btw, if you want to just keep adding to more to an existing file use a different pipe:
dir /s/b >> library.txt
That appends the directory being scanned, in this case whatever directory you are in at the time, to the end of the existing file. So if you use the original command FF2 presented only using the "append" pipe rather than the create new file pipe, you just need to change the directory names:
dir c:\
{library-name} /s/b >> c:\
{directory where you are keeping the book list file}list.txt
This is a simple command but more powerful than many people know. If you get stuck while in the CMD (also called a DOS window) just type
dir /? which will bring up a list of options for the
DIR command. Oh, btw, as a rule DOS commands are NOT case sensitive though some have switches (the /option thingy is a switch) can be case sensitive. I think that was a silly choice but, some are what they are. Just follow the help opened using the /? switch.
Last if the /? brings up a list too long for your screen, you can just use the left scroll bar or use a slightly different way of bringing up the list. Type it this way:
dir /? | more
This lets you view the info returned one page at a time. But the scroll bar on the right of the DOS window is the easiest option.

There are tons of other ways to make this work but FF2's is the easiest. I am sure there are free tools out there which will build a text file or even a spreadsheet file out of a directory listing automagically for you. One could Google for that as well.
have fun!! DOS is not hard...try Unix or Linux if you want cryptic and hard, but POWERFUL command line stuff. After all MS-DOS was pretty much a sripped down set of commands used by Unix or even CP/M anyway.