Writing a regex for a td agent
I'm guessing that maybe,
^(?<time>\S* \S* \S*) (?<host>\S*) (?<process>[^:]*): (?<priority>[^:]*):(?<message>.*)$might be what you're trying to write.
RegEx Demo 1
If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.
RegEx Circuit
jex.im visualizes regular expressions:
