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<h1>die</h1>
<div class="mod_az_list">
<a href="../index-functions.html">Perl functions A-Z</a> |
<a href="../index-functions-by-cat.html">Perl functions by category</a> |
<a href="../perlfunc.html">The 'perlfunc' manpage</a>
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<ul>
<li><a name="die-LIST"></a><b>die LIST</b>
<p> </p>
<p>Outside an <code class="inline"><a class="l_k" href="../functions/eval.html">eval</a></code>, prints the value of LIST to <code class="inline"><span class="w">STDERR</span></code>
and
exits with the current value of <code class="inline"><span class="i">$!</span></code>
(errno). If <code class="inline"><span class="i">$!</span></code>
is <code class="inline"><span class="n">0</span></code>
,
exits with the value of <code class="inline"><span class="s">(</span><span class="i">$?</span>>> <span class="n">8</span><span class="s">)</span></code>
(backtick `command`
status). If <code class="inline"><span class="s">(</span><span class="i">$?</span>>> <span class="n">8</span><span class="s">)</span></code>
is <code class="inline"><span class="n">0</span></code>
, exits with <code class="inline"><span class="n">255</span></code>
. Inside
an <code class="inline"><a class="l_k" href="../functions/eval.html">eval(),</a></code> the error message is stuffed into <code class="inline"><span class="i">$@</span></code>
and the
<code class="inline"><a class="l_k" href="../functions/eval.html">eval</a></code> is terminated with the undefined value. This makes
<code class="inline"><a class="l_k" href="../functions/die.html">die</a></code> the way to raise an exception.</p>
<p>Equivalent examples:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/die.html">die</a> <span class="q">"Can't cd to spool: $!\n"</span> unless <a class="l_k" href="../functions/chdir.html">chdir</a> <span class="q">'/usr/spool/news'</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/chdir.html">chdir</a> <span class="q">'/usr/spool/news'</span> or <a class="l_k" href="../functions/die.html">die</a> <span class="q">"Can't cd to spool: $!\n"</span></li></ol></pre><p>If the last element of LIST does not end in a newline, the current
script line number and input line number (if any) are also printed,
and a newline is supplied. Note that the "input line number" (also
known as "chunk") is subject to whatever notion of "line" happens to
be currently in effect, and is also available as the special variable
<code class="inline"><span class="i">$.</span></code>
. See <a href="../perlvar.html#%24%2f">"$/" in perlvar</a> and <a href="../perlvar.html#%24.">"$." in perlvar</a>.</p>
<p>Hint: sometimes appending <code class="inline"><span class="q">", stopped"</span></code>
to your message will cause it
to make better sense when the string <code class="inline"><span class="q">"at foo line 123"</span></code>
is appended.
Suppose you are running script "canasta".</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/die.html">die</a> <span class="q">"/etc/games is no good"</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/die.html">die</a> <span class="q">"/etc/games is no good, stopped"</span><span class="sc">;</span></li></ol></pre><p>produce, respectively</p>
<pre class="verbatim"><ol><li> /etc/games is no good at canasta line 123.</li><li> /etc/games is no good, stopped at canasta line 123.</li></ol></pre><p>See also exit(), warn(), and the Carp module.</p>
<p>If LIST is empty and <code class="inline"><span class="i">$@</span></code>
already contains a value (typically from a
previous eval) that value is reused after appending <code class="inline"><span class="q">"\t...propagated"</span></code>
.
