autodie - Replace functions with ones that succeed or die with lexical scope

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It is better to die() than to return() in failure. -- Klingon programming proverb.</code></pre> <p>The <code>autodie</code> pragma provides a convenient way to replace functions that normally return false on failure with equivalents that throw an exception on failure.</p> <p>The <code>autodie</code> pragma has <i>lexical scope</i>, meaning that functions and subroutines altered with <code>autodie</code> will only change their behaviour until the end of the enclosing block, file, or <code>eval</code>.</p> <p>If <code>system</code> is specified as an argument to <code>autodie</code>, then it uses <a href="/IPC::System::Simple">IPC::System::Simple</a> to do the heavy lifting. See the description of that module for more information.</p> <h1 id="EXCEPTIONS"><a class="permalink" href="#EXCEPTIONS">#</a>EXCEPTIONS</h1> <p>Exceptions produced by the <code>autodie</code> pragma are members of the <a href="/autodie::exception">autodie::exception</a> class. The preferred way to work with these exceptions under Perl 5.10 is as follows:</p> <pre><code>eval { use autodie; open(my $fh, '<', $some_file); my @records = <$fh>; # Do things with @records... close($fh); }; if ($@ and $@->isa('autodie::exception')) { if ($@->matches('open')) { print "Error from open\n"; } if ($@->matches(':io' )) { print "Non-open, IO error."; } } elsif ($@) { # A non-autodie exception. }</code></pre> <p>See <a href="/autodie::exception">autodie::exception</a> for further information on interrogating exceptions.</p> <h1 id="CATEGORIES"><a class="permalink" href="#CATEGORIES">#</a>CATEGORIES</h1> <p>Autodie uses a simple set of categories to group together similar built-ins. Requesting a category type (starting with a colon) will enable autodie for all built-ins beneath that category. For example, requesting <code>:file</code> will enable autodie for <code>close</code>, <code>fcntl</code>, <code>open</code> and <code>sysopen</code>.</p> <p>The categories are currently:</p> <pre><code class="plaintext">:all :default :io read seek sysread sysseek syswrite :dbm dbmclose dbmopen :file binmode close chmod chown fcntl flock ioctl open sysopen truncate :filesys chdir closedir opendir link mkdir readlink rename rmdir symlink unlink :ipc kill pipe :msg msgctl msgget msgrcv msgsnd :semaphore semctl semget semop :shm shmctl shmget shmread :socket accept bind connect getsockopt listen recv send setsockopt shutdown socketpair :threads fork :system system exec</code></pre> <p>Note that while the above category system is presently a strict hierarchy, this should not be assumed.</p> <p>A plain <code>use autodie</code> implies <code>use autodie qw(:default)</code>. Note that <code>system</code> and <code>exec</code> are not enabled by default. <code>system</code> requires the optional <a href="/IPC::System::Simple">IPC::System::Simple</a> module to be installed, and enabling <code>system</code> or <code>exec</code> will invalidate their exotic forms. See <a href="#BUGS">"BUGS"</a> below for more details.</p> <p>The syntax:</p> <pre><code>use autodie qw(:1.994);</code></pre> <p>allows the <code>:default</code> list from a particular version to be used. This provides the convenience of using the default methods, but the surety that no behavioral changes will occur if the <code>autodie</code> module is upgraded.</p> <p><code>autodie</code> can be enabled for all of Perl's built-ins, including <code>system</code> and <code>exec</code> with:</p> <pre><code>use autodie qw(:all);</code></pre> <h1 id="FUNCTION-SPECIFIC-NOTES"><a class="permalink" href="#FUNCTION-SPECIFIC-NOTES">#</a><a id="FUNCTION"></a>FUNCTION SPECIFIC NOTES</h1> <h2 id="print"><a class="permalink" href="#print">#</a>print</h2> <p>The autodie pragma <b>does not check calls to <code>print</code></b>.</p> <h2 id="flock"><a class="permalink" href="#flock">#</a>flock</h2> <p>It is not considered an error for <code>flock</code> to return false if it fails due to an <code>EWOULDBLOCK</code> (or equivalent) condition. This means one can still use the common convention of testing the return value of <code>flock</code> when called with the <code>LOCK_NB</code> option:</p> <pre><code>use autodie; if ( flock($fh, LOCK_EX | LOCK_NB) ) { # We have a lock }</code></pre> <p>Autodying <code>flock</code> will generate an exception if <code>flock</code> returns false with any other error.