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<span id="Testing-for-Texinfo-Commands"></span><div class="header">
<p>
Next: <a href="Conditional-Nesting.html" accesskey="n" rel="next">Conditional Nesting</a>, Previous: <a href="_0040set-_0040clear-_0040value.html" accesskey="p" rel="prev"><code>@set @clear @value</code></a>, Up: <a href="Conditionals.html" accesskey="u" rel="up">Conditionals</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
<span id="Testing-for-Texinfo-Commands_003a-_0040ifcommanddefined_002c-_0040ifcommandnotdefined"></span><h3 class="section">16.6 Testing for Texinfo Commands: <code>@ifcommanddefined</code>, <code>@ifcommandnotdefined</code></h3>
<span id="index-Testing-for-Texinfo-commands"></span>
<span id="index-Checking-for-Texinfo-commands"></span>
<span id="index-Texinfo-commands_002c-testing-for"></span>
<span id="index-Commands_002c-testing-for-Texinfo"></span>
<span id="index-Versions-of-Texinfo_002c-adapting-to"></span>
<span id="index-Features-of-Texinfo_002c-adapting-to"></span>
<span id="index-ifcommanddefined"></span>
<span id="index-ifcommandnotdefined"></span>
<p>Occasionally, you may want to arrange for your manual to test if a
given Texinfo command is available and (presumably) do some sort of
fallback formatting if not. There are conditionals
<code>@ifcommanddefined</code> and <code>@ifcommandnotdefined</code> to do this.
For example:
</p>
<div class="example">
<pre class="example">@ifcommanddefined node
Good, @samp{@@node} is defined.
@end ifcommanddefined
</pre></div>
<p>will output the expected ‘Good, ‘<samp>@node</samp>’ is defined.’.
</p>
<p>This conditional will also consider any new commands defined by
the document via <code>@macro</code>, <code>@alias</code>,
<code>@definfoenclose</code>, and <code>@def<span class="roman">(</span>code<span class="roman">)</span>index</code>
(see <a href="Defining-New-Texinfo-Commands.html">Defining New Texinfo Commands</a>) to be true. Caveat: the TeX
implementation reports internal TeX commands, in addition to all
the Texinfo commands, as being “defined”; the <code>makeinfo</code>
implementation is reliable in this regard, however.
</p>
<span id="index-NEWS-file-for-Texinfo"></span>
<p>You can check the <samp>NEWS</samp> file in the Texinfo source distribution
and linked from the Texinfo home page
(<a href="http://www.gnu.org/software/texinfo">http://www.gnu.org/software/texinfo</a>) to see when a particular
command was added.
</p>
<span id="index-txicommandconditionals"></span>
<p>These command-checking conditionals themselves were added in
Texinfo 5.0, released in 2013—decades after Texinfo’s
inception. In order to test if they themselves are available,
the predefined flag <code>txicommandconditionals</code> can be tested, like
this:
</p>
<div class="example">
<pre class="example">@ifset txicommandconditionals
@ifcommandnotdefined foobarnode
(Good, @samp{@@foobarnode} is not defined.)
@end ifcommandnotdefined
@end ifset
</pre></div>
<p>Since flags (see the previous section) were added early in the
existence of Texinfo, there is no problem with assuming they are
available.
</p>
<p>We recommend avoiding these tests whenever possible—which is usually
the case. For many software packages, it is reasonable for all
developers to have a given version of Texinfo (or newer) installed,
and thus no reason to worry about older versions. (It is
straightforward for anyone to download and install the Texinfo source;
it does not have any problematic dependencies.)
</p>
<p>The issue of Texinfo versions does not generally arise for end-users.
With properly distributed packages, users need not process the Texinfo
manual simply to build and install the package; they can use
preformatted Info (or other) output files. This is desirable in
general, to avoid unnecessary dependencies between packages
(see <a href="../standards/Releases.html#Releases">Releases</a> in <cite>GNU Coding Standards</cite>).
</p>
<hr>
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Next: <a href="Conditional-Nesting.html" accesskey="n" rel="next">Conditional Nesting</a>, Previous: <a href="_0040set-_0040clear-_0040value.html" accesskey="p" rel="prev"><code>@set @clear @value</code></a>, Up: <a href="Conditionals.html" accesskey="u" rel="up">Conditionals</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p>
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