I'm on my iMac, reading about bash from a book (learning the bash shell). It talks about these three files, but I can't find them. Am I to assume that these files don't have to be in and I can create them myself if I want to?

These files are hidden files.And these files will be there under your home directory. If you want to check this put ls -a in your home directory else try with the find command like,

   find ~ -type f -iname ".bash*"

I did that (in Darwin it's find ~ -iname ".bash*" and all I got was .bash_history

any idea where the logout files would be -- assuming they're optional and I can create them myself?

the .profile file is the substitute for .bash_profile according to the book -- and that file is in there.

I am pretty sure that they dont exist on a mac and you have to create them. afterwards so that your changes take effect, do

 source .bash_profile

Correct you have to create the files in OS X. As for log in/out hooks you don't set them in your ~/.bash_profile you set them in your ~/Library/Launchagents and use the loginhook.plist file to run log in and look out hooks, or use launchd to run them at log in and log out.

Let me update this thread since I'm currently reading about Environment variables.

I'm on OS X Snow Leopard, and I'm trying to find out where they are. The book I have (for bash general) says that they are in the .bash_profile file, but since I don't have that, where would they be? I looked in Libary/Launchagents but I didn't get the loginhookfile.plist you mentioned.

anywhere else I might look? I'm just curious -- I want to learn all about this stuff

Well, I recommend you read up on launchd, as it can run scripts at start up globally, when all users log in, or when a specific user logs in. Launchd is one launch daemon to rule them all so to speak.

For the loginhook, I actually misspoke (err mistyped?) earlier. I jumped a step ahead of myself. You need to modify the loginwindow.plist to enable a loginhook.

/Library/Preferences/com.apple.loginwindow.plist

Once you write your script you want to run, and place it in a system locally, you can modify that property list to run a loginhook script.

sudo defaults write com.apple.loginwindow LoginHook /path/to/script