grunt: why you might want to use file src-dest mapping expansions

Gruntfile.js

module.exports = function(grunt) {

  // Project configuration.
  grunt.initConfig({
    minify: {
      nofiles: {},
      manual: {
        files: [
          // Why specify all src-dest mappings manually...
          {src: 'lib/grunt.js', dest: 'build/grunt.min.js'},
          {src: 'lib/grunt/cli.js', dest: 'build/grunt/cli.min.js'},
          {src: 'lib/grunt/config.js', dest: 'build/grunt/config.min.js'},
          {src: 'lib/grunt/event.js', dest: 'build/grunt/event.min.js'},
          {src: 'lib/grunt/fail.js', dest: 'build/grunt/fail.min.js'},
          {src: 'lib/grunt/file.js', dest: 'build/grunt/file.min.js'},
          {src: 'lib/grunt/help.js', dest: 'build/grunt/help.min.js'},
          {src: 'lib/grunt/log.js', dest: 'build/grunt/log.min.js'},
          {src: 'lib/grunt/option.js', dest: 'build/grunt/option.min.js'},
          {src: 'lib/grunt/task.js', dest: 'build/grunt/task.min.js'},
          {src: 'lib/grunt/template.js', dest: 'build/grunt/template.min.js'},
          {src: 'lib/grunt/util.js', dest: 'build/grunt/util.min.js'},
        ]
      },
      automatic: {
        files: [
          // When you can have grunt create them for you dynamically?
          {
            expand: true,                 // Enable dynamic expansion.
            cwd: 'lib/',                  // Matches are relative to this path.
            src: ['**/*.js', '!util/**'], // Actual pattern(s) to match.
            dest: 'build/',               // Destination path prefix.
            ext: '.min.js',               // You can change the extension, too.
          }
        ]
      },
    },
  });

  grunt.registerMultiTask('minify', function() {
    // Warn on and remove invalid source files (if nonull was set).
    var files = this.files.filter(function(f) {
      if (!grunt.file.exists(f.src)) {
        grunt.log.warn('Source file "' + f.src + '" not found.');
        return false;
      } else {
        return true;
      }
    });
    // Minify all files.
    files.forEach(function(f) {
      grunt.log.writeln('Minify ' + f.src + ' -> ' + f.dest);
      // actually minify here, etc
    });
    // Report when done.
    grunt.log.writeln('Minified ' + files.length + ' files.');
  });

  grunt.registerTask('default', ['minify']);

};

output.txt

$ grunt
Running "minify:nofiles" (minify) task
Minified 0 files.

Running "minify:manual" (minify) task
Minify lib/grunt.js -> build/grunt.min.js
Minify lib/grunt/cli.js -> build/grunt/cli.min.js
Minify lib/grunt/config.js -> build/grunt/config.min.js
Minify lib/grunt/event.js -> build/grunt/event.min.js
Minify lib/grunt/fail.js -> build/grunt/fail.min.js
Minify lib/grunt/file.js -> build/grunt/file.min.js
Minify lib/grunt/help.js -> build/grunt/help.min.js
Minify lib/grunt/log.js -> build/grunt/log.min.js
Minify lib/grunt/option.js -> build/grunt/option.min.js
Minify lib/grunt/task.js -> build/grunt/task.min.js
Minify lib/grunt/template.js -> build/grunt/template.min.js
Minify lib/grunt/util.js -> build/grunt/util.min.js
Minified 12 files.

Running "minify:automatic" (minify) task
Minify lib/grunt.js -> build/grunt.min.js
Minify lib/grunt/cli.js -> build/grunt/cli.min.js
Minify lib/grunt/config.js -> build/grunt/config.min.js
Minify lib/grunt/event.js -> build/grunt/event.min.js
Minify lib/grunt/fail.js -> build/grunt/fail.min.js
Minify lib/grunt/file.js -> build/grunt/file.min.js
Minify lib/grunt/help.js -> build/grunt/help.min.js
Minify lib/grunt/log.js -> build/grunt/log.min.js
Minify lib/grunt/option.js -> build/grunt/option.min.js
Minify lib/grunt/task.js -> build/grunt/task.min.js
Minify lib/grunt/template.js -> build/grunt/template.min.js
Minify lib/grunt/util.js -> build/grunt/util.min.js
Minified 12 files.

Done, without errors.