Write all the GIT commit messages since the last tag (on the current branch) into a changelog file.

create_changelog.js

var usage_description = "Usage: node create_changelog.js MyChangelog.txt \"Changelog for nightly build version 0.9.0.1\""; 
var args = ParseArguments();
var spawn = require('child_process').spawn;
var fs = require('fs');
var prc = spawn('git', ['describe', '--tags', '--abbrev=0']);

prc.stdout.setEncoding('utf8');
prc.stdout.on('data', function (data) {
    var str = data.toString();
    var lines = str.split(/(\r?\n)/g);
	var tag = lines[0];
	
	since(tag, function(messages) {
		var path = args[0];
		var stream = fs.createWriteStream(path);
		stream.once('open', function(fd) {
			var header = args[1];
			stream.write(header + "\n");
			messages.forEach(function(m) {
				stream.write(m + "\n");
			});
			stream.end();
			console.log(path + ' was written successfully.');
		});
	});
});

function since(tag, callback){
	var prc = spawn('git', ['cherry', '-v', tag]);
	prc.stdout.setEncoding('utf8');
	prc.stdout.on('data', function (data) {
		var str = data.toString()
		var lines = str.split(/(\r?\n)/g);		
		var messages = [];
		lines.forEach(function(line){
			if (/\S/.test(line))
				messages.push('* ' + line.split('* ')[1]);
		});
		
		callback(messages);
	});
}

function ParseArguments() {
	var args = [];
	process.argv.slice(2).forEach(function (a) {
		args.push(a);
	});
	
	if (args.length != 2)
		throw usage_description;
	return args;
}