Grunt file that shows how dynamic config (and option!) values are not used in the grunt-contrib-concat task, but picked up by other tasks

file1.txt

my first file - used for concatenating

file2.txt

my second file - used for concatenating

Gruntfile.js

// Grunt file that shows how dynamic config (and option!) values
// are not used in the grunt-contrib-concat task. Run using 'grunt'
module.exports = function(grunt){

    grunt.initConfig({

        concat : {
            foo : {
                src: '<%= grunt.config.get("myfiles") %>',
                dest : 'outfile.txt'
            }
        },

        myTask : {
            bar : '<%= grunt.config.get("myfiles") %>'
        }
    });

    grunt.loadNpmTasks('grunt-contrib-concat');
    grunt.loadNpmTasks('grunt-contrib-concat');

    grunt.registerMultiTask('myTask', function() {
        grunt.log.writeln('myTask:' + this.target + ' data=' + this.data);
    });

    grunt.registerTask('default', ['myTask','concat']);

    grunt.config.set('myfiles',['file1.txt', 'file2.txt'])
}

The values set by grunt.config.set() are available for use, but seem not to be picked up by the concat task for some reason. You can see them being output by the myTask task.