diagnostics, splain - produce verbose warning diagnostics

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This is a development version of Perl. </div> <h1><a id="toc">CONTENTS</a></h1> <ul> <li> <a class="text-decoration-none" href="#NAME">NAME</a> </li> <li> <a class="text-decoration-none" href="#SYNOPSIS">SYNOPSIS</a> </li> <li> <a class="text-decoration-none" href="#DESCRIPTION">DESCRIPTION</a> <ul> <li> <a class="text-decoration-none" href="#The-diagnostics-Pragma">The diagnostics Pragma</a> </li> <li> <a class="text-decoration-none" href="#The-splain-Program">The splain Program</a> </li> </ul> </li> <li> <a class="text-decoration-none" href="#EXAMPLES">EXAMPLES</a> </li> <li> <a class="text-decoration-none" href="#INTERNALS">INTERNALS</a> </li> <li> <a class="text-decoration-none" href="#BUGS">BUGS</a> </li> <li> <a class="text-decoration-none" href="#AUTHOR">AUTHOR</a> </li> </ul> <h1 id="NAME"><a class="permalink" href="#NAME">#</a>NAME</h1> <p>diagnostics, splain - produce verbose warning diagnostics</p> <h1 id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">#</a>SYNOPSIS</h1> <p>Using the <code>diagnostics</code> pragma:</p> <pre><code>use diagnostics; use diagnostics -verbose; diagnostics->enable; diagnostics->disable;</code></pre> <p>Using the <code>splain</code> standalone filter program:</p> <pre><code class="plaintext">perl program 2>diag.out splain [-v] [-p] diag.out</code></pre> <p>Using diagnostics to get stack traces from a misbehaving script:</p> <pre><code class="plaintext">perl -Mdiagnostics=-traceonly my_script.pl</code></pre> <h1 id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">#</a>DESCRIPTION</h1> <h2 id="The-diagnostics-Pragma"><a class="permalink" href="#The-diagnostics-Pragma">#</a><a id="The"></a>The <code>diagnostics</code> Pragma</h2> <p>This module extends the terse diagnostics normally emitted by both the perl compiler and the perl interpreter (from running perl with a -w switch or <code>use warnings</code>), augmenting them with the more explicative and endearing descriptions found in <a href="/5.41.7/perldiag">perldiag</a>. Like the other pragmata, it affects the compilation phase of your program rather than merely the execution phase.</p> <p>To use in your program as a pragma, merely invoke</p> <pre><code>use diagnostics;</code></pre> <p>at the start (or near the start) of your program. (Note that this <i>does</i> enable perl's <b>-w</b> flag.) Your whole compilation will then be subject(ed :-) to the enhanced diagnostics. These still go out <b>STDERR</b>.</p> <p>Due to the interaction between runtime and compiletime issues, and because it's probably not a very good idea anyway, you may not use <code>no diagnostics</code> to turn them off at compiletime. However, you may control their behaviour at runtime using the <code>disable()</code> and <code>enable()</code> methods to turn them off and on respectively.</p> <p>The <b>-verbose</b> flag first prints out the <a href="/5.41.7/perldiag">perldiag</a> introduction before any other diagnostics. The $diagnostics::PRETTY variable can generate nicer escape sequences for pagers.</p> <p>Warnings dispatched from perl itself (or more accurately, those that match descriptions found in <a href="/5.41.7/perldiag">perldiag</a>) are only displayed once (no duplicate descriptions). User code generated warnings a la warn() are unaffected, allowing duplicate user messages to be displayed.</p> <p>This module also adds a stack trace to the error message when perl dies. This is useful for pinpointing what caused the death. The <b>-traceonly</b> (or just <b>-t</b>) flag turns off the explanations of warning messages leaving just the stack traces. So if your script is dieing, run it again with</p> <pre><code class="plaintext">perl -Mdiagnostics=-traceonly my_bad_script</code></pre> <p>to see the call stack at the time of death. By supplying the <b>-warntrace</b> (or just <b>-w</b>) flag, any warnings emitted will also come with a stack trace.