In the past couple of days, two people have written me email essentially saying: "Dan, this File_MARC library sounds great - but I can't figure out how to create a record from scratch with it! Can you please help me? Yes, when you're dealing with MARC, you'll quickly get all weepy and get help from anyone you can.
His example code is pretty simple - load the PEAR package into the script, create the record object and start adding fields to it. He shows various output methods ("pretty print", writing the raw data to a file, etc.) and the output to various other data structures like JSON and XML.