Using Node.js to create simple build tools. In this case, 'concat.js' which concatenates JS files (or, really any text files).

concat.js

var fs = require('fs');
var os = require('os');
var program = require('commander');

var importList = [];

//Options -- also sets up automatic --help message/usage info
program
  .version('0.0.1')
	.option('-f, --filelist [txtfile]', 'use an input file with a comma separated list of files to concat')
	.option('-s, --files [files]', 'specify the files to concat in the option')
	.option('-d, --dest [dest]', 'the destination file')
	.parse(process.argv);

//does the actual concatenating work
function concat(list, destPath) {

    var out = list.map(function(filePath){
			var current = filePath.trim();
            return fs.readFileSync(current);
        });
    fs.writeFileSync(destPath, out.join(os.EOL));
    console.log(' '+ destPath +' built.');
}

// do we need to display the help?
if (!program.filelist && !program.files || !program.dest) {
	program.help(); // exits automatically
}

// the js files are listed in a text file
if (program.filelist) {
	var string = fs.readFileSync(program.filelist).toString();
	//TODO replace EOL's with ',' so that either could be used.
	importList = string.split(',');
}

// there are js files on the command line.
if (program.files) {
	var list = program.files.split(',');
	// supports both a list file and command line, but list file goes first.
	importList = importList.concat(list);
}

// go.
concat(importList, program.dest.trim());

You'll need commander:
$ npm install commander