You can upload the file into the file cabinet for retrieval using nlapiLoadFile(id)
for parsing by scripts.
We use this strategy for processing:
var loadedInvoiceFile = nlapiLoadFile(invoiceFileId); //load the file
var loadedInvoiceString = loadedInvoiceFile.getValue(); //read its contents
var invoiceLines = loadedInvoiceString.split('\n'); //split on newlines
for (var i = 0; i < invoiceLines.length; i++) { //for each line do:
var cols = invoiceLines[i].split('\t'); //change delimeter here
...
}