By convention, the base Tomcat directory (e.g. /usr/local/apache-tomcat-5.5.2831) is referred to as $CATALINA_HOME. As a convenience, you should create a $CATALINA_HOME environment variable. For UNIX operating systems one typically modifies a startup file like ~/.bash_login to set and export shell variables while Mac users typically set and export environment variables in .bash_profile. For Windows, go to Start -> Control Panel -> System -> Advanced -> Environment Variables and set your Tomcat environment variables via the GUI.
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