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70 lines
2.0 KiB
70 lines
2.0 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
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<head>
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<title>
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ht://Dig: Configuration file format -- Variable Expansion
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</title>
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</head>
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<body bgcolor="#eef7ff">
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<h1>
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Configuration file format -- Variable Expansion
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</h1>
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<p>
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ht://Dig Copyright © 1995-2004 <a href="THANKS.html">The ht://Dig Group</a><br>
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Please see the file <a href="COPYING">COPYING</a> for
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license information.
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</p>
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<hr size="4" noshade>
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<p>
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Attribute values can contain
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references to other attributes. This is done similarly to how
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Perl, Bourne shell, and Makefiles use variables. The variables
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that are referenced will be expanded when the variable is used,
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not when it is defined. This means that attributes don't have
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to be defined in the order that they are used.
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</p>
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<p>
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Example attribute reference in an attribute value:
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</p>
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<blockquote>
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database_base: ${database_dir}/htdig
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</blockquote>
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<p>
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or
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</p>
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<blockquote>
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database_base: $database_dir/htdig
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</blockquote>
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<p>
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Many default values use the attribute expansion mechanism to
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make configuration easier and more generic.
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</p>
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<p>
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In addition to variable expansion, it is also possible to
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include the contents of a file as the value of an attribute.
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This is done by putting the filename in backquotes (`).
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Within the backquotes, variable expansion will still work so
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that files can be specified relative to some path. The
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backquotes and the filename will be replaced by the contents
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of the file if it exists. All whitespace (spaces, tabs,
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newlines, etc) in the file are condensed to one space before
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the substitution takes place. The following are some examples
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of the use of the backquoting scheme:
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</p>
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<blockquote>
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<table>
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<tr>
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<td nowrap>
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start_url: `${common_dir}/starting_points`<br>
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limit_urls_to: `${common_dir}/limit_list`
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</td>
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</tr>
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</table>
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</blockquote>
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<hr size="4" noshade>
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Last modified: $Date: 2004/05/28 13:15:18 $
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</body>
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</html>
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