Output valid xml when executing mvn help:effective-pom
As a workaround
mvn help:effective-pom | grep -v '\[INFO\|\[WARNING\|Downloading' | sed '1,2d' | xml sel -N x=http://maven.apache.org/POM/4.0.0 -t -c "/x:project/x:properties"will output the properties as xml.
You need xmlstarlet.
brew install xmlstarlet #OSXapt-get install xmlstarlet