</p> <h2 id="system/exec"><a class="permalink" href="#system/exec">#</a><a id="system"></a><a id="system-exec"></a>system/exec</h2> <p>The <code>system</code> built-in is considered to have failed in the following circumstances:</p> <ul> <li><p>The command does not start.</p> </li> <li><p>The command is killed by a signal.</p> </li> <li><p>The command returns a non-zero exit value (but see below).</p> </li> </ul> <p>On success, the autodying form of <code>system</code> returns the <i>exit value</i> rather than the contents of <code>$?</code>.</p> <p>Additional allowable exit values can be supplied as an optional first argument to autodying <code>system</code>:</p> <pre><code>system( [ 0, 1, 2 ], $cmd, @args); # 0,1,2 are good exit values</code></pre> <p><code>autodie</code> uses the <a href="/IPC::System::Simple">IPC::System::Simple</a> module to change <code>system</code>. See its documentation for further information.</p> <p>Applying <code>autodie</code> to <code>system</code> or <code>exec</code> causes the exotic forms <code>system { $cmd } @args </code> or <code>exec { $cmd } @args</code> to be considered a syntax error until the end of the lexical scope. If you really need to use the exotic form, you can call <code>CORE::system</code> or <code>CORE::exec</code> instead, or use <code>no autodie qw(system exec)</code> before calling the exotic form.</p> <h1 id="GOTCHAS"><a class="permalink" href="#GOTCHAS">#</a>GOTCHAS</h1> <p>Functions called in list context are assumed to have failed if they return an empty list, or a list consisting only of a single undef element.</p> <p>Some builtins (e.g. <code>chdir</code> or <code>truncate</code>) has a call signature that cannot completely be represented with a Perl prototype. This means that some valid Perl code will be invalid under autodie. As an example:</p> <pre><code>chdir(BAREWORD);</code></pre> <p>Without autodie (and assuming BAREWORD is an open filehandle/dirhandle) this is a valid call to chdir. But under autodie, <code>chdir</code> will behave like it had the prototype ";$" and thus BAREWORD will be a syntax error (under "use strict". Without strict, it will interpreted as a filename).</p> <h1 id="DIAGNOSTICS"><a class="permalink" href="#DIAGNOSTICS">#</a>DIAGNOSTICS</h1> <dl> <dt id=":void-cannot-be-used-with-lexical-scope"><a class="permalink" href="#:void-cannot-be-used-with-lexical-scope">#</a><a id="void-cannot-be-used-with-lexical-scope"></a>:void cannot be used with lexical scope</dt> <dd> <p>The <code>:void</code> option is supported in <a href="/Fatal">Fatal</a>, but not <code>autodie</code>. To workaround this, <code>autodie</code> may be explicitly disabled until the end of the current block with <code>no autodie</code>. To disable autodie for only a single function (eg, open) use <code>no autodie qw(open)</code>.</p> <p><code>autodie</code> performs no checking of called context to determine whether to throw an exception; the explicitness of error handling with <code>autodie</code> is a deliberate feature.</p> </dd> <dt id="No-user-hints-defined-for-%s"><a class="permalink" href="#No-user-hints-defined-for-%25s">#</a><a id="No"></a><a id="No-user-hints-defined-for-s"></a>No user hints defined for %s</dt> <dd> <p>You've insisted on hints for user-subroutines, either by pre-pending a <code>!</code> to the subroutine name itself, or earlier in the list of arguments to <code>autodie</code>. However the subroutine in question does not have any hints available.</p> </dd> </dl> <p>See also <a href="/Fatal#DIAGNOSTICS">"DIAGNOSTICS" in Fatal</a>.</p> <h1 id="Tips-and-Tricks"><a class="permalink" href="#Tips-and-Tricks">#</a><a id="Tips"></a>Tips and Tricks</h1> <h2 id="Importing-autodie-into-another-namespace-than-"caller""><a class="permalink" href="#Importing-autodie-into-another-namespace-than-%22caller%22">#</a><a id="Importing"></a><a id="Importing-autodie-into-another-namespace-than-caller"></a>Importing autodie into another namespace than "caller"</h2> <p>It is possible to import autodie into a different namespace by using <a href="/Import::Into">Import::Into</a>. However, you have to pass a "caller depth" (rather than a package name) for this to work correctly.</p> <h1 id="BUGS"><a class="permalink" href="#BUGS">#</a>BUGS</h1> <p>"Used only once" warnings can be generated when <code>autodie</code> or <code>Fatal</code> is used with package filehandles (eg, <code>FILE</code>). Scalar filehandles are strongly recommended instead.