That looks like a log file. My first comment would be to ask if the application producing that file has defined a formal grammar for that file (maybe not in ANTLR syntax, but a formal specification that commits that the output follows a prescribed format. Most logging will have some consistency to the start of the log line (often configurable within the application or logging framework), and would possibly allow you to know that every log line begins with something like:
Dec 17 14:00:01 103.56.229.11
But the remainder of the log entry will be basically free form. You might be able to take advantage of knowing that logs from of the same type follow a consistent pattern.
I’ve written a language using ANTLR, and sometimes have to do log file analysis. For log file analysis, I always reach for something like Ruby and make heaven usage of regular expressions to look for the particular log entries I’m interested in. It wouldn’t even come to mind to try and write an ANTLR grammar to pull a log file apart. I’d do something like check for a regular expression at the start of a line to identify if it begins a log entry and then gather all the lines until the next line that matches that pattern (it’s not unusual, to see log entries that are more than one line long). Then I can start applying regexes one by one to identify which type of log entry I’m looking at and pull out information I need based upon knowledge of consistency for that particular log.
If you really want to use ANTLR, you can probably work something out, but, if there’s no commitment on the part of the application producing the log file to follow a particular grammar, then I suspect you’ll be chasing exceptions for a very long time (or punt and put into a “gobble up everything until the next line (that starts with …)) type of rule, and then use it.
To me, the fact that you don’t need a parse tree result is probably a strong indication that ANTLR is overkill.