I have a rather large file with XML-style content. Each line contains one full XML entry. For example:

1:<Message><DNIS>1234</DNIS><UCID>3456</UCID><TransferGroup>XYZXYZ</TransferGroup></Message>
2:<Message><DNIS>9999</DNIS><UCID>2584</UCID><TransferGroup>ABCABC</TransferGroup></Message>
.....

I'm trying to figure a way to be able to go through the file, pull pertinent info, and print the output in a separate file delimited with commas:

output.txt:
1234,3456,XYZXYZ
9999,2584,ABCABC

I was able to achieve this via a series of greps with cuts for each value I want, but it takes far too long to run. I have 10,000+ entries to retrieve. I'm not very good with awk or sed or anything else that could prove more efficient. Can anyone help? Thanks!

One sed should be enough, try:

sed '
    s#^<Message><DNIS>##
    s#</DNIS><UCID>#,#
    s#</UCID><TransferGroup>#,#
    s#</TransferGroup></Message>$##
' input.txt > output.txt