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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<meta http-equiv="Content-Language" content="en"><title>Expressions</title></head>
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<h1>Expressions</h1>
<p>Rsyslog supports expressions at a growing number of places. So
far, they are supported for filtering messages.</p><p>C-like comments (/* some comment */) are supported <span style="font-weight: bold;">inside</span> the expression, but not yet in the rest of the configuration file.</p>
<p></p>
<h2>Formal Definition</h2>
<p>Below is the formal definition of expression format (in ABNF, RFC 2234):<br>
</p><pre>; The stuff immediately below here is a quick shot at how the config<br>; file ABNF *at whole* may look like. That is not really related to<br>; expressions, but for the time being I put it here. It will later be<br>; moved to a more appropriate place. -- rgerhards, 2008-02-22<br>?line? := cfsysline / cfli<br>cfsysline:= BOL "$" *char EOL ; how to handle the first line? (no EOL in front!)<br>BOL := ; Begin of Line - implicitely set on file beginning and after each EOL<br>EOL := 0x0a ;LF<br>if_stmt := "if" expr "then"<br>old_filter:= BOL facility "." severity ; no whitespace allowed between BOL and facility!<br>facility := "*" / "auth" / "authpriv" / "cron" / "daemon" / "kern" / "lpr" / <br> "mail" / "mark" / "news" / "security" / "syslog" / "user" / "uucp" / <br> "local0" .. "local7" / "mark"<br> ; The keyword security should not be used anymore<br> ; mark is just internal<br>severity := TBD ; not really relevant in this context<br><br>; and now the actual expression<br>expr := e_and *("or" e_and)<br>e_and := e_cmp *("and" e_cmp)<br>e_cmp := val 0*1(cmp_op val)<br>val := term *(("+" / "-") term)<br>term := factor *(("*" / "/" / "%") factor)<br>factor := ["not"] ["-"] terminal<br>terminal := var / constant / function / ( "(" expr ")" )<br>function := name "(" *("," expr) ")"<br>var := "$" varname<br>varname := msgvar / sysvar<br>msgvar := name<br>sysvar := "$" name<br>name := alpha *(alnum)<br>constant := string / number<br>string := simpstr / tplstr ; tplstr will be implemented in next phase<br>simpstr := "'" *char "'" ; use your imagination for char ;)<br>tplstr := '"' template '"' ; not initially implemented<br>number := ["-"] 1*digit ; 0nn = octal, 0xnn = hex, nn = decimal<br>cmp_op := "==" / "!=" / "<>" / "<" / ">" / "<=" / ">=" / "contains" / "startswith"<br>digit := %x30-39<br>alpha := "a" ... "z" # all letters<br>alnum :* alpha / digit / "_"<br></pre>
<p>[<a href="rsyslog_conf.html">rsyslog.conf overview</a>]
[<a href="manual.html">manual index</a>] [<a href="http://www.rsyslog.com/">rsyslog site</a>]</p>
<p><font size="2">This documentation is part of the
<a href="http://www.rsyslog.com/">rsyslog</a>
project.<br>
Copyright © 2008 by <a href="http://www.gerhards.net/rainer">Rainer
Gerhards</a> and
<a href="http://www.adiscon.com/">Adiscon</a>.
Released under the GNU GPL version 3 or higher.</font></p>
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