Audacity is designed primarily as a GUI application. For scripting / command line support it is often easier to use a command line application such as SoX http://sox.sourceforge.net/
If you really need to use Audacity for your purpose, then scripting support can be enabled by compiling Audacity from the source code and compiling the optional “mod-script-pipe” module. http://manual.audacityteam.org/man/Scripting Doing this is likely to be a steep learning curve on Windows unless you are already familiar with building C++ programs from source code. http://wiki.audacityteam.org/wiki/Developing_On_Windows