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<h4 class="subsection">10.4.1 The Stages of Word Expansion</h4>

<p>When word expansion is applied to a sequence of words, it performs the
following transformations in the order shown here:

     <ol type=1 start=1>
<li><a name="index-tilde-expansion-886"></a><dfn>Tilde expansion</dfn>: Replacement of &lsquo;<samp><span class="samp">~foo</span></samp>&rsquo; with the name of
the home directory of &lsquo;<samp><span class="samp">foo</span></samp>&rsquo;.

     <li>Next, three different transformations are applied in the same step,
from left to right:

          <ul>
<li><a name="index-variable-substitution-887"></a><a name="index-substitution-of-variables-and-commands-888"></a><dfn>Variable substitution</dfn>: Environment variables are substituted for
references such as &lsquo;<samp><span class="samp">$foo</span></samp>&rsquo;.

          <li><a name="index-command-substitution-889"></a><dfn>Command substitution</dfn>: Constructs such as &lsquo;<samp><span class="samp">`cat&nbsp;foo`</span></samp>&rsquo;<!-- /@w --> and
the equivalent &lsquo;<samp><span class="samp">$(cat&nbsp;foo)</span></samp>&rsquo;<!-- /@w --> are replaced with the output from
the inner command.

          <li><a name="index-arithmetic-expansion-890"></a><dfn>Arithmetic expansion</dfn>: Constructs such as &lsquo;<samp><span class="samp">$(($x-1))</span></samp>&rsquo; are
replaced with the result of the arithmetic computation. 
</ul>

     <li><a name="index-field-splitting-891"></a><dfn>Field splitting</dfn>: subdivision of the text into <dfn>words</dfn>.

     <li><a name="index-wildcard-expansion-892"></a><dfn>Wildcard expansion</dfn>: The replacement of a construct such as &lsquo;<samp><span class="samp">*.c</span></samp>&rsquo;
with a list of &lsquo;<samp><span class="samp">.c</span></samp>&rsquo; file names.  Wildcard expansion applies to an
entire word at a time, and replaces that word with 0 or more file names
that are themselves words.

     <li><a name="index-quote-removal-893"></a><a name="index-removal-of-quotes-894"></a><dfn>Quote removal</dfn>: The deletion of string-quotes, now that they have
done their job by inhibiting the above transformations when appropriate.
        </ol>

   <p>For the details of these transformations, and how to write the constructs
that use them, see <cite>The&nbsp;BASH&nbsp;Manual</cite><!-- /@w --> (to appear).

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