> In my own personal perfect world, all logs would be printed in the first column of log files using the epoch time in seconds, and we'd have a command which would convert from the epoch time to the local timezone.
For a small number of input formats `ts` from Joey Hess' moreutils¹ can do this. Its `-r` option pulls dates out of its input and reformats them, either as a relative timestamp by default(33m57s ago) or a user-specified format if given.
Your example becomes `tail | grep | ts -r %FT%T` or something like that.
It supports syslog format, a subset of ISO-8601, and a few others. It doesn't support epoch in seconds though, but Joey is nice to interact with if you were to offer a patch.
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This, among other reasons, is why I like all my logging going through systemd's journal nowadays. With journalctl you have a good choice of output options for date formatting or dumping as JSON if you want more.