can I write a shell script that can be called from apache as a web service
I have an apache web server running on an AIX box that has Informix SE databases that I'd like to retrieve information from. I'd like to implement a web service that I can use internally and I can write a shell script that can interpret xml and return it with message data but can find no information on how to implement it in apache.
Should this be possible - without php or anything else like, just with ksh?
Yes, you can implement a CGI with a very basic Apache configuration (see ScriptAlias in the default confiugration.
A minimal CGI shell script just needs to print a content-type header and followed by a blank line
The request body is available as stdin
Little executables and libraries exist to make CGI shell scripts easier to work with, but often they will not be needed. Plenty of examples for "CGI shell script" on any search engine.