You can use the (now obsolete) AppleEvent Carbon API to send an "Do Script" event to Terminal.app :
OSStatus doTerminalScript (NSString* script) {
AppleEvent evt;
OSStatus err;
// Build event
err = AEBuildAppleEvent(kAECoreSuite, kAEDoScript,
typeApplicationBundleID, "com.apple.terminal", 18L,
kAutoGenerateReturnID, kAnyTransactionID, &evt, NULL,
"'----':utf8(@)", strlen([script UTF8String]), [script UTF8String]);
if (err) return err;
AppleEvent res;
// Send event
err = AESendMessage(&evt, &res, kAEWaitReply, kAEDefaultTimeout);
AEDisposeDesc(&evt);
if (err) return err;
// Check for any errors from Terminal.app
AEDesc desc;
err = AEGetParamDesc(&res, keyErrorNumber, typeSInt32, &desc);
AEDisposeDesc(&res);
if (!err) {
AEGetDescData(&desc, &err, sizeof(err));
AEDisposeDesc(&desc);
} else if (err == errAEDescNotFound)
err = noErr;
return err;
}
Taken form here.
Note that Terminal.app must be launched with -[NSWorkspace launchApplication:]
if not running.
If wanted, it can be put in foreground with - [NSApplication activateWithOptions:]
As suggested by a comment, this can be easily ported to the more modern Scripting Bridge API.