When installing the current version of Event Stream Processor, you can either install to an entirely new directory, or you can install to the same directory as your previous version (or to the same directory as any installed Sybase product).
The installation process creates a version-based sub-directory under the base installation directory. If, for example, you are installing version 5.1 to a base installation directory called Sybase, the installer creates a sub-directory called ESP-5_1. This naming scheme allows more than one version of Event Stream Processor to coexist in the same base installation directory. Note, however, that the installer updates the ESP_HOME environment variable to point to the current version. Therefore, to run the previous version of Event Stream Processor after updating to the current version, manually modify the ESP_HOME environment variable to point to the previous installation sub-directory.
If you install the current version to a new base installation directory, you do not have to manually modify the ESP_HOME variable to run the previous version. However, each time you want to switch between versions, prior to starting Event Stream Processor, run the SYBASE.sh or SYBASE.csh file from the base installation directory of the version you want to run. This ensures all environment variables point to the correct installation.