Of course, it would be trivial to simply write your own subclass of RollingFileAppender, which programmatically determines the value of the LOG_ROOT variable in a platform-independent way.
This probably only requires about a dozen lines of code. Then follow these steps:
<appender name="CustomAppender" class="path.to.your.CustomAppender">
<param name="File" value="fileNameOnly.out" />
<param name="Append" value="true" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%m%n" />
</layout>
</appender>
File, LOG_ROOT .
, ,
-gMale