All files.

copy: {
  inplace: {
    files: [{
      expand: true,
      cwd: 'src',
      src: '**/*.js',
      dest: 'src'
    }],
    options: {
      process: function(content, filepath) {
        return content + '\n';
      }
    }
  }
}

Gruntfile.js

copy: {
  inplace: {
    files: {
      'file.js': 'file.js'
    },
    options: {
      process: function(content, filepath) {
        return content + '\n';
      }
    }
  }
}