CREATE A BASH SCRIPT TO RENAME FILES

Hello, I have several XML files with a filename that I want to change in order to have an easier way to locate the file i need for future references, I use Mac Os The actual filenames are almost a "random name". The new filename should look like the follow structure, see example bellow: [login to view URL] [login to view URL] [login to view URL] Where: a) "IMS421231I45" is the Vat ID that is actually in a specific field inside the file: " <emisor rfc="IMS421231I45">" b) "AUCJ710419SI6" is the Vat ID that is actually in a specific field inside the file: " <cfdi:Receptor rfc="AUCJ710419SI6">" c) "20170102" is the year, month and day YYYYMMDD inside the "fecha" field: <cfdi:Comprobante xmlns:cfdi="[login to view URL]" xmlns:tfd="[login to view URL]" xmlns:xsi="[login to view URL]" version="3.2" fecha="2016-07-27T12:04:50" sello="AZCqZuTbgKeBkf/3fXc1pVINRqPy73ULAC2SawmzcyfV9OgwsPoPpwH943nhC92xn7y/7FRbQ63qpk/8vRoGsR7nSW1txyslPiLnC3Gdi5fIUEojyRrZINQc1zB2RITLsEX9NIuAj1TnvCX48koOUCh+97ppzBiv1WT7nnKoGQs=" formaDePago="PAGO EN UNA SOLA EXHIBICION" noCertificado="00001000000304541622" certificado="MIIErDCCA6H" subTotal="4540.48" total="4540.48" tipoDeComprobante="ingreso" metodoDePago="Desconocido" LugarExpedicion="MEXICO" xsi:schemaLocation="[login to view URL] [login to view URL]"> d) The last tree digits is a secuence number, just in case the same "emisor" has issued to "receptor" more than one time in that specific date. I need a bash script to in a specific folder locate each field and rename the files according this criteria. I will run this script on a monthly basis. here you have 3 example files Hope someone can help me Regards Jorge