Environment Variables
The following environment variables are supported:
- HISTSIZE
- This variable is used to determine the maximum length of the command history list. If this variable is not present, the default length is 128. 
- HOME
- This variable is used to determine the pathname of the user's home directory, where a .mdbrc file may reside. If this variable is not present, no .mdbrc processing will occur. 
- SHELL
- This variable is used to determine the pathname of the shell used to process shell escapes requested using the ! meta-character. If this variable is not present, /bin/sh is used.