Octopress. Extract date from filename and add to post header.

index.js

var fs = require("fs");
var async = require("async");

var folder = "source/_posts";

fs.readdir(folder, function(err, result) {
  async.each(result, function(file, callback){
    var date = file.split("-").slice(0, 3).join("-"),
      dateStr = "date: "+date+" 00:00:00 +0100";

    fs.readFile(folder + "/" + file, "UTF-8", function read(err, content) {
      if(err) {
        return console.log(err);
      }
      var newContent = content.split("layout: post").join("layout: post\n" + dateStr);

      fs.writeFile(folder + "/" + file, newContent, function(err) {
        if(err) {
          return console.log(err);
        }

        console.log("The file was saved!");
        callback();
      });
    });
  }, function(err){
    if(err) {
      return console.log(err);
    }
    console.log("done");
  });
});