</p> <p>When using <code>autodie</code> or <code>Fatal</code> with user subroutines, the declaration of those subroutines must appear before the first use of <code>Fatal</code> or <code>autodie</code>, or have been exported from a module. Attempting to use <code>Fatal</code> or <code>autodie</code> on other user subroutines will result in a compile-time error.</p> <p>Due to a bug in Perl, <code>autodie</code> may "lose" any format which has the same name as an autodying built-in or function.</p> <p><code>autodie</code> may not work correctly if used inside a file with a name that looks like a string eval, such as <i>eval (3)</i>.</p> <h2 id="autodie-and-string-eval"><a class="permalink" href="#autodie-and-string-eval">#</a><a id="autodie"></a>autodie and string eval</h2> <p>Due to the current implementation of <code>autodie</code>, unexpected results may be seen when used near or with the string version of eval. <i>None of these bugs exist when using block eval</i>.</p> <p>Under Perl 5.8 only, <code>autodie</code> <i>does not</i> propagate into string <code>eval</code> statements, although it can be explicitly enabled inside a string <code>eval</code>.</p> <p>Under Perl 5.10 only, using a string eval when <code>autodie</code> is in effect can cause the autodie behaviour to leak into the surrounding scope. This can be worked around by using a <code>no autodie</code> at the end of the scope to explicitly remove autodie's effects, or by avoiding the use of string eval.</p> <p><i>None of these bugs exist when using block eval</i>. The use of <code>autodie</code> with block eval is considered good practice.</p> <h2 id="REPORTING-BUGS"><a class="permalink" href="#REPORTING-BUGS">#</a><a id="REPORTING"></a>REPORTING BUGS</h2> <p>Please report bugs via the GitHub Issue Tracker at <a href="https://github.com/pjf/autodie/issues">https://github.com/pjf/autodie/issues</a>.</p> <h1 id="FEEDBACK"><a class="permalink" href="#FEEDBACK">#</a>FEEDBACK</h1> <p>If you find this module useful, please consider rating it on metacpan at <a href="https://metacpan.org/pod/autodie">https://metacpan.org/pod/autodie</a> .</p> <p>The module author loves to hear how <code>autodie</code> has made your life better (or worse). Feedback can be sent to <pjf@perltraining.com.au>.</p> <h1 id="AUTHOR"><a class="permalink" href="#AUTHOR">#</a>AUTHOR</h1> <p>Copyright 2008-2009, Paul Fenwick <pjf@perltraining.com.au></p> <h1 id="LICENSE"><a class="permalink" href="#LICENSE">#</a>LICENSE</h1> <p>This module is free software. You may distribute it under the same terms as Perl itself.</p> <h1 id="SEE-ALSO"><a class="permalink" href="#SEE-ALSO">#</a><a id="SEE"></a>SEE ALSO</h1> <p><a href="/Fatal">Fatal</a>, <a href="/autodie::exception">autodie::exception</a>, <a href="/autodie::hints">autodie::hints</a>, <a href="/IPC::System::Simple">IPC::System::Simple</a></p> <p><i>Perl tips, autodie</i> at <a href="http://perltraining.com.au/tips/2008-08-20.html">http://perltraining.com.au/tips/2008-08-20.html</a></p> <h1 id="ACKNOWLEDGEMENTS"><a class="permalink" href="#ACKNOWLEDGEMENTS">#</a>ACKNOWLEDGEMENTS</h1> <p>Mark Reed and Roland Giersig -- Klingon translators.</p> <p>See the <i>AUTHORS</i> file for full credits. The latest version of this file can be found at <a href="https://github.com/pjf/autodie/tree/master/AUTHORS">https://github.com/pjf/autodie/tree/master/AUTHORS</a> .</p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p> <p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. Please contact them via the <a href="https://github.com/Perl/perl5/issues">Perl issue tracker</a>, the <a href="https://lists.perl.org/list/perl5-porters.html">mailing list</a>, or <a href="https://kiwiirc.com/client/irc.perl.org/p5p">IRC</a> to report any issues with the contents or format of the documentation.</p> </div> </div> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.slim.min.js" integrity="sha512-/DXTXr6nQodMUiq+IUJYCt2PPOUjrHJ9wFrqpJ3XkgPNOZVfMok7cRw6CSxyCQxXn6ozlESsSh1/sMCTF1rL/g==" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.1/umd/popper.min.js" integrity="sha512-ubuT8Z88WxezgSqf3RLuNi5lmjstiJcyezx34yIU2gAHonIi27Na7atqzUZCOoY4CExaoFumzOsFQ2Ch+I/HCw==" crossorigin="anonymous"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV" crossorigin="anonymous"></script> <script src="/js/highlight.pack.js"></script> <script>hljs.highlightAll();</script> </body> </html>

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autodie - Replace functions with ones that succeed or die with lexical scope - Perldoc Browser