This is useful for propagating exceptions:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/eval.html">eval</a> <span class="s">{</span> ... <span class="s">}</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/die.html">die</a> unless <span class="i">$@</span> =~ <span class="q">/Expected exception/</span><span class="sc">;</span></li></ol></pre><p>If LIST is empty and <code class="inline"><span class="i">$@</span></code>
contains an object reference that has a
<code class="inline"><span class="w">PROPAGATE</span></code>
method, that method will be called with additional file
and line number parameters. The return value replaces the value in
<code class="inline"><span class="i">$@</span></code>
. i.e. as if <code class="inline"><span class="i">$@</span> = <a class="l_k" href="../functions/eval.html">eval</a> <span class="s">{</span> <span class="i">$@</span><span class="i">->PROPAGATE</span><span class="s">(</span><span class="w">__FILE__</span><span class="cm">,</span> <span class="w">__LINE__</span><span class="s">)</span> <span class="s">}</span><span class="sc">;</span></code>
were called.</p>
<p>If <code class="inline"><span class="i">$@</span></code>
is empty then the string <code class="inline"><span class="q">"Died"</span></code>
is used.</p>
<p>die() can also be called with a reference argument. If this happens to be
trapped within an eval(), $@ contains the reference. This behavior permits
a more elaborate exception handling implementation using objects that
maintain arbitrary state about the nature of the exception. Such a scheme
is sometimes preferable to matching particular string values of $@ using
regular expressions. Because $@ is a global variable, and eval() may be
used within object implementations, care must be taken that analyzing the
error object doesn't replace the reference in the global variable. The
easiest solution is to make a local copy of the reference before doing
other manipulations. Here's an example:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/use.html">use</a> <span class="w">Scalar::Util</span> <span class="q">'blessed'</span><span class="sc">;</span></li><li></li><li> <a class="l_k" href="../functions/eval.html">eval</a> <span class="s">{</span> ... <span class="sc">;</span> <a class="l_k" href="../functions/die.html">die</a> <span class="w">Some::Module::Exception</span><span class="w">->new</span><span class="s">(</span> <span class="w">FOO</span> <span class="cm">=></span> <span class="q">"bar"</span> <span class="s">)</span> <span class="s">}</span><span class="sc">;</span></li><li> if <span class="s">(</span><a class="l_k" href="../functions/my.html">my</a> <span class="i">$ev_err</span> = <span class="i">$@</span><span class="s">)</span> <span class="s">{</span></li><li> if <span class="s">(</span><span class="i">blessed</span><span class="s">(</span><span class="i">$ev_err</span><span class="s">)</span> && <span class="i">$ev_err</span><span class="i">->isa</span><span class="s">(</span><span class="q">"Some::Module::Exception"</span><span class="s">)</span><span class="s">)</span> <span class="s">{</span></li><li> <span class="c"># handle Some::Module::Exception</span></li><li> <span class="s">}</span></li><li> else <span class="s">{</span></li><li> <span class="c"># handle all other possible exceptions</span></li><li> <span class="s">}</span></li><li> <span class="s">}</span></li></ol></pre><p>Because perl will stringify uncaught exception messages before displaying
them, you may want to overload stringification operations on such custom
exception objects. See <a href="../overload.html">overload</a> for details about that.</p>
<p>You can arrange for a callback to be run just before the <code class="inline"><a class="l_k" href="../functions/die.html">die</a></code>
does its deed, by setting the <code class="inline"><span class="i">$SIG</span>{<span class="w">__DIE__</span>}</code>
hook. The associated
handler will be called with the error text and can change the error
message, if it sees fit, by calling <code class="inline"><a class="l_k" href="../functions/die.html">die</a></code> again. See
<a href="../perlvar.html#%24SIG%7bexpr%7d">"$SIG{expr}" in perlvar</a> for details on setting <code class="inline"><span class="i">%SIG</span></code>
entries, and
<a href="#eval-BLOCK">"eval BLOCK"</a> for some examples. Although this feature was
to be run only right before your program was to exit, this is not
currently the case--the <code class="inline"><span class="i">$SIG</span>{<span class="w">__DIE__</span>}</code>
hook is currently called
even inside eval()ed blocks/strings! If one wants the hook to do
nothing in such situations, put</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/die.html">die</a> <span class="i">@_</span> if <span class="i">$^S</span><span class="sc">;</span></li></ol></pre><p>as the first line of the handler (see <a href="../perlvar.html#%24%5eS">"$^S" in perlvar</a>). Because
this promotes strange action at a distance, this counterintuitive
behavior may be fixed in a future release.</p>
</li>
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