Well, don't use readline to ask the user where he wants to go, then.

I have no idea what other things your huge modular script does, but whatever it does, it'll all go away once it exits - other than output redirected to a file, deleted/created files, and such - just like the cd command.

The best I can give you is:

1.- create a user for each project, so users can su to it and be in the right directory, with the right environment, etc.

2.- Use expect. Expect has an "interact' command which gives the user control of the shell back within the script.