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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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      <div id="breadCrumbs"><a href="index.html">Home</a> &gt; <a href="index-pragmas.html">Pragmas</a> &gt; strict</div>
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      <div id="contentBody"><div class="title_container"><div class="page_title">strict</div></div><ul><li><a href="#NAME">NAME</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><li><a href="#HISTORY">HISTORY</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>strict - Perl pragma to restrict unsafe constructs</p>
<a name="SYNOPSIS"></a><h1>SYNOPSIS</h1>
<pre class="verbatim">    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span><span class="sc">;</span></pre>
<pre class="verbatim">    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&quot;vars&quot;</span><span class="sc">;</span>
    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&quot;refs&quot;</span><span class="sc">;</span>
    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&quot;subs&quot;</span><span class="sc">;</span></pre>
<pre class="verbatim">    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span><span class="sc">;</span>
    <a class="l_k" href="functions/no.html">no</a> <span class="w">strict</span> <span class="q">&quot;vars&quot;</span><span class="sc">;</span></pre>
<a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>If no import list is supplied, all possible restrictions are assumed.
(This is the safest mode to operate in, but is sometimes too strict for
casual programming.)  Currently, there are three possible things to be
strict about:  "subs", "vars", and "refs".</p>
<ul>
<li><a name="'strict-refs'"></a><b><code class="inline"><span class="w">strict</span> <span class="w">refs</span></code>
</b>
<p>This generates a runtime error if you 
use symbolic references (see <a href="perlref.html">perlref</a>).</p>
<pre class="verbatim">    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&#39;refs&#39;</span><span class="sc">;</span>
    <span class="i">$ref</span> = \<span class="i">$foo</span><span class="sc">;</span>
    <a class="l_k" href="functions/print.html">print</a> <span class="i">$$ref</span><span class="sc">;</span>	<span class="c"># ok</span>
    <span class="i">$ref</span> = <span class="q">&quot;foo&quot;</span><span class="sc">;</span>
    <a class="l_k" href="functions/print.html">print</a> <span class="i">$$ref</span><span class="sc">;</span>	<span class="c"># runtime error; normally ok</span>
    <span class="i">$file</span> = <span class="q">&quot;STDOUT&quot;</span><span class="sc">;</span>
    <a class="l_k" href="functions/print.html">print</a> <span class="i">$file</span> <span class="q">&quot;Hi!&quot;</span><span class="sc">;</span>	<span class="c"># error; note: no comma after $file</span></pre>
<p>There is one exception to this rule:</p>
<pre class="verbatim">    <span class="i">$bar</span> = \<span class="i">&amp;</span>{<span class="q">&#39;foo&#39;</span>}<span class="sc">;</span>
    <span class="i">&amp;$bar</span><span class="sc">;</span></pre>
<p>is allowed so that <code class="inline"><a class="l_k" href="functions/goto.html">goto</a> <span class="i">&amp;$AUTOLOAD</span></code>
 would not break under stricture.</p>
</li>
<li><a name="'strict-vars'"></a><b><code class="inline"><span class="w">strict</span> <span class="w">vars</span></code>
</b>
<p>This generates a compile-time error if you access a variable that wasn't
declared via <code class="inline"><a class="l_k" href="functions/our.html">our</a></code> or <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">vars</span></code>
,
localized via <code class="inline"><a class="l_k" href="functions/my.html">my()</a></code>, or wasn't fully qualified.  Because this is to avoid
variable suicide problems and subtle dynamic scoping issues, a merely
local() variable isn't good enough.  See <a href="functions/my.html">my</a> and
<a href="functions/local.html">local</a>.</p>
<pre class="verbatim">    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&#39;vars&#39;</span><span class="sc">;</span>
    <span class="i">$X::foo</span> = <span class="n">1</span><span class="sc">;</span>	 <span class="c"># ok, fully qualified</span>
    <a class="l_k" href="functions/my.html">my</a> <span class="i">$foo</span> = <span class="n">10</span><span class="sc">;</span>	 <span class="c"># ok, my() var</span>
    <a class="l_k" href="functions/local.html">local</a> <span class="i">$foo</span> = <span class="n">9</span><span class="sc">;</span>	 <span class="c"># blows up</span></pre>
<pre class="verbatim"><a name="package-Cinna"></a>    package <span class="i">Cinna</span><span class="sc">;</span>
    <a class="l_k" href="functions/our.html">our</a> <span class="i">$bar</span><span class="sc">;</span>			<span class="c"># Declares $bar in current package</span>
    <span class="i">$bar</span> = <span class="q">&#39;HgS&#39;</span><span class="sc">;</span>		<span class="c"># ok, global declared via pragma</span></pre>
<p>The local() generated a compile-time error because you just touched a global
name without fully qualifying it.</p>
<p>Because of their special use by sort(), the variables $a and $b are
exempted from this check.</p>
</li>
<li><a name="'strict-subs'"></a><b><code class="inline"><span class="w">strict</span> <span class="w">subs</span></code>
</b>
<p>This disables the poetry optimization, generating a compile-time error if
you try to use a bareword identifier that's not a subroutine, unless it
is a simple identifier (no colons) and that it appears in curly braces or
on the left hand side of the <code class="inline"><span class="cm">=&gt;</span></code>
 symbol.</p>
<pre class="verbatim">    <a class="l_k" href="functions/use.html">use</a> <span class="w">strict</span> <span class="q">&#39;subs&#39;</span><span class="sc">;</span>
    <span class="i">$SIG</span>{<span class="w">PIPE</span>} = <span class="w">Plumber</span><span class="sc">;</span>   	<span class="c"># blows up</span>
    <span class="i">$SIG</span>{<span class="w">PIPE</span>} = <span class="q">&quot;Plumber&quot;</span><span class="sc">;</span> 	<span class="c"># just fine: quoted string is always ok</span>
    <span class="i">$SIG</span>{<span class="w">PIPE</span>} = \<span class="i">&amp;Plumber</span><span class="sc">;</span> 	<span class="c"># preferred form</span></pre>
</li>
</ul>
<p>See <a href="perlmodlib.html#Pragmatic-Modules">"Pragmatic Modules" in perlmodlib</a>.</p>
<a name="HISTORY"></a><h1>HISTORY</h1>
<p><code class="inline"><span class="w">strict</span> <span class="q">&#39;subs&#39;</span></code>
, with Perl 5.6.1, erroneously permitted to use an unquoted
compound identifier (e.g. <code class="inline"><span class="w">Foo::Bar</span></code>
) as a hash key (before <code class="inline"><span class="cm">=&gt;</span></code>
 or
inside curlies), but without forcing it always to a literal string.</p>
<p>Starting with Perl 5.8.1 strict is strict about its restrictions:
if unknown restrictions are used, the strict pragma will abort with</p>
<pre class="verbatim">    Unknown 'strict' tag(s) '...'</pre><p>As of version 1.04 (Perl 5.10), strict verifies that it is used as
"strict" to avoid the dreaded Strict trap on case insensitive file
systems.</p>
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