log4j2 logfile location, one for local Eclipse Dev one during deploy - eclipse

Question

I'm using log4j2 and have a rolling file configured in log4j2.xml as
<RollingFile name="a2.log" append="true"
fileName="C:/Dev/error_log/local_error_log_app_name.log"
filePattern="C:/Dev/error_log/local_error_log_app_name_-%d{MM-dd-yyyy}-%i.txt.gz">
This is good for local Eclipse Development but when I deploy to a JBOSS server I'd like the path and filename to be appropriate for that file system, without having to remember to edit the log4j2.xml file before deploying.
fileName="/www/logs/error_log/error_log_app_name.log"
I've seen the following posts
How to give dynamic file name in the appender in log4j.xml
Log4J2 - assigning file appender filename at runtime
and tried
fileName="$${sys:logFilename}" and fileName="${sys:logFilename}" but all that did was put a file ${sys in the Jboss bin folder `jboss-as-7.1.1.Final\bin'

Answer 1

Have you tried declaring a property in your config file?
The log4j2 docs have an example here:
http://logging.apache.org/log4j/2.x/manual/configuration.html#PropertySubstitution
If this does not work, please raise a ticket in the log4j2 issue tracker:
https://issues.apache.org/jira/browse/LOG4J2

Answer 2

When declaring a property in log4j2.xml, use double dollar signs $$
<Properties>
<Property name="filenameVariable">$${sys:errorLogFileName}</Property>
<Property name="filePatternVariable">$${sys:errorLogFilePattern}</Property>
</Properties>
and reference using single dollar sign $
<RollingFile name="a2.log" append="true"
fileName="${filename}"
filePattern="${filePattern}">
However it is not necessary to use a property. Just reference the system property directly, again with just single dollar sign
<RollingFile name="a2.log" append="true"
fileName="${sys:errorLogFileName}"
filePattern="${sys:errorLogFilePattern}">
And to the answer to my actual issue how to dynamically specify log file based on whether I am running locally in Eclipse or deployed to our server, I'm using
#Singleton
#Startup
public class StartupBean {
#PostConstruct
private void startup() {
if (File("C:/").exists()) {
System.setProperty("errorLogFileName", "C:/path/to/error_log.txt");
System.setProperty("errorLogFilePattern", "C:/path/to/error_log-%d{MM-dd-yyyy}-%i.txt.gz");
} else {
System.setProperty("errorLogFileName", "/unix/path/to/error_log.txt");
System.setProperty("errorLogFilePattern", "/unix/path/to/error_log-%d{MM-dd-yyyy}-%i.txt.gz");
}
}
}
Important! Without a system property set System.setProperty("whatever") the lookup in your log4j2.xml will fail and instead log4j will write to a file named as the first part of your lookup before the semicolon i.e. ${sys