Replace string in log4j2 filename in RollingFileAppender - regex

Question

I am trying to replace a string in a environment variable that I use in the filename as shown below. But the output file is generated literally with '%replace'. Is it possible to do such a replacement? If not, any other options? Essentially, I want to replace 'abc' with blank in the environment variable ${current.env}
<RollingFile name="FileA"
fileName="${sys:file.path}/%replace{${sys:current.env}}{'abc'}{}-xyz.log"
filePattern="${sys:file.path}/%replace{${sys:current.env}}{'abc'}{}-xyz-%d{yyyyMMdd-HHmm}.log">
<PatternLayout>
<pattern>%m%n</pattern>
</PatternLayout>
<Policies>
<OnStartupTriggeringPolicy />
<TimeBasedTriggeringPolicy />
</Policies>
<DefaultRolloverStrategy max="5" />
</RollingFile>

Answer 1

Here is some sample code showing how to create a custom lookup that is able to replace strings within the lookup result.
First the class that generates the logging:
package example;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class SomeClass {
private static final Logger log = LogManager.getLogger();
public static void main(String[] args){
log.info("Here's some info!");
log.error("Some error happened!");
}
}
Next the class that defines the custom lookup:
package example;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.lookup.StrLookup;
#Plugin(name = "sysWithReplace", category = "Lookup")
public class SystemLookupWithReplace implements StrLookup{
/**
* Lookup the value for the key.
* #param key the key to be looked up, may be null
* #return The value for the key.
*/
public String lookup(String key) {
if(key == null){
return null;
}
if(!key.contains(";")){
return System.getProperty(key);
}
String[] params = key.split(";");
String value = System.getProperty(params[0]);
if(params.length >= 2 && value != null){
if(params.length < 3){
return value.replace(params[1], "");
}
return value.replace(params[1], params[2]);
}
return value;
}
/**
* Lookup the value for the key using the data in the LogEvent.
* #param event The current LogEvent.
* #param key the key to be looked up, may be null
* #return The value associated with the key.
*/
public String lookup(LogEvent event, String key) {
return lookup(key);
}
}
Here is a sample log4j2.xml config file that uses the custom lookup:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %c ${sysWithReplace:os.name;dows 10;doze} - %msg%n" />
</Console>
</Appenders>
<Loggers>
<Root level="debug">
<AppenderRef ref="Console" level="info" />
</Root>
</Loggers>
</Configuration>
and finally the logging output (I'm running this on Windows 10 so it replaces the "dows 10" with "doze":
14:30:26.580 [main] INFO example.SomeClass Windoze - Here's some info!
14:30:26.581 [main] ERROR example.SomeClass Windoze - Some error happened!