RAR environment variable
Default switches may be added to the Windows environment variable, RAR, using the SET command. Most of switches specified in this variable are used only when WinRAR executed in the command line mode. Switches -cl, -cu, -tk , -tl, -p are used both in shell and in command line modes.
SET RAR=-s -m5 -md1024
will force WinRAR to create solid archives using best compression and a 1024 KB dictionary when executed in the command line mode.