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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 ‘<samp><span class="samp">~foo</span></samp>’ with the name of |
| the home directory of ‘<samp><span class="samp">foo</span></samp>’. |
| |
| <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 ‘<samp><span class="samp">$foo</span></samp>’. |
| |
| <li><a name="index-command-substitution-889"></a><dfn>Command substitution</dfn>: Constructs such as ‘<samp><span class="samp">`cat foo`</span></samp>’<!-- /@w --> and |
| the equivalent ‘<samp><span class="samp">$(cat foo)</span></samp>’<!-- /@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 ‘<samp><span class="samp">$(($x-1))</span></samp>’ 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 ‘<samp><span class="samp">*.c</span></samp>’ |
| with a list of ‘<samp><span class="samp">.c</span></samp>’ 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 BASH Manual</cite><!-- /@w --> (to appear). |
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