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<html><head><title>nomatch mode - property replacer - rsyslog.conf</title></head>
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<h1>nomatch mode - property replacer - rsyslog.con</h1>
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<p>This is a part of the <a href="rsyslog_conf.html">rsyslog.conf documentation</a>
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of the <a href="property_replacer.html">property replacer</a>.</p>
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<p><b>The "nomatch-Mode" specifies which string the property replacer
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shall return if a regular expression did not find the search string.</b>. Traditionally,
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the string "**NO MATCH**" was returned, but many people complained this was almost never useful.
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Still, this mode is support as "<b>DFLT</b>" for legacy configurations.
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<p>Three additional and potentially useful modes exist: in one (<b>BLANK</b>) a blank string
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is returned. This is probably useful for inserting values into databases where no
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value shall be inserted if the expression could not be found.
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<p>A similar mode is "<b>ZERO</b>" where the string "0" is returned. This is suitable
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for numerical values. A use case may be
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that you record a traffic log based on firewall rules and the "bytes transmitted" counter
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is extracted via a regular expression. If no "bytes transmitted" counter is available
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in the current message, it is probably a good idea to return an empty string, which the
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database layer can turn into a zero.
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<p>The other mode is "<b>FIELD</b>", in which the complete field is returned. This may be useful
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in cases where absense of a match is considered a failure and the message that triggered
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<p>If in doubt, <b>it is highly suggested to use the
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<a href="http://www.rsyslog.com/tool-regex">rsyslog online regular expression
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checker and generator</a> to see these options in action</b>. With that online tool,
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you can craft regular expressions based on samples and try out the different modes.
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<h2>Summary of nomatch Modes</h2>
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<table border="1" cellspacing="0">
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<tr><td><b>Mode</b></td><td><b>Returned</b></td></tr>
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<tr><td>DFLT</td><td>"**NO MATCH**"</td></tr>
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<tr><td>BLANK</td><td>"" (empty string)</td></tr>
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<tr><td>ZERO</td><td>"0"</td></tr>
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<tr><td>FIELD</td><td>full content of original field</td></tr>
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<tr><td> </td><td><a href="http://www.rsyslog.com/tool-regex">Interactive Tool</a></td></tr>
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<p>[<a href="manual.html">manual index</a>]
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[<a href="rsyslog_conf.html">rsyslog.conf</a>]
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[<a href="http://www.rsyslog.com/">rsyslog site</a>]</p>
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<p><font size="2">This documentation is part of the
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<a href="http://www.rsyslog.com/">rsyslog</a> project.<br>
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Copyright © 2008 by <a href="http://www.gerhards.net/rainer">Rainer Gerhards</a> and
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<a href="http://www.adiscon.com/">Adiscon</a>. Released under the GNU GPL
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version 2 or higher.</font></p>
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