ant command does not generating apk file

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http://stackoverflow.com – I am using Ant to build my application.my app uses a library project.so first of all i had run the below command in commandline to generate the build.xml in my project. "android update project --target 5 -p path_of_my_project -l path_of_my_library_project" (my application's build target is 4.0).Above command generated a build.xml file in my project.Then i run "ant" command in command prompt.it has shown the result as BUILD SUCCESSFULL. but when i checked my project's bin folder there is no apk file is generated.what is the issue?I did not make any changes in build.xml file.do i need to add (HowTos)