By default, Ant is looking for a file named build.xml in the current directory. If you don’t want to rename the file or the file is in another directory you can specify the file name or path by using the -buildfile option. You can also use -file or -f to achieve the same behaviour. After the option type the name or directory containing the file.
ant -buildfile foo.xml
ant -file bar/foo.xml
// Ant is looking for the build.xml in this directory
ant -f bar/