What is the best way to obfuscate a shell script in AIX? The problem is that as a shared user, I would like that others don't know the code.
Don't try do it. It can't be done. There are programs that are sold as shell obfuscators, but they only obfuscate the script against attackers who aren't going to spend any effort to break it. Obfuscators can, however, break in interesting ways.
If you wanted obfuscation to hide passwords or other sensitive data: that's not possible. The data would be easy to observe at runtime — obfuscated or not, at some point the data has to be deobfuscated in order to be processed. If you need to protect sensitive data, you need an account that you don't share with people you don't trust.
If you wanted obfuscation to hide the logic of your script: don't do it. If your script is valuable enough that somebody will want to find out how it works, an obfuscator won't protect you. If your script isn't that valuable, it's not worth obfuscating.
If you set no read/write permissions then they can't read it. You could still set execute permissions.
How big is the aix shell source. If you understand it well, can you replicate your logic in a Python (assume you know Python). If you could do it, then you can use PyInstaller to compile it in binary.
I would not advice C as it may be an overkill.