How to Install the IDL Astronomy Library?
(This is my method. You can do it differently.)
1. Go to the IDL Astronomy Library download site and download the entire package.
2. Unpack the files and move all program files to a single directory. Let's call it MY_IDL
3. In your .cshrc (or whatever) file, add a line:
setenv IDL_PATH <default IDL lib path>:MY_IDL
For example, in my case, it is:
setenv IDL_PATH /usr/local/rsi/idl/lib:/users/whwang/IDL