</p> <h2 id="The-splain-Program"><a class="permalink" href="#The-splain-Program">#</a><a id="The1"></a>The <i>splain</i> Program</h2> <p>Another program, <i>splain</i> is actually nothing more than a link to the (executable) <i>diagnostics.pm</i> module, as well as a link to the <i>diagnostics.pod</i> documentation. The <b>-v</b> flag is like the <code>use diagnostics -verbose</code> directive. The <b>-p</b> flag is like the $diagnostics::PRETTY variable. Since you're post-processing with <i>splain</i>, there's no sense in being able to enable() or disable() processing.</p> <p>Output from <i>splain</i> is directed to <b>STDOUT</b>, unlike the pragma.</p> <h1 id="EXAMPLES"><a class="permalink" href="#EXAMPLES">#</a>EXAMPLES</h1> <p>The following file is certain to trigger a few errors at both runtime and compiletime:</p> <pre><code>use diagnostics; print NOWHERE "nothing\n"; print STDERR "\n\tThis message should be unadorned.\n"; warn "\tThis is a user warning"; print "\nDIAGNOSTIC TESTER: Please enter a <CR> here: "; my $a, $b = scalar <STDIN>; print "\n"; print $x/$y;</code></pre> <p>If you prefer to run your program first and look at its problem afterwards, do this:</p> <pre><code class="plaintext">perl -w test.pl 2>test.out ./splain < test.out</code></pre> <p>Note that this is not in general possible in shells of more dubious heritage, as the theoretical</p> <pre><code class="plaintext">(perl -w test.pl >/dev/tty) >& test.out ./splain < test.out</code></pre> <p>Because you just moved the existing <b>stdout</b> to somewhere else.</p> <p>If you don't want to modify your source code, but still have on-the-fly warnings, do this:</p> <pre><code class="plaintext">exec 3>&1; perl -w test.pl 2>&1 1>&3 3>&- | splain 1>&2 3>&- </code></pre> <p>Nifty, eh?</p> <p>If you want to control warnings on the fly, do something like this. Make sure you do the <code>use</code> first, or you won't be able to get at the enable() or disable() methods.</p> <pre><code> use diagnostics; # checks entire compilation phase print "\ntime for 1st bogus diags: SQUAWKINGS\n"; print BOGUS1 'nada'; print "done with 1st bogus\n"; diagnostics->disable; # only turns off runtime warnings print "\ntime for 2nd bogus: (squelched)\n"; print BOGUS2 'nada'; print "done with 2nd bogus\n"; diagnostics->enable; # turns back on runtime warnings print "\ntime for 3rd bogus: SQUAWKINGS\n"; print BOGUS3 'nada'; print "done with 3rd bogus\n"; diagnostics->disable; print "\ntime for 4th bogus: (squelched)\n"; print BOGUS4 'nada'; print "done with 4th bogus\n";</code></pre> <h1 id="INTERNALS"><a class="permalink" href="#INTERNALS">#</a>INTERNALS</h1> <p>Diagnostic messages derive from the <i>perldiag.pod</i> file when available at runtime. Otherwise, they may be embedded in the file itself when the splain package is built. See the <i>Makefile</i> for details.</p> <p>If an extant $SIG{__WARN__} handler is discovered, it will continue to be honored, but only after the diagnostics::splainthis() function (the module's $SIG{__WARN__} interceptor) has had its way with your warnings.</p> <p>There is a $diagnostics::DEBUG variable you may set if you're desperately curious what sorts of things are being intercepted.</p> <pre><code>BEGIN { $diagnostics::DEBUG = 1 } </code></pre> <h1 id="BUGS"><a class="permalink" href="#BUGS">#</a>BUGS</h1> <p>Not being able to say "no diagnostics" is annoying, but may not be insurmountable.</p> <p>The <code>-pretty</code> directive is called too late to affect matters. You have to do this instead, and <i>before</i> you load the module.</p> <pre><code>BEGIN { $diagnostics::PRETTY = 1 } </code></pre> <p>I could start up faster by delaying compilation until it should be needed, but this gets a "panic: top_level" when using the pragma form in Perl 5.001e.</p> <p>While it's true that this documentation is somewhat subserious, if you use a program named <i>splain</i>, you should expect a bit of whimsy.</p> <h1 id="AUTHOR"><a class="permalink" href="#AUTHOR">#</a>AUTHOR</h1> <p>Tom Christiansen <<i>tchrist@mox.perl.com</i>>, 25 June 1995.</p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). 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