I think that Shell Programming questions are perfectly appropriate here. I would actually prefer that this site be the main repository for Shell Scripting questions, because I have trouble navigating the noise at SO. Even http://stackoverflow.com/questions/tagged/shellhttps://stackoverflow.com/questions/tagged/shell is sometimes filled with distracting questions which are only tangentially shell-related. But I know that SO will dominate the Shell Scripting arena for now.
The line between the Unix OS and Shell Scripting is blurry. Shell scripting is essentially a bunch of Operating System commands which are strung together. Maybe this is in a script or maybe this is a one-liner at your prompt.
This is different then C programming, where gethostbyname(3) can only be used within the program, after compilation, etc.
However, advanced shell scripting questions will receive more responses at SO. But sometimes the questions are asked in a System Administration context, whereas the answers at SO are largely from a programming context.