# Customizing Environment Variables

Commonly used environment variables that you can specify in the shell include:

SIM_DATA_PATH

Define a list of directories for Vorpal to search data files from, in order to hold a central repository for EEDL, LXCAT and other files. When a data file is needed in a simulation, Vorpal will search it in order of current directory and all directories listed in SIM_DATA_PATH. One can set up this environment variable before running VSimComposer. The default SIM_DATA_PATH in the distribution contains potentially useful data files.