGV BUS)</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">strict</span> <span class="q">qw(subs vars refs)</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">subs</span> <span class="q">qw(afunc blurfl)</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">warnings</span> <span class="q">qw(all)</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/use.html">use</a> <a class="l_k" href="../functions/sort.html">sort</a> <span class="q">qw(stable _quicksort _mergesort)</span><span class="sc">;</span></li></ol></pre><p>Some of these pseudo-modules import semantics into the current
block scope (like <code class="inline"><span class="w">strict</span></code>
or <code class="inline"><span class="w">integer</span></code>
, unlike ordinary modules,
which import symbols into the current package (which are effective
through the end of the file).</p>
<p>There's a corresponding <code class="inline"><a class="l_k" href="../functions/no.html">no</a></code> command that unimports meanings imported
by <code class="inline"><a class="l_k" href="../functions/use.html">use</a></code>, i.e., it calls <code class="inline"><span class="w">unimport</span> <span class="w">Module</span> <span class="w">LIST</span></code>
instead of <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code>.
It behaves exactly as <code class="inline"><a class="l_k" href="../functions/import.html">import</a></code> does with respect to VERSION, an
omitted LIST, empty LIST, or no unimport method being found.</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/no.html">no</a> <span class="w">integer</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/no.html">no</a> <span class="w">strict</span> <span class="q">'refs'</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/no.html">no</a> <span class="w">warnings</span><span class="sc">;</span></li></ol></pre><p>See <a href="../perlmodlib.html">perlmodlib</a> for a list of standard modules and pragmas. See <a href="../perlrun.html">perlrun</a>
for the <code class="inline">-M</code>
and <code class="inline">-m</code> command-line options to perl that give <code class="inline"><a class="l_k" href="../functions/use.html">use</a></code>
functionality from the command-line.</p>
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