detecting location of installer

I have looked around and have not yet found the answer to this simple question:

What is the command (maybe an example?) for detecting the location of my installer, i.e. what drive?

Never mind -- I was mixing apples with oranges, and asking a question that doesn't need to be asked.

For future reference, it's $EXEDIR for the directory and the System plug-in for the complete path including the filename.

Thank you very much for that valuable bit of education, which also led me to better understand how to use the NSIS website.