Ant command does not create apk file

I am using Ant to build my application application.my uses the project.so library, first of all, I ran the below command in command line to generate build.xml in my project.

" update for Android project --target 5 -p path_of_my_project -l path_of_my_library_project "

(my app build target is 4.0). Aveve team generated a build.xml file in my project. Then I ran "ant" command on the command line .it showed the result as BUILD SUCCESSFULL. but when i checked the project bin folder the apk file is not generated. What is the problem? I haven't made any changes to the build.xml file. Do I need to add something to this in order to generate the assembly?