iTunes can be controlled via AppleScript. This plugin appears to talk to iTunes via a CLI the author wrote in Objective-C which uses Scripting Bridge to talk to iTunes. Scripting Bridge is a cocoa interface to scriptable applications.
Many OS X applications expose part or all of their functionality via AppleScript. To get some idea of what an application offers you can fire up AppleScript Editor, then open the dictionary for a given application. (Rarely, an application will expose more than is shown in its dictionary.)
Now, AppleScript is a truly detestable language, so avoid using it directly at all costs. :-) http://appscript.sourceforge.net/ is much more friendly.
Many OS X applications expose part or all of their functionality via AppleScript. To get some idea of what an application offers you can fire up AppleScript Editor, then open the dictionary for a given application. (Rarely, an application will expose more than is shown in its dictionary.)
Now, AppleScript is a truly detestable language, so avoid using it directly at all costs. :-) http://appscript.sourceforge.net/ is much more friendly.