My general technique would be to start by extracting a list of all ALARM_ID strings from the XML file. Because of the size, assuming the XML is fairly predictable, it might be best to do this with a simple regular expression. Then use map to convert that list to a hash where the ALARM_ID strings are the keys and the values are all "1".

Then loop through the text file, line by line. Extract the alarm ID from the line; if it's in the hash described in the previous paragraph, then print "Success\n" as output; otherwise, print the line as output.