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Targets
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v0.91
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<h1>Targets</h1>
<p>A target has these attributes:</p>
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Attribute</th>
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Description</th>
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Required</th>
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<td>name</td>
<td>The name of the target.</td>
<td>Yes</td>
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<td>depends</td>
<td>A comma-separated list of names of targets on which this target depends.</td>
<td>No</td>
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<td>if</td>
<td>An expression that should evaluate to <b>true</b> in order for this target to
execute.</td>
<td>No</td>
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<td>unless</td>
<td>An expression that, when evaluated to <b>true</b>, will cause the target to be
skipped.</td>
<td>No</td>
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<td>description</td>
<td>A short description of this target's function.</td>
<td>No</td>
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<p>
The optional <code>description</code> attribute can be used to provide a
one-line description of this target, which is printed by the <code style="whitespace: nowrap;">
-projecthelp</code> command-line option.</p>
<h3><a id="dependencies" />Dependencies</h3>
<p>
A target can depend on other targets. You might have a target for
compiling, for example, and a target for creating a distributable. You
can only build a distributable when you have compiled first, so the distribute
target <em>depends on</em> the compile target. NAnt resolves these
dependencies.</p>
<p>
NAnt tries to execute the targets in the <code>depends</code> attribute in the
order they appear from left to right. It is possible that a target can
get executed earlier when an earlier target depends on it:</p>
<pre class="code">
<target name="A"/>
<target name="B" depends="A" />
<target name="C" depends="B" />
<target name="D" depends="C,B,A" />
</pre>
<p>
Suppose we want to execute target D. From its <code>depends</code> attribute,
you might think that first target C, then B and then A is executed.
Wrong! C depends on B, and B depends on A, so first A is executed, then
B, then C, and finally D.</p>
<p>
A target gets executed only once, even when more than one target depends on it
(see the previous example). However, when the <a href="../tasks/call.html"><call></a>
task is used to execute a target, both the target and all its dependent targets
will be re-executed.</p>
<h3><a id="wild-targets" />Wild Targets</h3>
<p>
A target can be marked as <i>wild</i> by setting the <code>name</code> attribute
to "*". A build file can contain up to one wild target, and it is executed if
and only if the invoked target does not exist in the current build file. <i>Wild</i>
targets let you define how to handle invalid requests, or provide generic
behavior for unknown targets. For example:</p>
<pre class="code">
<target name="A" />
<target name="B" />
<target name="*" />
</pre>
<p>
The last target is executed if the invoked target is neither A nor B.</p>
<h3><a id="conditional-execution" />Conditional Execution</h3>
<p>
A target also has the ability to perform its execution if or unless a property
has been set. This allows, for example, better control on the building
process depending on the state of the system (OS, command-line property
defines, etc.). To make a target <i>sense</i> this property, you should
add the <code>if</code> or <code>unless</code> attribute with an expression
that the target should react to. For example:</p>
<pre class="code">
<target name="build-module-A" if="${module-A-present}" />
<target name="build-own-fake-module-A" unless="${file::exists('fake-module-a.dll')}" />
</pre>
<p>
If no <code>if</code> and no <code>unless</code> attribute is present, the
target will always be executed.</p>
<p><b>Note:</b> the dependencies of a target are always executed before testing the
target's condition.</p>
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