build_include: {
  main: {
    files: [
      // includes files within path
      {expand: true, src: ['path/*'], dest: 'dest/', filter: 'isFile'},

      // includes files within path and its sub-directories
      {expand: true, src: ['path/**'], dest: 'dest/'},

      // makes all src relative to cwd
      {expand: true, cwd: 'path/', src: ['**'], dest: 'dest/'},

      // flattens results to a single level
      {expand: true, flatten: true, src: ['path/**'], dest: 'dest/', filter: 'isFile'},
    ],
  },
},

This task supports all the file mapping format Grunt supports. Please read Globbing patterns and Building the files object dynamically for additional details.

Here are some additional examples, given the following file tree:

$ tree -I node_modules
.
├── Gruntfile.js
└── src
    ├── a
    └── subdir
        └── b

2 directories, 3 files

• build_include a single file tree
• build_include without full path
• Flattening the filepath output
• Troubleshooting
• Grunt File