Can I add changelog property to liquibase.properties file?

this is my liquibase.properties file:

1. #Liquibase.properties
2. driver: oracle.jdbc.OracleDriver
3. classpath: ojdbc7.jar
4. url: jdbc:oracle:thin:@10.0.2.1:1521:mydb
5. username: USER
6. password: pswd

this is my command:

1. liquibase --changeLogFile results/changelog.xml --logLevel debug -Dconnection_string="USER/pswd@mydb" update

I would like to use command like this:

1. liquibase --changeLogFile results/changelog.xml --logLevel debug update

So i need add connection_string property to liquibase.properties file. Any idea?

I need connection_string property, because i have executeCommand tag in my changeset:

        <executeCommand executable="sqlplus">
            <arg value="${connection_string}" />
            <arg value="@/home/svn/dml/INSERT_INTO_COUNTRIES.sql" />
        </executeCommand>