Script to monitor a directory for new STL files and run slic3r when new ones are added.

octoslic3r.js

var fs = require('fs'),
spawn = require('child_process').spawn,

dir = process.argv[2],
cmd = process.argv[3],
timer = process.argv[4] || 10000,

running_file = "";

function run_update(file, rcmd) {
    return function() {
	if (running_file === "") {
	    running_file = file;
	    rcmd = rcmd.replace("%f", file);
	    var s = spawn('slic3r', rcmd.split(' '));

	    s.stdout.on('data', function(d) {
		console.log(d.toString());
	    });

	    s.stderr.on('data', function(d) {
		console.log(d.toString());
	    });

	    s.on('close', function(code) {
		console.log("finished '%s' with code '%d'", rcmd, code);
		running_file = "";
	    });
	} else {
	    return;
	}
    };
}

fs.exists(dir, function(exists) {
    if (exists) {
	console.log("Watching '%s'", dir);
	fs.watch(dir, function(e, fname) {
	    if (fname.match(/\.stl$/i)) {
		setTimeout(run_update(dir + '/' + fname, cmd), timer);
	    }
	});
    } else {
	console.log("'%s' does not exist.", dir);
	process.exit();
    }
});

Use in the following way:

node octoslic3r.js /home/octo/.octoprint/uploads '--load /home/octo/printer_settings.ini %f'

%f will be replaced with the file that is being added.

First argument is the directory you want to monitor.
Second argument is the command line options to be passed to slic3r.
A third and optional argument can be supplied as the time to wait prior to running Slic3r (default is 10 seconds)