As you will be able to tell from the URL, this script doesn't generate the barcode at all, but instead goes off to the totally useful terryburton.co.uk website to get the barcode. That site has a barcode generator which displays the barcode in the web page. I'm wanting to have a list of barcodes on a sheet of paper so that I can order stuff from Tesco using my iPhone and the Tesco App which scans barcodes, so I will therefore have a bunch of barcodes of regular things that we buy on said bit of paper. And the easiest way to get those barcodes on to a single bit of paper is to generate all the barcodes from the barcode code, rather than trying to peel off the barcodes from the products themselves. Hence this script.

Call the script with a 13 digit number, it will then write a PNG file with the barcode number to the directory you currently reside in.